Merge tag 'landlock_v34' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security

Pull Landlock LSM from James Morris:
 "Add Landlock, a new LSM from Mickaël Salaün.

  Briefly, Landlock provides for unprivileged application sandboxing.

  From Mickaël's cover letter:
    "The goal of Landlock is to enable to restrict ambient rights (e.g.
     global filesystem access) for a set of processes. Because Landlock
     is a stackable LSM [1], it makes possible to create safe security
     sandboxes as new security layers in addition to the existing
     system-wide access-controls. This kind of sandbox is expected to
     help mitigate the security impact of bugs or unexpected/malicious
     behaviors in user-space applications. Landlock empowers any
     process, including unprivileged ones, to securely restrict
     themselves.

     Landlock is inspired by seccomp-bpf but instead of filtering
     syscalls and their raw arguments, a Landlock rule can restrict the
     use of kernel objects like file hierarchies, according to the
     kernel semantic. Landlock also takes inspiration from other OS
     sandbox mechanisms: XNU Sandbox, FreeBSD Capsicum or OpenBSD
     Pledge/Unveil.

     In this current form, Landlock misses some access-control features.
     This enables to minimize this patch series and ease review. This
     series still addresses multiple use cases, especially with the
     combined use of seccomp-bpf: applications with built-in sandboxing,
     init systems, security sandbox tools and security-oriented APIs [2]"

  The cover letter and v34 posting is here:

      https://lore.kernel.org/linux-security-module/20210422154123.13086-1-mic@digikod.net/

  See also:

      https://landlock.io/

  This code has had extensive design discussion and review over several
  years"

Link: https://lore.kernel.org/lkml/50db058a-7dde-441b-a7f9-f6837fe8b69f@schaufler-ca.com/ [1]
Link: https://lore.kernel.org/lkml/f646e1c7-33cf-333f-070c-0a40ad0468cd@digikod.net/ [2]

* tag 'landlock_v34' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security:
  landlock: Enable user space to infer supported features
  landlock: Add user and kernel documentation
  samples/landlock: Add a sandbox manager example
  selftests/landlock: Add user space tests
  landlock: Add syscall implementations
  arch: Wire up Landlock syscalls
  fs,security: Add sb_delete hook
  landlock: Support filesystem access-control
  LSM: Infrastructure management of the superblock
  landlock: Add ptrace restrictions
  landlock: Set up the security framework and manage credentials
  landlock: Add ruleset and domain management
  landlock: Add object management

Documentation/security/index.rst

@@ -16,3 +16,4 @@ Security Documentation
    siphash
    tpm/index
    digsig
+   landlock

Documentation/security/landlock.rst

+.. SPDX-License-Identifier: GPL-2.0
+.. Copyright © 2017-2020 Mickaël Salaün <mic@digikod.net>
+.. Copyright © 2019-2020 ANSSI
+
+==================================
+Landlock LSM: kernel documentation
+==================================
+
+:Author: Mickaël Salaün
+:Date: March 2021
+
+Landlock's goal is to create scoped access-control (i.e. sandboxing).  To
+harden a whole system, this feature should be available to any process,
+including unprivileged ones.  Because such process may be compromised or
+backdoored (i.e. untrusted), Landlock's features must be safe to use from the
+kernel and other processes point of view.  Landlock's interface must therefore
+expose a minimal attack surface.
+
+Landlock is designed to be usable by unprivileged processes while following the
+system security policy enforced by other access control mechanisms (e.g. DAC,
+LSM).  Indeed, a Landlock rule shall not interfere with other access-controls
+enforced on the system, only add more restrictions.
+
+Any user can enforce Landlock rulesets on their processes.  They are merged and
+evaluated according to the inherited ones in a way that ensures that only more
+constraints can be added.
+
+User space documentation can be found here: :doc:`/userspace-api/landlock`.
+
+Guiding principles for safe access controls
+===========================================
+
+* A Landlock rule shall be focused on access control on kernel objects instead
+  of syscall filtering (i.e. syscall arguments), which is the purpose of
+  seccomp-bpf.
+* To avoid multiple kinds of side-channel attacks (e.g. leak of security
+  policies, CPU-based attacks), Landlock rules shall not be able to
+  programmatically communicate with user space.
+* Kernel access check shall not slow down access request from unsandboxed
+  processes.
+* Computation related to Landlock operations (e.g. enforcing a ruleset) shall
+  only impact the processes requesting them.
+
+Tests
+=====
+
+Userspace tests for backward compatibility, ptrace restrictions and filesystem
+support can be found here: `tools/testing/selftests/landlock/`_.
+
+Kernel structures
+=================
+
+Object
+------
+
+.. kernel-doc:: security/landlock/object.h
+    :identifiers:
+
+Filesystem
+----------
+
+.. kernel-doc:: security/landlock/fs.h
+    :identifiers:
+
+Ruleset and domain
+------------------
+
+A domain is a read-only ruleset tied to a set of subjects (i.e. tasks'
+credentials).  Each time a ruleset is enforced on a task, the current domain is
+duplicated and the ruleset is imported as a new layer of rules in the new
+domain.  Indeed, once in a domain, each rule is tied to a layer level.  To
+grant access to an object, at least one rule of each layer must allow the
+requested action on the object.  A task can then only transit to a new domain
+that is the intersection of the constraints from the current domain and those
+of a ruleset provided by the task.
+
+The definition of a subject is implicit for a task sandboxing itself, which
+makes the reasoning much easier and helps avoid pitfalls.
+
+.. kernel-doc:: security/landlock/ruleset.h
+    :identifiers:
+
+.. Links
+.. _tools/testing/selftests/landlock/:
+   https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/tools/testing/selftests/landlock/

Documentation/userspace-api/index.rst

@@ -18,6 +18,7 @@ place where this information is gathered.
 
    no_new_privs
    seccomp_filter
+   landlock
    unshare
    spec_ctrl
    accelerators/ocxl

Documentation/userspace-api/landlock.rst

+.. SPDX-License-Identifier: GPL-2.0
+.. Copyright © 2017-2020 Mickaël Salaün <mic@digikod.net>
+.. Copyright © 2019-2020 ANSSI
+.. Copyright © 2021 Microsoft Corporation
+
+=====================================
+Landlock: unprivileged access control
+=====================================
+
+:Author: Mickaël Salaün
+:Date: March 2021
+
+The goal of Landlock is to enable to restrict ambient rights (e.g. global
+filesystem access) for a set of processes.  Because Landlock is a stackable
+LSM, it makes possible to create safe security sandboxes as new security layers
+in addition to the existing system-wide access-controls. This kind of sandbox
+is expected to help mitigate the security impact of bugs or
+unexpected/malicious behaviors in user space applications.  Landlock empowers
+any process, including unprivileged ones, to securely restrict themselves.
+
+Landlock rules
+==============
+
+A Landlock rule describes an action on an object.  An object is currently a
+file hierarchy, and the related filesystem actions are defined with `access
+rights`_.  A set of rules is aggregated in a ruleset, which can then restrict
+the thread enforcing it, and its future children.
+
+Defining and enforcing a security policy
+----------------------------------------
+
+We first need to create the ruleset that will contain our rules.  For this
+example, the ruleset will contain rules that only allow read actions, but write
+actions will be denied.  The ruleset then needs to handle both of these kind of
+actions.
+
+.. code-block:: c
+
+    int ruleset_fd;
+    struct landlock_ruleset_attr ruleset_attr = {
+        .handled_access_fs =
+            LANDLOCK_ACCESS_FS_EXECUTE |
+            LANDLOCK_ACCESS_FS_WRITE_FILE |
+            LANDLOCK_ACCESS_FS_READ_FILE |
+            LANDLOCK_ACCESS_FS_READ_DIR |
+            LANDLOCK_ACCESS_FS_REMOVE_DIR |
+            LANDLOCK_ACCESS_FS_REMOVE_FILE |
+            LANDLOCK_ACCESS_FS_MAKE_CHAR |
+            LANDLOCK_ACCESS_FS_MAKE_DIR |
+            LANDLOCK_ACCESS_FS_MAKE_REG |
+            LANDLOCK_ACCESS_FS_MAKE_SOCK |
+            LANDLOCK_ACCESS_FS_MAKE_FIFO |
+            LANDLOCK_ACCESS_FS_MAKE_BLOCK |
+            LANDLOCK_ACCESS_FS_MAKE_SYM,
+    };
+
+    ruleset_fd = landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);
+    if (ruleset_fd < 0) {
+        perror("Failed to create a ruleset");
+        return 1;
+    }
+
+We can now add a new rule to this ruleset thanks to the returned file
+descriptor referring to this ruleset.  The rule will only allow reading the
+file hierarchy ``/usr``.  Without another rule, write actions would then be
+denied by the ruleset.  To add ``/usr`` to the ruleset, we open it with the
+``O_PATH`` flag and fill the &struct landlock_path_beneath_attr with this file
+descriptor.
+
+.. code-block:: c
+
+    int err;
+    struct landlock_path_beneath_attr path_beneath = {
+        .allowed_access =
+            LANDLOCK_ACCESS_FS_EXECUTE |
+            LANDLOCK_ACCESS_FS_READ_FILE |
+            LANDLOCK_ACCESS_FS_READ_DIR,
+    };
+
+    path_beneath.parent_fd = open("/usr", O_PATH | O_CLOEXEC);
+    if (path_beneath.parent_fd < 0) {
+        perror("Failed to open file");
+        close(ruleset_fd);
+        return 1;
+    }
+    err = landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH,
+                            &path_beneath, 0);
+    close(path_beneath.parent_fd);
+    if (err) {
+        perror("Failed to update ruleset");
+        close(ruleset_fd);
+        return 1;
+    }
+
+We now have a ruleset with one rule allowing read access to ``/usr`` while
+denying all other handled accesses for the filesystem.  The next step is to
+restrict the current thread from gaining more privileges (e.g. thanks to a SUID
+binary).
+
+.. code-block:: c
+
+    if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
+        perror("Failed to restrict privileges");
+        close(ruleset_fd);
+        return 1;
+    }
+
+The current thread is now ready to sandbox itself with the ruleset.
+
+.. code-block:: c
+
+    if (landlock_restrict_self(ruleset_fd, 0)) {
+        perror("Failed to enforce ruleset");
+        close(ruleset_fd);
+        return 1;
+    }
+    close(ruleset_fd);
+
+If the `landlock_restrict_self` system call succeeds, the current thread is now
+restricted and this policy will be enforced on all its subsequently created
+children as well.  Once a thread is landlocked, there is no way to remove its
+security policy; only adding more restrictions is allowed.  These threads are
+now in a new Landlock domain, merge of their parent one (if any) with the new
+ruleset.
+
+Full working code can be found in `samples/landlock/sandboxer.c`_.
+
+Layers of file path access rights
+---------------------------------
+
+Each time a thread enforces a ruleset on itself, it updates its Landlock domain
+with a new layer of policy.  Indeed, this complementary policy is stacked with
+the potentially other rulesets already restricting this thread.  A sandboxed
+thread can then safely add more constraints to itself with a new enforced
+ruleset.
+
+One policy layer grants access to a file path if at least one of its rules
+encountered on the path grants the access.  A sandboxed thread can only access
+a file path if all its enforced policy layers grant the access as well as all
+the other system access controls (e.g. filesystem DAC, other LSM policies,
+etc.).
+
+Bind mounts and OverlayFS
+-------------------------
+
+Landlock enables to restrict access to file hierarchies, which means that these
+access rights can be propagated with bind mounts (cf.
+:doc:`/filesystems/sharedsubtree`) but not with :doc:`/filesystems/overlayfs`.
+
+A bind mount mirrors a source file hierarchy to a destination.  The destination
+hierarchy is then composed of the exact same files, on which Landlock rules can
+be tied, either via the source or the destination path.  These rules restrict
+access when they are encountered on a path, which means that they can restrict
+access to multiple file hierarchies at the same time, whether these hierarchies
+are the result of bind mounts or not.
+
+An OverlayFS mount point consists of upper and lower layers.  These layers are
+combined in a merge directory, result of the mount point.  This merge hierarchy
+may include files from the upper and lower layers, but modifications performed
+on the merge hierarchy only reflects on the upper layer.  From a Landlock
+policy point of view, each OverlayFS layers and merge hierarchies are
+standalone and contains their own set of files and directories, which is
+different from bind mounts.  A policy restricting an OverlayFS layer will not
+restrict the resulted merged hierarchy, and vice versa.  Landlock users should
+then only think about file hierarchies they want to allow access to, regardless
+of the underlying filesystem.
+
+Inheritance
+-----------
+
+Every new thread resulting from a :manpage:`clone(2)` inherits Landlock domain
+restrictions from its parent.  This is similar to the seccomp inheritance (cf.
+:doc:`/userspace-api/seccomp_filter`) or any other LSM dealing with task's
+:manpage:`credentials(7)`.  For instance, one process's thread may apply
+Landlock rules to itself, but they will not be automatically applied to other
+sibling threads (unlike POSIX thread credential changes, cf.
+:manpage:`nptl(7)`).
+
+When a thread sandboxes itself, we have the guarantee that the related security
+policy will stay enforced on all this thread's descendants.  This allows
+creating standalone and modular security policies per application, which will
+automatically be composed between themselves according to their runtime parent
+policies.
+
+Ptrace restrictions
+-------------------
+
+A sandboxed process has less privileges than a non-sandboxed process and must
+then be subject to additional restrictions when manipulating another process.
+To be allowed to use :manpage:`ptrace(2)` and related syscalls on a target
+process, a sandboxed process should have a subset of the target process rules,
+which means the tracee must be in a sub-domain of the tracer.
+
+Kernel interface
+================
+
+Access rights
+-------------
+
+.. kernel-doc:: include/uapi/linux/landlock.h
+    :identifiers: fs_access
+
+Creating a new ruleset
+----------------------
+
+.. kernel-doc:: security/landlock/syscalls.c
+    :identifiers: sys_landlock_create_ruleset
+
+.. kernel-doc:: include/uapi/linux/landlock.h
+    :identifiers: landlock_ruleset_attr
+
+Extending a ruleset
+-------------------
+
+.. kernel-doc:: security/landlock/syscalls.c
+    :identifiers: sys_landlock_add_rule
+
+.. kernel-doc:: include/uapi/linux/landlock.h
+    :identifiers: landlock_rule_type landlock_path_beneath_attr
+
+Enforcing a ruleset
+-------------------
+
+.. kernel-doc:: security/landlock/syscalls.c
+    :identifiers: sys_landlock_restrict_self
+
+Current limitations
+===================
+
+File renaming and linking
+-------------------------
+
+Because Landlock targets unprivileged access controls, it is needed to properly
+handle composition of rules.  Such property also implies rules nesting.
+Properly handling multiple layers of ruleset, each one of them able to restrict
+access to files, also implies to inherit the ruleset restrictions from a parent
+to its hierarchy.  Because files are identified and restricted by their
+hierarchy, moving or linking a file from one directory to another implies to
+propagate the hierarchy constraints.  To protect against privilege escalations
+through renaming or linking, and for the sake of simplicity, Landlock currently
+limits linking and renaming to the same directory.  Future Landlock evolutions
+will enable more flexibility for renaming and linking, with dedicated ruleset
+flags.
+
+Filesystem topology modification
+--------------------------------
+
+As for file renaming and linking, a sandboxed thread cannot modify its
+filesystem topology, whether via :manpage:`mount(2)` or
+:manpage:`pivot_root(2)`.  However, :manpage:`chroot(2)` calls are not denied.
+
+Special filesystems
+-------------------
+
+Access to regular files and directories can be restricted by Landlock,
+according to the handled accesses of a ruleset.  However, files that do not
+come from a user-visible filesystem (e.g. pipe, socket), but can still be
+accessed through ``/proc/<pid>/fd/*``, cannot currently be explicitly
+restricted.  Likewise, some special kernel filesystems such as nsfs, which can
+be accessed through ``/proc/<pid>/ns/*``, cannot currently be explicitly
+restricted.  However, thanks to the `ptrace restrictions`_, access to such
+sensitive ``/proc`` files are automatically restricted according to domain
+hierarchies.  Future Landlock evolutions could still enable to explicitly
+restrict such paths with dedicated ruleset flags.
+
+Ruleset layers
+--------------
+
+There is a limit of 64 layers of stacked rulesets.  This can be an issue for a
+task willing to enforce a new ruleset in complement to its 64 inherited
+rulesets.  Once this limit is reached, sys_landlock_restrict_self() returns
+E2BIG.  It is then strongly suggested to carefully build rulesets once in the
+life of a thread, especially for applications able to launch other applications
+that may also want to sandbox themselves (e.g. shells, container managers,
+etc.).
+
+Memory usage
+------------
+
+Kernel memory allocated to create rulesets is accounted and can be restricted
+by the :doc:`/admin-guide/cgroup-v1/memory`.
+
+Questions and answers
+=====================
+
+What about user space sandbox managers?
+---------------------------------------
+
+Using user space process to enforce restrictions on kernel resources can lead
+to race conditions or inconsistent evaluations (i.e. `Incorrect mirroring of
+the OS code and state
+<https://www.ndss-symposium.org/ndss2003/traps-and-pitfalls-practical-problems-system-call-interposition-based-security-tools/>`_).
+
+What about namespaces and containers?
+-------------------------------------
+
+Namespaces can help create sandboxes but they are not designed for
+access-control and then miss useful features for such use case (e.g. no
+fine-grained restrictions).  Moreover, their complexity can lead to security
+issues, especially when untrusted processes can manipulate them (cf.
+`Controlling access to user namespaces <https://lwn.net/Articles/673597/>`_).
+
+Additional documentation
+========================
+
+* :doc:`/security/landlock`
+* https://landlock.io
+
+.. Links
+.. _samples/landlock/sandboxer.c:
+   https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/samples/landlock/sandboxer.c

MAINTAINERS

@@ -10191,6 +10191,21 @@ F:	net/core/sock_map.c
 F:	net/ipv4/tcp_bpf.c
 F:	net/ipv4/udp_bpf.c
 
+LANDLOCK SECURITY MODULE
+M:	Mickaël Salaün <mic@digikod.net>
+L:	linux-security-module@vger.kernel.org
+S:	Supported
+W:	https://landlock.io
+T:	git https://github.com/landlock-lsm/linux.git
+F:	Documentation/security/landlock.rst
+F:	Documentation/userspace-api/landlock.rst
+F:	include/uapi/linux/landlock.h
+F:	samples/landlock/
+F:	security/landlock/
+F:	tools/testing/selftests/landlock/
+K:	landlock
+K:	LANDLOCK
+
 LANTIQ / INTEL Ethernet drivers
 M:	Hauke Mehrtens <hauke@hauke-m.de>
 L:	netdev@vger.kernel.org

arch/Kconfig

@@ -1068,6 +1068,13 @@ config COMPAT_32BIT_TIME
 config ARCH_NO_PREEMPT
 	bool
 
+config ARCH_EPHEMERAL_INODES
+	def_bool n
+	help
+	  An arch should select this symbol if it doesn't keep track of inode
+	  instances on its own, but instead relies on something else (e.g. the
+	  host kernel for an UML kernel).
+
 config ARCH_SUPPORTS_RT
 	bool
 

arch/alpha/kernel/syscalls/syscall.tbl

@@ -483,3 +483,6 @@
 551	common	epoll_pwait2			sys_epoll_pwait2
 552	common	mount_setattr			sys_mount_setattr
 553	common	quotactl_path			sys_quotactl_path
+554	common	landlock_create_ruleset		sys_landlock_create_ruleset
+555	common	landlock_add_rule		sys_landlock_add_rule
+556	common	landlock_restrict_self		sys_landlock_restrict_self

arch/arm/tools/syscall.tbl

@@ -457,3 +457,6 @@
 441	common	epoll_pwait2			sys_epoll_pwait2
 442	common	mount_setattr			sys_mount_setattr
 443	common	quotactl_path			sys_quotactl_path
+444	common	landlock_create_ruleset		sys_landlock_create_ruleset
+445	common	landlock_add_rule		sys_landlock_add_rule
+446	common	landlock_restrict_self		sys_landlock_restrict_self

arch/arm64/include/asm/unistd.h

@@ -38,7 +38,7 @@
 #define __ARM_NR_compat_set_tls		(__ARM_NR_COMPAT_BASE + 5)
 #define __ARM_NR_COMPAT_END		(__ARM_NR_COMPAT_BASE + 0x800)
 
-#define __NR_compat_syscalls		444
+#define __NR_compat_syscalls		447
 #endif
 
 #define __ARCH_WANT_SYS_CLONE

arch/arm64/include/asm/unistd32.h

@@ -895,6 +895,12 @@ __SYSCALL(__NR_epoll_pwait2, compat_sys_epoll_pwait2)
 __SYSCALL(__NR_mount_setattr, sys_mount_setattr)
 #define __NR_quotactl_path 443
 __SYSCALL(__NR_quotactl_path, sys_quotactl_path)
+#define __NR_landlock_create_ruleset 444
+__SYSCALL(__NR_landlock_create_ruleset, sys_landlock_create_ruleset)
+#define __NR_landlock_add_rule 445
+__SYSCALL(__NR_landlock_add_rule, sys_landlock_add_rule)
+#define __NR_landlock_restrict_self 446
+__SYSCALL(__NR_landlock_restrict_self, sys_landlock_restrict_self)
 
 /*
  * Please add new compat syscalls above this comment and update

arch/ia64/kernel/syscalls/syscall.tbl

@@ -364,3 +364,6 @@
 441	common	epoll_pwait2			sys_epoll_pwait2
 442	common	mount_setattr			sys_mount_setattr
 443	common	quotactl_path			sys_quotactl_path
+444	common	landlock_create_ruleset		sys_landlock_create_ruleset
+445	common	landlock_add_rule		sys_landlock_add_rule
+446	common	landlock_restrict_self		sys_landlock_restrict_self

arch/m68k/kernel/syscalls/syscall.tbl

@@ -443,3 +443,6 @@
 441	common	epoll_pwait2			sys_epoll_pwait2
 442	common	mount_setattr			sys_mount_setattr
 443	common	quotactl_path			sys_quotactl_path
+444	common	landlock_create_ruleset		sys_landlock_create_ruleset
+445	common	landlock_add_rule		sys_landlock_add_rule
+446	common	landlock_restrict_self		sys_landlock_restrict_self

arch/microblaze/kernel/syscalls/syscall.tbl

@@ -449,3 +449,6 @@
 441	common	epoll_pwait2			sys_epoll_pwait2
 442	common	mount_setattr			sys_mount_setattr
 443	common	quotactl_path			sys_quotactl_path
+444	common	landlock_create_ruleset		sys_landlock_create_ruleset
+445	common	landlock_add_rule		sys_landlock_add_rule
+446	common	landlock_restrict_self		sys_landlock_restrict_self

arch/mips/kernel/syscalls/syscall_n32.tbl

@@ -382,3 +382,6 @@
 441	n32	epoll_pwait2			compat_sys_epoll_pwait2
 442	n32	mount_setattr			sys_mount_setattr
 443	n32	quotactl_path			sys_quotactl_path
+444	n32	landlock_create_ruleset		sys_landlock_create_ruleset
+445	n32	landlock_add_rule		sys_landlock_add_rule
+446	n32	landlock_restrict_self		sys_landlock_restrict_self

arch/mips/kernel/syscalls/syscall_n64.tbl

@@ -358,3 +358,6 @@
 441	n64	epoll_pwait2			sys_epoll_pwait2
 442	n64	mount_setattr			sys_mount_setattr
 443	n64	quotactl_path			sys_quotactl_path
+444	n64	landlock_create_ruleset		sys_landlock_create_ruleset
+445	n64	landlock_add_rule		sys_landlock_add_rule
+446	n64	landlock_restrict_self		sys_landlock_restrict_self

arch/mips/kernel/syscalls/syscall_o32.tbl

@@ -431,3 +431,6 @@
 441	o32	epoll_pwait2			sys_epoll_pwait2		compat_sys_epoll_pwait2
 442	o32	mount_setattr			sys_mount_setattr
 443	o32	quotactl_path			sys_quotactl_path
+444	o32	landlock_create_ruleset		sys_landlock_create_ruleset
+445	o32	landlock_add_rule		sys_landlock_add_rule
+446	o32	landlock_restrict_self		sys_landlock_restrict_self

arch/parisc/kernel/syscalls/syscall.tbl

@@ -441,3 +441,6 @@
 441	common	epoll_pwait2			sys_epoll_pwait2		compat_sys_epoll_pwait2
 442	common	mount_setattr			sys_mount_setattr
 443	common	quotactl_path			sys_quotactl_path
+444	common	landlock_create_ruleset		sys_landlock_create_ruleset
+445	common	landlock_add_rule		sys_landlock_add_rule
+446	common	landlock_restrict_self		sys_landlock_restrict_self

arch/powerpc/kernel/syscalls/syscall.tbl

@@ -523,3 +523,6 @@
 441	common	epoll_pwait2			sys_epoll_pwait2		compat_sys_epoll_pwait2
 442	common	mount_setattr			sys_mount_setattr
 443	common	quotactl_path			sys_quotactl_path
+444	common	landlock_create_ruleset		sys_landlock_create_ruleset
+445	common	landlock_add_rule		sys_landlock_add_rule
+446	common	landlock_restrict_self		sys_landlock_restrict_self

arch/s390/kernel/syscalls/syscall.tbl

@@ -446,3 +446,6 @@
 441  common	epoll_pwait2		sys_epoll_pwait2		compat_sys_epoll_pwait2
 442  common	mount_setattr		sys_mount_setattr		sys_mount_setattr
 443  common	quotactl_path		sys_quotactl_path		sys_quotactl_path
+444  common	landlock_create_ruleset	sys_landlock_create_ruleset	sys_landlock_create_ruleset
+445  common	landlock_add_rule	sys_landlock_add_rule		sys_landlock_add_rule
+446  common	landlock_restrict_self	sys_landlock_restrict_self	sys_landlock_restrict_self

arch/sh/kernel/syscalls/syscall.tbl

@@ -446,3 +446,6 @@
 441	common	epoll_pwait2			sys_epoll_pwait2
 442	common	mount_setattr			sys_mount_setattr
 443	common	quotactl_path			sys_quotactl_path
+444	common	landlock_create_ruleset		sys_landlock_create_ruleset
+445	common	landlock_add_rule		sys_landlock_add_rule
+446	common	landlock_restrict_self		sys_landlock_restrict_self

arch/sparc/kernel/syscalls/syscall.tbl

@@ -489,3 +489,6 @@
 441	common	epoll_pwait2			sys_epoll_pwait2		compat_sys_epoll_pwait2
 442	common	mount_setattr			sys_mount_setattr
 443	common	quotactl_path			sys_quotactl_path
+444	common	landlock_create_ruleset		sys_landlock_create_ruleset
+445	common	landlock_add_rule		sys_landlock_add_rule
+446	common	landlock_restrict_self		sys_landlock_restrict_self

arch/um/Kconfig

@@ -5,6 +5,7 @@ menu "UML-specific options"
 config UML
 	bool
 	default y
+	select ARCH_EPHEMERAL_INODES
 	select ARCH_HAS_KCOV
 	select ARCH_NO_PREEMPT
 	select HAVE_ARCH_AUDITSYSCALL

arch/x86/entry/syscalls/syscall_32.tbl

@@ -448,3 +448,6 @@
 441	i386	epoll_pwait2		sys_epoll_pwait2		compat_sys_epoll_pwait2
 442	i386	mount_setattr		sys_mount_setattr
 443	i386	quotactl_path		sys_quotactl_path
+444	i386	landlock_create_ruleset	sys_landlock_create_ruleset
+445	i386	landlock_add_rule	sys_landlock_add_rule
+446	i386	landlock_restrict_self	sys_landlock_restrict_self

arch/x86/entry/syscalls/syscall_64.tbl

@@ -365,6 +365,9 @@
 441	common	epoll_pwait2		sys_epoll_pwait2
 442	common	mount_setattr		sys_mount_setattr
 443	common	quotactl_path		sys_quotactl_path
+444	common	landlock_create_ruleset	sys_landlock_create_ruleset
+445	common	landlock_add_rule	sys_landlock_add_rule
+446	common	landlock_restrict_self	sys_landlock_restrict_self
 
 #
 # Due to a historical design error, certain syscalls are numbered differently

arch/xtensa/kernel/syscalls/syscall.tbl

@@ -414,3 +414,6 @@
 441	common	epoll_pwait2			sys_epoll_pwait2
 442	common	mount_setattr			sys_mount_setattr
 443	common	quotactl_path			sys_quotactl_path
+444	common	landlock_create_ruleset		sys_landlock_create_ruleset
+445	common	landlock_add_rule		sys_landlock_add_rule
+446	common	landlock_restrict_self		sys_landlock_restrict_self

fs/super.c

@@ -454,6 +454,7 @@ void generic_shutdown_super(struct super_block *sb)
 		evict_inodes(sb);
 		/* only nonzero refcount inodes can have marks */
 		fsnotify_sb_delete(sb);
+		security_sb_delete(sb);
 
 		if (sb->s_dio_done_wq) {
 			destroy_workqueue(sb->s_dio_done_wq);

include/linux/lsm_hook_defs.h

@@ -59,6 +59,7 @@ LSM_HOOK(int, 0, fs_context_dup, struct fs_context *fc,
 LSM_HOOK(int, -ENOPARAM, fs_context_parse_param, struct fs_context *fc,
 	 struct fs_parameter *param)
 LSM_HOOK(int, 0, sb_alloc_security, struct super_block *sb)
+LSM_HOOK(void, LSM_RET_VOID, sb_delete, struct super_block *sb)
 LSM_HOOK(void, LSM_RET_VOID, sb_free_security, struct super_block *sb)
 LSM_HOOK(void, LSM_RET_VOID, sb_free_mnt_opts, void *mnt_opts)
 LSM_HOOK(int, 0, sb_eat_lsm_opts, char *orig, void **mnt_opts)

include/linux/lsm_hooks.h

@@ -108,6 +108,9 @@
  *	allocated.
  *	@sb contains the super_block structure to be modified.
  *	Return 0 if operation was successful.
+ * @sb_delete:
+ *	Release objects tied to a superblock (e.g. inodes).
+ *	@sb contains the super_block structure being released.
  * @sb_free_security:
  *	Deallocate and clear the sb->s_security field.
  *	@sb contains the super_block structure to be modified.
@@ -1585,6 +1588,7 @@ struct lsm_blob_sizes {
 	int	lbs_cred;
 	int	lbs_file;
 	int	lbs_inode;
+	int	lbs_superblock;
 	int	lbs_ipc;
 	int	lbs_msg_msg;
 	int	lbs_task;

include/linux/security.h

@@ -291,6 +291,7 @@ void security_bprm_committed_creds(struct linux_binprm *bprm);
 int security_fs_context_dup(struct fs_context *fc, struct fs_context *src_fc);
 int security_fs_context_parse_param(struct fs_context *fc, struct fs_parameter *param);
 int security_sb_alloc(struct super_block *sb);
+void security_sb_delete(struct super_block *sb);
 void security_sb_free(struct super_block *sb);
 void security_free_mnt_opts(void **mnt_opts);
 int security_sb_eat_lsm_opts(char *options, void **mnt_opts);
@@ -633,6 +634,9 @@ static inline int security_sb_alloc(struct super_block *sb)
 	return 0;
 }
 
+static inline void security_sb_delete(struct super_block *sb)
+{ }
+
 static inline void security_sb_free(struct super_block *sb)
 { }
 

include/linux/syscalls.h

@@ -69,6 +69,8 @@ struct io_uring_params;
 struct clone_args;
 struct open_how;
 struct mount_attr;
+struct landlock_ruleset_attr;
+enum landlock_rule_type;
 
 #include <linux/types.h>
 #include <linux/aio_abi.h>
@@ -1043,6 +1045,11 @@ asmlinkage long sys_pidfd_send_signal(int pidfd, int sig,
 				       siginfo_t __user *info,
 				       unsigned int flags);
 asmlinkage long sys_pidfd_getfd(int pidfd, int fd, unsigned int flags);
+asmlinkage long sys_landlock_create_ruleset(const struct landlock_ruleset_attr __user *attr,
+		size_t size, __u32 flags);
+asmlinkage long sys_landlock_add_rule(int ruleset_fd, enum landlock_rule_type rule_type,
+		const void __user *rule_attr, __u32 flags);
+asmlinkage long sys_landlock_restrict_self(int ruleset_fd, __u32 flags);
 
 /*
  * Architecture-specific system calls

include/uapi/asm-generic/unistd.h

@@ -866,8 +866,15 @@ __SYSCALL(__NR_mount_setattr, sys_mount_setattr)
 #define __NR_quotactl_path 443
 __SYSCALL(__NR_quotactl_path, sys_quotactl_path)
 
+#define __NR_landlock_create_ruleset 444
+__SYSCALL(__NR_landlock_create_ruleset, sys_landlock_create_ruleset)
+#define __NR_landlock_add_rule 445
+__SYSCALL(__NR_landlock_add_rule, sys_landlock_add_rule)
+#define __NR_landlock_restrict_self 446
+__SYSCALL(__NR_landlock_restrict_self, sys_landlock_restrict_self)
+
 #undef __NR_syscalls
-#define __NR_syscalls 444
+#define __NR_syscalls 447
 
 /*
  * 32 bit systems traditionally used different

include/uapi/linux/landlock.h

+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/*
+ * Landlock - User space API
+ *
+ * Copyright © 2017-2020 Mickaël Salaün <mic@digikod.net>
+ * Copyright © 2018-2020 ANSSI
+ */
+
+#ifndef _UAPI_LINUX_LANDLOCK_H
+#define _UAPI_LINUX_LANDLOCK_H
+
+#include <linux/types.h>
+
+/**
+ * struct landlock_ruleset_attr - Ruleset definition
+ *
+ * Argument of sys_landlock_create_ruleset().  This structure can grow in
+ * future versions.
+ */
+struct landlock_ruleset_attr {
+	/**
+	 * @handled_access_fs: Bitmask of actions (cf. `Filesystem flags`_)
+	 * that is handled by this ruleset and should then be forbidden if no
+	 * rule explicitly allow them.  This is needed for backward
+	 * compatibility reasons.
+	 */
+	__u64 handled_access_fs;
+};
+
+/*
+ * sys_landlock_create_ruleset() flags:
+ *
+ * - %LANDLOCK_CREATE_RULESET_VERSION: Get the highest supported Landlock ABI
+ *   version.
+ */
+#define LANDLOCK_CREATE_RULESET_VERSION			(1U << 0)
+
+/**
+ * enum landlock_rule_type - Landlock rule type
+ *
+ * Argument of sys_landlock_add_rule().
+ */
+enum landlock_rule_type {
+	/**
+	 * @LANDLOCK_RULE_PATH_BENEATH: Type of a &struct
+	 * landlock_path_beneath_attr .
+	 */
+	LANDLOCK_RULE_PATH_BENEATH = 1,
+};
+
+/**
+ * struct landlock_path_beneath_attr - Path hierarchy definition
+ *
+ * Argument of sys_landlock_add_rule().
+ */
+struct landlock_path_beneath_attr {
+	/**
+	 * @allowed_access: Bitmask of allowed actions for this file hierarchy
+	 * (cf. `Filesystem flags`_).
+	 */
+	__u64 allowed_access;
+	/**
+	 * @parent_fd: File descriptor, open with ``O_PATH``, which identifies
+	 * the parent directory of a file hierarchy, or just a file.
+	 */
+	__s32 parent_fd;
+	/*
+	 * This struct is packed to avoid trailing reserved members.
+	 * Cf. security/landlock/syscalls.c:build_check_abi()
+	 */
+} __attribute__((packed));
+
+/**
+ * DOC: fs_access
+ *
+ * A set of actions on kernel objects may be defined by an attribute (e.g.
+ * &struct landlock_path_beneath_attr) including a bitmask of access.
+ *
+ * Filesystem flags
+ * ~~~~~~~~~~~~~~~~
+ *
+ * These flags enable to restrict a sandboxed process to a set of actions on
+ * files and directories.  Files or directories opened before the sandboxing
+ * are not subject to these restrictions.
+ *
+ * A file can only receive these access rights:
+ *
+ * - %LANDLOCK_ACCESS_FS_EXECUTE: Execute a file.
+ * - %LANDLOCK_ACCESS_FS_WRITE_FILE: Open a file with write access.
+ * - %LANDLOCK_ACCESS_FS_READ_FILE: Open a file with read access.
+ *
+ * A directory can receive access rights related to files or directories.  The
+ * following access right is applied to the directory itself, and the
+ * directories beneath it:
+ *
+ * - %LANDLOCK_ACCESS_FS_READ_DIR: Open a directory or list its content.
+ *
+ * However, the following access rights only apply to the content of a
+ * directory, not the directory itself:
+ *
+ * - %LANDLOCK_ACCESS_FS_REMOVE_DIR: Remove an empty directory or rename one.
+ * - %LANDLOCK_ACCESS_FS_REMOVE_FILE: Unlink (or rename) a file.
+ * - %LANDLOCK_ACCESS_FS_MAKE_CHAR: Create (or rename or link) a character
+ *   device.
+ * - %LANDLOCK_ACCESS_FS_MAKE_DIR: Create (or rename) a directory.
+ * - %LANDLOCK_ACCESS_FS_MAKE_REG: Create (or rename or link) a regular file.
+ * - %LANDLOCK_ACCESS_FS_MAKE_SOCK: Create (or rename or link) a UNIX domain
+ *   socket.
+ * - %LANDLOCK_ACCESS_FS_MAKE_FIFO: Create (or rename or link) a named pipe.
+ * - %LANDLOCK_ACCESS_FS_MAKE_BLOCK: Create (or rename or link) a block device.
+ * - %LANDLOCK_ACCESS_FS_MAKE_SYM: Create (or rename or link) a symbolic link.
+ *
+ * .. warning::
+ *
+ *   It is currently not possible to restrict some file-related actions
+ *   accessible through these syscall families: :manpage:`chdir(2)`,
+ *   :manpage:`truncate(2)`, :manpage:`stat(2)`, :manpage:`flock(2)`,
+ *   :manpage:`chmod(2)`, :manpage:`chown(2)`, :manpage:`setxattr(2)`,
+ *   :manpage:`utime(2)`, :manpage:`ioctl(2)`, :manpage:`fcntl(2)`,
+ *   :manpage:`access(2)`.
+ *   Future Landlock evolutions will enable to restrict them.
+ */
+#define LANDLOCK_ACCESS_FS_EXECUTE			(1ULL << 0)
+#define LANDLOCK_ACCESS_FS_WRITE_FILE			(1ULL << 1)
+#define LANDLOCK_ACCESS_FS_READ_FILE			(1ULL << 2)
+#define LANDLOCK_ACCESS_FS_READ_DIR			(1ULL << 3)
+#define LANDLOCK_ACCESS_FS_REMOVE_DIR			(1ULL << 4)
+#define LANDLOCK_ACCESS_FS_REMOVE_FILE			(1ULL << 5)
+#define LANDLOCK_ACCESS_FS_MAKE_CHAR			(1ULL << 6)
+#define LANDLOCK_ACCESS_FS_MAKE_DIR			(1ULL << 7)
+#define LANDLOCK_ACCESS_FS_MAKE_REG			(1ULL << 8)
+#define LANDLOCK_ACCESS_FS_MAKE_SOCK			(1ULL << 9)
+#define LANDLOCK_ACCESS_FS_MAKE_FIFO			(1ULL << 10)
+#define LANDLOCK_ACCESS_FS_MAKE_BLOCK			(1ULL << 11)
+#define LANDLOCK_ACCESS_FS_MAKE_SYM			(1ULL << 12)
+
+#endif /* _UAPI_LINUX_LANDLOCK_H */

kernel/sys_ni.c

@@ -267,6 +267,11 @@ COND_SYSCALL(request_key);
 COND_SYSCALL(keyctl);
 COND_SYSCALL_COMPAT(keyctl);
 
+/* security/landlock/syscalls.c */
+COND_SYSCALL(landlock_create_ruleset);
+COND_SYSCALL(landlock_add_rule);
+COND_SYSCALL(landlock_restrict_self);
+
 /* arch/example/kernel/sys_example.c */
 
 /* mm/fadvise.c */

samples/Kconfig

@@ -124,6 +124,13 @@ config SAMPLE_HIDRAW
 	bool "hidraw sample"
 	depends on CC_CAN_LINK && HEADERS_INSTALL
 
+config SAMPLE_LANDLOCK
+	bool "Landlock example"
+	depends on CC_CAN_LINK && HEADERS_INSTALL
+	help
+	  Build a simple Landlock sandbox manager able to start a process
+	  restricted by a user-defined filesystem access control policy.
+
 config SAMPLE_PIDFD
 	bool "pidfd sample"
 	depends on CC_CAN_LINK && HEADERS_INSTALL

samples/Makefile

@@ -11,6 +11,7 @@ obj-$(CONFIG_SAMPLE_KDB)		+= kdb/
 obj-$(CONFIG_SAMPLE_KFIFO)		+= kfifo/
 obj-$(CONFIG_SAMPLE_KOBJECT)		+= kobject/
 obj-$(CONFIG_SAMPLE_KPROBES)		+= kprobes/
+subdir-$(CONFIG_SAMPLE_LANDLOCK)	+= landlock
 obj-$(CONFIG_SAMPLE_LIVEPATCH)		+= livepatch/
 subdir-$(CONFIG_SAMPLE_PIDFD)		+= pidfd
 obj-$(CONFIG_SAMPLE_QMI_CLIENT)		+= qmi/

samples/landlock/.gitignore

+/sandboxer

samples/landlock/Makefile

+# SPDX-License-Identifier: BSD-3-Clause
+
+userprogs-always-y := sandboxer
+
+userccflags += -I usr/include
+
+.PHONY: all clean
+
+all:
+	$(MAKE) -C ../.. samples/landlock/
+
+clean:
+	$(MAKE) -C ../.. M=samples/landlock/ clean

samples/landlock/sandboxer.c

+// SPDX-License-Identifier: BSD-3-Clause
+/*
+ * Simple Landlock sandbox manager able to launch a process restricted by a
+ * user-defined filesystem access control policy.
+ *
+ * Copyright © 2017-2020 Mickaël Salaün <mic@digikod.net>
+ * Copyright © 2020 ANSSI
+ */
+
+#define _GNU_SOURCE
+#include <errno.h>
+#include <fcntl.h>
+#include <linux/landlock.h>
+#include <linux/prctl.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/prctl.h>
+#include <sys/stat.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+#ifndef landlock_create_ruleset
+static inline int landlock_create_ruleset(
+		const struct landlock_ruleset_attr *const attr,
+		const size_t size, const __u32 flags)
+{
+	return syscall(__NR_landlock_create_ruleset, attr, size, flags);
+}
+#endif
+
+#ifndef landlock_add_rule
+static inline int landlock_add_rule(const int ruleset_fd,
+		const enum landlock_rule_type rule_type,
+		const void *const rule_attr, const __u32 flags)
+{
+	return syscall(__NR_landlock_add_rule, ruleset_fd, rule_type,
+			rule_attr, flags);
+}
+#endif
+
+#ifndef landlock_restrict_self
+static inline int landlock_restrict_self(const int ruleset_fd,
+		const __u32 flags)
+{
+	return syscall(__NR_landlock_restrict_self, ruleset_fd, flags);
+}
+#endif
+
+#define ENV_FS_RO_NAME "LL_FS_RO"
+#define ENV_FS_RW_NAME "LL_FS_RW"
+#define ENV_PATH_TOKEN ":"
+
+static int parse_path(char *env_path, const char ***const path_list)
+{
+	int i, num_paths = 0;
+
+	if (env_path) {
+		num_paths++;
+		for (i = 0; env_path[i]; i++) {
+			if (env_path[i] == ENV_PATH_TOKEN[0])
+				num_paths++;
+		}
+	}
+	*path_list = malloc(num_paths * sizeof(**path_list));
+	for (i = 0; i < num_paths; i++)
+		(*path_list)[i] = strsep(&env_path, ENV_PATH_TOKEN);
+
+	return num_paths;
+}
+
+#define ACCESS_FILE ( \
+	LANDLOCK_ACCESS_FS_EXECUTE | \
+	LANDLOCK_ACCESS_FS_WRITE_FILE | \
+	LANDLOCK_ACCESS_FS_READ_FILE)
+
+static int populate_ruleset(
+		const char *const env_var, const int ruleset_fd,
+		const __u64 allowed_access)
+{
+	int num_paths, i, ret = 1;
+	char *env_path_name;
+	const char **path_list = NULL;
+	struct landlock_path_beneath_attr path_beneath = {
+		.parent_fd = -1,
+	};
+
+	env_path_name = getenv(env_var);
+	if (!env_path_name) {
+		/* Prevents users to forget a setting. */
+		fprintf(stderr, "Missing environment variable %s\n", env_var);
+		return 1;
+	}
+	env_path_name = strdup(env_path_name);
+	unsetenv(env_var);
+	num_paths = parse_path(env_path_name, &path_list);
+	if (num_paths == 1 && path_list[0][0] == '\0') {
+		/*
+		 * Allows to not use all possible restrictions (e.g. use
+		 * LL_FS_RO without LL_FS_RW).
+		 */
+		ret = 0;
+		goto out_free_name;
+	}
+
+	for (i = 0; i < num_paths; i++) {
+		struct stat statbuf;
+
+		path_beneath.parent_fd = open(path_list[i], O_PATH |
+				O_CLOEXEC);
+		if (path_beneath.parent_fd < 0) {
+			fprintf(stderr, "Failed to open \"%s\": %s\n",
+					path_list[i],
+					strerror(errno));
+			goto out_free_name;
+		}
+		if (fstat(path_beneath.parent_fd, &statbuf)) {
+			close(path_beneath.parent_fd);
+			goto out_free_name;
+		}
+		path_beneath.allowed_access = allowed_access;
+		if (!S_ISDIR(statbuf.st_mode))
+			path_beneath.allowed_access &= ACCESS_FILE;
+		if (landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH,
+					&path_beneath, 0)) {
+			fprintf(stderr, "Failed to update the ruleset with \"%s\": %s\n",
+					path_list[i], strerror(errno));
+			close(path_beneath.parent_fd);
+			goto out_free_name;
+		}
+		close(path_beneath.parent_fd);
+	}
+	ret = 0;
+
+out_free_name:
+	free(env_path_name);
+	return ret;
+}
+
+#define ACCESS_FS_ROUGHLY_READ ( \
+	LANDLOCK_ACCESS_FS_EXECUTE | \
+	LANDLOCK_ACCESS_FS_READ_FILE | \
+	LANDLOCK_ACCESS_FS_READ_DIR)
+
+#define ACCESS_FS_ROUGHLY_WRITE ( \
+	LANDLOCK_ACCESS_FS_WRITE_FILE | \
+	LANDLOCK_ACCESS_FS_REMOVE_DIR | \
+	LANDLOCK_ACCESS_FS_REMOVE_FILE | \
+	LANDLOCK_ACCESS_FS_MAKE_CHAR | \
+	LANDLOCK_ACCESS_FS_MAKE_DIR | \
+	LANDLOCK_ACCESS_FS_MAKE_REG | \
+	LANDLOCK_ACCESS_FS_MAKE_SOCK | \
+	LANDLOCK_ACCESS_FS_MAKE_FIFO | \
+	LANDLOCK_ACCESS_FS_MAKE_BLOCK | \
+	LANDLOCK_ACCESS_FS_MAKE_SYM)
+
+int main(const int argc, char *const argv[], char *const *const envp)
+{
+	const char *cmd_path;
+	char *const *cmd_argv;
+	int ruleset_fd;
+	struct landlock_ruleset_attr ruleset_attr = {
+		.handled_access_fs = ACCESS_FS_ROUGHLY_READ |
+			ACCESS_FS_ROUGHLY_WRITE,
+	};
+
+	if (argc < 2) {
+		fprintf(stderr, "usage: %s=\"...\" %s=\"...\" %s <cmd> [args]...\n\n",
+				ENV_FS_RO_NAME, ENV_FS_RW_NAME, argv[0]);
+		fprintf(stderr, "Launch a command in a restricted environment.\n\n");
+		fprintf(stderr, "Environment variables containing paths, "
+				"each separated by a colon:\n");
+		fprintf(stderr, "* %s: list of paths allowed to be used in a read-only way.\n",
+				ENV_FS_RO_NAME);
+		fprintf(stderr, "* %s: list of paths allowed to be used in a read-write way.\n",
+				ENV_FS_RW_NAME);
+		fprintf(stderr, "\nexample:\n"
+				"%s=\"/bin:/lib:/usr:/proc:/etc:/dev/urandom\" "
+				"%s=\"/dev/null:/dev/full:/dev/zero:/dev/pts:/tmp\" "
+				"%s bash -i\n",
+				ENV_FS_RO_NAME, ENV_FS_RW_NAME, argv[0]);
+		return 1;
+	}
+
+	ruleset_fd = landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);
+	if (ruleset_fd < 0) {
+		const int err = errno;
+
+		perror("Failed to create a ruleset");
+		switch (err) {
+		case ENOSYS:
+			fprintf(stderr, "Hint: Landlock is not supported by the current kernel. "
+					"To support it, build the kernel with "
+					"CONFIG_SECURITY_LANDLOCK=y and prepend "
+					"\"landlock,\" to the content of CONFIG_LSM.\n");
+			break;
+		case EOPNOTSUPP:
+			fprintf(stderr, "Hint: Landlock is currently disabled. "
+					"It can be enabled in the kernel configuration by "
+					"prepending \"landlock,\" to the content of CONFIG_LSM, "
+					"or at boot time by setting the same content to the "
+					"\"lsm\" kernel parameter.\n");
+			break;
+		}
+		return 1;
+	}
+	if (populate_ruleset(ENV_FS_RO_NAME, ruleset_fd,
+				ACCESS_FS_ROUGHLY_READ)) {
+		goto err_close_ruleset;
+	}
+	if (populate_ruleset(ENV_FS_RW_NAME, ruleset_fd,
+				ACCESS_FS_ROUGHLY_READ | ACCESS_FS_ROUGHLY_WRITE)) {
+		goto err_close_ruleset;
+	}
+	if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
+		perror("Failed to restrict privileges");
+		goto err_close_ruleset;
+	}
+	if (landlock_restrict_self(ruleset_fd, 0)) {
+		perror("Failed to enforce ruleset");
+		goto err_close_ruleset;
+	}
+	close(ruleset_fd);
+
+	cmd_path = argv[1];
+	cmd_argv = argv + 1;
+	execvpe(cmd_path, cmd_argv, envp);
+	fprintf(stderr, "Failed to execute \"%s\": %s\n", cmd_path,
+			strerror(errno));
+	fprintf(stderr, "Hint: access to the binary, the interpreter or "
+			"shared libraries may be denied.\n");
+	return 1;
+
+err_close_ruleset:
+	close(ruleset_fd);
+	return 1;
+}

security/Kconfig

@@ -238,6 +238,7 @@ source "security/loadpin/Kconfig"
 source "security/yama/Kconfig"
 source "security/safesetid/Kconfig"
 source "security/lockdown/Kconfig"
+source "security/landlock/Kconfig"
 
 source "security/integrity/Kconfig"
 
@@ -277,11 +278,11 @@ endchoice
 
 config LSM
 	string "Ordered list of enabled LSMs"
-	default "lockdown,yama,loadpin,safesetid,integrity,smack,selinux,tomoyo,apparmor,bpf" if DEFAULT_SECURITY_SMACK
-	default "lockdown,yama,loadpin,safesetid,integrity,apparmor,selinux,smack,tomoyo,bpf" if DEFAULT_SECURITY_APPARMOR
-	default "lockdown,yama,loadpin,safesetid,integrity,tomoyo,bpf" if DEFAULT_SECURITY_TOMOYO
-	default "lockdown,yama,loadpin,safesetid,integrity,bpf" if DEFAULT_SECURITY_DAC
-	default "lockdown,yama,loadpin,safesetid,integrity,selinux,smack,tomoyo,apparmor,bpf"
+	default "landlock,lockdown,yama,loadpin,safesetid,integrity,smack,selinux,tomoyo,apparmor,bpf" if DEFAULT_SECURITY_SMACK
+	default "landlock,lockdown,yama,loadpin,safesetid,integrity,apparmor,selinux,smack,tomoyo,bpf" if DEFAULT_SECURITY_APPARMOR
+	default "landlock,lockdown,yama,loadpin,safesetid,integrity,tomoyo,bpf" if DEFAULT_SECURITY_TOMOYO
+	default "landlock,lockdown,yama,loadpin,safesetid,integrity,bpf" if DEFAULT_SECURITY_DAC
+	default "landlock,lockdown,yama,loadpin,safesetid,integrity,selinux,smack,tomoyo,apparmor,bpf"
 	help
 	  A comma-separated list of LSMs, in initialization order.
 	  Any LSMs left off this list will be ignored. This can be

security/Makefile

@@ -13,6 +13,7 @@ subdir-$(CONFIG_SECURITY_LOADPIN)	+= loadpin
 subdir-$(CONFIG_SECURITY_SAFESETID)    += safesetid
 subdir-$(CONFIG_SECURITY_LOCKDOWN_LSM)	+= lockdown
 subdir-$(CONFIG_BPF_LSM)		+= bpf
+subdir-$(CONFIG_SECURITY_LANDLOCK)	+= landlock
 
 # always enable default capabilities
 obj-y					+= commoncap.o
@@ -32,6 +33,7 @@ obj-$(CONFIG_SECURITY_SAFESETID)       += safesetid/
 obj-$(CONFIG_SECURITY_LOCKDOWN_LSM)	+= lockdown/
 obj-$(CONFIG_CGROUPS)			+= device_cgroup.o
 obj-$(CONFIG_BPF_LSM)			+= bpf/
+obj-$(CONFIG_SECURITY_LANDLOCK)		+= landlock/
 
 # Object integrity file lists
 subdir-$(CONFIG_INTEGRITY)		+= integrity

security/landlock/Kconfig

+# SPDX-License-Identifier: GPL-2.0-only
+
+config SECURITY_LANDLOCK
+	bool "Landlock support"
+	depends on SECURITY && !ARCH_EPHEMERAL_INODES
+	select SECURITY_PATH
+	help
+	  Landlock is a sandboxing mechanism that enables processes to restrict
+	  themselves (and their future children) by gradually enforcing
+	  tailored access control policies.  A Landlock security policy is a
+	  set of access rights (e.g. open a file in read-only, make a
+	  directory, etc.) tied to a file hierarchy.  Such policy can be
+	  configured and enforced by any processes for themselves using the
+	  dedicated system calls: landlock_create_ruleset(),
+	  landlock_add_rule(), and landlock_restrict_self().
+
+	  See Documentation/userspace-api/landlock.rst for further information.
+
+	  If you are unsure how to answer this question, answer N.  Otherwise,
+	  you should also prepend "landlock," to the content of CONFIG_LSM to
+	  enable Landlock at boot time.

security/landlock/Makefile

+obj-$(CONFIG_SECURITY_LANDLOCK) := landlock.o
+
+landlock-y := setup.o syscalls.o object.o ruleset.o \
+	cred.o ptrace.o fs.o

security/landlock/common.h

+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Landlock LSM - Common constants and helpers
+ *
+ * Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net>
+ * Copyright © 2018-2020 ANSSI
+ */
+
+#ifndef _SECURITY_LANDLOCK_COMMON_H
+#define _SECURITY_LANDLOCK_COMMON_H
+
+#define LANDLOCK_NAME "landlock"
+
+#ifdef pr_fmt
+#undef pr_fmt
+#endif
+
+#define pr_fmt(fmt) LANDLOCK_NAME ": " fmt
+
+#endif /* _SECURITY_LANDLOCK_COMMON_H */

security/landlock/cred.c

+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Landlock LSM - Credential hooks
+ *
+ * Copyright © 2017-2020 Mickaël Salaün <mic@digikod.net>
+ * Copyright © 2018-2020 ANSSI
+ */
+
+#include <linux/cred.h>
+#include <linux/lsm_hooks.h>
+
+#include "common.h"
+#include "cred.h"
+#include "ruleset.h"
+#include "setup.h"
+
+static int hook_cred_prepare(struct cred *const new,
+		const struct cred *const old, const gfp_t gfp)
+{
+	struct landlock_ruleset *const old_dom = landlock_cred(old)->domain;
+
+	if (old_dom) {
+		landlock_get_ruleset(old_dom);
+		landlock_cred(new)->domain = old_dom;
+	}
+	return 0;
+}
+
+static void hook_cred_free(struct cred *const cred)
+{
+	struct landlock_ruleset *const dom = landlock_cred(cred)->domain;
+
+	if (dom)
+		landlock_put_ruleset_deferred(dom);
+}
+
+static struct security_hook_list landlock_hooks[] __lsm_ro_after_init = {
+	LSM_HOOK_INIT(cred_prepare, hook_cred_prepare),
+	LSM_HOOK_INIT(cred_free, hook_cred_free),
+};
+
+__init void landlock_add_cred_hooks(void)
+{
+	security_add_hooks(landlock_hooks, ARRAY_SIZE(landlock_hooks),
+			LANDLOCK_NAME);
+}

security/landlock/cred.h

+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Landlock LSM - Credential hooks
+ *
+ * Copyright © 2019-2020 Mickaël Salaün <mic@digikod.net>
+ * Copyright © 2019-2020 ANSSI
+ */
+
+#ifndef _SECURITY_LANDLOCK_CRED_H
+#define _SECURITY_LANDLOCK_CRED_H
+
+#include <linux/cred.h>
+#include <linux/init.h>
+#include <linux/rcupdate.h>
+
+#include "ruleset.h"
+#include "setup.h"
+
+struct landlock_cred_security {
+	struct landlock_ruleset *domain;
+};
+
+static inline struct landlock_cred_security *landlock_cred(
+		const struct cred *cred)
+{
+	return cred->security + landlock_blob_sizes.lbs_cred;
+}
+
+static inline const struct landlock_ruleset *landlock_get_current_domain(void)
+{
+	return landlock_cred(current_cred())->domain;
+}
+
+/*
+ * The call needs to come from an RCU read-side critical section.
+ */
+static inline const struct landlock_ruleset *landlock_get_task_domain(
+		const struct task_struct *const task)
+{
+	return landlock_cred(__task_cred(task))->domain;
+}
+
+static inline bool landlocked(const struct task_struct *const task)
+{
+	bool has_dom;
+
+	if (task == current)
+		return !!landlock_get_current_domain();
+
+	rcu_read_lock();
+	has_dom = !!landlock_get_task_domain(task);
+	rcu_read_unlock();
+	return has_dom;
+}
+
+__init void landlock_add_cred_hooks(void);
+
+#endif /* _SECURITY_LANDLOCK_CRED_H */

security/landlock/fs.c

+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Landlock LSM - Filesystem management and hooks
+ *
+ * Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net>
+ * Copyright © 2018-2020 ANSSI
+ */
+
+#include <linux/atomic.h>
+#include <linux/bitops.h>
+#include <linux/bits.h>
+#include <linux/compiler_types.h>
+#include <linux/dcache.h>
+#include <linux/err.h>
+#include <linux/fs.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/limits.h>
+#include <linux/list.h>
+#include <linux/lsm_hooks.h>
+#include <linux/mount.h>
+#include <linux/namei.h>
+#include <linux/path.h>
+#include <linux/rcupdate.h>
+#include <linux/spinlock.h>
+#include <linux/stat.h>
+#include <linux/types.h>
+#include <linux/wait_bit.h>
+#include <linux/workqueue.h>
+#include <uapi/linux/landlock.h>
+
+#include "common.h"
+#include "cred.h"
+#include "fs.h"
+#include "limits.h"
+#include "object.h"
+#include "ruleset.h"
+#include "setup.h"
+
+/* Underlying object management */
+
+static void release_inode(struct landlock_object *const object)
+	__releases(object->lock)
+{
+	struct inode *const inode = object->underobj;
+	struct super_block *sb;
+
+	if (!inode) {
+		spin_unlock(&object->lock);
+		return;
+	}
+
+	/*
+	 * Protects against concurrent use by hook_sb_delete() of the reference
+	 * to the underlying inode.
+	 */
+	object->underobj = NULL;
+	/*
+	 * Makes sure that if the filesystem is concurrently unmounted,
+	 * hook_sb_delete() will wait for us to finish iput().
+	 */
+	sb = inode->i_sb;
+	atomic_long_inc(&landlock_superblock(sb)->inode_refs);
+	spin_unlock(&object->lock);
+	/*
+	 * Because object->underobj was not NULL, hook_sb_delete() and
+	 * get_inode_object() guarantee that it is safe to reset
+	 * landlock_inode(inode)->object while it is not NULL.  It is therefore
+	 * not necessary to lock inode->i_lock.
+	 */
+	rcu_assign_pointer(landlock_inode(inode)->object, NULL);
+	/*
+	 * Now, new rules can safely be tied to @inode with get_inode_object().
+	 */
+
+	iput(inode);
+	if (atomic_long_dec_and_test(&landlock_superblock(sb)->inode_refs))
+		wake_up_var(&landlock_superblock(sb)->inode_refs);
+}
+
+static const struct landlock_object_underops landlock_fs_underops = {
+	.release = release_inode
+};
+
+/* Ruleset management */
+
+static struct landlock_object *get_inode_object(struct inode *const inode)
+{
+	struct landlock_object *object, *new_object;
+	struct landlock_inode_security *inode_sec = landlock_inode(inode);
+
+	rcu_read_lock();
+retry:
+	object = rcu_dereference(inode_sec->object);
+	if (object) {
+		if (likely(refcount_inc_not_zero(&object->usage))) {
+			rcu_read_unlock();
+			return object;
+		}
+		/*
+		 * We are racing with release_inode(), the object is going
+		 * away.  Wait for release_inode(), then retry.
+		 */
+		spin_lock(&object->lock);
+		spin_unlock(&object->lock);
+		goto retry;
+	}
+	rcu_read_unlock();
+
+	/*
+	 * If there is no object tied to @inode, then create a new one (without
+	 * holding any locks).
+	 */
+	new_object = landlock_create_object(&landlock_fs_underops, inode);
+	if (IS_ERR(new_object))
+		return new_object;
+
+	/*
+	 * Protects against concurrent calls to get_inode_object() or
+	 * hook_sb_delete().
+	 */
+	spin_lock(&inode->i_lock);
+	if (unlikely(rcu_access_pointer(inode_sec->object))) {
+		/* Someone else just created the object, bail out and retry. */
+		spin_unlock(&inode->i_lock);
+		kfree(new_object);
+
+		rcu_read_lock();
+		goto retry;
+	}
+
+	/*
+	 * @inode will be released by hook_sb_delete() on its superblock
+	 * shutdown, or by release_inode() when no more ruleset references the
+	 * related object.
+	 */
+	ihold(inode);
+	rcu_assign_pointer(inode_sec->object, new_object);
+	spin_unlock(&inode->i_lock);
+	return new_object;
+}
+
+/* All access rights that can be tied to files. */
+#define ACCESS_FILE ( \
+	LANDLOCK_ACCESS_FS_EXECUTE | \
+	LANDLOCK_ACCESS_FS_WRITE_FILE | \
+	LANDLOCK_ACCESS_FS_READ_FILE)
+
+/*
+ * @path: Should have been checked by get_path_from_fd().
+ */
+int landlock_append_fs_rule(struct landlock_ruleset *const ruleset,
+		const struct path *const path, u32 access_rights)
+{
+	int err;
+	struct landlock_object *object;
+
+	/* Files only get access rights that make sense. */
+	if (!d_is_dir(path->dentry) && (access_rights | ACCESS_FILE) !=
+			ACCESS_FILE)
+		return -EINVAL;
+	if (WARN_ON_ONCE(ruleset->num_layers != 1))
+		return -EINVAL;
+
+	/* Transforms relative access rights to absolute ones. */
+	access_rights |= LANDLOCK_MASK_ACCESS_FS & ~ruleset->fs_access_masks[0];
+	object = get_inode_object(d_backing_inode(path->dentry));
+	if (IS_ERR(object))
+		return PTR_ERR(object);
+	mutex_lock(&ruleset->lock);
+	err = landlock_insert_rule(ruleset, object, access_rights);
+	mutex_unlock(&ruleset->lock);
+	/*
+	 * No need to check for an error because landlock_insert_rule()
+	 * increments the refcount for the new object if needed.
+	 */
+	landlock_put_object(object);
+	return err;
+}
+
+/* Access-control management */
+
+static inline u64 unmask_layers(
+		const struct landlock_ruleset *const domain,
+		const struct path *const path, const u32 access_request,
+		u64 layer_mask)
+{
+	const struct landlock_rule *rule;
+	const struct inode *inode;
+	size_t i;
+
+	if (d_is_negative(path->dentry))
+		/* Ignore nonexistent leafs. */
+		return layer_mask;
+	inode = d_backing_inode(path->dentry);
+	rcu_read_lock();
+	rule = landlock_find_rule(domain,
+			rcu_dereference(landlock_inode(inode)->object));
+	rcu_read_unlock();
+	if (!rule)
+		return layer_mask;
+
+	/*
+	 * An access is granted if, for each policy layer, at least one rule
+	 * encountered on the pathwalk grants the requested accesses,
+	 * regardless of their position in the layer stack.  We must then check
+	 * the remaining layers for each inode, from the first added layer to
+	 * the last one.
+	 */
+	for (i = 0; i < rule->num_layers; i++) {
+		const struct landlock_layer *const layer = &rule->layers[i];
+		const u64 layer_level = BIT_ULL(layer->level - 1);
+
+		/* Checks that the layer grants access to the full request. */
+		if ((layer->access & access_request) == access_request) {
+			layer_mask &= ~layer_level;
+
+			if (layer_mask == 0)
+				return layer_mask;
+		}
+	}
+	return layer_mask;
+}
+
+static int check_access_path(const struct landlock_ruleset *const domain,
+		const struct path *const path, u32 access_request)
+{
+	bool allowed = false;
+	struct path walker_path;
+	u64 layer_mask;
+	size_t i;
+
+	/* Make sure all layers can be checked. */
+	BUILD_BUG_ON(BITS_PER_TYPE(layer_mask) < LANDLOCK_MAX_NUM_LAYERS);
+
+	if (!access_request)
+		return 0;
+	if (WARN_ON_ONCE(!domain || !path))
+		return 0;
+	/*
+	 * Allows access to pseudo filesystems that will never be mountable
+	 * (e.g. sockfs, pipefs), but can still be reachable through
+	 * /proc/<pid>/fd/<file-descriptor> .
+	 */
+	if ((path->dentry->d_sb->s_flags & SB_NOUSER) ||
+			(d_is_positive(path->dentry) &&
+			 unlikely(IS_PRIVATE(d_backing_inode(path->dentry)))))
+		return 0;
+	if (WARN_ON_ONCE(domain->num_layers < 1))
+		return -EACCES;
+
+	/* Saves all layers handling a subset of requested accesses. */
+	layer_mask = 0;
+	for (i = 0; i < domain->num_layers; i++) {
+		if (domain->fs_access_masks[i] & access_request)
+			layer_mask |= BIT_ULL(i);
+	}
+	/* An access request not handled by the domain is allowed. */
+	if (layer_mask == 0)
+		return 0;
+
+	walker_path = *path;
+	path_get(&walker_path);
+	/*
+	 * We need to walk through all the hierarchy to not miss any relevant
+	 * restriction.
+	 */
+	while (true) {
+		struct dentry *parent_dentry;
+
+		layer_mask = unmask_layers(domain, &walker_path,
+				access_request, layer_mask);
+		if (layer_mask == 0) {
+			/* Stops when a rule from each layer grants access. */
+			allowed = true;
+			break;
+		}
+
+jump_up:
+		if (walker_path.dentry == walker_path.mnt->mnt_root) {
+			if (follow_up(&walker_path)) {
+				/* Ignores hidden mount points. */
+				goto jump_up;
+			} else {
+				/*
+				 * Stops at the real root.  Denies access
+				 * because not all layers have granted access.
+				 */
+				allowed = false;
+				break;
+			}
+		}
+		if (unlikely(IS_ROOT(walker_path.dentry))) {
+			/*
+			 * Stops at disconnected root directories.  Only allows
+			 * access to internal filesystems (e.g. nsfs, which is
+			 * reachable through /proc/<pid>/ns/<namespace>).
+			 */
+			allowed = !!(walker_path.mnt->mnt_flags & MNT_INTERNAL);
+			break;
+		}
+		parent_dentry = dget_parent(walker_path.dentry);
+		dput(walker_path.dentry);
+		walker_path.dentry = parent_dentry;
+	}
+	path_put(&walker_path);
+	return allowed ? 0 : -EACCES;
+}
+
+static inline int current_check_access_path(const struct path *const path,
+		const u32 access_request)
+{
+	const struct landlock_ruleset *const dom =
+		landlock_get_current_domain();
+
+	if (!dom)
+		return 0;
+	return check_access_path(dom, path, access_request);
+}
+
+/* Inode hooks */
+
+static void hook_inode_free_security(struct inode *const inode)
+{
+	/*
+	 * All inodes must already have been untied from their object by
+	 * release_inode() or hook_sb_delete().
+	 */
+	WARN_ON_ONCE(landlock_inode(inode)->object);
+}
+
+/* Super-block hooks */
+
+/*
+ * Release the inodes used in a security policy.
+ *
+ * Cf. fsnotify_unmount_inodes() and invalidate_inodes()
+ */
+static void hook_sb_delete(struct super_block *const sb)
+{
+	struct inode *inode, *prev_inode = NULL;
+
+	if (!landlock_initialized)
+		return;
+
+	spin_lock(&sb->s_inode_list_lock);
+	list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
+		struct landlock_object *object;
+
+		/* Only handles referenced inodes. */
+		if (!atomic_read(&inode->i_count))
+			continue;
+
+		/*
+		 * Protects against concurrent modification of inode (e.g.
+		 * from get_inode_object()).
+		 */
+		spin_lock(&inode->i_lock);
+		/*
+		 * Checks I_FREEING and I_WILL_FREE  to protect against a race
+		 * condition when release_inode() just called iput(), which
+		 * could lead to a NULL dereference of inode->security or a
+		 * second call to iput() for the same Landlock object.  Also
+		 * checks I_NEW because such inode cannot be tied to an object.
+		 */
+		if (inode->i_state & (I_FREEING | I_WILL_FREE | I_NEW)) {
+			spin_unlock(&inode->i_lock);
+			continue;
+		}
+
+		rcu_read_lock();
+		object = rcu_dereference(landlock_inode(inode)->object);
+		if (!object) {
+			rcu_read_unlock();
+			spin_unlock(&inode->i_lock);
+			continue;
+		}
+		/* Keeps a reference to this inode until the next loop walk. */
+		__iget(inode);
+		spin_unlock(&inode->i_lock);
+
+		/*
+		 * If there is no concurrent release_inode() ongoing, then we
+		 * are in charge of calling iput() on this inode, otherwise we
+		 * will just wait for it to finish.
+		 */
+		spin_lock(&object->lock);
+		if (object->underobj == inode) {
+			object->underobj = NULL;
+			spin_unlock(&object->lock);
+			rcu_read_unlock();
+
+			/*
+			 * Because object->underobj was not NULL,
+			 * release_inode() and get_inode_object() guarantee
+			 * that it is safe to reset
+			 * landlock_inode(inode)->object while it is not NULL.
+			 * It is therefore not necessary to lock inode->i_lock.
+			 */
+			rcu_assign_pointer(landlock_inode(inode)->object, NULL);
+			/*
+			 * At this point, we own the ihold() reference that was
+			 * originally set up by get_inode_object() and the
+			 * __iget() reference that we just set in this loop
+			 * walk.  Therefore the following call to iput() will
+			 * not sleep nor drop the inode because there is now at
+			 * least two references to it.
+			 */
+			iput(inode);
+		} else {
+			spin_unlock(&object->lock);
+			rcu_read_unlock();
+		}
+
+		if (prev_inode) {
+			/*
+			 * At this point, we still own the __iget() reference
+			 * that we just set in this loop walk.  Therefore we
+			 * can drop the list lock and know that the inode won't
+			 * disappear from under us until the next loop walk.
+			 */
+			spin_unlock(&sb->s_inode_list_lock);
+			/*
+			 * We can now actually put the inode reference from the
+			 * previous loop walk, which is not needed anymore.
+			 */
+			iput(prev_inode);
+			cond_resched();
+			spin_lock(&sb->s_inode_list_lock);
+		}
+		prev_inode = inode;
+	}
+	spin_unlock(&sb->s_inode_list_lock);
+
+	/* Puts the inode reference from the last loop walk, if any. */
+	if (prev_inode)
+		iput(prev_inode);
+	/* Waits for pending iput() in release_inode(). */
+	wait_var_event(&landlock_superblock(sb)->inode_refs, !atomic_long_read(
+				&landlock_superblock(sb)->inode_refs));
+}
+
+/*
+ * Because a Landlock security policy is defined according to the filesystem
+ * topology (i.e. the mount namespace), changing it may grant access to files
+ * not previously allowed.
+ *
+ * To make it simple, deny any filesystem topology modification by landlocked
+ * processes.  Non-landlocked processes may still change the namespace of a
+ * landlocked process, but this kind of threat must be handled by a system-wide
+ * access-control security policy.
+ *
+ * This could be lifted in the future if Landlock can safely handle mount
+ * namespace updates requested by a landlocked process.  Indeed, we could
+ * update the current domain (which is currently read-only) by taking into
+ * account the accesses of the source and the destination of a new mount point.
+ * However, it would also require to make all the child domains dynamically
+ * inherit these new constraints.  Anyway, for backward compatibility reasons,
+ * a dedicated user space option would be required (e.g. as a ruleset flag).
+ */
+static int hook_sb_mount(const char *const dev_name,
+		const struct path *const path, const char *const type,
+		const unsigned long flags, void *const data)
+{
+	if (!landlock_get_current_domain())
+		return 0;
+	return -EPERM;
+}
+
+static int hook_move_mount(const struct path *const from_path,
+		const struct path *const to_path)
+{
+	if (!landlock_get_current_domain())
+		return 0;
+	return -EPERM;
+}
+
+/*
+ * Removing a mount point may reveal a previously hidden file hierarchy, which
+ * may then grant access to files, which may have previously been forbidden.
+ */
+static int hook_sb_umount(struct vfsmount *const mnt, const int flags)
+{
+	if (!landlock_get_current_domain())
+		return 0;
+	return -EPERM;
+}
+
+static int hook_sb_remount(struct super_block *const sb, void *const mnt_opts)
+{
+	if (!landlock_get_current_domain())
+		return 0;
+	return -EPERM;
+}
+
+/*
+ * pivot_root(2), like mount(2), changes the current mount namespace.  It must
+ * then be forbidden for a landlocked process.
+ *
+ * However, chroot(2) may be allowed because it only changes the relative root
+ * directory of the current process.  Moreover, it can be used to restrict the
+ * view of the filesystem.
+ */
+static int hook_sb_pivotroot(const struct path *const old_path,
+		const struct path *const new_path)
+{
+	if (!landlock_get_current_domain())
+		return 0;
+	return -EPERM;
+}
+
+/* Path hooks */
+
+static inline u32 get_mode_access(const umode_t mode)
+{
+	switch (mode & S_IFMT) {
+	case S_IFLNK:
+		return LANDLOCK_ACCESS_FS_MAKE_SYM;
+	case 0:
+		/* A zero mode translates to S_IFREG. */
+	case S_IFREG:
+		return LANDLOCK_ACCESS_FS_MAKE_REG;
+	case S_IFDIR:
+		return LANDLOCK_ACCESS_FS_MAKE_DIR;
+	case S_IFCHR:
+		return LANDLOCK_ACCESS_FS_MAKE_CHAR;
+	case S_IFBLK:
+		return LANDLOCK_ACCESS_FS_MAKE_BLOCK;
+	case S_IFIFO:
+		return LANDLOCK_ACCESS_FS_MAKE_FIFO;
+	case S_IFSOCK:
+		return LANDLOCK_ACCESS_FS_MAKE_SOCK;
+	default:
+		WARN_ON_ONCE(1);
+		return 0;
+	}
+}
+
+/*
+ * Creating multiple links or renaming may lead to privilege escalations if not
+ * handled properly.  Indeed, we must be sure that the source doesn't gain more
+ * privileges by being accessible from the destination.  This is getting more
+ * complex when dealing with multiple layers.  The whole picture can be seen as
+ * a multilayer partial ordering problem.  A future version of Landlock will
+ * deal with that.
+ */
+static int hook_path_link(struct dentry *const old_dentry,
+		const struct path *const new_dir,
+		struct dentry *const new_dentry)
+{
+	const struct landlock_ruleset *const dom =
+		landlock_get_current_domain();
+
+	if (!dom)
+		return 0;
+	/* The mount points are the same for old and new paths, cf. EXDEV. */
+	if (old_dentry->d_parent != new_dir->dentry)
+		/* Gracefully forbids reparenting. */
+		return -EXDEV;
+	if (unlikely(d_is_negative(old_dentry)))
+		return -ENOENT;
+	return check_access_path(dom, new_dir,
+			get_mode_access(d_backing_inode(old_dentry)->i_mode));
+}
+
+static inline u32 maybe_remove(const struct dentry *const dentry)
+{
+	if (d_is_negative(dentry))
+		return 0;
+	return d_is_dir(dentry) ? LANDLOCK_ACCESS_FS_REMOVE_DIR :
+		LANDLOCK_ACCESS_FS_REMOVE_FILE;
+}
+
+static int hook_path_rename(const struct path *const old_dir,
+		struct dentry *const old_dentry,
+		const struct path *const new_dir,
+		struct dentry *const new_dentry)
+{
+	const struct landlock_ruleset *const dom =
+		landlock_get_current_domain();
+
+	if (!dom)
+		return 0;
+	/* The mount points are the same for old and new paths, cf. EXDEV. */
+	if (old_dir->dentry != new_dir->dentry)
+		/* Gracefully forbids reparenting. */
+		return -EXDEV;
+	if (unlikely(d_is_negative(old_dentry)))
+		return -ENOENT;
+	/* RENAME_EXCHANGE is handled because directories are the same. */
+	return check_access_path(dom, old_dir, maybe_remove(old_dentry) |
+			maybe_remove(new_dentry) |
+			get_mode_access(d_backing_inode(old_dentry)->i_mode));
+}
+
+static int hook_path_mkdir(const struct path *const dir,
+		struct dentry *const dentry, const umode_t mode)
+{
+	return current_check_access_path(dir, LANDLOCK_ACCESS_FS_MAKE_DIR);
+}
+
+static int hook_path_mknod(const struct path *const dir,
+		struct dentry *const dentry, const umode_t mode,
+		const unsigned int dev)
+{
+	const struct landlock_ruleset *const dom =
+		landlock_get_current_domain();
+
+	if (!dom)
+		return 0;
+	return check_access_path(dom, dir, get_mode_access(mode));
+}
+
+static int hook_path_symlink(const struct path *const dir,
+		struct dentry *const dentry, const char *const old_name)
+{
+	return current_check_access_path(dir, LANDLOCK_ACCESS_FS_MAKE_SYM);
+}
+
+static int hook_path_unlink(const struct path *const dir,
+		struct dentry *const dentry)
+{
+	return current_check_access_path(dir, LANDLOCK_ACCESS_FS_REMOVE_FILE);
+}
+
+static int hook_path_rmdir(const struct path *const dir,
+		struct dentry *const dentry)
+{
+	return current_check_access_path(dir, LANDLOCK_ACCESS_FS_REMOVE_DIR);
+}
+
+/* File hooks */
+
+static inline u32 get_file_access(const struct file *const file)
+{
+	u32 access = 0;
+
+	if (file->f_mode & FMODE_READ) {
+		/* A directory can only be opened in read mode. */
+		if (S_ISDIR(file_inode(file)->i_mode))
+			return LANDLOCK_ACCESS_FS_READ_DIR;
+		access = LANDLOCK_ACCESS_FS_READ_FILE;
+	}
+	if (file->f_mode & FMODE_WRITE)
+		access |= LANDLOCK_ACCESS_FS_WRITE_FILE;
+	/* __FMODE_EXEC is indeed part of f_flags, not f_mode. */
+	if (file->f_flags & __FMODE_EXEC)
+		access |= LANDLOCK_ACCESS_FS_EXECUTE;
+	return access;
+}
+
+static int hook_file_open(struct file *const file)
+{
+	const struct landlock_ruleset *const dom =
+		landlock_get_current_domain();
+
+	if (!dom)
+		return 0;
+	/*
+	 * Because a file may be opened with O_PATH, get_file_access() may
+	 * return 0.  This case will be handled with a future Landlock
+	 * evolution.
+	 */
+	return check_access_path(dom, &file->f_path, get_file_access(file));
+}
+
+static struct security_hook_list landlock_hooks[] __lsm_ro_after_init = {
+	LSM_HOOK_INIT(inode_free_security, hook_inode_free_security),
+
+	LSM_HOOK_INIT(sb_delete, hook_sb_delete),
+	LSM_HOOK_INIT(sb_mount, hook_sb_mount),
+	LSM_HOOK_INIT(move_mount, hook_move_mount),
+	LSM_HOOK_INIT(sb_umount, hook_sb_umount),
+	LSM_HOOK_INIT(sb_remount, hook_sb_remount),
+	LSM_HOOK_INIT(sb_pivotroot, hook_sb_pivotroot),
+
+	LSM_HOOK_INIT(path_link, hook_path_link),
+	LSM_HOOK_INIT(path_rename, hook_path_rename),
+	LSM_HOOK_INIT(path_mkdir, hook_path_mkdir),
+	LSM_HOOK_INIT(path_mknod, hook_path_mknod),
+	LSM_HOOK_INIT(path_symlink, hook_path_symlink),
+	LSM_HOOK_INIT(path_unlink, hook_path_unlink),
+	LSM_HOOK_INIT(path_rmdir, hook_path_rmdir),
+
+	LSM_HOOK_INIT(file_open, hook_file_open),
+};
+
+__init void landlock_add_fs_hooks(void)
+{
+	security_add_hooks(landlock_hooks, ARRAY_SIZE(landlock_hooks),
+			LANDLOCK_NAME);
+}

security/landlock/fs.h

+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Landlock LSM - Filesystem management and hooks
+ *
+ * Copyright © 2017-2020 Mickaël Salaün <mic@digikod.net>
+ * Copyright © 2018-2020 ANSSI
+ */
+
+#ifndef _SECURITY_LANDLOCK_FS_H
+#define _SECURITY_LANDLOCK_FS_H
+
+#include <linux/fs.h>
+#include <linux/init.h>
+#include <linux/rcupdate.h>
+
+#include "ruleset.h"
+#include "setup.h"
+
+/**
+ * struct landlock_inode_security - Inode security blob
+ *
+ * Enable to reference a &struct landlock_object tied to an inode (i.e.
+ * underlying object).
+ */
+struct landlock_inode_security {
+	/**
+	 * @object: Weak pointer to an allocated object.  All assignments of a
+	 * new object are protected by the underlying inode->i_lock.  However,
+	 * atomically disassociating @object from the inode is only protected
+	 * by @object->lock, from the time @object's usage refcount drops to
+	 * zero to the time this pointer is nulled out (cf. release_inode() and
+	 * hook_sb_delete()).  Indeed, such disassociation doesn't require
+	 * inode->i_lock thanks to the careful rcu_access_pointer() check
+	 * performed by get_inode_object().
+	 */
+	struct landlock_object __rcu *object;
+};
+
+/**
+ * struct landlock_superblock_security - Superblock security blob
+ *
+ * Enable hook_sb_delete() to wait for concurrent calls to release_inode().
+ */
+struct landlock_superblock_security {
+	/**
+	 * @inode_refs: Number of pending inodes (from this superblock) that
+	 * are being released by release_inode().
+	 * Cf. struct super_block->s_fsnotify_inode_refs .
+	 */
+	atomic_long_t inode_refs;
+};
+
+static inline struct landlock_inode_security *landlock_inode(
+		const struct inode *const inode)
+{
+	return inode->i_security + landlock_blob_sizes.lbs_inode;
+}
+
+static inline struct landlock_superblock_security *landlock_superblock(
+		const struct super_block *const superblock)
+{
+	return superblock->s_security + landlock_blob_sizes.lbs_superblock;
+}
+
+__init void landlock_add_fs_hooks(void);
+
+int landlock_append_fs_rule(struct landlock_ruleset *const ruleset,
+		const struct path *const path, u32 access_hierarchy);
+
+#endif /* _SECURITY_LANDLOCK_FS_H */

security/landlock/limits.h

+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Landlock LSM - Limits for different components
+ *
+ * Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net>
+ * Copyright © 2018-2020 ANSSI
+ */
+
+#ifndef _SECURITY_LANDLOCK_LIMITS_H
+#define _SECURITY_LANDLOCK_LIMITS_H
+
+#include <linux/limits.h>
+#include <uapi/linux/landlock.h>
+
+#define LANDLOCK_MAX_NUM_LAYERS		64
+#define LANDLOCK_MAX_NUM_RULES		U32_MAX
+
+#define LANDLOCK_LAST_ACCESS_FS		LANDLOCK_ACCESS_FS_MAKE_SYM
+#define LANDLOCK_MASK_ACCESS_FS		((LANDLOCK_LAST_ACCESS_FS << 1) - 1)
+
+#endif /* _SECURITY_LANDLOCK_LIMITS_H */

security/landlock/object.c

+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Landlock LSM - Object management
+ *
+ * Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net>
+ * Copyright © 2018-2020 ANSSI
+ */
+
+#include <linux/bug.h>
+#include <linux/compiler_types.h>
+#include <linux/err.h>
+#include <linux/kernel.h>
+#include <linux/rcupdate.h>
+#include <linux/refcount.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+
+#include "object.h"
+
+struct landlock_object *landlock_create_object(
+		const struct landlock_object_underops *const underops,
+		void *const underobj)
+{
+	struct landlock_object *new_object;
+
+	if (WARN_ON_ONCE(!underops || !underobj))
+		return ERR_PTR(-ENOENT);
+	new_object = kzalloc(sizeof(*new_object), GFP_KERNEL_ACCOUNT);
+	if (!new_object)
+		return ERR_PTR(-ENOMEM);
+	refcount_set(&new_object->usage, 1);
+	spin_lock_init(&new_object->lock);
+	new_object->underops = underops;
+	new_object->underobj = underobj;
+	return new_object;
+}
+
+/*
+ * The caller must own the object (i.e. thanks to object->usage) to safely put
+ * it.
+ */
+void landlock_put_object(struct landlock_object *const object)
+{
+	/*
+	 * The call to @object->underops->release(object) might sleep, e.g.
+	 * because of iput().
+	 */
+	might_sleep();
+	if (!object)
+		return;
+
+	/*
+	 * If the @object's refcount cannot drop to zero, we can just decrement
+	 * the refcount without holding a lock. Otherwise, the decrement must
+	 * happen under @object->lock for synchronization with things like
+	 * get_inode_object().
+	 */
+	if (refcount_dec_and_lock(&object->usage, &object->lock)) {
+		__acquire(&object->lock);
+		/*
+		 * With @object->lock initially held, remove the reference from
+		 * @object->underobj to @object (if it still exists).
+		 */
+		object->underops->release(object);
+		kfree_rcu(object, rcu_free);
+	}
+}

security/landlock/object.h

+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Landlock LSM - Object management
+ *
+ * Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net>
+ * Copyright © 2018-2020 ANSSI
+ */
+
+#ifndef _SECURITY_LANDLOCK_OBJECT_H
+#define _SECURITY_LANDLOCK_OBJECT_H
+
+#include <linux/compiler_types.h>
+#include <linux/refcount.h>
+#include <linux/spinlock.h>
+
+struct landlock_object;
+
+/**
+ * struct landlock_object_underops - Operations on an underlying object
+ */
+struct landlock_object_underops {
+	/**
+	 * @release: Releases the underlying object (e.g. iput() for an inode).
+	 */
+	void (*release)(struct landlock_object *const object)
+		__releases(object->lock);
+};
+
+/**
+ * struct landlock_object - Security blob tied to a kernel object
+ *
+ * The goal of this structure is to enable to tie a set of ephemeral access
+ * rights (pertaining to different domains) to a kernel object (e.g an inode)
+ * in a safe way.  This implies to handle concurrent use and modification.
+ *
+ * The lifetime of a &struct landlock_object depends on the rules referring to
+ * it.
+ */
+struct landlock_object {
+	/**
+	 * @usage: This counter is used to tie an object to the rules matching
+	 * it or to keep it alive while adding a new rule.  If this counter
+	 * reaches zero, this struct must not be modified, but this counter can
+	 * still be read from within an RCU read-side critical section.  When
+	 * adding a new rule to an object with a usage counter of zero, we must
+	 * wait until the pointer to this object is set to NULL (or recycled).
+	 */
+	refcount_t usage;
+	/**
+	 * @lock: Protects against concurrent modifications.  This lock must be
+	 * held from the time @usage drops to zero until any weak references
+	 * from @underobj to this object have been cleaned up.
+	 *
+	 * Lock ordering: inode->i_lock nests inside this.
+	 */
+	spinlock_t lock;
+	/**
+	 * @underobj: Used when cleaning up an object and to mark an object as
+	 * tied to its underlying kernel structure.  This pointer is protected
+	 * by @lock.  Cf. landlock_release_inodes() and release_inode().
+	 */
+	void *underobj;
+	union {
+		/**
+		 * @rcu_free: Enables lockless use of @usage, @lock and
+		 * @underobj from within an RCU read-side critical section.
+		 * @rcu_free and @underops are only used by
+		 * landlock_put_object().
+		 */
+		struct rcu_head rcu_free;
+		/**
+		 * @underops: Enables landlock_put_object() to release the
+		 * underlying object (e.g. inode).
+		 */
+		const struct landlock_object_underops *underops;
+	};
+};
+
+struct landlock_object *landlock_create_object(
+		const struct landlock_object_underops *const underops,
+		void *const underobj);
+
+void landlock_put_object(struct landlock_object *const object);
+
+static inline void landlock_get_object(struct landlock_object *const object)
+{
+	if (object)
+		refcount_inc(&object->usage);
+}
+
+#endif /* _SECURITY_LANDLOCK_OBJECT_H */

security/landlock/ptrace.c

+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Landlock LSM - Ptrace hooks
+ *
+ * Copyright © 2017-2020 Mickaël Salaün <mic@digikod.net>
+ * Copyright © 2019-2020 ANSSI
+ */
+
+#include <asm/current.h>
+#include <linux/cred.h>
+#include <linux/errno.h>
+#include <linux/kernel.h>
+#include <linux/lsm_hooks.h>
+#include <linux/rcupdate.h>
+#include <linux/sched.h>
+
+#include "common.h"
+#include "cred.h"
+#include "ptrace.h"
+#include "ruleset.h"
+#include "setup.h"
+
+/**
+ * domain_scope_le - Checks domain ordering for scoped ptrace
+ *
+ * @parent: Parent domain.
+ * @child: Potential child of @parent.
+ *
+ * Checks if the @parent domain is less or equal to (i.e. an ancestor, which
+ * means a subset of) the @child domain.
+ */
+static bool domain_scope_le(const struct landlock_ruleset *const parent,
+		const struct landlock_ruleset *const child)
+{
+	const struct landlock_hierarchy *walker;
+
+	if (!parent)
+		return true;
+	if (!child)
+		return false;
+	for (walker = child->hierarchy; walker; walker = walker->parent) {
+		if (walker == parent->hierarchy)
+			/* @parent is in the scoped hierarchy of @child. */
+			return true;
+	}
+	/* There is no relationship between @parent and @child. */
+	return false;
+}
+
+static bool task_is_scoped(const struct task_struct *const parent,
+		const struct task_struct *const child)
+{
+	bool is_scoped;
+	const struct landlock_ruleset *dom_parent, *dom_child;
+
+	rcu_read_lock();
+	dom_parent = landlock_get_task_domain(parent);
+	dom_child = landlock_get_task_domain(child);
+	is_scoped = domain_scope_le(dom_parent, dom_child);
+	rcu_read_unlock();
+	return is_scoped;
+}
+
+static int task_ptrace(const struct task_struct *const parent,
+		const struct task_struct *const child)
+{
+	/* Quick return for non-landlocked tasks. */
+	if (!landlocked(parent))
+		return 0;
+	if (task_is_scoped(parent, child))
+		return 0;
+	return -EPERM;
+}
+
+/**
+ * hook_ptrace_access_check - Determines whether the current process may access
+ *			      another
+ *
+ * @child: Process to be accessed.
+ * @mode: Mode of attachment.
+ *
+ * If the current task has Landlock rules, then the child must have at least
+ * the same rules.  Else denied.
+ *
+ * Determines whether a process may access another, returning 0 if permission
+ * granted, -errno if denied.
+ */
+static int hook_ptrace_access_check(struct task_struct *const child,
+		const unsigned int mode)
+{
+	return task_ptrace(current, child);
+}
+
+/**
+ * hook_ptrace_traceme - Determines whether another process may trace the
+ *			 current one
+ *
+ * @parent: Task proposed to be the tracer.
+ *
+ * If the parent has Landlock rules, then the current task must have the same
+ * or more rules.  Else denied.
+ *
+ * Determines whether the nominated task is permitted to trace the current
+ * process, returning 0 if permission is granted, -errno if denied.
+ */
+static int hook_ptrace_traceme(struct task_struct *const parent)
+{
+	return task_ptrace(parent, current);
+}
+
+static struct security_hook_list landlock_hooks[] __lsm_ro_after_init = {
+	LSM_HOOK_INIT(ptrace_access_check, hook_ptrace_access_check),
+	LSM_HOOK_INIT(ptrace_traceme, hook_ptrace_traceme),
+};
+
+__init void landlock_add_ptrace_hooks(void)
+{
+	security_add_hooks(landlock_hooks, ARRAY_SIZE(landlock_hooks),
+			LANDLOCK_NAME);
+}

security/landlock/ptrace.h

+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Landlock LSM - Ptrace hooks
+ *
+ * Copyright © 2017-2019 Mickaël Salaün <mic@digikod.net>
+ * Copyright © 2019 ANSSI
+ */
+
+#ifndef _SECURITY_LANDLOCK_PTRACE_H
+#define _SECURITY_LANDLOCK_PTRACE_H
+
+__init void landlock_add_ptrace_hooks(void);
+
+#endif /* _SECURITY_LANDLOCK_PTRACE_H */

security/landlock/ruleset.c

+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Landlock LSM - Ruleset management
+ *
+ * Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net>
+ * Copyright © 2018-2020 ANSSI
+ */
+
+#include <linux/bits.h>
+#include <linux/bug.h>
+#include <linux/compiler_types.h>
+#include <linux/err.h>
+#include <linux/errno.h>
+#include <linux/kernel.h>
+#include <linux/lockdep.h>
+#include <linux/overflow.h>
+#include <linux/rbtree.h>
+#include <linux/refcount.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/workqueue.h>
+
+#include "limits.h"
+#include "object.h"
+#include "ruleset.h"
+
+static struct landlock_ruleset *create_ruleset(const u32 num_layers)
+{
+	struct landlock_ruleset *new_ruleset;
+
+	new_ruleset = kzalloc(struct_size(new_ruleset, fs_access_masks,
+				num_layers), GFP_KERNEL_ACCOUNT);
+	if (!new_ruleset)
+		return ERR_PTR(-ENOMEM);
+	refcount_set(&new_ruleset->usage, 1);
+	mutex_init(&new_ruleset->lock);
+	new_ruleset->root = RB_ROOT;
+	new_ruleset->num_layers = num_layers;
+	/*
+	 * hierarchy = NULL
+	 * num_rules = 0
+	 * fs_access_masks[] = 0
+	 */
+	return new_ruleset;
+}
+
+struct landlock_ruleset *landlock_create_ruleset(const u32 fs_access_mask)
+{
+	struct landlock_ruleset *new_ruleset;
+
+	/* Informs about useless ruleset. */
+	if (!fs_access_mask)
+		return ERR_PTR(-ENOMSG);
+	new_ruleset = create_ruleset(1);
+	if (!IS_ERR(new_ruleset))
+		new_ruleset->fs_access_masks[0] = fs_access_mask;
+	return new_ruleset;
+}
+
+static void build_check_rule(void)
+{
+	const struct landlock_rule rule = {
+		.num_layers = ~0,
+	};
+
+	BUILD_BUG_ON(rule.num_layers < LANDLOCK_MAX_NUM_LAYERS);
+}
+
+static struct landlock_rule *create_rule(
+		struct landlock_object *const object,
+		const struct landlock_layer (*const layers)[],
+		const u32 num_layers,
+		const struct landlock_layer *const new_layer)
+{
+	struct landlock_rule *new_rule;
+	u32 new_num_layers;
+
+	build_check_rule();
+	if (new_layer) {
+		/* Should already be checked by landlock_merge_ruleset(). */
+		if (WARN_ON_ONCE(num_layers >= LANDLOCK_MAX_NUM_LAYERS))
+			return ERR_PTR(-E2BIG);
+		new_num_layers = num_layers + 1;
+	} else {
+		new_num_layers = num_layers;
+	}
+	new_rule = kzalloc(struct_size(new_rule, layers, new_num_layers),
+			GFP_KERNEL_ACCOUNT);
+	if (!new_rule)
+		return ERR_PTR(-ENOMEM);
+	RB_CLEAR_NODE(&new_rule->node);
+	landlock_get_object(object);
+	new_rule->object = object;
+	new_rule->num_layers = new_num_layers;
+	/* Copies the original layer stack. */
+	memcpy(new_rule->layers, layers,
+			flex_array_size(new_rule, layers, num_layers));
+	if (new_layer)
+		/* Adds a copy of @new_layer on the layer stack. */
+		new_rule->layers[new_rule->num_layers - 1] = *new_layer;
+	return new_rule;
+}
+
+static void free_rule(struct landlock_rule *const rule)
+{
+	might_sleep();
+	if (!rule)
+		return;
+	landlock_put_object(rule->object);
+	kfree(rule);
+}
+
+static void build_check_ruleset(void)
+{
+	const struct landlock_ruleset ruleset = {
+		.num_rules = ~0,
+		.num_layers = ~0,
+	};
+	typeof(ruleset.fs_access_masks[0]) fs_access_mask = ~0;
+
+	BUILD_BUG_ON(ruleset.num_rules < LANDLOCK_MAX_NUM_RULES);
+	BUILD_BUG_ON(ruleset.num_layers < LANDLOCK_MAX_NUM_LAYERS);
+	BUILD_BUG_ON(fs_access_mask < LANDLOCK_MASK_ACCESS_FS);
+}
+
+/**
+ * insert_rule - Create and insert a rule in a ruleset
+ *
+ * @ruleset: The ruleset to be updated.
+ * @object: The object to build the new rule with.  The underlying kernel
+ *          object must be held by the caller.
+ * @layers: One or multiple layers to be copied into the new rule.
+ * @num_layers: The number of @layers entries.
+ *
+ * When user space requests to add a new rule to a ruleset, @layers only
+ * contains one entry and this entry is not assigned to any level.  In this
+ * case, the new rule will extend @ruleset, similarly to a boolean OR between
+ * access rights.
+ *
+ * When merging a ruleset in a domain, or copying a domain, @layers will be
+ * added to @ruleset as new constraints, similarly to a boolean AND between
+ * access rights.
+ */
+static int insert_rule(struct landlock_ruleset *const ruleset,
+		struct landlock_object *const object,
+		const struct landlock_layer (*const layers)[],
+		size_t num_layers)
+{
+	struct rb_node **walker_node;
+	struct rb_node *parent_node = NULL;
+	struct landlock_rule *new_rule;
+
+	might_sleep();
+	lockdep_assert_held(&ruleset->lock);
+	if (WARN_ON_ONCE(!object || !layers))
+		return -ENOENT;
+	walker_node = &(ruleset->root.rb_node);
+	while (*walker_node) {
+		struct landlock_rule *const this = rb_entry(*walker_node,
+				struct landlock_rule, node);
+
+		if (this->object != object) {
+			parent_node = *walker_node;
+			if (this->object < object)
+				walker_node = &((*walker_node)->rb_right);
+			else
+				walker_node = &((*walker_node)->rb_left);
+			continue;
+		}
+
+		/* Only a single-level layer should match an existing rule. */
+		if (WARN_ON_ONCE(num_layers != 1))
+			return -EINVAL;
+
+		/* If there is a matching rule, updates it. */
+		if ((*layers)[0].level == 0) {
+			/*
+			 * Extends access rights when the request comes from
+			 * landlock_add_rule(2), i.e. @ruleset is not a domain.
+			 */
+			if (WARN_ON_ONCE(this->num_layers != 1))
+				return -EINVAL;
+			if (WARN_ON_ONCE(this->layers[0].level != 0))
+				return -EINVAL;
+			this->layers[0].access |= (*layers)[0].access;
+			return 0;
+		}
+
+		if (WARN_ON_ONCE(this->layers[0].level == 0))
+			return -EINVAL;
+
+		/*
+		 * Intersects access rights when it is a merge between a
+		 * ruleset and a domain.
+		 */
+		new_rule = create_rule(object, &this->layers, this->num_layers,
+				&(*layers)[0]);
+		if (IS_ERR(new_rule))
+			return PTR_ERR(new_rule);
+		rb_replace_node(&this->node, &new_rule->node, &ruleset->root);
+		free_rule(this);
+		return 0;
+	}
+
+	/* There is no match for @object. */
+	build_check_ruleset();
+	if (ruleset->num_rules >= LANDLOCK_MAX_NUM_RULES)
+		return -E2BIG;
+	new_rule = create_rule(object, layers, num_layers, NULL);
+	if (IS_ERR(new_rule))
+		return PTR_ERR(new_rule);
+	rb_link_node(&new_rule->node, parent_node, walker_node);
+	rb_insert_color(&new_rule->node, &ruleset->root);
+	ruleset->num_rules++;
+	return 0;
+}
+
+static void build_check_layer(void)
+{
+	const struct landlock_layer layer = {
+		.level = ~0,
+		.access = ~0,
+	};
+
+	BUILD_BUG_ON(layer.level < LANDLOCK_MAX_NUM_LAYERS);
+	BUILD_BUG_ON(layer.access < LANDLOCK_MASK_ACCESS_FS);
+}
+
+/* @ruleset must be locked by the caller. */
+int landlock_insert_rule(struct landlock_ruleset *const ruleset,
+		struct landlock_object *const object, const u32 access)
+{
+	struct landlock_layer layers[] = {{
+		.access = access,
+		/* When @level is zero, insert_rule() extends @ruleset. */
+		.level = 0,
+	}};
+
+	build_check_layer();
+	return insert_rule(ruleset, object, &layers, ARRAY_SIZE(layers));
+}
+
+static inline void get_hierarchy(struct landlock_hierarchy *const hierarchy)
+{
+	if (hierarchy)
+		refcount_inc(&hierarchy->usage);
+}
+
+static void put_hierarchy(struct landlock_hierarchy *hierarchy)
+{
+	while (hierarchy && refcount_dec_and_test(&hierarchy->usage)) {
+		const struct landlock_hierarchy *const freeme = hierarchy;
+
+		hierarchy = hierarchy->parent;
+		kfree(freeme);
+	}
+}
+
+static int merge_ruleset(struct landlock_ruleset *const dst,
+		struct landlock_ruleset *const src)
+{
+	struct landlock_rule *walker_rule, *next_rule;
+	int err = 0;
+
+	might_sleep();
+	/* Should already be checked by landlock_merge_ruleset() */
+	if (WARN_ON_ONCE(!src))
+		return 0;
+	/* Only merge into a domain. */
+	if (WARN_ON_ONCE(!dst || !dst->hierarchy))
+		return -EINVAL;
+
+	/* Locks @dst first because we are its only owner. */
+	mutex_lock(&dst->lock);
+	mutex_lock_nested(&src->lock, SINGLE_DEPTH_NESTING);
+
+	/* Stacks the new layer. */
+	if (WARN_ON_ONCE(src->num_layers != 1 || dst->num_layers < 1)) {
+		err = -EINVAL;
+		goto out_unlock;
+	}
+	dst->fs_access_masks[dst->num_layers - 1] = src->fs_access_masks[0];
+
+	/* Merges the @src tree. */
+	rbtree_postorder_for_each_entry_safe(walker_rule, next_rule,
+			&src->root, node) {
+		struct landlock_layer layers[] = {{
+			.level = dst->num_layers,
+		}};
+
+		if (WARN_ON_ONCE(walker_rule->num_layers != 1)) {
+			err = -EINVAL;
+			goto out_unlock;
+		}
+		if (WARN_ON_ONCE(walker_rule->layers[0].level != 0)) {
+			err = -EINVAL;
+			goto out_unlock;
+		}
+		layers[0].access = walker_rule->layers[0].access;
+		err = insert_rule(dst, walker_rule->object, &layers,
+				ARRAY_SIZE(layers));
+		if (err)
+			goto out_unlock;
+	}
+
+out_unlock:
+	mutex_unlock(&src->lock);
+	mutex_unlock(&dst->lock);
+	return err;
+}
+
+static int inherit_ruleset(struct landlock_ruleset *const parent,
+		struct landlock_ruleset *const child)
+{
+	struct landlock_rule *walker_rule, *next_rule;
+	int err = 0;
+
+	might_sleep();
+	if (!parent)
+		return 0;
+
+	/* Locks @child first because we are its only owner. */
+	mutex_lock(&child->lock);
+	mutex_lock_nested(&parent->lock, SINGLE_DEPTH_NESTING);
+
+	/* Copies the @parent tree. */
+	rbtree_postorder_for_each_entry_safe(walker_rule, next_rule,
+			&parent->root, node) {
+		err = insert_rule(child, walker_rule->object,
+				&walker_rule->layers, walker_rule->num_layers);
+		if (err)
+			goto out_unlock;
+	}
+
+	if (WARN_ON_ONCE(child->num_layers <= parent->num_layers)) {
+		err = -EINVAL;
+		goto out_unlock;
+	}
+	/* Copies the parent layer stack and leaves a space for the new layer. */
+	memcpy(child->fs_access_masks, parent->fs_access_masks,
+			flex_array_size(parent, fs_access_masks, parent->num_layers));
+
+	if (WARN_ON_ONCE(!parent->hierarchy)) {
+		err = -EINVAL;
+		goto out_unlock;
+	}
+	get_hierarchy(parent->hierarchy);
+	child->hierarchy->parent = parent->hierarchy;
+
+out_unlock:
+	mutex_unlock(&parent->lock);
+	mutex_unlock(&child->lock);
+	return err;
+}
+
+static void free_ruleset(struct landlock_ruleset *const ruleset)
+{
+	struct landlock_rule *freeme, *next;
+
+	might_sleep();
+	rbtree_postorder_for_each_entry_safe(freeme, next, &ruleset->root,
+			node)
+		free_rule(freeme);
+	put_hierarchy(ruleset->hierarchy);
+	kfree(ruleset);
+}
+
+void landlock_put_ruleset(struct landlock_ruleset *const ruleset)
+{
+	might_sleep();
+	if (ruleset && refcount_dec_and_test(&ruleset->usage))
+		free_ruleset(ruleset);
+}
+
+static void free_ruleset_work(struct work_struct *const work)
+{
+	struct landlock_ruleset *ruleset;
+
+	ruleset = container_of(work, struct landlock_ruleset, work_free);
+	free_ruleset(ruleset);
+}
+
+void landlock_put_ruleset_deferred(struct landlock_ruleset *const ruleset)
+{
+	if (ruleset && refcount_dec_and_test(&ruleset->usage)) {
+		INIT_WORK(&ruleset->work_free, free_ruleset_work);
+		schedule_work(&ruleset->work_free);
+	}
+}
+
+/**
+ * landlock_merge_ruleset - Merge a ruleset with a domain
+ *
+ * @parent: Parent domain.
+ * @ruleset: New ruleset to be merged.
+ *
+ * Returns the intersection of @parent and @ruleset, or returns @parent if
+ * @ruleset is empty, or returns a duplicate of @ruleset if @parent is empty.
+ */
+struct landlock_ruleset *landlock_merge_ruleset(
+		struct landlock_ruleset *const parent,
+		struct landlock_ruleset *const ruleset)
+{
+	struct landlock_ruleset *new_dom;
+	u32 num_layers;
+	int err;
+
+	might_sleep();
+	if (WARN_ON_ONCE(!ruleset || parent == ruleset))
+		return ERR_PTR(-EINVAL);
+
+	if (parent) {
+		if (parent->num_layers >= LANDLOCK_MAX_NUM_LAYERS)
+			return ERR_PTR(-E2BIG);
+		num_layers = parent->num_layers + 1;
+	} else {
+		num_layers = 1;
+	}
+
+	/* Creates a new domain... */
+	new_dom = create_ruleset(num_layers);
+	if (IS_ERR(new_dom))
+		return new_dom;
+	new_dom->hierarchy = kzalloc(sizeof(*new_dom->hierarchy),
+			GFP_KERNEL_ACCOUNT);
+	if (!new_dom->hierarchy) {
+		err = -ENOMEM;
+		goto out_put_dom;
+	}
+	refcount_set(&new_dom->hierarchy->usage, 1);
+
+	/* ...as a child of @parent... */
+	err = inherit_ruleset(parent, new_dom);
+	if (err)
+		goto out_put_dom;
+
+	/* ...and including @ruleset. */
+	err = merge_ruleset(new_dom, ruleset);
+	if (err)
+		goto out_put_dom;
+
+	return new_dom;
+
+out_put_dom:
+	landlock_put_ruleset(new_dom);
+	return ERR_PTR(err);
+}
+
+/*
+ * The returned access has the same lifetime as @ruleset.
+ */
+const struct landlock_rule *landlock_find_rule(
+		const struct landlock_ruleset *const ruleset,
+		const struct landlock_object *const object)
+{
+	const struct rb_node *node;
+
+	if (!object)
+		return NULL;
+	node = ruleset->root.rb_node;
+	while (node) {
+		struct landlock_rule *this = rb_entry(node,
+				struct landlock_rule, node);
+
+		if (this->object == object)
+			return this;
+		if (this->object < object)
+			node = node->rb_right;
+		else
+			node = node->rb_left;
+	}
+	return NULL;
+}

security/landlock/ruleset.h

+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Landlock LSM - Ruleset management
+ *
+ * Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net>
+ * Copyright © 2018-2020 ANSSI
+ */
+
+#ifndef _SECURITY_LANDLOCK_RULESET_H
+#define _SECURITY_LANDLOCK_RULESET_H
+
+#include <linux/mutex.h>
+#include <linux/rbtree.h>
+#include <linux/refcount.h>
+#include <linux/workqueue.h>
+
+#include "object.h"
+
+/**
+ * struct landlock_layer - Access rights for a given layer
+ */
+struct landlock_layer {
+	/**
+	 * @level: Position of this layer in the layer stack.
+	 */
+	u16 level;
+	/**
+	 * @access: Bitfield of allowed actions on the kernel object.  They are
+	 * relative to the object type (e.g. %LANDLOCK_ACTION_FS_READ).
+	 */
+	u16 access;
+};
+
+/**
+ * struct landlock_rule - Access rights tied to an object
+ */
+struct landlock_rule {
+	/**
+	 * @node: Node in the ruleset's red-black tree.
+	 */
+	struct rb_node node;
+	/**
+	 * @object: Pointer to identify a kernel object (e.g. an inode).  This
+	 * is used as a key for this ruleset element.  This pointer is set once
+	 * and never modified.  It always points to an allocated object because
+	 * each rule increments the refcount of its object.
+	 */
+	struct landlock_object *object;
+	/**
+	 * @num_layers: Number of entries in @layers.
+	 */
+	u32 num_layers;
+	/**
+	 * @layers: Stack of layers, from the latest to the newest, implemented
+	 * as a flexible array member (FAM).
+	 */
+	struct landlock_layer layers[];
+};
+
+/**
+ * struct landlock_hierarchy - Node in a ruleset hierarchy
+ */
+struct landlock_hierarchy {
+	/**
+	 * @parent: Pointer to the parent node, or NULL if it is a root
+	 * Landlock domain.
+	 */
+	struct landlock_hierarchy *parent;
+	/**
+	 * @usage: Number of potential children domains plus their parent
+	 * domain.
+	 */
+	refcount_t usage;
+};
+
+/**
+ * struct landlock_ruleset - Landlock ruleset
+ *
+ * This data structure must contain unique entries, be updatable, and quick to
+ * match an object.
+ */
+struct landlock_ruleset {
+	/**
+	 * @root: Root of a red-black tree containing &struct landlock_rule
+	 * nodes.  Once a ruleset is tied to a process (i.e. as a domain), this
+	 * tree is immutable until @usage reaches zero.
+	 */
+	struct rb_root root;
+	/**
+	 * @hierarchy: Enables hierarchy identification even when a parent
+	 * domain vanishes.  This is needed for the ptrace protection.
+	 */
+	struct landlock_hierarchy *hierarchy;
+	union {
+		/**
+		 * @work_free: Enables to free a ruleset within a lockless
+		 * section.  This is only used by
+		 * landlock_put_ruleset_deferred() when @usage reaches zero.
+		 * The fields @lock, @usage, @num_rules, @num_layers and
+		 * @fs_access_masks are then unused.
+		 */
+		struct work_struct work_free;
+		struct {
+			/**
+			 * @lock: Protects against concurrent modifications of
+			 * @root, if @usage is greater than zero.
+			 */
+			struct mutex lock;
+			/**
+			 * @usage: Number of processes (i.e. domains) or file
+			 * descriptors referencing this ruleset.
+			 */
+			refcount_t usage;
+			/**
+			 * @num_rules: Number of non-overlapping (i.e. not for
+			 * the same object) rules in this ruleset.
+			 */
+			u32 num_rules;
+			/**
+			 * @num_layers: Number of layers that are used in this
+			 * ruleset.  This enables to check that all the layers
+			 * allow an access request.  A value of 0 identifies a
+			 * non-merged ruleset (i.e. not a domain).
+			 */
+			u32 num_layers;
+			/**
+			 * @fs_access_masks: Contains the subset of filesystem
+			 * actions that are restricted by a ruleset.  A domain
+			 * saves all layers of merged rulesets in a stack
+			 * (FAM), starting from the first layer to the last
+			 * one.  These layers are used when merging rulesets,
+			 * for user space backward compatibility (i.e.
+			 * future-proof), and to properly handle merged
+			 * rulesets without overlapping access rights.  These
+			 * layers are set once and never changed for the
+			 * lifetime of the ruleset.
+			 */
+			u16 fs_access_masks[];
+		};
+	};
+};
+
+struct landlock_ruleset *landlock_create_ruleset(const u32 fs_access_mask);
+
+void landlock_put_ruleset(struct landlock_ruleset *const ruleset);
+void landlock_put_ruleset_deferred(struct landlock_ruleset *const ruleset);
+
+int landlock_insert_rule(struct landlock_ruleset *const ruleset,
+		struct landlock_object *const object, const u32 access);
+
+struct landlock_ruleset *landlock_merge_ruleset(
+		struct landlock_ruleset *const parent,
+		struct landlock_ruleset *const ruleset);
+
+const struct landlock_rule *landlock_find_rule(
+		const struct landlock_ruleset *const ruleset,
+		const struct landlock_object *const object);
+
+static inline void landlock_get_ruleset(struct landlock_ruleset *const ruleset)
+{
+	if (ruleset)
+		refcount_inc(&ruleset->usage);
+}
+
+#endif /* _SECURITY_LANDLOCK_RULESET_H */

security/landlock/setup.c

+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Landlock LSM - Security framework setup
+ *
+ * Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net>
+ * Copyright © 2018-2020 ANSSI
+ */
+
+#include <linux/init.h>
+#include <linux/lsm_hooks.h>
+
+#include "common.h"
+#include "cred.h"
+#include "fs.h"
+#include "ptrace.h"
+#include "setup.h"
+
+bool landlock_initialized __lsm_ro_after_init = false;
+
+struct lsm_blob_sizes landlock_blob_sizes __lsm_ro_after_init = {
+	.lbs_cred = sizeof(struct landlock_cred_security),
+	.lbs_inode = sizeof(struct landlock_inode_security),
+	.lbs_superblock = sizeof(struct landlock_superblock_security),
+};
+
+static int __init landlock_init(void)
+{
+	landlock_add_cred_hooks();
+	landlock_add_ptrace_hooks();
+	landlock_add_fs_hooks();
+	landlock_initialized = true;
+	pr_info("Up and running.\n");
+	return 0;
+}
+
+DEFINE_LSM(LANDLOCK_NAME) = {
+	.name = LANDLOCK_NAME,
+	.init = landlock_init,
+	.blobs = &landlock_blob_sizes,
+};

security/landlock/setup.h

+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Landlock LSM - Security framework setup
+ *
+ * Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net>
+ * Copyright © 2018-2020 ANSSI
+ */
+
+#ifndef _SECURITY_LANDLOCK_SETUP_H
+#define _SECURITY_LANDLOCK_SETUP_H
+
+#include <linux/lsm_hooks.h>
+
+extern bool landlock_initialized;
+
+extern struct lsm_blob_sizes landlock_blob_sizes;
+
+#endif /* _SECURITY_LANDLOCK_SETUP_H */

security/landlock/syscalls.c

+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Landlock LSM - System call implementations and user space interfaces
+ *
+ * Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net>
+ * Copyright © 2018-2020 ANSSI
+ */
+
+#include <asm/current.h>
+#include <linux/anon_inodes.h>
+#include <linux/build_bug.h>
+#include <linux/capability.h>
+#include <linux/compiler_types.h>
+#include <linux/dcache.h>
+#include <linux/err.h>
+#include <linux/errno.h>
+#include <linux/fs.h>
+#include <linux/limits.h>
+#include <linux/mount.h>
+#include <linux/path.h>
+#include <linux/sched.h>
+#include <linux/security.h>
+#include <linux/stddef.h>
+#include <linux/syscalls.h>
+#include <linux/types.h>
+#include <linux/uaccess.h>
+#include <uapi/linux/landlock.h>
+
+#include "cred.h"
+#include "fs.h"
+#include "limits.h"
+#include "ruleset.h"
+#include "setup.h"
+
+/**
+ * copy_min_struct_from_user - Safe future-proof argument copying
+ *
+ * Extend copy_struct_from_user() to check for consistent user buffer.
+ *
+ * @dst: Kernel space pointer or NULL.
+ * @ksize: Actual size of the data pointed to by @dst.
+ * @ksize_min: Minimal required size to be copied.
+ * @src: User space pointer or NULL.
+ * @usize: (Alleged) size of the data pointed to by @src.
+ */
+static __always_inline int copy_min_struct_from_user(void *const dst,
+		const size_t ksize, const size_t ksize_min,
+		const void __user *const src, const size_t usize)
+{
+	/* Checks buffer inconsistencies. */
+	BUILD_BUG_ON(!dst);
+	if (!src)
+		return -EFAULT;
+
+	/* Checks size ranges. */
+	BUILD_BUG_ON(ksize <= 0);
+	BUILD_BUG_ON(ksize < ksize_min);
+	if (usize < ksize_min)
+		return -EINVAL;
+	if (usize > PAGE_SIZE)
+		return -E2BIG;
+
+	/* Copies user buffer and fills with zeros. */
+	return copy_struct_from_user(dst, ksize, src, usize);
+}
+
+/*
+ * This function only contains arithmetic operations with constants, leading to
+ * BUILD_BUG_ON().  The related code is evaluated and checked at build time,
+ * but it is then ignored thanks to compiler optimizations.
+ */
+static void build_check_abi(void)
+{
+	struct landlock_ruleset_attr ruleset_attr;
+	struct landlock_path_beneath_attr path_beneath_attr;
+	size_t ruleset_size, path_beneath_size;
+
+	/*
+	 * For each user space ABI structures, first checks that there is no
+	 * hole in them, then checks that all architectures have the same
+	 * struct size.
+	 */
+	ruleset_size = sizeof(ruleset_attr.handled_access_fs);
+	BUILD_BUG_ON(sizeof(ruleset_attr) != ruleset_size);
+	BUILD_BUG_ON(sizeof(ruleset_attr) != 8);
+
+	path_beneath_size = sizeof(path_beneath_attr.allowed_access);
+	path_beneath_size += sizeof(path_beneath_attr.parent_fd);
+	BUILD_BUG_ON(sizeof(path_beneath_attr) != path_beneath_size);
+	BUILD_BUG_ON(sizeof(path_beneath_attr) != 12);
+}
+
+/* Ruleset handling */
+
+static int fop_ruleset_release(struct inode *const inode,
+		struct file *const filp)
+{
+	struct landlock_ruleset *ruleset = filp->private_data;
+
+	landlock_put_ruleset(ruleset);
+	return 0;
+}
+
+static ssize_t fop_dummy_read(struct file *const filp, char __user *const buf,
+		const size_t size, loff_t *const ppos)
+{
+	/* Dummy handler to enable FMODE_CAN_READ. */
+	return -EINVAL;
+}
+
+static ssize_t fop_dummy_write(struct file *const filp,
+		const char __user *const buf, const size_t size,
+		loff_t *const ppos)
+{
+	/* Dummy handler to enable FMODE_CAN_WRITE. */
+	return -EINVAL;
+}
+
+/*
+ * A ruleset file descriptor enables to build a ruleset by adding (i.e.
+ * writing) rule after rule, without relying on the task's context.  This
+ * reentrant design is also used in a read way to enforce the ruleset on the
+ * current task.
+ */
+static const struct file_operations ruleset_fops = {
+	.release = fop_ruleset_release,
+	.read = fop_dummy_read,
+	.write = fop_dummy_write,
+};
+
+#define LANDLOCK_ABI_VERSION	1
+
+/**
+ * sys_landlock_create_ruleset - Create a new ruleset
+ *
+ * @attr: Pointer to a &struct landlock_ruleset_attr identifying the scope of
+ *        the new ruleset.
+ * @size: Size of the pointed &struct landlock_ruleset_attr (needed for
+ *        backward and forward compatibility).
+ * @flags: Supported value: %LANDLOCK_CREATE_RULESET_VERSION.
+ *
+ * This system call enables to create a new Landlock ruleset, and returns the
+ * related file descriptor on success.
+ *
+ * If @flags is %LANDLOCK_CREATE_RULESET_VERSION and @attr is NULL and @size is
+ * 0, then the returned value is the highest supported Landlock ABI version
+ * (starting at 1).
+ *
+ * Possible returned errors are:
+ *
+ * - EOPNOTSUPP: Landlock is supported by the kernel but disabled at boot time;
+ * - EINVAL: unknown @flags, or unknown access, or too small @size;
+ * - E2BIG or EFAULT: @attr or @size inconsistencies;
+ * - ENOMSG: empty &landlock_ruleset_attr.handled_access_fs.
+ */
+SYSCALL_DEFINE3(landlock_create_ruleset,
+		const struct landlock_ruleset_attr __user *const, attr,
+		const size_t, size, const __u32, flags)
+{
+	struct landlock_ruleset_attr ruleset_attr;
+	struct landlock_ruleset *ruleset;
+	int err, ruleset_fd;
+
+	/* Build-time checks. */
+	build_check_abi();
+
+	if (!landlock_initialized)
+		return -EOPNOTSUPP;
+
+	if (flags) {
+		if ((flags == LANDLOCK_CREATE_RULESET_VERSION)
+				&& !attr && !size)
+			return LANDLOCK_ABI_VERSION;
+		return -EINVAL;
+	}
+
+	/* Copies raw user space buffer. */
+	err = copy_min_struct_from_user(&ruleset_attr, sizeof(ruleset_attr),
+			offsetofend(typeof(ruleset_attr), handled_access_fs),
+			attr, size);
+	if (err)
+		return err;
+
+	/* Checks content (and 32-bits cast). */
+	if ((ruleset_attr.handled_access_fs | LANDLOCK_MASK_ACCESS_FS) !=
+			LANDLOCK_MASK_ACCESS_FS)
+		return -EINVAL;
+
+	/* Checks arguments and transforms to kernel struct. */
+	ruleset = landlock_create_ruleset(ruleset_attr.handled_access_fs);
+	if (IS_ERR(ruleset))
+		return PTR_ERR(ruleset);
+
+	/* Creates anonymous FD referring to the ruleset. */
+	ruleset_fd = anon_inode_getfd("landlock-ruleset", &ruleset_fops,
+			ruleset, O_RDWR | O_CLOEXEC);
+	if (ruleset_fd < 0)
+		landlock_put_ruleset(ruleset);
+	return ruleset_fd;
+}
+
+/*
+ * Returns an owned ruleset from a FD. It is thus needed to call
+ * landlock_put_ruleset() on the return value.
+ */
+static struct landlock_ruleset *get_ruleset_from_fd(const int fd,
+		const fmode_t mode)
+{
+	struct fd ruleset_f;
+	struct landlock_ruleset *ruleset;
+
+	ruleset_f = fdget(fd);
+	if (!ruleset_f.file)
+		return ERR_PTR(-EBADF);
+
+	/* Checks FD type and access right. */
+	if (ruleset_f.file->f_op != &ruleset_fops) {
+		ruleset = ERR_PTR(-EBADFD);
+		goto out_fdput;
+	}
+	if (!(ruleset_f.file->f_mode & mode)) {
+		ruleset = ERR_PTR(-EPERM);
+		goto out_fdput;
+	}
+	ruleset = ruleset_f.file->private_data;
+	if (WARN_ON_ONCE(ruleset->num_layers != 1)) {
+		ruleset = ERR_PTR(-EINVAL);
+		goto out_fdput;
+	}
+	landlock_get_ruleset(ruleset);
+
+out_fdput:
+	fdput(ruleset_f);
+	return ruleset;
+}
+
+/* Path handling */
+
+/*
+ * @path: Must call put_path(@path) after the call if it succeeded.
+ */
+static int get_path_from_fd(const s32 fd, struct path *const path)
+{
+	struct fd f;
+	int err = 0;
+
+	BUILD_BUG_ON(!__same_type(fd,
+		((struct landlock_path_beneath_attr *)NULL)->parent_fd));
+
+	/* Handles O_PATH. */
+	f = fdget_raw(fd);
+	if (!f.file)
+		return -EBADF;
+	/*
+	 * Forbids ruleset FDs, internal filesystems (e.g. nsfs), including
+	 * pseudo filesystems that will never be mountable (e.g. sockfs,
+	 * pipefs).
+	 */
+	if ((f.file->f_op == &ruleset_fops) ||
+			(f.file->f_path.mnt->mnt_flags & MNT_INTERNAL) ||
+			(f.file->f_path.dentry->d_sb->s_flags & SB_NOUSER) ||
+			d_is_negative(f.file->f_path.dentry) ||
+			IS_PRIVATE(d_backing_inode(f.file->f_path.dentry))) {
+		err = -EBADFD;
+		goto out_fdput;
+	}
+	*path = f.file->f_path;
+	path_get(path);
+
+out_fdput:
+	fdput(f);
+	return err;
+}
+
+/**
+ * sys_landlock_add_rule - Add a new rule to a ruleset
+ *
+ * @ruleset_fd: File descriptor tied to the ruleset that should be extended
+ *		with the new rule.
+ * @rule_type: Identify the structure type pointed to by @rule_attr (only
+ *             LANDLOCK_RULE_PATH_BENEATH for now).
+ * @rule_attr: Pointer to a rule (only of type &struct
+ *             landlock_path_beneath_attr for now).
+ * @flags: Must be 0.
+ *
+ * This system call enables to define a new rule and add it to an existing
+ * ruleset.
+ *
+ * Possible returned errors are:
+ *
+ * - EOPNOTSUPP: Landlock is supported by the kernel but disabled at boot time;
+ * - EINVAL: @flags is not 0, or inconsistent access in the rule (i.e.
+ *   &landlock_path_beneath_attr.allowed_access is not a subset of the rule's
+ *   accesses);
+ * - ENOMSG: Empty accesses (e.g. &landlock_path_beneath_attr.allowed_access);
+ * - EBADF: @ruleset_fd is not a file descriptor for the current thread, or a
+ *   member of @rule_attr is not a file descriptor as expected;
+ * - EBADFD: @ruleset_fd is not a ruleset file descriptor, or a member of
+ *   @rule_attr is not the expected file descriptor type (e.g. file open
+ *   without O_PATH);
+ * - EPERM: @ruleset_fd has no write access to the underlying ruleset;
+ * - EFAULT: @rule_attr inconsistency.
+ */
+SYSCALL_DEFINE4(landlock_add_rule,
+		const int, ruleset_fd, const enum landlock_rule_type, rule_type,
+		const void __user *const, rule_attr, const __u32, flags)
+{
+	struct landlock_path_beneath_attr path_beneath_attr;
+	struct path path;
+	struct landlock_ruleset *ruleset;
+	int res, err;
+
+	if (!landlock_initialized)
+		return -EOPNOTSUPP;
+
+	/* No flag for now. */
+	if (flags)
+		return -EINVAL;
+
+	if (rule_type != LANDLOCK_RULE_PATH_BENEATH)
+		return -EINVAL;
+
+	/* Copies raw user space buffer, only one type for now. */
+	res = copy_from_user(&path_beneath_attr, rule_attr,
+			sizeof(path_beneath_attr));
+	if (res)
+		return -EFAULT;
+
+	/* Gets and checks the ruleset. */
+	ruleset = get_ruleset_from_fd(ruleset_fd, FMODE_CAN_WRITE);
+	if (IS_ERR(ruleset))
+		return PTR_ERR(ruleset);
+
+	/*
+	 * Informs about useless rule: empty allowed_access (i.e. deny rules)
+	 * are ignored in path walks.
+	 */
+	if (!path_beneath_attr.allowed_access) {
+		err = -ENOMSG;
+		goto out_put_ruleset;
+	}
+	/*
+	 * Checks that allowed_access matches the @ruleset constraints
+	 * (ruleset->fs_access_masks[0] is automatically upgraded to 64-bits).
+	 */
+	if ((path_beneath_attr.allowed_access | ruleset->fs_access_masks[0]) !=
+			ruleset->fs_access_masks[0]) {
+		err = -EINVAL;
+		goto out_put_ruleset;
+	}
+
+	/* Gets and checks the new rule. */
+	err = get_path_from_fd(path_beneath_attr.parent_fd, &path);
+	if (err)
+		goto out_put_ruleset;
+
+	/* Imports the new rule. */
+	err = landlock_append_fs_rule(ruleset, &path,
+			path_beneath_attr.allowed_access);
+	path_put(&path);
+
+out_put_ruleset:
+	landlock_put_ruleset(ruleset);
+	return err;
+}
+
+/* Enforcement */
+
+/**
+ * sys_landlock_restrict_self - Enforce a ruleset on the calling thread
+ *
+ * @ruleset_fd: File descriptor tied to the ruleset to merge with the target.
+ * @flags: Must be 0.
+ *
+ * This system call enables to enforce a Landlock ruleset on the current
+ * thread.  Enforcing a ruleset requires that the task has CAP_SYS_ADMIN in its
+ * namespace or is running with no_new_privs.  This avoids scenarios where
+ * unprivileged tasks can affect the behavior of privileged children.
+ *
+ * Possible returned errors are:
+ *
+ * - EOPNOTSUPP: Landlock is supported by the kernel but disabled at boot time;
+ * - EINVAL: @flags is not 0.
+ * - EBADF: @ruleset_fd is not a file descriptor for the current thread;
+ * - EBADFD: @ruleset_fd is not a ruleset file descriptor;
+ * - EPERM: @ruleset_fd has no read access to the underlying ruleset, or the
+ *   current thread is not running with no_new_privs, or it doesn't have
+ *   CAP_SYS_ADMIN in its namespace.
+ * - E2BIG: The maximum number of stacked rulesets is reached for the current
+ *   thread.
+ */
+SYSCALL_DEFINE2(landlock_restrict_self,
+		const int, ruleset_fd, const __u32, flags)
+{
+	struct landlock_ruleset *new_dom, *ruleset;
+	struct cred *new_cred;
+	struct landlock_cred_security *new_llcred;
+	int err;
+
+	if (!landlock_initialized)
+		return -EOPNOTSUPP;
+
+	/* No flag for now. */
+	if (flags)
+		return -EINVAL;
+
+	/*
+	 * Similar checks as for seccomp(2), except that an -EPERM may be
+	 * returned.
+	 */
+	if (!task_no_new_privs(current) &&
+			!ns_capable_noaudit(current_user_ns(), CAP_SYS_ADMIN))
+		return -EPERM;
+
+	/* Gets and checks the ruleset. */
+	ruleset = get_ruleset_from_fd(ruleset_fd, FMODE_CAN_READ);
+	if (IS_ERR(ruleset))
+		return PTR_ERR(ruleset);
+
+	/* Prepares new credentials. */
+	new_cred = prepare_creds();
+	if (!new_cred) {
+		err = -ENOMEM;
+		goto out_put_ruleset;
+	}
+	new_llcred = landlock_cred(new_cred);
+
+	/*
+	 * There is no possible race condition while copying and manipulating
+	 * the current credentials because they are dedicated per thread.
+	 */
+	new_dom = landlock_merge_ruleset(new_llcred->domain, ruleset);
+	if (IS_ERR(new_dom)) {
+		err = PTR_ERR(new_dom);
+		goto out_put_creds;
+	}
+
+	/* Replaces the old (prepared) domain. */
+	landlock_put_ruleset(new_llcred->domain);
+	new_llcred->domain = new_dom;
+
+	landlock_put_ruleset(ruleset);
+	return commit_creds(new_cred);
+
+out_put_creds:
+	abort_creds(new_cred);
+
+out_put_ruleset:
+	landlock_put_ruleset(ruleset);
+	return err;
+}

security/security.c

@@ -203,6 +203,7 @@ static void __init lsm_set_blob_sizes(struct lsm_blob_sizes *needed)
 	lsm_set_blob_size(&needed->lbs_inode, &blob_sizes.lbs_inode);
 	lsm_set_blob_size(&needed->lbs_ipc, &blob_sizes.lbs_ipc);
 	lsm_set_blob_size(&needed->lbs_msg_msg, &blob_sizes.lbs_msg_msg);
+	lsm_set_blob_size(&needed->lbs_superblock, &blob_sizes.lbs_superblock);
 	lsm_set_blob_size(&needed->lbs_task, &blob_sizes.lbs_task);
 }
 
@@ -333,12 +334,13 @@ static void __init ordered_lsm_init(void)
 	for (lsm = ordered_lsms; *lsm; lsm++)
 		prepare_lsm(*lsm);
 
-	init_debug("cred blob size     = %d\n", blob_sizes.lbs_cred);
-	init_debug("file blob size     = %d\n", blob_sizes.lbs_file);
-	init_debug("inode blob size    = %d\n", blob_sizes.lbs_inode);
-	init_debug("ipc blob size      = %d\n", blob_sizes.lbs_ipc);
-	init_debug("msg_msg blob size  = %d\n", blob_sizes.lbs_msg_msg);
-	init_debug("task blob size     = %d\n", blob_sizes.lbs_task);
+	init_debug("cred blob size       = %d\n", blob_sizes.lbs_cred);
+	init_debug("file blob size       = %d\n", blob_sizes.lbs_file);
+	init_debug("inode blob size      = %d\n", blob_sizes.lbs_inode);
+	init_debug("ipc blob size        = %d\n", blob_sizes.lbs_ipc);
+	init_debug("msg_msg blob size    = %d\n", blob_sizes.lbs_msg_msg);
+	init_debug("superblock blob size = %d\n", blob_sizes.lbs_superblock);
+	init_debug("task blob size       = %d\n", blob_sizes.lbs_task);
 
 	/*
 	 * Create any kmem_caches needed for blobs
@@ -670,6 +672,27 @@ static void __init lsm_early_task(struct task_struct *task)
 		panic("%s: Early task alloc failed.\n", __func__);
 }
 
+/**
+ * lsm_superblock_alloc - allocate a composite superblock blob
+ * @sb: the superblock that needs a blob
+ *
+ * Allocate the superblock blob for all the modules
+ *
+ * Returns 0, or -ENOMEM if memory can't be allocated.
+ */
+static int lsm_superblock_alloc(struct super_block *sb)
+{
+	if (blob_sizes.lbs_superblock == 0) {
+		sb->s_security = NULL;
+		return 0;
+	}
+
+	sb->s_security = kzalloc(blob_sizes.lbs_superblock, GFP_KERNEL);
+	if (sb->s_security == NULL)
+		return -ENOMEM;
+	return 0;
+}
+
 /*
  * The default value of the LSM hook is defined in linux/lsm_hook_defs.h and
  * can be accessed with:
@@ -867,12 +890,26 @@ int security_fs_context_parse_param(struct fs_context *fc, struct fs_parameter *
 
 int security_sb_alloc(struct super_block *sb)
 {
-	return call_int_hook(sb_alloc_security, 0, sb);
+	int rc = lsm_superblock_alloc(sb);
+
+	if (unlikely(rc))
+		return rc;
+	rc = call_int_hook(sb_alloc_security, 0, sb);
+	if (unlikely(rc))
+		security_sb_free(sb);
+	return rc;
+}
+
+void security_sb_delete(struct super_block *sb)
+{
+	call_void_hook(sb_delete, sb);
 }
 
 void security_sb_free(struct super_block *sb)
 {
 	call_void_hook(sb_free_security, sb);
+	kfree(sb->s_security);
+	sb->s_security = NULL;
 }
 
 void security_free_mnt_opts(void **mnt_opts)

security/selinux/hooks.c

@@ -358,7 +358,7 @@ static void inode_free_security(struct inode *inode)
 
 	if (!isec)
 		return;
-	sbsec = inode->i_sb->s_security;
+	sbsec = selinux_superblock(inode->i_sb);
 	/*
 	 * As not all inode security structures are in a list, we check for
 	 * empty list outside of the lock to make sure that we won't waste
@@ -376,13 +376,6 @@ static void inode_free_security(struct inode *inode)
 	}
 }
 
-static void superblock_free_security(struct super_block *sb)
-{
-	struct superblock_security_struct *sbsec = sb->s_security;
-	sb->s_security = NULL;
-	kfree(sbsec);
-}
-
 struct selinux_mnt_opts {
 	const char *fscontext, *context, *rootcontext, *defcontext;
 };
@@ -494,7 +487,7 @@ static int selinux_is_genfs_special_handling(struct super_block *sb)
 
 static int selinux_is_sblabel_mnt(struct super_block *sb)
 {
-	struct superblock_security_struct *sbsec = sb->s_security;
+	struct superblock_security_struct *sbsec = selinux_superblock(sb);
 
 	/*
 	 * IMPORTANT: Double-check logic in this function when adding a new
@@ -571,7 +564,7 @@ static int sb_check_xattr_support(struct super_block *sb)
 
 static int sb_finish_set_opts(struct super_block *sb)
 {
-	struct superblock_security_struct *sbsec = sb->s_security;
+	struct superblock_security_struct *sbsec = selinux_superblock(sb);
 	struct dentry *root = sb->s_root;
 	struct inode *root_inode = d_backing_inode(root);
 	int rc = 0;
@@ -662,7 +655,7 @@ static int selinux_set_mnt_opts(struct super_block *sb,
 				unsigned long *set_kern_flags)
 {
 	const struct cred *cred = current_cred();
-	struct superblock_security_struct *sbsec = sb->s_security;
+	struct superblock_security_struct *sbsec = selinux_superblock(sb);
 	struct dentry *root = sb->s_root;
 	struct selinux_mnt_opts *opts = mnt_opts;
 	struct inode_security_struct *root_isec;
@@ -900,8 +893,8 @@ static int selinux_set_mnt_opts(struct super_block *sb,
 static int selinux_cmp_sb_context(const struct super_block *oldsb,
 				    const struct super_block *newsb)
 {
-	struct superblock_security_struct *old = oldsb->s_security;
-	struct superblock_security_struct *new = newsb->s_security;
+	struct superblock_security_struct *old = selinux_superblock(oldsb);
+	struct superblock_security_struct *new = selinux_superblock(newsb);
 	char oldflags = old->flags & SE_MNTMASK;
 	char newflags = new->flags & SE_MNTMASK;
 
@@ -933,8 +926,9 @@ static int selinux_sb_clone_mnt_opts(const struct super_block *oldsb,
 					unsigned long *set_kern_flags)
 {
 	int rc = 0;
-	const struct superblock_security_struct *oldsbsec = oldsb->s_security;
-	struct superblock_security_struct *newsbsec = newsb->s_security;
+	const struct superblock_security_struct *oldsbsec =
+						selinux_superblock(oldsb);
+	struct superblock_security_struct *newsbsec = selinux_superblock(newsb);
 
 	int set_fscontext =	(oldsbsec->flags & FSCONTEXT_MNT);
 	int set_context =	(oldsbsec->flags & CONTEXT_MNT);
@@ -1113,7 +1107,7 @@ static int show_sid(struct seq_file *m, u32 sid)
 
 static int selinux_sb_show_options(struct seq_file *m, struct super_block *sb)
 {
-	struct superblock_security_struct *sbsec = sb->s_security;
+	struct superblock_security_struct *sbsec = selinux_superblock(sb);
 	int rc;
 
 	if (!(sbsec->flags & SE_SBINITIALIZED))
@@ -1464,7 +1458,7 @@ static int inode_doinit_with_dentry(struct inode *inode, struct dentry *opt_dent
 	if (isec->sclass == SECCLASS_FILE)
 		isec->sclass = inode_mode_to_security_class(inode->i_mode);
 
-	sbsec = inode->i_sb->s_security;
+	sbsec = selinux_superblock(inode->i_sb);
 	if (!(sbsec->flags & SE_SBINITIALIZED)) {
 		/* Defer initialization until selinux_complete_init,
 		   after the initial policy is loaded and the security
@@ -1815,7 +1809,8 @@ selinux_determine_inode_label(const struct task_security_struct *tsec,
 				 const struct qstr *name, u16 tclass,
 				 u32 *_new_isid)
 {
-	const struct superblock_security_struct *sbsec = dir->i_sb->s_security;
+	const struct superblock_security_struct *sbsec =
+						selinux_superblock(dir->i_sb);
 
 	if ((sbsec->flags & SE_SBINITIALIZED) &&
 	    (sbsec->behavior == SECURITY_FS_USE_MNTPOINT)) {
@@ -1846,7 +1841,7 @@ static int may_create(struct inode *dir,
 	int rc;
 
 	dsec = inode_security(dir);
-	sbsec = dir->i_sb->s_security;
+	sbsec = selinux_superblock(dir->i_sb);
 
 	sid = tsec->sid;
 
@@ -1995,7 +1990,7 @@ static int superblock_has_perm(const struct cred *cred,
 	struct superblock_security_struct *sbsec;
 	u32 sid = cred_sid(cred);
 
-	sbsec = sb->s_security;
+	sbsec = selinux_superblock(sb);
 	return avc_has_perm(&selinux_state,
 			    sid, sbsec->sid, SECCLASS_FILESYSTEM, perms, ad);
 }
@@ -2617,11 +2612,7 @@ static void selinux_bprm_committed_creds(struct linux_binprm *bprm)
 
 static int selinux_sb_alloc_security(struct super_block *sb)
 {
-	struct superblock_security_struct *sbsec;
-
-	sbsec = kzalloc(sizeof(struct superblock_security_struct), GFP_KERNEL);
-	if (!sbsec)
-		return -ENOMEM;
+	struct superblock_security_struct *sbsec = selinux_superblock(sb);
 
 	mutex_init(&sbsec->lock);
 	INIT_LIST_HEAD(&sbsec->isec_head);
@@ -2629,16 +2620,10 @@ static int selinux_sb_alloc_security(struct super_block *sb)
 	sbsec->sid = SECINITSID_UNLABELED;
 	sbsec->def_sid = SECINITSID_FILE;
 	sbsec->mntpoint_sid = SECINITSID_UNLABELED;
-	sb->s_security = sbsec;
 
 	return 0;
 }
 
-static void selinux_sb_free_security(struct super_block *sb)
-{
-	superblock_free_security(sb);
-}
-
 static inline int opt_len(const char *s)
 {
 	bool open_quote = false;
@@ -2772,7 +2757,7 @@ static int selinux_sb_mnt_opts_compat(struct super_block *sb, void *mnt_opts)
 static int selinux_sb_remount(struct super_block *sb, void *mnt_opts)
 {
 	struct selinux_mnt_opts *opts = mnt_opts;
-	struct superblock_security_struct *sbsec = sb->s_security;
+	struct superblock_security_struct *sbsec = selinux_superblock(sb);
 	u32 sid;
 	int rc;
 
@@ -3010,7 +2995,7 @@ static int selinux_inode_init_security(struct inode *inode, struct inode *dir,
 	int rc;
 	char *context;
 
-	sbsec = dir->i_sb->s_security;
+	sbsec = selinux_superblock(dir->i_sb);
 
 	newsid = tsec->create_sid;
 
@@ -3312,7 +3297,7 @@ static int selinux_inode_setxattr(struct user_namespace *mnt_userns,
 	if (!selinux_initialized(&selinux_state))
 		return (inode_owner_or_capable(mnt_userns, inode) ? 0 : -EPERM);
 
-	sbsec = inode->i_sb->s_security;
+	sbsec = selinux_superblock(inode->i_sb);
 	if (!(sbsec->flags & SBLABEL_MNT))
 		return -EOPNOTSUPP;
 
@@ -3557,13 +3542,14 @@ static int selinux_inode_setsecurity(struct inode *inode, const char *name,
 				     const void *value, size_t size, int flags)
 {
 	struct inode_security_struct *isec = inode_security_novalidate(inode);
-	struct superblock_security_struct *sbsec = inode->i_sb->s_security;
+	struct superblock_security_struct *sbsec;
 	u32 newsid;
 	int rc;
 
 	if (strcmp(name, XATTR_SELINUX_SUFFIX))
 		return -EOPNOTSUPP;
 
+	sbsec = selinux_superblock(inode->i_sb);
 	if (!(sbsec->flags & SBLABEL_MNT))
 		return -EOPNOTSUPP;
 
@@ -7065,6 +7051,7 @@ struct lsm_blob_sizes selinux_blob_sizes __lsm_ro_after_init = {
 	.lbs_inode = sizeof(struct inode_security_struct),
 	.lbs_ipc = sizeof(struct ipc_security_struct),
 	.lbs_msg_msg = sizeof(struct msg_security_struct),
+	.lbs_superblock = sizeof(struct superblock_security_struct),
 };
 
 #ifdef CONFIG_PERF_EVENTS
@@ -7165,7 +7152,6 @@ static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
 	LSM_HOOK_INIT(bprm_committing_creds, selinux_bprm_committing_creds),
 	LSM_HOOK_INIT(bprm_committed_creds, selinux_bprm_committed_creds),
 
-	LSM_HOOK_INIT(sb_free_security, selinux_sb_free_security),
 	LSM_HOOK_INIT(sb_free_mnt_opts, selinux_free_mnt_opts),
 	LSM_HOOK_INIT(sb_mnt_opts_compat, selinux_sb_mnt_opts_compat),
 	LSM_HOOK_INIT(sb_remount, selinux_sb_remount),

security/selinux/include/objsec.h

@@ -188,4 +188,10 @@ static inline u32 current_sid(void)
 	return tsec->sid;
 }
 
+static inline struct superblock_security_struct *selinux_superblock(
+					const struct super_block *superblock)
+{
+	return superblock->s_security + selinux_blob_sizes.lbs_superblock;
+}
+
 #endif /* _SELINUX_OBJSEC_H_ */

security/selinux/ss/services.c

@@ -47,6 +47,7 @@
 #include <linux/sched.h>
 #include <linux/audit.h>
 #include <linux/vmalloc.h>
+#include <linux/lsm_hooks.h>
 #include <net/netlabel.h>
 
 #include "flask.h"
@@ -2955,7 +2956,7 @@ int security_fs_use(struct selinux_state *state, struct super_block *sb)
 	struct sidtab *sidtab;
 	int rc;
 	struct ocontext *c;
-	struct superblock_security_struct *sbsec = sb->s_security;
+	struct superblock_security_struct *sbsec = selinux_superblock(sb);
 	const char *fstype = sb->s_type->name;
 
 	if (!selinux_initialized(state)) {

security/smack/smack.h

@@ -357,6 +357,12 @@ static inline struct smack_known **smack_ipc(const struct kern_ipc_perm *ipc)
 	return ipc->security + smack_blob_sizes.lbs_ipc;
 }
 
+static inline struct superblock_smack *smack_superblock(
+					const struct super_block *superblock)
+{
+	return superblock->s_security + smack_blob_sizes.lbs_superblock;
+}
+
 /*
  * Is the directory transmuting?
  */

security/smack/smack_lsm.c

@@ -535,12 +535,7 @@ static int smack_syslog(int typefrom_file)
  */
 static int smack_sb_alloc_security(struct super_block *sb)
 {
-	struct superblock_smack *sbsp;
-
-	sbsp = kzalloc(sizeof(struct superblock_smack), GFP_KERNEL);
-
-	if (sbsp == NULL)
-		return -ENOMEM;
+	struct superblock_smack *sbsp = smack_superblock(sb);
 
 	sbsp->smk_root = &smack_known_floor;
 	sbsp->smk_default = &smack_known_floor;
@@ -549,22 +544,10 @@ static int smack_sb_alloc_security(struct super_block *sb)
 	/*
 	 * SMK_SB_INITIALIZED will be zero from kzalloc.
 	 */
-	sb->s_security = sbsp;
 
 	return 0;
 }
 
-/**
- * smack_sb_free_security - free a superblock blob
- * @sb: the superblock getting the blob
- *
- */
-static void smack_sb_free_security(struct super_block *sb)
-{
-	kfree(sb->s_security);
-	sb->s_security = NULL;
-}
-
 struct smack_mnt_opts {
 	const char *fsdefault, *fsfloor, *fshat, *fsroot, *fstransmute;
 };
@@ -772,7 +755,7 @@ static int smack_set_mnt_opts(struct super_block *sb,
 {
 	struct dentry *root = sb->s_root;
 	struct inode *inode = d_backing_inode(root);
-	struct superblock_smack *sp = sb->s_security;
+	struct superblock_smack *sp = smack_superblock(sb);
 	struct inode_smack *isp;
 	struct smack_known *skp;
 	struct smack_mnt_opts *opts = mnt_opts;
@@ -871,7 +854,7 @@ static int smack_set_mnt_opts(struct super_block *sb,
  */
 static int smack_sb_statfs(struct dentry *dentry)
 {
-	struct superblock_smack *sbp = dentry->d_sb->s_security;
+	struct superblock_smack *sbp = smack_superblock(dentry->d_sb);
 	int rc;
 	struct smk_audit_info ad;
 
@@ -905,7 +888,7 @@ static int smack_bprm_creds_for_exec(struct linux_binprm *bprm)
 	if (isp->smk_task == NULL || isp->smk_task == bsp->smk_task)
 		return 0;
 
-	sbsp = inode->i_sb->s_security;
+	sbsp = smack_superblock(inode->i_sb);
 	if ((sbsp->smk_flags & SMK_SB_UNTRUSTED) &&
 	    isp->smk_task != sbsp->smk_root)
 		return 0;
@@ -1157,7 +1140,7 @@ static int smack_inode_rename(struct inode *old_inode,
  */
 static int smack_inode_permission(struct inode *inode, int mask)
 {
-	struct superblock_smack *sbsp = inode->i_sb->s_security;
+	struct superblock_smack *sbsp = smack_superblock(inode->i_sb);
 	struct smk_audit_info ad;
 	int no_block = mask & MAY_NOT_BLOCK;
 	int rc;
@@ -1400,7 +1383,7 @@ static int smack_inode_removexattr(struct user_namespace *mnt_userns,
 	 */
 	if (strcmp(name, XATTR_NAME_SMACK) == 0) {
 		struct super_block *sbp = dentry->d_sb;
-		struct superblock_smack *sbsp = sbp->s_security;
+		struct superblock_smack *sbsp = smack_superblock(sbp);
 
 		isp->smk_inode = sbsp->smk_default;
 	} else if (strcmp(name, XATTR_NAME_SMACKEXEC) == 0)
@@ -1670,7 +1653,7 @@ static int smack_mmap_file(struct file *file,
 	isp = smack_inode(file_inode(file));
 	if (isp->smk_mmap == NULL)
 		return 0;
-	sbsp = file_inode(file)->i_sb->s_security;
+	sbsp = smack_superblock(file_inode(file)->i_sb);
 	if (sbsp->smk_flags & SMK_SB_UNTRUSTED &&
 	    isp->smk_mmap != sbsp->smk_root)
 		return -EACCES;
@@ -3299,7 +3282,7 @@ static void smack_d_instantiate(struct dentry *opt_dentry, struct inode *inode)
 		return;
 
 	sbp = inode->i_sb;
-	sbsp = sbp->s_security;
+	sbsp = smack_superblock(sbp);
 	/*
 	 * We're going to use the superblock default label
 	 * if there's no label on the file.
@@ -4714,6 +4697,7 @@ struct lsm_blob_sizes smack_blob_sizes __lsm_ro_after_init = {
 	.lbs_inode = sizeof(struct inode_smack),
 	.lbs_ipc = sizeof(struct smack_known *),
 	.lbs_msg_msg = sizeof(struct smack_known *),
+	.lbs_superblock = sizeof(struct superblock_smack),
 };
 
 static struct security_hook_list smack_hooks[] __lsm_ro_after_init = {
@@ -4725,7 +4709,6 @@ static struct security_hook_list smack_hooks[] __lsm_ro_after_init = {
 	LSM_HOOK_INIT(fs_context_parse_param, smack_fs_context_parse_param),
 
 	LSM_HOOK_INIT(sb_alloc_security, smack_sb_alloc_security),
-	LSM_HOOK_INIT(sb_free_security, smack_sb_free_security),
 	LSM_HOOK_INIT(sb_free_mnt_opts, smack_free_mnt_opts),
 	LSM_HOOK_INIT(sb_eat_lsm_opts, smack_sb_eat_lsm_opts),
 	LSM_HOOK_INIT(sb_statfs, smack_sb_statfs),

tools/testing/selftests/Makefile

@@ -25,6 +25,7 @@ TARGETS += ir
 TARGETS += kcmp
 TARGETS += kexec
 TARGETS += kvm
+TARGETS += landlock
 TARGETS += lib
 TARGETS += livepatch
 TARGETS += lkdtm

tools/testing/selftests/landlock/.gitignore

+/*_test
+/true

tools/testing/selftests/landlock/Makefile

+# SPDX-License-Identifier: GPL-2.0
+
+CFLAGS += -Wall -O2
+
+src_test := $(wildcard *_test.c)
+
+TEST_GEN_PROGS := $(src_test:.c=)
+
+TEST_GEN_PROGS_EXTENDED := true
+
+KSFT_KHDR_INSTALL := 1
+OVERRIDE_TARGETS := 1
+include ../lib.mk
+
+khdr_dir = $(top_srcdir)/usr/include
+
+$(khdr_dir)/linux/landlock.h: khdr
+	@:
+
+$(OUTPUT)/true: true.c
+	$(LINK.c) $< $(LDLIBS) -o $@ -static
+
+$(OUTPUT)/%_test: %_test.c $(khdr_dir)/linux/landlock.h ../kselftest_harness.h common.h
+	$(LINK.c) $< $(LDLIBS) -o $@ -lcap -I$(khdr_dir)

tools/testing/selftests/landlock/base_test.c

+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Landlock tests - Common user space base
+ *
+ * Copyright © 2017-2020 Mickaël Salaün <mic@digikod.net>
+ * Copyright © 2019-2020 ANSSI
+ */
+
+#define _GNU_SOURCE
+#include <errno.h>
+#include <fcntl.h>
+#include <linux/landlock.h>
+#include <string.h>
+#include <sys/prctl.h>
+#include <sys/socket.h>
+#include <sys/types.h>
+
+#include "common.h"
+
+#ifndef O_PATH
+#define O_PATH		010000000
+#endif
+
+TEST(inconsistent_attr) {
+	const long page_size = sysconf(_SC_PAGESIZE);
+	char *const buf = malloc(page_size + 1);
+	struct landlock_ruleset_attr *const ruleset_attr = (void *)buf;
+
+	ASSERT_NE(NULL, buf);
+
+	/* Checks copy_from_user(). */
+	ASSERT_EQ(-1, landlock_create_ruleset(ruleset_attr, 0, 0));
+	/* The size if less than sizeof(struct landlock_attr_enforce). */
+	ASSERT_EQ(EINVAL, errno);
+	ASSERT_EQ(-1, landlock_create_ruleset(ruleset_attr, 1, 0));
+	ASSERT_EQ(EINVAL, errno);
+
+	ASSERT_EQ(-1, landlock_create_ruleset(NULL, 1, 0));
+	/* The size if less than sizeof(struct landlock_attr_enforce). */
+	ASSERT_EQ(EFAULT, errno);
+
+	ASSERT_EQ(-1, landlock_create_ruleset(NULL,
+				sizeof(struct landlock_ruleset_attr), 0));
+	ASSERT_EQ(EFAULT, errno);
+
+	ASSERT_EQ(-1, landlock_create_ruleset(ruleset_attr, page_size + 1, 0));
+	ASSERT_EQ(E2BIG, errno);
+
+	ASSERT_EQ(-1, landlock_create_ruleset(ruleset_attr,
+				sizeof(struct landlock_ruleset_attr), 0));
+	ASSERT_EQ(ENOMSG, errno);
+	ASSERT_EQ(-1, landlock_create_ruleset(ruleset_attr, page_size, 0));
+	ASSERT_EQ(ENOMSG, errno);
+
+	/* Checks non-zero value. */
+	buf[page_size - 2] = '.';
+	ASSERT_EQ(-1, landlock_create_ruleset(ruleset_attr, page_size, 0));
+	ASSERT_EQ(E2BIG, errno);
+
+	ASSERT_EQ(-1, landlock_create_ruleset(ruleset_attr, page_size + 1, 0));
+	ASSERT_EQ(E2BIG, errno);
+
+	free(buf);
+}
+
+TEST(abi_version) {
+	const struct landlock_ruleset_attr ruleset_attr = {
+		.handled_access_fs = LANDLOCK_ACCESS_FS_READ_FILE,
+	};
+	ASSERT_EQ(1, landlock_create_ruleset(NULL, 0,
+				LANDLOCK_CREATE_RULESET_VERSION));
+
+	ASSERT_EQ(-1, landlock_create_ruleset(&ruleset_attr, 0,
+				LANDLOCK_CREATE_RULESET_VERSION));
+	ASSERT_EQ(EINVAL, errno);
+
+	ASSERT_EQ(-1, landlock_create_ruleset(NULL, sizeof(ruleset_attr),
+				LANDLOCK_CREATE_RULESET_VERSION));
+	ASSERT_EQ(EINVAL, errno);
+
+	ASSERT_EQ(-1, landlock_create_ruleset(&ruleset_attr,
+				sizeof(ruleset_attr),
+				LANDLOCK_CREATE_RULESET_VERSION));
+	ASSERT_EQ(EINVAL, errno);
+
+	ASSERT_EQ(-1, landlock_create_ruleset(NULL, 0,
+				LANDLOCK_CREATE_RULESET_VERSION | 1 << 31));
+	ASSERT_EQ(EINVAL, errno);
+}
+
+TEST(inval_create_ruleset_flags) {
+	const int last_flag = LANDLOCK_CREATE_RULESET_VERSION;
+	const int invalid_flag = last_flag << 1;
+	const struct landlock_ruleset_attr ruleset_attr = {
+		.handled_access_fs = LANDLOCK_ACCESS_FS_READ_FILE,
+	};
+
+	ASSERT_EQ(-1, landlock_create_ruleset(NULL, 0, invalid_flag));
+	ASSERT_EQ(EINVAL, errno);
+
+	ASSERT_EQ(-1, landlock_create_ruleset(&ruleset_attr, 0, invalid_flag));
+	ASSERT_EQ(EINVAL, errno);
+
+	ASSERT_EQ(-1, landlock_create_ruleset(NULL, sizeof(ruleset_attr),
+				invalid_flag));
+	ASSERT_EQ(EINVAL, errno);
+
+	ASSERT_EQ(-1, landlock_create_ruleset(&ruleset_attr,
+				sizeof(ruleset_attr), invalid_flag));
+	ASSERT_EQ(EINVAL, errno);
+}
+
+TEST(empty_path_beneath_attr) {
+	const struct landlock_ruleset_attr ruleset_attr = {
+		.handled_access_fs = LANDLOCK_ACCESS_FS_EXECUTE,
+	};
+	const int ruleset_fd = landlock_create_ruleset(&ruleset_attr,
+			sizeof(ruleset_attr), 0);
+
+	ASSERT_LE(0, ruleset_fd);
+
+	/* Similar to struct landlock_path_beneath_attr.parent_fd = 0 */
+	ASSERT_EQ(-1, landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH,
+				NULL, 0));
+	ASSERT_EQ(EFAULT, errno);
+	ASSERT_EQ(0, close(ruleset_fd));
+}
+
+TEST(inval_fd_enforce) {
+	ASSERT_EQ(0, prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0));
+
+	ASSERT_EQ(-1, landlock_restrict_self(-1, 0));
+	ASSERT_EQ(EBADF, errno);
+}
+
+TEST(unpriv_enforce_without_no_new_privs) {
+	int err;
+
+	drop_caps(_metadata);
+	err = landlock_restrict_self(-1, 0);
+	ASSERT_EQ(EPERM, errno);
+	ASSERT_EQ(err, -1);
+}
+
+TEST(ruleset_fd_io)
+{
+	struct landlock_ruleset_attr ruleset_attr = {
+		.handled_access_fs = LANDLOCK_ACCESS_FS_READ_FILE,
+	};
+	int ruleset_fd;
+	char buf;
+
+	drop_caps(_metadata);
+	ruleset_fd = landlock_create_ruleset(&ruleset_attr,
+			sizeof(ruleset_attr), 0);
+	ASSERT_LE(0, ruleset_fd);
+
+	ASSERT_EQ(-1, write(ruleset_fd, ".", 1));
+	ASSERT_EQ(EINVAL, errno);
+	ASSERT_EQ(-1, read(ruleset_fd, &buf, 1));
+	ASSERT_EQ(EINVAL, errno);
+
+	ASSERT_EQ(0, close(ruleset_fd));
+}
+
+/* Tests enforcement of a ruleset FD transferred through a UNIX socket. */
+TEST(ruleset_fd_transfer)
+{
+	struct landlock_ruleset_attr ruleset_attr = {
+		.handled_access_fs = LANDLOCK_ACCESS_FS_READ_DIR,
+	};
+	struct landlock_path_beneath_attr path_beneath_attr = {
+		.allowed_access = LANDLOCK_ACCESS_FS_READ_DIR,
+	};
+	int ruleset_fd_tx, dir_fd;
+	union {
+		/* Aligned ancillary data buffer. */
+		char buf[CMSG_SPACE(sizeof(ruleset_fd_tx))];
+		struct cmsghdr _align;
+	} cmsg_tx = {};
+	char data_tx = '.';
+	struct iovec io = {
+		.iov_base = &data_tx,
+		.iov_len = sizeof(data_tx),
+	};
+	struct msghdr msg = {
+		.msg_iov = &io,
+		.msg_iovlen = 1,
+		.msg_control = &cmsg_tx.buf,
+		.msg_controllen = sizeof(cmsg_tx.buf),
+	};
+	struct cmsghdr *cmsg;
+	int socket_fds[2];
+	pid_t child;
+	int status;
+
+	drop_caps(_metadata);
+
+	/* Creates a test ruleset with a simple rule. */
+	ruleset_fd_tx = landlock_create_ruleset(&ruleset_attr,
+			sizeof(ruleset_attr), 0);
+	ASSERT_LE(0, ruleset_fd_tx);
+	path_beneath_attr.parent_fd = open("/tmp", O_PATH | O_NOFOLLOW |
+			O_DIRECTORY | O_CLOEXEC);
+	ASSERT_LE(0, path_beneath_attr.parent_fd);
+	ASSERT_EQ(0, landlock_add_rule(ruleset_fd_tx, LANDLOCK_RULE_PATH_BENEATH,
+				&path_beneath_attr, 0));
+	ASSERT_EQ(0, close(path_beneath_attr.parent_fd));
+
+	cmsg = CMSG_FIRSTHDR(&msg);
+	ASSERT_NE(NULL, cmsg);
+	cmsg->cmsg_len = CMSG_LEN(sizeof(ruleset_fd_tx));
+	cmsg->cmsg_level = SOL_SOCKET;
+	cmsg->cmsg_type = SCM_RIGHTS;
+	memcpy(CMSG_DATA(cmsg), &ruleset_fd_tx, sizeof(ruleset_fd_tx));
+
+	/* Sends the ruleset FD over a socketpair and then close it. */
+	ASSERT_EQ(0, socketpair(AF_UNIX, SOCK_STREAM | SOCK_CLOEXEC, 0, socket_fds));
+	ASSERT_EQ(sizeof(data_tx), sendmsg(socket_fds[0], &msg, 0));
+	ASSERT_EQ(0, close(socket_fds[0]));
+	ASSERT_EQ(0, close(ruleset_fd_tx));
+
+	child = fork();
+	ASSERT_LE(0, child);
+	if (child == 0) {
+		int ruleset_fd_rx;
+
+		*(char *)msg.msg_iov->iov_base = '\0';
+		ASSERT_EQ(sizeof(data_tx), recvmsg(socket_fds[1], &msg, MSG_CMSG_CLOEXEC));
+		ASSERT_EQ('.', *(char *)msg.msg_iov->iov_base);
+		ASSERT_EQ(0, close(socket_fds[1]));
+		cmsg = CMSG_FIRSTHDR(&msg);
+		ASSERT_EQ(cmsg->cmsg_len, CMSG_LEN(sizeof(ruleset_fd_tx)));
+		memcpy(&ruleset_fd_rx, CMSG_DATA(cmsg), sizeof(ruleset_fd_tx));
+
+		/* Enforces the received ruleset on the child. */
+		ASSERT_EQ(0, prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0));
+		ASSERT_EQ(0, landlock_restrict_self(ruleset_fd_rx, 0));
+		ASSERT_EQ(0, close(ruleset_fd_rx));
+
+		/* Checks that the ruleset enforcement. */
+		ASSERT_EQ(-1, open("/", O_RDONLY | O_DIRECTORY | O_CLOEXEC));
+		ASSERT_EQ(EACCES, errno);
+		dir_fd = open("/tmp", O_RDONLY | O_DIRECTORY | O_CLOEXEC);
+		ASSERT_LE(0, dir_fd);
+		ASSERT_EQ(0, close(dir_fd));
+		_exit(_metadata->passed ? EXIT_SUCCESS : EXIT_FAILURE);
+		return;
+	}
+
+	ASSERT_EQ(0, close(socket_fds[1]));
+
+	/* Checks that the parent is unrestricted. */
+	dir_fd = open("/", O_RDONLY | O_DIRECTORY | O_CLOEXEC);
+	ASSERT_LE(0, dir_fd);
+	ASSERT_EQ(0, close(dir_fd));
+	dir_fd = open("/tmp", O_RDONLY | O_DIRECTORY | O_CLOEXEC);
+	ASSERT_LE(0, dir_fd);
+	ASSERT_EQ(0, close(dir_fd));
+
+	ASSERT_EQ(child, waitpid(child, &status, 0));
+	ASSERT_EQ(1, WIFEXITED(status));
+	ASSERT_EQ(EXIT_SUCCESS, WEXITSTATUS(status));
+}
+
+TEST_HARNESS_MAIN

tools/testing/selftests/landlock/common.h

+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Landlock test helpers
+ *
+ * Copyright © 2017-2020 Mickaël Salaün <mic@digikod.net>
+ * Copyright © 2019-2020 ANSSI
+ * Copyright © 2021 Microsoft Corporation
+ */
+
+#include <errno.h>
+#include <linux/landlock.h>
+#include <sys/capability.h>
+#include <sys/syscall.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include "../kselftest_harness.h"
+
+#ifndef ARRAY_SIZE
+#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
+#endif
+
+/*
+ * TEST_F_FORK() is useful when a test drop privileges but the corresponding
+ * FIXTURE_TEARDOWN() requires them (e.g. to remove files from a directory
+ * where write actions are denied).  For convenience, FIXTURE_TEARDOWN() is
+ * also called when the test failed, but not when FIXTURE_SETUP() failed.  For
+ * this to be possible, we must not call abort() but instead exit smoothly
+ * (hence the step print).
+ */
+#define TEST_F_FORK(fixture_name, test_name) \
+	static void fixture_name##_##test_name##_child( \
+		struct __test_metadata *_metadata, \
+		FIXTURE_DATA(fixture_name) *self, \
+		const FIXTURE_VARIANT(fixture_name) *variant); \
+	TEST_F(fixture_name, test_name) \
+	{ \
+		int status; \
+		const pid_t child = fork(); \
+		if (child < 0) \
+			abort(); \
+		if (child == 0) { \
+			_metadata->no_print = 1; \
+			fixture_name##_##test_name##_child(_metadata, self, variant); \
+			if (_metadata->skip) \
+				_exit(255); \
+			if (_metadata->passed) \
+				_exit(0); \
+			_exit(_metadata->step); \
+		} \
+		if (child != waitpid(child, &status, 0)) \
+			abort(); \
+		if (WIFSIGNALED(status) || !WIFEXITED(status)) { \
+			_metadata->passed = 0; \
+			_metadata->step = 1; \
+			return; \
+		} \
+		switch (WEXITSTATUS(status)) { \
+		case 0: \
+			_metadata->passed = 1; \
+			break; \
+		case 255: \
+			_metadata->passed = 1; \
+			_metadata->skip = 1; \
+			break; \
+		default: \
+			_metadata->passed = 0; \
+			_metadata->step = WEXITSTATUS(status); \
+			break; \
+		} \
+	} \
+	static void fixture_name##_##test_name##_child( \
+		struct __test_metadata __attribute__((unused)) *_metadata, \
+		FIXTURE_DATA(fixture_name) __attribute__((unused)) *self, \
+		const FIXTURE_VARIANT(fixture_name) \
+			__attribute__((unused)) *variant)
+
+#ifndef landlock_create_ruleset
+static inline int landlock_create_ruleset(
+		const struct landlock_ruleset_attr *const attr,
+		const size_t size, const __u32 flags)
+{
+	return syscall(__NR_landlock_create_ruleset, attr, size, flags);
+}
+#endif
+
+#ifndef landlock_add_rule
+static inline int landlock_add_rule(const int ruleset_fd,
+		const enum landlock_rule_type rule_type,
+		const void *const rule_attr, const __u32 flags)
+{
+	return syscall(__NR_landlock_add_rule, ruleset_fd, rule_type,
+			rule_attr, flags);
+}
+#endif
+
+#ifndef landlock_restrict_self
+static inline int landlock_restrict_self(const int ruleset_fd,
+		const __u32 flags)
+{
+	return syscall(__NR_landlock_restrict_self, ruleset_fd, flags);
+}
+#endif
+
+static void _init_caps(struct __test_metadata *const _metadata, bool drop_all)
+{
+	cap_t cap_p;
+	/* Only these three capabilities are useful for the tests. */
+	const cap_value_t caps[] = {
+		CAP_DAC_OVERRIDE,
+		CAP_MKNOD,
+		CAP_SYS_ADMIN,
+		CAP_SYS_CHROOT,
+	};
+
+	cap_p = cap_get_proc();
+	EXPECT_NE(NULL, cap_p) {
+		TH_LOG("Failed to cap_get_proc: %s", strerror(errno));
+	}
+	EXPECT_NE(-1, cap_clear(cap_p)) {
+		TH_LOG("Failed to cap_clear: %s", strerror(errno));
+	}
+	if (!drop_all) {
+		EXPECT_NE(-1, cap_set_flag(cap_p, CAP_PERMITTED,
+					ARRAY_SIZE(caps), caps, CAP_SET)) {
+			TH_LOG("Failed to cap_set_flag: %s", strerror(errno));
+		}
+	}
+	EXPECT_NE(-1, cap_set_proc(cap_p)) {
+		TH_LOG("Failed to cap_set_proc: %s", strerror(errno));
+	}
+	EXPECT_NE(-1, cap_free(cap_p)) {
+		TH_LOG("Failed to cap_free: %s", strerror(errno));
+	}
+}
+
+/* We cannot put such helpers in a library because of kselftest_harness.h . */
+__attribute__((__unused__))
+static void disable_caps(struct __test_metadata *const _metadata)
+{
+	_init_caps(_metadata, false);
+}
+
+__attribute__((__unused__))
+static void drop_caps(struct __test_metadata *const _metadata)
+{
+	_init_caps(_metadata, true);
+}
+
+static void _effective_cap(struct __test_metadata *const _metadata,
+		const cap_value_t caps, const cap_flag_value_t value)
+{
+	cap_t cap_p;
+
+	cap_p = cap_get_proc();
+	EXPECT_NE(NULL, cap_p) {
+		TH_LOG("Failed to cap_get_proc: %s", strerror(errno));
+	}
+	EXPECT_NE(-1, cap_set_flag(cap_p, CAP_EFFECTIVE, 1, &caps, value)) {
+		TH_LOG("Failed to cap_set_flag: %s", strerror(errno));
+	}
+	EXPECT_NE(-1, cap_set_proc(cap_p)) {
+		TH_LOG("Failed to cap_set_proc: %s", strerror(errno));
+	}
+	EXPECT_NE(-1, cap_free(cap_p)) {
+		TH_LOG("Failed to cap_free: %s", strerror(errno));
+	}
+}
+
+__attribute__((__unused__))
+static void set_cap(struct __test_metadata *const _metadata,
+		const cap_value_t caps)
+{
+	_effective_cap(_metadata, caps, CAP_SET);
+}
+
+__attribute__((__unused__))
+static void clear_cap(struct __test_metadata *const _metadata,
+		const cap_value_t caps)
+{
+	_effective_cap(_metadata, caps, CAP_CLEAR);
+}

tools/testing/selftests/landlock/config

+CONFIG_OVERLAY_FS=y
+CONFIG_SECURITY_LANDLOCK=y
+CONFIG_SECURITY_PATH=y
+CONFIG_SECURITY=y
+CONFIG_SHMEM=y
+CONFIG_TMPFS_XATTR=y
+CONFIG_TMPFS=y

tools/testing/selftests/landlock/fs_test.c

+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Landlock tests - Filesystem
+ *
+ * Copyright © 2017-2020 Mickaël Salaün <mic@digikod.net>
+ * Copyright © 2020 ANSSI
+ * Copyright © 2020-2021 Microsoft Corporation
+ */
+
+#define _GNU_SOURCE
+#include <fcntl.h>
+#include <linux/landlock.h>
+#include <sched.h>
+#include <string.h>
+#include <sys/capability.h>
+#include <sys/mount.h>
+#include <sys/prctl.h>
+#include <sys/sendfile.h>
+#include <sys/stat.h>
+#include <sys/sysmacros.h>
+#include <unistd.h>
+
+#include "common.h"
+
+#define TMP_DIR		"tmp"
+#define BINARY_PATH	"./true"
+
+/* Paths (sibling number and depth) */
+static const char dir_s1d1[] = TMP_DIR "/s1d1";
+static const char file1_s1d1[] = TMP_DIR "/s1d1/f1";
+static const char file2_s1d1[] = TMP_DIR "/s1d1/f2";
+static const char dir_s1d2[] = TMP_DIR "/s1d1/s1d2";
+static const char file1_s1d2[] = TMP_DIR "/s1d1/s1d2/f1";
+static const char file2_s1d2[] = TMP_DIR "/s1d1/s1d2/f2";
+static const char dir_s1d3[] = TMP_DIR "/s1d1/s1d2/s1d3";
+static const char file1_s1d3[] = TMP_DIR "/s1d1/s1d2/s1d3/f1";
+static const char file2_s1d3[] = TMP_DIR "/s1d1/s1d2/s1d3/f2";
+
+static const char dir_s2d1[] = TMP_DIR "/s2d1";
+static const char file1_s2d1[] = TMP_DIR "/s2d1/f1";
+static const char dir_s2d2[] = TMP_DIR "/s2d1/s2d2";
+static const char file1_s2d2[] = TMP_DIR "/s2d1/s2d2/f1";
+static const char dir_s2d3[] = TMP_DIR "/s2d1/s2d2/s2d3";
+static const char file1_s2d3[] = TMP_DIR "/s2d1/s2d2/s2d3/f1";
+static const char file2_s2d3[] = TMP_DIR "/s2d1/s2d2/s2d3/f2";
+
+static const char dir_s3d1[] = TMP_DIR "/s3d1";
+/* dir_s3d2 is a mount point. */
+static const char dir_s3d2[] = TMP_DIR "/s3d1/s3d2";
+static const char dir_s3d3[] = TMP_DIR "/s3d1/s3d2/s3d3";
+
+/*
+ * layout1 hierarchy:
+ *
+ * tmp
+ * ├── s1d1
+ * │   ├── f1
+ * │   ├── f2
+ * │   └── s1d2
+ * │       ├── f1
+ * │       ├── f2
+ * │       └── s1d3
+ * │           ├── f1
+ * │           └── f2
+ * ├── s2d1
+ * │   ├── f1
+ * │   └── s2d2
+ * │       ├── f1
+ * │       └── s2d3
+ * │           ├── f1
+ * │           └── f2
+ * └── s3d1
+ *     └── s3d2
+ *         └── s3d3
+ */
+
+static void mkdir_parents(struct __test_metadata *const _metadata,
+		const char *const path)
+{
+	char *walker;
+	const char *parent;
+	int i, err;
+
+	ASSERT_NE(path[0], '\0');
+	walker = strdup(path);
+	ASSERT_NE(NULL, walker);
+	parent = walker;
+	for (i = 1; walker[i]; i++) {
+		if (walker[i] != '/')
+			continue;
+		walker[i] = '\0';
+		err = mkdir(parent, 0700);
+		ASSERT_FALSE(err && errno != EEXIST) {
+			TH_LOG("Failed to create directory \"%s\": %s",
+					parent, strerror(errno));
+		}
+		walker[i] = '/';
+	}
+	free(walker);
+}
+
+static void create_directory(struct __test_metadata *const _metadata,
+		const char *const path)
+{
+	mkdir_parents(_metadata, path);
+	ASSERT_EQ(0, mkdir(path, 0700)) {
+		TH_LOG("Failed to create directory \"%s\": %s", path,
+				strerror(errno));
+	}
+}
+
+static void create_file(struct __test_metadata *const _metadata,
+		const char *const path)
+{
+	mkdir_parents(_metadata, path);
+	ASSERT_EQ(0, mknod(path, S_IFREG | 0700, 0)) {
+		TH_LOG("Failed to create file \"%s\": %s", path,
+				strerror(errno));
+	}
+}
+
+static int remove_path(const char *const path)
+{
+	char *walker;
+	int i, ret, err = 0;
+
+	walker = strdup(path);
+	if (!walker) {
+		err = ENOMEM;
+		goto out;
+	}
+	if (unlink(path) && rmdir(path)) {
+		if (errno != ENOENT)
+			err = errno;
+		goto out;
+	}
+	for (i = strlen(walker); i > 0; i--) {
+		if (walker[i] != '/')
+			continue;
+		walker[i] = '\0';
+		ret = rmdir(walker);
+		if (ret) {
+			if (errno != ENOTEMPTY && errno != EBUSY)
+				err = errno;
+			goto out;
+		}
+		if (strcmp(walker, TMP_DIR) == 0)
+			goto out;
+	}
+
+out:
+	free(walker);
+	return err;
+}
+
+static void prepare_layout(struct __test_metadata *const _metadata)
+{
+	disable_caps(_metadata);
+	umask(0077);
+	create_directory(_metadata, TMP_DIR);
+
+	/*
+	 * Do not pollute the rest of the system: creates a private mount point
+	 * for tests relying on pivot_root(2) and move_mount(2).
+	 */
+	set_cap(_metadata, CAP_SYS_ADMIN);
+	ASSERT_EQ(0, unshare(CLONE_NEWNS));
+	ASSERT_EQ(0, mount("tmp", TMP_DIR, "tmpfs", 0, "size=4m,mode=700"));
+	ASSERT_EQ(0, mount(NULL, TMP_DIR, NULL, MS_PRIVATE | MS_REC, NULL));
+	clear_cap(_metadata, CAP_SYS_ADMIN);
+}
+
+static void cleanup_layout(struct __test_metadata *const _metadata)
+{
+	set_cap(_metadata, CAP_SYS_ADMIN);
+	EXPECT_EQ(0, umount(TMP_DIR));
+	clear_cap(_metadata, CAP_SYS_ADMIN);
+	EXPECT_EQ(0, remove_path(TMP_DIR));
+}
+
+static void create_layout1(struct __test_metadata *const _metadata)
+{
+	create_file(_metadata, file1_s1d1);
+	create_file(_metadata, file1_s1d2);
+	create_file(_metadata, file1_s1d3);
+	create_file(_metadata, file2_s1d1);
+	create_file(_metadata, file2_s1d2);
+	create_file(_metadata, file2_s1d3);
+
+	create_file(_metadata, file1_s2d1);
+	create_file(_metadata, file1_s2d2);
+	create_file(_metadata, file1_s2d3);
+	create_file(_metadata, file2_s2d3);
+
+	create_directory(_metadata, dir_s3d2);
+	set_cap(_metadata, CAP_SYS_ADMIN);
+	ASSERT_EQ(0, mount("tmp", dir_s3d2, "tmpfs", 0, "size=4m,mode=700"));
+	clear_cap(_metadata, CAP_SYS_ADMIN);
+
+	ASSERT_EQ(0, mkdir(dir_s3d3, 0700));
+}
+
+static void remove_layout1(struct __test_metadata *const _metadata)
+{
+	EXPECT_EQ(0, remove_path(file2_s1d3));
+	EXPECT_EQ(0, remove_path(file2_s1d2));
+	EXPECT_EQ(0, remove_path(file2_s1d1));
+	EXPECT_EQ(0, remove_path(file1_s1d3));
+	EXPECT_EQ(0, remove_path(file1_s1d2));
+	EXPECT_EQ(0, remove_path(file1_s1d1));
+
+	EXPECT_EQ(0, remove_path(file2_s2d3));
+	EXPECT_EQ(0, remove_path(file1_s2d3));
+	EXPECT_EQ(0, remove_path(file1_s2d2));
+	EXPECT_EQ(0, remove_path(file1_s2d1));
+
+	EXPECT_EQ(0, remove_path(dir_s3d3));
+	set_cap(_metadata, CAP_SYS_ADMIN);
+	umount(dir_s3d2);
+	clear_cap(_metadata, CAP_SYS_ADMIN);
+	EXPECT_EQ(0, remove_path(dir_s3d2));
+}
+
+FIXTURE(layout1) {
+};
+
+FIXTURE_SETUP(layout1)
+{
+	prepare_layout(_metadata);
+
+	create_layout1(_metadata);
+}
+
+FIXTURE_TEARDOWN(layout1)
+{
+	remove_layout1(_metadata);
+
+	cleanup_layout(_metadata);
+}
+
+/*
+ * This helper enables to use the ASSERT_* macros and print the line number
+ * pointing to the test caller.
+ */
+static int test_open_rel(const int dirfd, const char *const path, const int flags)
+{
+	int fd;
+
+	/* Works with file and directories. */
+	fd = openat(dirfd, path, flags | O_CLOEXEC);
+	if (fd < 0)
+		return errno;
+	/*
+	 * Mixing error codes from close(2) and open(2) should not lead to any
+	 * (access type) confusion for this test.
+	 */
+	if (close(fd) != 0)
+		return errno;
+	return 0;
+}
+
+static int test_open(const char *const path, const int flags)
+{
+	return test_open_rel(AT_FDCWD, path, flags);
+}
+
+TEST_F_FORK(layout1, no_restriction)
+{
+	ASSERT_EQ(0, test_open(dir_s1d1, O_RDONLY));
+	ASSERT_EQ(0, test_open(file1_s1d1, O_RDONLY));
+	ASSERT_EQ(0, test_open(file2_s1d1, O_RDONLY));
+	ASSERT_EQ(0, test_open(dir_s1d2, O_RDONLY));
+	ASSERT_EQ(0, test_open(file1_s1d2, O_RDONLY));
+	ASSERT_EQ(0, test_open(file2_s1d2, O_RDONLY));
+	ASSERT_EQ(0, test_open(dir_s1d3, O_RDONLY));
+	ASSERT_EQ(0, test_open(file1_s1d3, O_RDONLY));
+
+	ASSERT_EQ(0, test_open(dir_s2d1, O_RDONLY));
+	ASSERT_EQ(0, test_open(file1_s2d1, O_RDONLY));
+	ASSERT_EQ(0, test_open(dir_s2d2, O_RDONLY));
+	ASSERT_EQ(0, test_open(file1_s2d2, O_RDONLY));
+	ASSERT_EQ(0, test_open(dir_s2d3, O_RDONLY));
+	ASSERT_EQ(0, test_open(file1_s2d3, O_RDONLY));
+
+	ASSERT_EQ(0, test_open(dir_s3d1, O_RDONLY));
+	ASSERT_EQ(0, test_open(dir_s3d2, O_RDONLY));
+	ASSERT_EQ(0, test_open(dir_s3d3, O_RDONLY));
+}
+
+TEST_F_FORK(layout1, inval)
+{
+	struct landlock_path_beneath_attr path_beneath = {
+		.allowed_access = LANDLOCK_ACCESS_FS_READ_FILE |
+			LANDLOCK_ACCESS_FS_WRITE_FILE,
+		.parent_fd = -1,
+	};
+	struct landlock_ruleset_attr ruleset_attr = {
+		.handled_access_fs = LANDLOCK_ACCESS_FS_READ_FILE |
+			LANDLOCK_ACCESS_FS_WRITE_FILE,
+	};
+	int ruleset_fd;
+
+	path_beneath.parent_fd = open(dir_s1d2, O_PATH | O_DIRECTORY |
+			O_CLOEXEC);
+	ASSERT_LE(0, path_beneath.parent_fd);
+
+	ruleset_fd = open(dir_s1d1, O_PATH | O_DIRECTORY | O_CLOEXEC);
+	ASSERT_LE(0, ruleset_fd);
+	ASSERT_EQ(-1, landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH,
+				&path_beneath, 0));
+	/* Returns EBADF because ruleset_fd is not a landlock-ruleset FD. */
+	ASSERT_EQ(EBADF, errno);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	ruleset_fd = open(dir_s1d1, O_DIRECTORY | O_CLOEXEC);
+	ASSERT_LE(0, ruleset_fd);
+	ASSERT_EQ(-1, landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH,
+				&path_beneath, 0));
+	/* Returns EBADFD because ruleset_fd is not a valid ruleset. */
+	ASSERT_EQ(EBADFD, errno);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/* Gets a real ruleset. */
+	ruleset_fd = landlock_create_ruleset(&ruleset_attr,
+			sizeof(ruleset_attr), 0);
+	ASSERT_LE(0, ruleset_fd);
+	ASSERT_EQ(0, landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH,
+				&path_beneath, 0));
+	ASSERT_EQ(0, close(path_beneath.parent_fd));
+
+	/* Tests without O_PATH. */
+	path_beneath.parent_fd = open(dir_s1d2, O_DIRECTORY | O_CLOEXEC);
+	ASSERT_LE(0, path_beneath.parent_fd);
+	ASSERT_EQ(0, landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH,
+				&path_beneath, 0));
+	ASSERT_EQ(0, close(path_beneath.parent_fd));
+
+	/* Tests with a ruleset FD. */
+	path_beneath.parent_fd = ruleset_fd;
+	ASSERT_EQ(-1, landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH,
+				&path_beneath, 0));
+	ASSERT_EQ(EBADFD, errno);
+
+	/* Checks unhandled allowed_access. */
+	path_beneath.parent_fd = open(dir_s1d2, O_PATH | O_DIRECTORY |
+			O_CLOEXEC);
+	ASSERT_LE(0, path_beneath.parent_fd);
+
+	/* Test with legitimate values. */
+	path_beneath.allowed_access |= LANDLOCK_ACCESS_FS_EXECUTE;
+	ASSERT_EQ(-1, landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH,
+				&path_beneath, 0));
+	ASSERT_EQ(EINVAL, errno);
+	path_beneath.allowed_access &= ~LANDLOCK_ACCESS_FS_EXECUTE;
+
+	/* Test with unknown (64-bits) value. */
+	path_beneath.allowed_access |= (1ULL << 60);
+	ASSERT_EQ(-1, landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH,
+				&path_beneath, 0));
+	ASSERT_EQ(EINVAL, errno);
+	path_beneath.allowed_access &= ~(1ULL << 60);
+
+	/* Test with no access. */
+	path_beneath.allowed_access = 0;
+	ASSERT_EQ(-1, landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH,
+				&path_beneath, 0));
+	ASSERT_EQ(ENOMSG, errno);
+	path_beneath.allowed_access &= ~(1ULL << 60);
+
+	ASSERT_EQ(0, close(path_beneath.parent_fd));
+
+	/* Enforces the ruleset. */
+	ASSERT_EQ(0, prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0));
+	ASSERT_EQ(0, landlock_restrict_self(ruleset_fd, 0));
+
+	ASSERT_EQ(0, close(ruleset_fd));
+}
+
+#define ACCESS_FILE ( \
+	LANDLOCK_ACCESS_FS_EXECUTE | \
+	LANDLOCK_ACCESS_FS_WRITE_FILE | \
+	LANDLOCK_ACCESS_FS_READ_FILE)
+
+#define ACCESS_LAST LANDLOCK_ACCESS_FS_MAKE_SYM
+
+#define ACCESS_ALL ( \
+	ACCESS_FILE | \
+	LANDLOCK_ACCESS_FS_READ_DIR | \
+	LANDLOCK_ACCESS_FS_REMOVE_DIR | \
+	LANDLOCK_ACCESS_FS_REMOVE_FILE | \
+	LANDLOCK_ACCESS_FS_MAKE_CHAR | \
+	LANDLOCK_ACCESS_FS_MAKE_DIR | \
+	LANDLOCK_ACCESS_FS_MAKE_REG | \
+	LANDLOCK_ACCESS_FS_MAKE_SOCK | \
+	LANDLOCK_ACCESS_FS_MAKE_FIFO | \
+	LANDLOCK_ACCESS_FS_MAKE_BLOCK | \
+	ACCESS_LAST)
+
+TEST_F_FORK(layout1, file_access_rights)
+{
+	__u64 access;
+	int err;
+	struct landlock_path_beneath_attr path_beneath = {};
+	struct landlock_ruleset_attr ruleset_attr = {
+		.handled_access_fs = ACCESS_ALL,
+	};
+	const int ruleset_fd = landlock_create_ruleset(&ruleset_attr,
+			sizeof(ruleset_attr), 0);
+
+	ASSERT_LE(0, ruleset_fd);
+
+	/* Tests access rights for files. */
+	path_beneath.parent_fd = open(file1_s1d2, O_PATH | O_CLOEXEC);
+	ASSERT_LE(0, path_beneath.parent_fd);
+	for (access = 1; access <= ACCESS_LAST; access <<= 1) {
+		path_beneath.allowed_access = access;
+		err = landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH,
+				&path_beneath, 0);
+		if ((access | ACCESS_FILE) == ACCESS_FILE) {
+			ASSERT_EQ(0, err);
+		} else {
+			ASSERT_EQ(-1, err);
+			ASSERT_EQ(EINVAL, errno);
+		}
+	}
+	ASSERT_EQ(0, close(path_beneath.parent_fd));
+}
+
+static void add_path_beneath(struct __test_metadata *const _metadata,
+		const int ruleset_fd, const __u64 allowed_access,
+		const char *const path)
+{
+	struct landlock_path_beneath_attr path_beneath = {
+		.allowed_access = allowed_access,
+	};
+
+	path_beneath.parent_fd = open(path, O_PATH | O_CLOEXEC);
+	ASSERT_LE(0, path_beneath.parent_fd) {
+		TH_LOG("Failed to open directory \"%s\": %s", path,
+				strerror(errno));
+	}
+	ASSERT_EQ(0, landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH,
+				&path_beneath, 0)) {
+		TH_LOG("Failed to update the ruleset with \"%s\": %s", path,
+				strerror(errno));
+	}
+	ASSERT_EQ(0, close(path_beneath.parent_fd));
+}
+
+struct rule {
+	const char *path;
+	__u64 access;
+};
+
+#define ACCESS_RO ( \
+	LANDLOCK_ACCESS_FS_READ_FILE | \
+	LANDLOCK_ACCESS_FS_READ_DIR)
+
+#define ACCESS_RW ( \
+	ACCESS_RO | \
+	LANDLOCK_ACCESS_FS_WRITE_FILE)
+
+static int create_ruleset(struct __test_metadata *const _metadata,
+		const __u64 handled_access_fs, const struct rule rules[])
+{
+	int ruleset_fd, i;
+	struct landlock_ruleset_attr ruleset_attr = {
+		.handled_access_fs = handled_access_fs,
+	};
+
+	ASSERT_NE(NULL, rules) {
+		TH_LOG("No rule list");
+	}
+	ASSERT_NE(NULL, rules[0].path) {
+		TH_LOG("Empty rule list");
+	}
+
+	ruleset_fd = landlock_create_ruleset(&ruleset_attr,
+			sizeof(ruleset_attr), 0);
+	ASSERT_LE(0, ruleset_fd) {
+		TH_LOG("Failed to create a ruleset: %s", strerror(errno));
+	}
+
+	for (i = 0; rules[i].path; i++) {
+		add_path_beneath(_metadata, ruleset_fd, rules[i].access,
+				rules[i].path);
+	}
+	return ruleset_fd;
+}
+
+static void enforce_ruleset(struct __test_metadata *const _metadata,
+		const int ruleset_fd)
+{
+	ASSERT_EQ(0, prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0));
+	ASSERT_EQ(0, landlock_restrict_self(ruleset_fd, 0)) {
+		TH_LOG("Failed to enforce ruleset: %s", strerror(errno));
+	}
+}
+
+TEST_F_FORK(layout1, proc_nsfs)
+{
+	const struct rule rules[] = {
+		{
+			.path = "/dev/null",
+			.access = LANDLOCK_ACCESS_FS_READ_FILE |
+				LANDLOCK_ACCESS_FS_WRITE_FILE,
+		},
+		{}
+	};
+	struct landlock_path_beneath_attr path_beneath;
+	const int ruleset_fd = create_ruleset(_metadata, rules[0].access |
+			LANDLOCK_ACCESS_FS_READ_DIR, rules);
+
+	ASSERT_LE(0, ruleset_fd);
+	ASSERT_EQ(0, test_open("/proc/self/ns/mnt", O_RDONLY));
+
+	enforce_ruleset(_metadata, ruleset_fd);
+
+	ASSERT_EQ(EACCES, test_open("/", O_RDONLY));
+	ASSERT_EQ(EACCES, test_open("/dev", O_RDONLY));
+	ASSERT_EQ(0, test_open("/dev/null", O_RDONLY));
+	ASSERT_EQ(EACCES, test_open("/dev/full", O_RDONLY));
+
+	ASSERT_EQ(EACCES, test_open("/proc", O_RDONLY));
+	ASSERT_EQ(EACCES, test_open("/proc/self", O_RDONLY));
+	ASSERT_EQ(EACCES, test_open("/proc/self/ns", O_RDONLY));
+	/*
+	 * Because nsfs is an internal filesystem, /proc/self/ns/mnt is a
+	 * disconnected path.  Such path cannot be identified and must then be
+	 * allowed.
+	 */
+	ASSERT_EQ(0, test_open("/proc/self/ns/mnt", O_RDONLY));
+
+	/*
+	 * Checks that it is not possible to add nsfs-like filesystem
+	 * references to a ruleset.
+	 */
+	path_beneath.allowed_access = LANDLOCK_ACCESS_FS_READ_FILE |
+		LANDLOCK_ACCESS_FS_WRITE_FILE,
+	path_beneath.parent_fd = open("/proc/self/ns/mnt", O_PATH | O_CLOEXEC);
+	ASSERT_LE(0, path_beneath.parent_fd);
+	ASSERT_EQ(-1, landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH,
+				&path_beneath, 0));
+	ASSERT_EQ(EBADFD, errno);
+	ASSERT_EQ(0, close(path_beneath.parent_fd));
+}
+
+TEST_F_FORK(layout1, unpriv) {
+	const struct rule rules[] = {
+		{
+			.path = dir_s1d2,
+			.access = ACCESS_RO,
+		},
+		{}
+	};
+	int ruleset_fd;
+
+	drop_caps(_metadata);
+
+	ruleset_fd = create_ruleset(_metadata, ACCESS_RO, rules);
+	ASSERT_LE(0, ruleset_fd);
+	ASSERT_EQ(-1, landlock_restrict_self(ruleset_fd, 0));
+	ASSERT_EQ(EPERM, errno);
+
+	/* enforce_ruleset() calls prctl(no_new_privs). */
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+}
+
+TEST_F_FORK(layout1, effective_access)
+{
+	const struct rule rules[] = {
+		{
+			.path = dir_s1d2,
+			.access = ACCESS_RO,
+		},
+		{
+			.path = file1_s2d2,
+			.access = LANDLOCK_ACCESS_FS_READ_FILE |
+				LANDLOCK_ACCESS_FS_WRITE_FILE,
+		},
+		{}
+	};
+	const int ruleset_fd = create_ruleset(_metadata, ACCESS_RW, rules);
+	char buf;
+	int reg_fd;
+
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/* Tests on a directory. */
+	ASSERT_EQ(EACCES, test_open("/", O_RDONLY));
+	ASSERT_EQ(EACCES, test_open(dir_s1d1, O_RDONLY));
+	ASSERT_EQ(EACCES, test_open(file1_s1d1, O_RDONLY));
+	ASSERT_EQ(0, test_open(dir_s1d2, O_RDONLY));
+	ASSERT_EQ(0, test_open(file1_s1d2, O_RDONLY));
+	ASSERT_EQ(0, test_open(dir_s1d3, O_RDONLY));
+	ASSERT_EQ(0, test_open(file1_s1d3, O_RDONLY));
+
+	/* Tests on a file. */
+	ASSERT_EQ(EACCES, test_open(dir_s2d2, O_RDONLY));
+	ASSERT_EQ(0, test_open(file1_s2d2, O_RDONLY));
+
+	/* Checks effective read and write actions. */
+	reg_fd = open(file1_s2d2, O_RDWR | O_CLOEXEC);
+	ASSERT_LE(0, reg_fd);
+	ASSERT_EQ(1, write(reg_fd, ".", 1));
+	ASSERT_LE(0, lseek(reg_fd, 0, SEEK_SET));
+	ASSERT_EQ(1, read(reg_fd, &buf, 1));
+	ASSERT_EQ('.', buf);
+	ASSERT_EQ(0, close(reg_fd));
+
+	/* Just in case, double-checks effective actions. */
+	reg_fd = open(file1_s2d2, O_RDONLY | O_CLOEXEC);
+	ASSERT_LE(0, reg_fd);
+	ASSERT_EQ(-1, write(reg_fd, &buf, 1));
+	ASSERT_EQ(EBADF, errno);
+	ASSERT_EQ(0, close(reg_fd));
+}
+
+TEST_F_FORK(layout1, unhandled_access)
+{
+	const struct rule rules[] = {
+		{
+			.path = dir_s1d2,
+			.access = ACCESS_RO,
+		},
+		{}
+	};
+	/* Here, we only handle read accesses, not write accesses. */
+	const int ruleset_fd = create_ruleset(_metadata, ACCESS_RO, rules);
+
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/*
+	 * Because the policy does not handle LANDLOCK_ACCESS_FS_WRITE_FILE,
+	 * opening for write-only should be allowed, but not read-write.
+	 */
+	ASSERT_EQ(0, test_open(file1_s1d1, O_WRONLY));
+	ASSERT_EQ(EACCES, test_open(file1_s1d1, O_RDWR));
+
+	ASSERT_EQ(0, test_open(file1_s1d2, O_WRONLY));
+	ASSERT_EQ(0, test_open(file1_s1d2, O_RDWR));
+}
+
+TEST_F_FORK(layout1, ruleset_overlap)
+{
+	const struct rule rules[] = {
+		/* These rules should be ORed among them. */
+		{
+			.path = dir_s1d2,
+			.access = LANDLOCK_ACCESS_FS_READ_FILE |
+				LANDLOCK_ACCESS_FS_WRITE_FILE,
+		},
+		{
+			.path = dir_s1d2,
+			.access = LANDLOCK_ACCESS_FS_READ_FILE |
+				LANDLOCK_ACCESS_FS_READ_DIR,
+		},
+		{}
+	};
+	const int ruleset_fd = create_ruleset(_metadata, ACCESS_RW, rules);
+
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/* Checks s1d1 hierarchy. */
+	ASSERT_EQ(EACCES, test_open(file1_s1d1, O_RDONLY));
+	ASSERT_EQ(EACCES, test_open(file1_s1d1, O_WRONLY));
+	ASSERT_EQ(EACCES, test_open(file1_s1d1, O_RDWR));
+	ASSERT_EQ(EACCES, test_open(dir_s1d1, O_RDONLY | O_DIRECTORY));
+
+	/* Checks s1d2 hierarchy. */
+	ASSERT_EQ(0, test_open(file1_s1d2, O_RDONLY));
+	ASSERT_EQ(0, test_open(file1_s1d2, O_WRONLY));
+	ASSERT_EQ(0, test_open(file1_s1d2, O_RDWR));
+	ASSERT_EQ(0, test_open(dir_s1d2, O_RDONLY | O_DIRECTORY));
+
+	/* Checks s1d3 hierarchy. */
+	ASSERT_EQ(0, test_open(file1_s1d3, O_RDONLY));
+	ASSERT_EQ(0, test_open(file1_s1d3, O_WRONLY));
+	ASSERT_EQ(0, test_open(file1_s1d3, O_RDWR));
+	ASSERT_EQ(0, test_open(dir_s1d3, O_RDONLY | O_DIRECTORY));
+}
+
+TEST_F_FORK(layout1, non_overlapping_accesses)
+{
+	const struct rule layer1[] = {
+		{
+			.path = dir_s1d2,
+			.access = LANDLOCK_ACCESS_FS_MAKE_REG,
+		},
+		{}
+	};
+	const struct rule layer2[] = {
+		{
+			.path = dir_s1d3,
+			.access = LANDLOCK_ACCESS_FS_REMOVE_FILE,
+		},
+		{}
+	};
+	int ruleset_fd;
+
+	ASSERT_EQ(0, unlink(file1_s1d1));
+	ASSERT_EQ(0, unlink(file1_s1d2));
+
+	ruleset_fd = create_ruleset(_metadata, LANDLOCK_ACCESS_FS_MAKE_REG,
+			layer1);
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	ASSERT_EQ(-1, mknod(file1_s1d1, S_IFREG | 0700, 0));
+	ASSERT_EQ(EACCES, errno);
+	ASSERT_EQ(0, mknod(file1_s1d2, S_IFREG | 0700, 0));
+	ASSERT_EQ(0, unlink(file1_s1d2));
+
+	ruleset_fd = create_ruleset(_metadata, LANDLOCK_ACCESS_FS_REMOVE_FILE,
+			layer2);
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/* Unchanged accesses for file creation. */
+	ASSERT_EQ(-1, mknod(file1_s1d1, S_IFREG | 0700, 0));
+	ASSERT_EQ(EACCES, errno);
+	ASSERT_EQ(0, mknod(file1_s1d2, S_IFREG | 0700, 0));
+
+	/* Checks file removing. */
+	ASSERT_EQ(-1, unlink(file1_s1d2));
+	ASSERT_EQ(EACCES, errno);
+	ASSERT_EQ(0, unlink(file1_s1d3));
+}
+
+TEST_F_FORK(layout1, interleaved_masked_accesses)
+{
+	/*
+	 * Checks overly restrictive rules:
+	 * layer 1: allows R   s1d1/s1d2/s1d3/file1
+	 * layer 2: allows RW  s1d1/s1d2/s1d3
+	 *          allows  W  s1d1/s1d2
+	 *          denies R   s1d1/s1d2
+	 * layer 3: allows R   s1d1
+	 * layer 4: allows R   s1d1/s1d2
+	 *          denies  W  s1d1/s1d2
+	 * layer 5: allows R   s1d1/s1d2
+	 * layer 6: allows   X ----
+	 * layer 7: allows  W  s1d1/s1d2
+	 *          denies R   s1d1/s1d2
+	 */
+	const struct rule layer1_read[] = {
+		/* Allows read access to file1_s1d3 with the first layer. */
+		{
+			.path = file1_s1d3,
+			.access = LANDLOCK_ACCESS_FS_READ_FILE,
+		},
+		{}
+	};
+	/* First rule with write restrictions. */
+	const struct rule layer2_read_write[] = {
+		/* Start by granting read-write access via its parent directory... */
+		{
+			.path = dir_s1d3,
+			.access = LANDLOCK_ACCESS_FS_READ_FILE |
+				LANDLOCK_ACCESS_FS_WRITE_FILE,
+		},
+		/* ...but also denies read access via its grandparent directory. */
+		{
+			.path = dir_s1d2,
+			.access = LANDLOCK_ACCESS_FS_WRITE_FILE,
+		},
+		{}
+	};
+	const struct rule layer3_read[] = {
+		/* Allows read access via its great-grandparent directory. */
+		{
+			.path = dir_s1d1,
+			.access = LANDLOCK_ACCESS_FS_READ_FILE,
+		},
+		{}
+	};
+	const struct rule layer4_read_write[] = {
+		/*
+		 * Try to confuse the deny access by denying write (but not
+		 * read) access via its grandparent directory.
+		 */
+		{
+			.path = dir_s1d2,
+			.access = LANDLOCK_ACCESS_FS_READ_FILE,
+		},
+		{}
+	};
+	const struct rule layer5_read[] = {
+		/*
+		 * Try to override layer2's deny read access by explicitly
+		 * allowing read access via file1_s1d3's grandparent.
+		 */
+		{
+			.path = dir_s1d2,
+			.access = LANDLOCK_ACCESS_FS_READ_FILE,
+		},
+		{}
+	};
+	const struct rule layer6_execute[] = {
+		/*
+		 * Restricts an unrelated file hierarchy with a new access
+		 * (non-overlapping) type.
+		 */
+		{
+			.path = dir_s2d1,
+			.access = LANDLOCK_ACCESS_FS_EXECUTE,
+		},
+		{}
+	};
+	const struct rule layer7_read_write[] = {
+		/*
+		 * Finally, denies read access to file1_s1d3 via its
+		 * grandparent.
+		 */
+		{
+			.path = dir_s1d2,
+			.access = LANDLOCK_ACCESS_FS_WRITE_FILE,
+		},
+		{}
+	};
+	int ruleset_fd;
+
+	ruleset_fd = create_ruleset(_metadata, LANDLOCK_ACCESS_FS_READ_FILE,
+			layer1_read);
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/* Checks that read access is granted for file1_s1d3 with layer 1. */
+	ASSERT_EQ(0, test_open(file1_s1d3, O_RDWR));
+	ASSERT_EQ(EACCES, test_open(file2_s1d3, O_RDONLY));
+	ASSERT_EQ(0, test_open(file2_s1d3, O_WRONLY));
+
+	ruleset_fd = create_ruleset(_metadata, LANDLOCK_ACCESS_FS_READ_FILE |
+			LANDLOCK_ACCESS_FS_WRITE_FILE, layer2_read_write);
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/* Checks that previous access rights are unchanged with layer 2. */
+	ASSERT_EQ(0, test_open(file1_s1d3, O_RDWR));
+	ASSERT_EQ(EACCES, test_open(file2_s1d3, O_RDONLY));
+	ASSERT_EQ(0, test_open(file2_s1d3, O_WRONLY));
+
+	ruleset_fd = create_ruleset(_metadata, LANDLOCK_ACCESS_FS_READ_FILE,
+			layer3_read);
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/* Checks that previous access rights are unchanged with layer 3. */
+	ASSERT_EQ(0, test_open(file1_s1d3, O_RDWR));
+	ASSERT_EQ(EACCES, test_open(file2_s1d3, O_RDONLY));
+	ASSERT_EQ(0, test_open(file2_s1d3, O_WRONLY));
+
+	/* This time, denies write access for the file hierarchy. */
+	ruleset_fd = create_ruleset(_metadata, LANDLOCK_ACCESS_FS_READ_FILE |
+			LANDLOCK_ACCESS_FS_WRITE_FILE, layer4_read_write);
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/*
+	 * Checks that the only change with layer 4 is that write access is
+	 * denied.
+	 */
+	ASSERT_EQ(0, test_open(file1_s1d3, O_RDONLY));
+	ASSERT_EQ(EACCES, test_open(file1_s1d3, O_WRONLY));
+	ASSERT_EQ(EACCES, test_open(file2_s1d3, O_RDONLY));
+	ASSERT_EQ(EACCES, test_open(file2_s1d3, O_WRONLY));
+
+	ruleset_fd = create_ruleset(_metadata, LANDLOCK_ACCESS_FS_READ_FILE,
+			layer5_read);
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/* Checks that previous access rights are unchanged with layer 5. */
+	ASSERT_EQ(0, test_open(file1_s1d3, O_RDONLY));
+	ASSERT_EQ(EACCES, test_open(file1_s1d3, O_WRONLY));
+	ASSERT_EQ(EACCES, test_open(file2_s1d3, O_WRONLY));
+	ASSERT_EQ(EACCES, test_open(file2_s1d3, O_RDONLY));
+
+	ruleset_fd = create_ruleset(_metadata, LANDLOCK_ACCESS_FS_EXECUTE,
+			layer6_execute);
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/* Checks that previous access rights are unchanged with layer 6. */
+	ASSERT_EQ(0, test_open(file1_s1d3, O_RDONLY));
+	ASSERT_EQ(EACCES, test_open(file1_s1d3, O_WRONLY));
+	ASSERT_EQ(EACCES, test_open(file2_s1d3, O_WRONLY));
+	ASSERT_EQ(EACCES, test_open(file2_s1d3, O_RDONLY));
+
+	ruleset_fd = create_ruleset(_metadata, LANDLOCK_ACCESS_FS_READ_FILE |
+			LANDLOCK_ACCESS_FS_WRITE_FILE, layer7_read_write);
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/* Checks read access is now denied with layer 7. */
+	ASSERT_EQ(EACCES, test_open(file1_s1d3, O_RDONLY));
+	ASSERT_EQ(EACCES, test_open(file1_s1d3, O_WRONLY));
+	ASSERT_EQ(EACCES, test_open(file2_s1d3, O_WRONLY));
+	ASSERT_EQ(EACCES, test_open(file2_s1d3, O_RDONLY));
+}
+
+TEST_F_FORK(layout1, inherit_subset)
+{
+	const struct rule rules[] = {
+		{
+			.path = dir_s1d2,
+			.access = LANDLOCK_ACCESS_FS_READ_FILE |
+				LANDLOCK_ACCESS_FS_READ_DIR,
+		},
+		{}
+	};
+	const int ruleset_fd = create_ruleset(_metadata, ACCESS_RW, rules);
+
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+
+	ASSERT_EQ(EACCES, test_open(file1_s1d1, O_WRONLY));
+	ASSERT_EQ(EACCES, test_open(dir_s1d1, O_RDONLY | O_DIRECTORY));
+
+	/* Write access is forbidden. */
+	ASSERT_EQ(EACCES, test_open(file1_s1d2, O_WRONLY));
+	/* Readdir access is allowed. */
+	ASSERT_EQ(0, test_open(dir_s1d2, O_RDONLY | O_DIRECTORY));
+
+	/* Write access is forbidden. */
+	ASSERT_EQ(EACCES, test_open(file1_s1d3, O_WRONLY));
+	/* Readdir access is allowed. */
+	ASSERT_EQ(0, test_open(dir_s1d3, O_RDONLY | O_DIRECTORY));
+
+	/*
+	 * Tests shared rule extension: the following rules should not grant
+	 * any new access, only remove some.  Once enforced, these rules are
+	 * ANDed with the previous ones.
+	 */
+	add_path_beneath(_metadata, ruleset_fd, LANDLOCK_ACCESS_FS_WRITE_FILE,
+			dir_s1d2);
+	/*
+	 * According to ruleset_fd, dir_s1d2 should now have the
+	 * LANDLOCK_ACCESS_FS_READ_FILE and LANDLOCK_ACCESS_FS_WRITE_FILE
+	 * access rights (even if this directory is opened a second time).
+	 * However, when enforcing this updated ruleset, the ruleset tied to
+	 * the current process (i.e. its domain) will still only have the
+	 * dir_s1d2 with LANDLOCK_ACCESS_FS_READ_FILE and
+	 * LANDLOCK_ACCESS_FS_READ_DIR accesses, but
+	 * LANDLOCK_ACCESS_FS_WRITE_FILE must not be allowed because it would
+	 * be a privilege escalation.
+	 */
+	enforce_ruleset(_metadata, ruleset_fd);
+
+	/* Same tests and results as above. */
+	ASSERT_EQ(EACCES, test_open(file1_s1d1, O_WRONLY));
+	ASSERT_EQ(EACCES, test_open(dir_s1d1, O_RDONLY | O_DIRECTORY));
+
+	/* It is still forbidden to write in file1_s1d2. */
+	ASSERT_EQ(EACCES, test_open(file1_s1d2, O_WRONLY));
+	/* Readdir access is still allowed. */
+	ASSERT_EQ(0, test_open(dir_s1d2, O_RDONLY | O_DIRECTORY));
+
+	/* It is still forbidden to write in file1_s1d3. */
+	ASSERT_EQ(EACCES, test_open(file1_s1d3, O_WRONLY));
+	/* Readdir access is still allowed. */
+	ASSERT_EQ(0, test_open(dir_s1d3, O_RDONLY | O_DIRECTORY));
+
+	/*
+	 * Try to get more privileges by adding new access rights to the parent
+	 * directory: dir_s1d1.
+	 */
+	add_path_beneath(_metadata, ruleset_fd, ACCESS_RW, dir_s1d1);
+	enforce_ruleset(_metadata, ruleset_fd);
+
+	/* Same tests and results as above. */
+	ASSERT_EQ(EACCES, test_open(file1_s1d1, O_WRONLY));
+	ASSERT_EQ(EACCES, test_open(dir_s1d1, O_RDONLY | O_DIRECTORY));
+
+	/* It is still forbidden to write in file1_s1d2. */
+	ASSERT_EQ(EACCES, test_open(file1_s1d2, O_WRONLY));
+	/* Readdir access is still allowed. */
+	ASSERT_EQ(0, test_open(dir_s1d2, O_RDONLY | O_DIRECTORY));
+
+	/* It is still forbidden to write in file1_s1d3. */
+	ASSERT_EQ(EACCES, test_open(file1_s1d3, O_WRONLY));
+	/* Readdir access is still allowed. */
+	ASSERT_EQ(0, test_open(dir_s1d3, O_RDONLY | O_DIRECTORY));
+
+	/*
+	 * Now, dir_s1d3 get a new rule tied to it, only allowing
+	 * LANDLOCK_ACCESS_FS_WRITE_FILE.  The (kernel internal) difference is
+	 * that there was no rule tied to it before.
+	 */
+	add_path_beneath(_metadata, ruleset_fd, LANDLOCK_ACCESS_FS_WRITE_FILE,
+			dir_s1d3);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/*
+	 * Same tests and results as above, except for open(dir_s1d3) which is
+	 * now denied because the new rule mask the rule previously inherited
+	 * from dir_s1d2.
+	 */
+
+	/* Same tests and results as above. */
+	ASSERT_EQ(EACCES, test_open(file1_s1d1, O_WRONLY));
+	ASSERT_EQ(EACCES, test_open(dir_s1d1, O_RDONLY | O_DIRECTORY));
+
+	/* It is still forbidden to write in file1_s1d2. */
+	ASSERT_EQ(EACCES, test_open(file1_s1d2, O_WRONLY));
+	/* Readdir access is still allowed. */
+	ASSERT_EQ(0, test_open(dir_s1d2, O_RDONLY | O_DIRECTORY));
+
+	/* It is still forbidden to write in file1_s1d3. */
+	ASSERT_EQ(EACCES, test_open(file1_s1d3, O_WRONLY));
+	/*
+	 * Readdir of dir_s1d3 is still allowed because of the OR policy inside
+	 * the same layer.
+	 */
+	ASSERT_EQ(0, test_open(dir_s1d3, O_RDONLY | O_DIRECTORY));
+}
+
+TEST_F_FORK(layout1, inherit_superset)
+{
+	const struct rule rules[] = {
+		{
+			.path = dir_s1d3,
+			.access = ACCESS_RO,
+		},
+		{}
+	};
+	const int ruleset_fd = create_ruleset(_metadata, ACCESS_RW, rules);
+
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+
+	/* Readdir access is denied for dir_s1d2. */
+	ASSERT_EQ(EACCES, test_open(dir_s1d2, O_RDONLY | O_DIRECTORY));
+	/* Readdir access is allowed for dir_s1d3. */
+	ASSERT_EQ(0, test_open(dir_s1d3, O_RDONLY | O_DIRECTORY));
+	/* File access is allowed for file1_s1d3. */
+	ASSERT_EQ(0, test_open(file1_s1d3, O_RDONLY));
+
+	/* Now dir_s1d2, parent of dir_s1d3, gets a new rule tied to it. */
+	add_path_beneath(_metadata, ruleset_fd, LANDLOCK_ACCESS_FS_READ_FILE |
+			LANDLOCK_ACCESS_FS_READ_DIR, dir_s1d2);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/* Readdir access is still denied for dir_s1d2. */
+	ASSERT_EQ(EACCES, test_open(dir_s1d2, O_RDONLY | O_DIRECTORY));
+	/* Readdir access is still allowed for dir_s1d3. */
+	ASSERT_EQ(0, test_open(dir_s1d3, O_RDONLY | O_DIRECTORY));
+	/* File access is still allowed for file1_s1d3. */
+	ASSERT_EQ(0, test_open(file1_s1d3, O_RDONLY));
+}
+
+TEST_F_FORK(layout1, max_layers)
+{
+	int i, err;
+	const struct rule rules[] = {
+		{
+			.path = dir_s1d2,
+			.access = ACCESS_RO,
+		},
+		{}
+	};
+	const int ruleset_fd = create_ruleset(_metadata, ACCESS_RW, rules);
+
+	ASSERT_LE(0, ruleset_fd);
+	for (i = 0; i < 64; i++)
+		enforce_ruleset(_metadata, ruleset_fd);
+
+	for (i = 0; i < 2; i++) {
+		err = landlock_restrict_self(ruleset_fd, 0);
+		ASSERT_EQ(-1, err);
+		ASSERT_EQ(E2BIG, errno);
+	}
+	ASSERT_EQ(0, close(ruleset_fd));
+}
+
+TEST_F_FORK(layout1, empty_or_same_ruleset)
+{
+	struct landlock_ruleset_attr ruleset_attr = {};
+	int ruleset_fd;
+
+	/* Tests empty handled_access_fs. */
+	ruleset_fd = landlock_create_ruleset(&ruleset_attr,
+			sizeof(ruleset_attr), 0);
+	ASSERT_LE(-1, ruleset_fd);
+	ASSERT_EQ(ENOMSG, errno);
+
+	/* Enforces policy which deny read access to all files. */
+	ruleset_attr.handled_access_fs = LANDLOCK_ACCESS_FS_READ_FILE;
+	ruleset_fd = landlock_create_ruleset(&ruleset_attr,
+			sizeof(ruleset_attr), 0);
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(EACCES, test_open(file1_s1d1, O_RDONLY));
+	ASSERT_EQ(0, test_open(dir_s1d1, O_RDONLY));
+
+	/* Nests a policy which deny read access to all directories. */
+	ruleset_attr.handled_access_fs = LANDLOCK_ACCESS_FS_READ_DIR;
+	ruleset_fd = landlock_create_ruleset(&ruleset_attr,
+			sizeof(ruleset_attr), 0);
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(EACCES, test_open(file1_s1d1, O_RDONLY));
+	ASSERT_EQ(EACCES, test_open(dir_s1d1, O_RDONLY));
+
+	/* Enforces a second time with the same ruleset. */
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+}
+
+TEST_F_FORK(layout1, rule_on_mountpoint)
+{
+	const struct rule rules[] = {
+		{
+			.path = dir_s1d1,
+			.access = ACCESS_RO,
+		},
+		{
+			/* dir_s3d2 is a mount point. */
+			.path = dir_s3d2,
+			.access = ACCESS_RO,
+		},
+		{}
+	};
+	const int ruleset_fd = create_ruleset(_metadata, ACCESS_RW, rules);
+
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	ASSERT_EQ(0, test_open(dir_s1d1, O_RDONLY));
+
+	ASSERT_EQ(EACCES, test_open(dir_s2d1, O_RDONLY));
+
+	ASSERT_EQ(EACCES, test_open(dir_s3d1, O_RDONLY));
+	ASSERT_EQ(0, test_open(dir_s3d2, O_RDONLY));
+	ASSERT_EQ(0, test_open(dir_s3d3, O_RDONLY));
+}
+
+TEST_F_FORK(layout1, rule_over_mountpoint)
+{
+	const struct rule rules[] = {
+		{
+			.path = dir_s1d1,
+			.access = ACCESS_RO,
+		},
+		{
+			/* dir_s3d2 is a mount point. */
+			.path = dir_s3d1,
+			.access = ACCESS_RO,
+		},
+		{}
+	};
+	const int ruleset_fd = create_ruleset(_metadata, ACCESS_RW, rules);
+
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	ASSERT_EQ(0, test_open(dir_s1d1, O_RDONLY));
+
+	ASSERT_EQ(EACCES, test_open(dir_s2d1, O_RDONLY));
+
+	ASSERT_EQ(0, test_open(dir_s3d1, O_RDONLY));
+	ASSERT_EQ(0, test_open(dir_s3d2, O_RDONLY));
+	ASSERT_EQ(0, test_open(dir_s3d3, O_RDONLY));
+}
+
+/*
+ * This test verifies that we can apply a landlock rule on the root directory
+ * (which might require special handling).
+ */
+TEST_F_FORK(layout1, rule_over_root_allow_then_deny)
+{
+	struct rule rules[] = {
+		{
+			.path = "/",
+			.access = ACCESS_RO,
+		},
+		{}
+	};
+	int ruleset_fd = create_ruleset(_metadata, ACCESS_RW, rules);
+
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/* Checks allowed access. */
+	ASSERT_EQ(0, test_open("/", O_RDONLY));
+	ASSERT_EQ(0, test_open(dir_s1d1, O_RDONLY));
+
+	rules[0].access = LANDLOCK_ACCESS_FS_READ_FILE;
+	ruleset_fd = create_ruleset(_metadata, ACCESS_RW, rules);
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/* Checks denied access (on a directory). */
+	ASSERT_EQ(EACCES, test_open("/", O_RDONLY));
+	ASSERT_EQ(EACCES, test_open(dir_s1d1, O_RDONLY));
+}
+
+TEST_F_FORK(layout1, rule_over_root_deny)
+{
+	const struct rule rules[] = {
+		{
+			.path = "/",
+			.access = LANDLOCK_ACCESS_FS_READ_FILE,
+		},
+		{}
+	};
+	const int ruleset_fd = create_ruleset(_metadata, ACCESS_RW, rules);
+
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/* Checks denied access (on a directory). */
+	ASSERT_EQ(EACCES, test_open("/", O_RDONLY));
+	ASSERT_EQ(EACCES, test_open(dir_s1d1, O_RDONLY));
+}
+
+TEST_F_FORK(layout1, rule_inside_mount_ns)
+{
+	const struct rule rules[] = {
+		{
+			.path = "s3d3",
+			.access = ACCESS_RO,
+		},
+		{}
+	};
+	int ruleset_fd;
+
+	set_cap(_metadata, CAP_SYS_ADMIN);
+	ASSERT_EQ(0, syscall(SYS_pivot_root, dir_s3d2, dir_s3d3)) {
+		TH_LOG("Failed to pivot root: %s", strerror(errno));
+	};
+	ASSERT_EQ(0, chdir("/"));
+	clear_cap(_metadata, CAP_SYS_ADMIN);
+
+	ruleset_fd = create_ruleset(_metadata, ACCESS_RW, rules);
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	ASSERT_EQ(0, test_open("s3d3", O_RDONLY));
+	ASSERT_EQ(EACCES, test_open("/", O_RDONLY));
+}
+
+TEST_F_FORK(layout1, mount_and_pivot)
+{
+	const struct rule rules[] = {
+		{
+			.path = dir_s3d2,
+			.access = ACCESS_RO,
+		},
+		{}
+	};
+	const int ruleset_fd = create_ruleset(_metadata, ACCESS_RW, rules);
+
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	set_cap(_metadata, CAP_SYS_ADMIN);
+	ASSERT_EQ(-1, mount(NULL, dir_s3d2, NULL, MS_RDONLY, NULL));
+	ASSERT_EQ(EPERM, errno);
+	ASSERT_EQ(-1, syscall(SYS_pivot_root, dir_s3d2, dir_s3d3));
+	ASSERT_EQ(EPERM, errno);
+	clear_cap(_metadata, CAP_SYS_ADMIN);
+}
+
+TEST_F_FORK(layout1, move_mount)
+{
+	const struct rule rules[] = {
+		{
+			.path = dir_s3d2,
+			.access = ACCESS_RO,
+		},
+		{}
+	};
+	const int ruleset_fd = create_ruleset(_metadata, ACCESS_RW, rules);
+
+	ASSERT_LE(0, ruleset_fd);
+
+	set_cap(_metadata, CAP_SYS_ADMIN);
+	ASSERT_EQ(0, syscall(SYS_move_mount, AT_FDCWD, dir_s3d2, AT_FDCWD,
+				dir_s1d2, 0)) {
+		TH_LOG("Failed to move mount: %s", strerror(errno));
+	}
+
+	ASSERT_EQ(0, syscall(SYS_move_mount, AT_FDCWD, dir_s1d2, AT_FDCWD,
+				dir_s3d2, 0));
+	clear_cap(_metadata, CAP_SYS_ADMIN);
+
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	set_cap(_metadata, CAP_SYS_ADMIN);
+	ASSERT_EQ(-1, syscall(SYS_move_mount, AT_FDCWD, dir_s3d2, AT_FDCWD,
+				dir_s1d2, 0));
+	ASSERT_EQ(EPERM, errno);
+	clear_cap(_metadata, CAP_SYS_ADMIN);
+}
+
+TEST_F_FORK(layout1, release_inodes)
+{
+	const struct rule rules[] = {
+		{
+			.path = dir_s1d1,
+			.access = ACCESS_RO,
+		},
+		{
+			.path = dir_s3d2,
+			.access = ACCESS_RO,
+		},
+		{
+			.path = dir_s3d3,
+			.access = ACCESS_RO,
+		},
+		{}
+	};
+	const int ruleset_fd = create_ruleset(_metadata, ACCESS_RW, rules);
+
+	ASSERT_LE(0, ruleset_fd);
+	/* Unmount a file hierarchy while it is being used by a ruleset. */
+	set_cap(_metadata, CAP_SYS_ADMIN);
+	ASSERT_EQ(0, umount(dir_s3d2));
+	clear_cap(_metadata, CAP_SYS_ADMIN);
+
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	ASSERT_EQ(0, test_open(file1_s1d1, O_RDONLY));
+	ASSERT_EQ(EACCES, test_open(dir_s3d2, O_RDONLY));
+	/* This dir_s3d3 would not be allowed and does not exist anyway. */
+	ASSERT_EQ(ENOENT, test_open(dir_s3d3, O_RDONLY));
+}
+
+enum relative_access {
+	REL_OPEN,
+	REL_CHDIR,
+	REL_CHROOT_ONLY,
+	REL_CHROOT_CHDIR,
+};
+
+static void test_relative_path(struct __test_metadata *const _metadata,
+		const enum relative_access rel)
+{
+	/*
+	 * Common layer to check that chroot doesn't ignore it (i.e. a chroot
+	 * is not a disconnected root directory).
+	 */
+	const struct rule layer1_base[] = {
+		{
+			.path = TMP_DIR,
+			.access = ACCESS_RO,
+		},
+		{}
+	};
+	const struct rule layer2_subs[] = {
+		{
+			.path = dir_s1d2,
+			.access = ACCESS_RO,
+		},
+		{
+			.path = dir_s2d2,
+			.access = ACCESS_RO,
+		},
+		{}
+	};
+	int dirfd, ruleset_fd;
+
+	ruleset_fd = create_ruleset(_metadata, ACCESS_RW, layer1_base);
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	ruleset_fd = create_ruleset(_metadata, ACCESS_RW, layer2_subs);
+
+	ASSERT_LE(0, ruleset_fd);
+	switch (rel) {
+	case REL_OPEN:
+	case REL_CHDIR:
+		break;
+	case REL_CHROOT_ONLY:
+		ASSERT_EQ(0, chdir(dir_s2d2));
+		break;
+	case REL_CHROOT_CHDIR:
+		ASSERT_EQ(0, chdir(dir_s1d2));
+		break;
+	default:
+		ASSERT_TRUE(false);
+		return;
+	}
+
+	set_cap(_metadata, CAP_SYS_CHROOT);
+	enforce_ruleset(_metadata, ruleset_fd);
+
+	switch (rel) {
+	case REL_OPEN:
+		dirfd = open(dir_s1d2, O_DIRECTORY);
+		ASSERT_LE(0, dirfd);
+		break;
+	case REL_CHDIR:
+		ASSERT_EQ(0, chdir(dir_s1d2));
+		dirfd = AT_FDCWD;
+		break;
+	case REL_CHROOT_ONLY:
+		/* Do chroot into dir_s1d2 (relative to dir_s2d2). */
+		ASSERT_EQ(0, chroot("../../s1d1/s1d2")) {
+			TH_LOG("Failed to chroot: %s", strerror(errno));
+		}
+		dirfd = AT_FDCWD;
+		break;
+	case REL_CHROOT_CHDIR:
+		/* Do chroot into dir_s1d2. */
+		ASSERT_EQ(0, chroot(".")) {
+			TH_LOG("Failed to chroot: %s", strerror(errno));
+		}
+		dirfd = AT_FDCWD;
+		break;
+	}
+
+	ASSERT_EQ((rel == REL_CHROOT_CHDIR) ? 0 : EACCES,
+			test_open_rel(dirfd, "..", O_RDONLY));
+	ASSERT_EQ(0, test_open_rel(dirfd, ".", O_RDONLY));
+
+	if (rel == REL_CHROOT_ONLY) {
+		/* The current directory is dir_s2d2. */
+		ASSERT_EQ(0, test_open_rel(dirfd, "./s2d3", O_RDONLY));
+	} else {
+		/* The current directory is dir_s1d2. */
+		ASSERT_EQ(0, test_open_rel(dirfd, "./s1d3", O_RDONLY));
+	}
+
+	if (rel == REL_CHROOT_ONLY || rel == REL_CHROOT_CHDIR) {
+		/* Checks the root dir_s1d2. */
+		ASSERT_EQ(0, test_open_rel(dirfd, "/..", O_RDONLY));
+		ASSERT_EQ(0, test_open_rel(dirfd, "/", O_RDONLY));
+		ASSERT_EQ(0, test_open_rel(dirfd, "/f1", O_RDONLY));
+		ASSERT_EQ(0, test_open_rel(dirfd, "/s1d3", O_RDONLY));
+	}
+
+	if (rel != REL_CHROOT_CHDIR) {
+		ASSERT_EQ(EACCES, test_open_rel(dirfd, "../../s1d1", O_RDONLY));
+		ASSERT_EQ(0, test_open_rel(dirfd, "../../s1d1/s1d2", O_RDONLY));
+		ASSERT_EQ(0, test_open_rel(dirfd, "../../s1d1/s1d2/s1d3", O_RDONLY));
+
+		ASSERT_EQ(EACCES, test_open_rel(dirfd, "../../s2d1", O_RDONLY));
+		ASSERT_EQ(0, test_open_rel(dirfd, "../../s2d1/s2d2", O_RDONLY));
+		ASSERT_EQ(0, test_open_rel(dirfd, "../../s2d1/s2d2/s2d3", O_RDONLY));
+	}
+
+	if (rel == REL_OPEN)
+		ASSERT_EQ(0, close(dirfd));
+	ASSERT_EQ(0, close(ruleset_fd));
+}
+
+TEST_F_FORK(layout1, relative_open)
+{
+	test_relative_path(_metadata, REL_OPEN);
+}
+
+TEST_F_FORK(layout1, relative_chdir)
+{
+	test_relative_path(_metadata, REL_CHDIR);
+}
+
+TEST_F_FORK(layout1, relative_chroot_only)
+{
+	test_relative_path(_metadata, REL_CHROOT_ONLY);
+}
+
+TEST_F_FORK(layout1, relative_chroot_chdir)
+{
+	test_relative_path(_metadata, REL_CHROOT_CHDIR);
+}
+
+static void copy_binary(struct __test_metadata *const _metadata,
+		const char *const dst_path)
+{
+	int dst_fd, src_fd;
+	struct stat statbuf;
+
+	dst_fd = open(dst_path, O_WRONLY | O_TRUNC | O_CLOEXEC);
+	ASSERT_LE(0, dst_fd) {
+		TH_LOG("Failed to open \"%s\": %s", dst_path,
+				strerror(errno));
+	}
+	src_fd = open(BINARY_PATH, O_RDONLY | O_CLOEXEC);
+	ASSERT_LE(0, src_fd) {
+		TH_LOG("Failed to open \"" BINARY_PATH "\": %s",
+				strerror(errno));
+	}
+	ASSERT_EQ(0, fstat(src_fd, &statbuf));
+	ASSERT_EQ(statbuf.st_size, sendfile(dst_fd, src_fd, 0,
+				statbuf.st_size));
+	ASSERT_EQ(0, close(src_fd));
+	ASSERT_EQ(0, close(dst_fd));
+}
+
+static void test_execute(struct __test_metadata *const _metadata,
+		const int err, const char *const path)
+{
+	int status;
+	char *const argv[] = {(char *)path, NULL};
+	const pid_t child = fork();
+
+	ASSERT_LE(0, child);
+	if (child == 0) {
+		ASSERT_EQ(err ? -1 : 0, execve(path, argv, NULL)) {
+			TH_LOG("Failed to execute \"%s\": %s", path,
+					strerror(errno));
+		};
+		ASSERT_EQ(err, errno);
+		_exit(_metadata->passed ? 2 : 1);
+		return;
+	}
+	ASSERT_EQ(child, waitpid(child, &status, 0));
+	ASSERT_EQ(1, WIFEXITED(status));
+	ASSERT_EQ(err ? 2 : 0, WEXITSTATUS(status)) {
+		TH_LOG("Unexpected return code for \"%s\": %s", path,
+				strerror(errno));
+	};
+}
+
+TEST_F_FORK(layout1, execute)
+{
+	const struct rule rules[] = {
+		{
+			.path = dir_s1d2,
+			.access = LANDLOCK_ACCESS_FS_EXECUTE,
+		},
+		{}
+	};
+	const int ruleset_fd = create_ruleset(_metadata, rules[0].access,
+			rules);
+
+	ASSERT_LE(0, ruleset_fd);
+	copy_binary(_metadata, file1_s1d1);
+	copy_binary(_metadata, file1_s1d2);
+	copy_binary(_metadata, file1_s1d3);
+
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	ASSERT_EQ(0, test_open(dir_s1d1, O_RDONLY));
+	ASSERT_EQ(0, test_open(file1_s1d1, O_RDONLY));
+	test_execute(_metadata, EACCES, file1_s1d1);
+
+	ASSERT_EQ(0, test_open(dir_s1d2, O_RDONLY));
+	ASSERT_EQ(0, test_open(file1_s1d2, O_RDONLY));
+	test_execute(_metadata, 0, file1_s1d2);
+
+	ASSERT_EQ(0, test_open(dir_s1d3, O_RDONLY));
+	ASSERT_EQ(0, test_open(file1_s1d3, O_RDONLY));
+	test_execute(_metadata, 0, file1_s1d3);
+}
+
+TEST_F_FORK(layout1, link)
+{
+	const struct rule rules[] = {
+		{
+			.path = dir_s1d2,
+			.access = LANDLOCK_ACCESS_FS_MAKE_REG,
+		},
+		{}
+	};
+	const int ruleset_fd = create_ruleset(_metadata, rules[0].access,
+			rules);
+
+	ASSERT_LE(0, ruleset_fd);
+
+	ASSERT_EQ(0, unlink(file1_s1d1));
+	ASSERT_EQ(0, unlink(file1_s1d2));
+	ASSERT_EQ(0, unlink(file1_s1d3));
+
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	ASSERT_EQ(-1, link(file2_s1d1, file1_s1d1));
+	ASSERT_EQ(EACCES, errno);
+	/* Denies linking because of reparenting. */
+	ASSERT_EQ(-1, link(file1_s2d1, file1_s1d2));
+	ASSERT_EQ(EXDEV, errno);
+	ASSERT_EQ(-1, link(file2_s1d2, file1_s1d3));
+	ASSERT_EQ(EXDEV, errno);
+
+	ASSERT_EQ(0, link(file2_s1d2, file1_s1d2));
+	ASSERT_EQ(0, link(file2_s1d3, file1_s1d3));
+}
+
+TEST_F_FORK(layout1, rename_file)
+{
+	const struct rule rules[] = {
+		{
+			.path = dir_s1d3,
+			.access = LANDLOCK_ACCESS_FS_REMOVE_FILE,
+		},
+		{
+			.path = dir_s2d2,
+			.access = LANDLOCK_ACCESS_FS_REMOVE_FILE,
+		},
+		{}
+	};
+	const int ruleset_fd = create_ruleset(_metadata, rules[0].access,
+			rules);
+
+	ASSERT_LE(0, ruleset_fd);
+
+	ASSERT_EQ(0, unlink(file1_s1d1));
+	ASSERT_EQ(0, unlink(file1_s1d2));
+
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/*
+	 * Tries to replace a file, from a directory that allows file removal,
+	 * but to a different directory (which also allows file removal).
+	 */
+	ASSERT_EQ(-1, rename(file1_s2d3, file1_s1d3));
+	ASSERT_EQ(EXDEV, errno);
+	ASSERT_EQ(-1, renameat2(AT_FDCWD, file1_s2d3, AT_FDCWD, file1_s1d3,
+				RENAME_EXCHANGE));
+	ASSERT_EQ(EXDEV, errno);
+	ASSERT_EQ(-1, renameat2(AT_FDCWD, file1_s2d3, AT_FDCWD, dir_s1d3,
+				RENAME_EXCHANGE));
+	ASSERT_EQ(EXDEV, errno);
+
+	/*
+	 * Tries to replace a file, from a directory that denies file removal,
+	 * to a different directory (which allows file removal).
+	 */
+	ASSERT_EQ(-1, rename(file1_s2d1, file1_s1d3));
+	ASSERT_EQ(EXDEV, errno);
+	ASSERT_EQ(-1, renameat2(AT_FDCWD, file1_s2d1, AT_FDCWD, file1_s1d3,
+				RENAME_EXCHANGE));
+	ASSERT_EQ(EXDEV, errno);
+	ASSERT_EQ(-1, renameat2(AT_FDCWD, dir_s2d2, AT_FDCWD, file1_s1d3,
+				RENAME_EXCHANGE));
+	ASSERT_EQ(EXDEV, errno);
+
+	/* Exchanges files and directories that partially allow removal. */
+	ASSERT_EQ(-1, renameat2(AT_FDCWD, dir_s2d2, AT_FDCWD, file1_s2d1,
+				RENAME_EXCHANGE));
+	ASSERT_EQ(EACCES, errno);
+	ASSERT_EQ(-1, renameat2(AT_FDCWD, file1_s2d1, AT_FDCWD, dir_s2d2,
+				RENAME_EXCHANGE));
+	ASSERT_EQ(EACCES, errno);
+
+	/* Renames files with different parents. */
+	ASSERT_EQ(-1, rename(file1_s2d2, file1_s1d2));
+	ASSERT_EQ(EXDEV, errno);
+	ASSERT_EQ(0, unlink(file1_s1d3));
+	ASSERT_EQ(-1, rename(file1_s2d1, file1_s1d3));
+	ASSERT_EQ(EXDEV, errno);
+
+	/* Exchanges and renames files with same parent. */
+	ASSERT_EQ(0, renameat2(AT_FDCWD, file2_s2d3, AT_FDCWD, file1_s2d3,
+				RENAME_EXCHANGE));
+	ASSERT_EQ(0, rename(file2_s2d3, file1_s2d3));
+
+	/* Exchanges files and directories with same parent, twice. */
+	ASSERT_EQ(0, renameat2(AT_FDCWD, file1_s2d2, AT_FDCWD, dir_s2d3,
+				RENAME_EXCHANGE));
+	ASSERT_EQ(0, renameat2(AT_FDCWD, file1_s2d2, AT_FDCWD, dir_s2d3,
+				RENAME_EXCHANGE));
+}
+
+TEST_F_FORK(layout1, rename_dir)
+{
+	const struct rule rules[] = {
+		{
+			.path = dir_s1d2,
+			.access = LANDLOCK_ACCESS_FS_REMOVE_DIR,
+		},
+		{
+			.path = dir_s2d1,
+			.access = LANDLOCK_ACCESS_FS_REMOVE_DIR,
+		},
+		{}
+	};
+	const int ruleset_fd = create_ruleset(_metadata, rules[0].access,
+			rules);
+
+	ASSERT_LE(0, ruleset_fd);
+
+	/* Empties dir_s1d3 to allow renaming. */
+	ASSERT_EQ(0, unlink(file1_s1d3));
+	ASSERT_EQ(0, unlink(file2_s1d3));
+
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/* Exchanges and renames directory to a different parent. */
+	ASSERT_EQ(-1, renameat2(AT_FDCWD, dir_s2d3, AT_FDCWD, dir_s1d3,
+				RENAME_EXCHANGE));
+	ASSERT_EQ(EXDEV, errno);
+	ASSERT_EQ(-1, rename(dir_s2d3, dir_s1d3));
+	ASSERT_EQ(EXDEV, errno);
+	ASSERT_EQ(-1, renameat2(AT_FDCWD, file1_s2d2, AT_FDCWD, dir_s1d3,
+				RENAME_EXCHANGE));
+	ASSERT_EQ(EXDEV, errno);
+
+	/*
+	 * Exchanges directory to the same parent, which doesn't allow
+	 * directory removal.
+	 */
+	ASSERT_EQ(-1, renameat2(AT_FDCWD, dir_s1d1, AT_FDCWD, dir_s2d1,
+				RENAME_EXCHANGE));
+	ASSERT_EQ(EACCES, errno);
+	ASSERT_EQ(-1, renameat2(AT_FDCWD, file1_s1d1, AT_FDCWD, dir_s1d2,
+				RENAME_EXCHANGE));
+	ASSERT_EQ(EACCES, errno);
+
+	/*
+	 * Exchanges and renames directory to the same parent, which allows
+	 * directory removal.
+	 */
+	ASSERT_EQ(0, renameat2(AT_FDCWD, dir_s1d3, AT_FDCWD, file1_s1d2,
+				RENAME_EXCHANGE));
+	ASSERT_EQ(0, unlink(dir_s1d3));
+	ASSERT_EQ(0, mkdir(dir_s1d3, 0700));
+	ASSERT_EQ(0, rename(file1_s1d2, dir_s1d3));
+	ASSERT_EQ(0, rmdir(dir_s1d3));
+}
+
+TEST_F_FORK(layout1, remove_dir)
+{
+	const struct rule rules[] = {
+		{
+			.path = dir_s1d2,
+			.access = LANDLOCK_ACCESS_FS_REMOVE_DIR,
+		},
+		{}
+	};
+	const int ruleset_fd = create_ruleset(_metadata, rules[0].access,
+			rules);
+
+	ASSERT_LE(0, ruleset_fd);
+
+	ASSERT_EQ(0, unlink(file1_s1d1));
+	ASSERT_EQ(0, unlink(file1_s1d2));
+	ASSERT_EQ(0, unlink(file1_s1d3));
+	ASSERT_EQ(0, unlink(file2_s1d3));
+
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	ASSERT_EQ(0, rmdir(dir_s1d3));
+	ASSERT_EQ(0, mkdir(dir_s1d3, 0700));
+	ASSERT_EQ(0, unlinkat(AT_FDCWD, dir_s1d3, AT_REMOVEDIR));
+
+	/* dir_s1d2 itself cannot be removed. */
+	ASSERT_EQ(-1, rmdir(dir_s1d2));
+	ASSERT_EQ(EACCES, errno);
+	ASSERT_EQ(-1, unlinkat(AT_FDCWD, dir_s1d2, AT_REMOVEDIR));
+	ASSERT_EQ(EACCES, errno);
+	ASSERT_EQ(-1, rmdir(dir_s1d1));
+	ASSERT_EQ(EACCES, errno);
+	ASSERT_EQ(-1, unlinkat(AT_FDCWD, dir_s1d1, AT_REMOVEDIR));
+	ASSERT_EQ(EACCES, errno);
+}
+
+TEST_F_FORK(layout1, remove_file)
+{
+	const struct rule rules[] = {
+		{
+			.path = dir_s1d2,
+			.access = LANDLOCK_ACCESS_FS_REMOVE_FILE,
+		},
+		{}
+	};
+	const int ruleset_fd = create_ruleset(_metadata, rules[0].access,
+			rules);
+
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	ASSERT_EQ(-1, unlink(file1_s1d1));
+	ASSERT_EQ(EACCES, errno);
+	ASSERT_EQ(-1, unlinkat(AT_FDCWD, file1_s1d1, 0));
+	ASSERT_EQ(EACCES, errno);
+	ASSERT_EQ(0, unlink(file1_s1d2));
+	ASSERT_EQ(0, unlinkat(AT_FDCWD, file1_s1d3, 0));
+}
+
+static void test_make_file(struct __test_metadata *const _metadata,
+		const __u64 access, const mode_t mode, const dev_t dev)
+{
+	const struct rule rules[] = {
+		{
+			.path = dir_s1d2,
+			.access = access,
+		},
+		{}
+	};
+	const int ruleset_fd = create_ruleset(_metadata, access, rules);
+
+	ASSERT_LE(0, ruleset_fd);
+
+	ASSERT_EQ(0, unlink(file1_s1d1));
+	ASSERT_EQ(0, unlink(file2_s1d1));
+	ASSERT_EQ(0, mknod(file2_s1d1, mode | 0400, dev)) {
+		TH_LOG("Failed to make file \"%s\": %s",
+				file2_s1d1, strerror(errno));
+	};
+
+	ASSERT_EQ(0, unlink(file1_s1d2));
+	ASSERT_EQ(0, unlink(file2_s1d2));
+
+	ASSERT_EQ(0, unlink(file1_s1d3));
+	ASSERT_EQ(0, unlink(file2_s1d3));
+
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	ASSERT_EQ(-1, mknod(file1_s1d1, mode | 0400, dev));
+	ASSERT_EQ(EACCES, errno);
+	ASSERT_EQ(-1, link(file2_s1d1, file1_s1d1));
+	ASSERT_EQ(EACCES, errno);
+	ASSERT_EQ(-1, rename(file2_s1d1, file1_s1d1));
+	ASSERT_EQ(EACCES, errno);
+
+	ASSERT_EQ(0, mknod(file1_s1d2, mode | 0400, dev)) {
+		TH_LOG("Failed to make file \"%s\": %s",
+				file1_s1d2, strerror(errno));
+	};
+	ASSERT_EQ(0, link(file1_s1d2, file2_s1d2));
+	ASSERT_EQ(0, unlink(file2_s1d2));
+	ASSERT_EQ(0, rename(file1_s1d2, file2_s1d2));
+
+	ASSERT_EQ(0, mknod(file1_s1d3, mode | 0400, dev));
+	ASSERT_EQ(0, link(file1_s1d3, file2_s1d3));
+	ASSERT_EQ(0, unlink(file2_s1d3));
+	ASSERT_EQ(0, rename(file1_s1d3, file2_s1d3));
+}
+
+TEST_F_FORK(layout1, make_char)
+{
+	/* Creates a /dev/null device. */
+	set_cap(_metadata, CAP_MKNOD);
+	test_make_file(_metadata, LANDLOCK_ACCESS_FS_MAKE_CHAR, S_IFCHR,
+			makedev(1, 3));
+}
+
+TEST_F_FORK(layout1, make_block)
+{
+	/* Creates a /dev/loop0 device. */
+	set_cap(_metadata, CAP_MKNOD);
+	test_make_file(_metadata, LANDLOCK_ACCESS_FS_MAKE_BLOCK, S_IFBLK,
+			makedev(7, 0));
+}
+
+TEST_F_FORK(layout1, make_reg_1)
+{
+	test_make_file(_metadata, LANDLOCK_ACCESS_FS_MAKE_REG, S_IFREG, 0);
+}
+
+TEST_F_FORK(layout1, make_reg_2)
+{
+	test_make_file(_metadata, LANDLOCK_ACCESS_FS_MAKE_REG, 0, 0);
+}
+
+TEST_F_FORK(layout1, make_sock)
+{
+	test_make_file(_metadata, LANDLOCK_ACCESS_FS_MAKE_SOCK, S_IFSOCK, 0);
+}
+
+TEST_F_FORK(layout1, make_fifo)
+{
+	test_make_file(_metadata, LANDLOCK_ACCESS_FS_MAKE_FIFO, S_IFIFO, 0);
+}
+
+TEST_F_FORK(layout1, make_sym)
+{
+	const struct rule rules[] = {
+		{
+			.path = dir_s1d2,
+			.access = LANDLOCK_ACCESS_FS_MAKE_SYM,
+		},
+		{}
+	};
+	const int ruleset_fd = create_ruleset(_metadata, rules[0].access,
+			rules);
+
+	ASSERT_LE(0, ruleset_fd);
+
+	ASSERT_EQ(0, unlink(file1_s1d1));
+	ASSERT_EQ(0, unlink(file2_s1d1));
+	ASSERT_EQ(0, symlink("none", file2_s1d1));
+
+	ASSERT_EQ(0, unlink(file1_s1d2));
+	ASSERT_EQ(0, unlink(file2_s1d2));
+
+	ASSERT_EQ(0, unlink(file1_s1d3));
+	ASSERT_EQ(0, unlink(file2_s1d3));
+
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	ASSERT_EQ(-1, symlink("none", file1_s1d1));
+	ASSERT_EQ(EACCES, errno);
+	ASSERT_EQ(-1, link(file2_s1d1, file1_s1d1));
+	ASSERT_EQ(EACCES, errno);
+	ASSERT_EQ(-1, rename(file2_s1d1, file1_s1d1));
+	ASSERT_EQ(EACCES, errno);
+
+	ASSERT_EQ(0, symlink("none", file1_s1d2));
+	ASSERT_EQ(0, link(file1_s1d2, file2_s1d2));
+	ASSERT_EQ(0, unlink(file2_s1d2));
+	ASSERT_EQ(0, rename(file1_s1d2, file2_s1d2));
+
+	ASSERT_EQ(0, symlink("none", file1_s1d3));
+	ASSERT_EQ(0, link(file1_s1d3, file2_s1d3));
+	ASSERT_EQ(0, unlink(file2_s1d3));
+	ASSERT_EQ(0, rename(file1_s1d3, file2_s1d3));
+}
+
+TEST_F_FORK(layout1, make_dir)
+{
+	const struct rule rules[] = {
+		{
+			.path = dir_s1d2,
+			.access = LANDLOCK_ACCESS_FS_MAKE_DIR,
+		},
+		{}
+	};
+	const int ruleset_fd = create_ruleset(_metadata, rules[0].access,
+			rules);
+
+	ASSERT_LE(0, ruleset_fd);
+
+	ASSERT_EQ(0, unlink(file1_s1d1));
+	ASSERT_EQ(0, unlink(file1_s1d2));
+	ASSERT_EQ(0, unlink(file1_s1d3));
+
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/* Uses file_* as directory names. */
+	ASSERT_EQ(-1, mkdir(file1_s1d1, 0700));
+	ASSERT_EQ(EACCES, errno);
+	ASSERT_EQ(0, mkdir(file1_s1d2, 0700));
+	ASSERT_EQ(0, mkdir(file1_s1d3, 0700));
+}
+
+static int open_proc_fd(struct __test_metadata *const _metadata, const int fd,
+		const int open_flags)
+{
+	static const char path_template[] = "/proc/self/fd/%d";
+	char procfd_path[sizeof(path_template) + 10];
+	const int procfd_path_size = snprintf(procfd_path, sizeof(procfd_path),
+			path_template, fd);
+
+	ASSERT_LT(procfd_path_size, sizeof(procfd_path));
+	return open(procfd_path, open_flags);
+}
+
+TEST_F_FORK(layout1, proc_unlinked_file)
+{
+	const struct rule rules[] = {
+		{
+			.path = file1_s1d2,
+			.access = LANDLOCK_ACCESS_FS_READ_FILE,
+		},
+		{}
+	};
+	int reg_fd, proc_fd;
+	const int ruleset_fd = create_ruleset(_metadata,
+			LANDLOCK_ACCESS_FS_READ_FILE |
+			LANDLOCK_ACCESS_FS_WRITE_FILE, rules);
+
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	ASSERT_EQ(EACCES, test_open(file1_s1d2, O_RDWR));
+	ASSERT_EQ(0, test_open(file1_s1d2, O_RDONLY));
+	reg_fd = open(file1_s1d2, O_RDONLY | O_CLOEXEC);
+	ASSERT_LE(0, reg_fd);
+	ASSERT_EQ(0, unlink(file1_s1d2));
+
+	proc_fd = open_proc_fd(_metadata, reg_fd, O_RDONLY | O_CLOEXEC);
+	ASSERT_LE(0, proc_fd);
+	ASSERT_EQ(0, close(proc_fd));
+
+	proc_fd = open_proc_fd(_metadata, reg_fd, O_RDWR | O_CLOEXEC);
+	ASSERT_EQ(-1, proc_fd) {
+		TH_LOG("Successfully opened /proc/self/fd/%d: %s",
+				reg_fd, strerror(errno));
+	}
+	ASSERT_EQ(EACCES, errno);
+
+	ASSERT_EQ(0, close(reg_fd));
+}
+
+TEST_F_FORK(layout1, proc_pipe)
+{
+	int proc_fd;
+	int pipe_fds[2];
+	char buf = '\0';
+	const struct rule rules[] = {
+		{
+			.path = dir_s1d2,
+			.access = LANDLOCK_ACCESS_FS_READ_FILE |
+				LANDLOCK_ACCESS_FS_WRITE_FILE,
+		},
+		{}
+	};
+	/* Limits read and write access to files tied to the filesystem. */
+	const int ruleset_fd = create_ruleset(_metadata, rules[0].access,
+			rules);
+
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/* Checks enforcement for normal files. */
+	ASSERT_EQ(0, test_open(file1_s1d2, O_RDWR));
+	ASSERT_EQ(EACCES, test_open(file1_s1d1, O_RDWR));
+
+	/* Checks access to pipes through FD. */
+	ASSERT_EQ(0, pipe2(pipe_fds, O_CLOEXEC));
+	ASSERT_EQ(1, write(pipe_fds[1], ".", 1)) {
+		TH_LOG("Failed to write in pipe: %s", strerror(errno));
+	}
+	ASSERT_EQ(1, read(pipe_fds[0], &buf, 1));
+	ASSERT_EQ('.', buf);
+
+	/* Checks write access to pipe through /proc/self/fd . */
+	proc_fd = open_proc_fd(_metadata, pipe_fds[1], O_WRONLY | O_CLOEXEC);
+	ASSERT_LE(0, proc_fd);
+	ASSERT_EQ(1, write(proc_fd, ".", 1)) {
+		TH_LOG("Failed to write through /proc/self/fd/%d: %s",
+				pipe_fds[1], strerror(errno));
+	}
+	ASSERT_EQ(0, close(proc_fd));
+
+	/* Checks read access to pipe through /proc/self/fd . */
+	proc_fd = open_proc_fd(_metadata, pipe_fds[0], O_RDONLY | O_CLOEXEC);
+	ASSERT_LE(0, proc_fd);
+	buf = '\0';
+	ASSERT_EQ(1, read(proc_fd, &buf, 1)) {
+		TH_LOG("Failed to read through /proc/self/fd/%d: %s",
+				pipe_fds[1], strerror(errno));
+	}
+	ASSERT_EQ(0, close(proc_fd));
+
+	ASSERT_EQ(0, close(pipe_fds[0]));
+	ASSERT_EQ(0, close(pipe_fds[1]));
+}
+
+FIXTURE(layout1_bind) {
+};
+
+FIXTURE_SETUP(layout1_bind)
+{
+	prepare_layout(_metadata);
+
+	create_layout1(_metadata);
+
+	set_cap(_metadata, CAP_SYS_ADMIN);
+	ASSERT_EQ(0, mount(dir_s1d2, dir_s2d2, NULL, MS_BIND, NULL));
+	clear_cap(_metadata, CAP_SYS_ADMIN);
+}
+
+FIXTURE_TEARDOWN(layout1_bind)
+{
+	set_cap(_metadata, CAP_SYS_ADMIN);
+	EXPECT_EQ(0, umount(dir_s2d2));
+	clear_cap(_metadata, CAP_SYS_ADMIN);
+
+	remove_layout1(_metadata);
+
+	cleanup_layout(_metadata);
+}
+
+static const char bind_dir_s1d3[] = TMP_DIR "/s2d1/s2d2/s1d3";
+static const char bind_file1_s1d3[] = TMP_DIR "/s2d1/s2d2/s1d3/f1";
+
+/*
+ * layout1_bind hierarchy:
+ *
+ * tmp
+ * ├── s1d1
+ * │   ├── f1
+ * │   ├── f2
+ * │   └── s1d2
+ * │       ├── f1
+ * │       ├── f2
+ * │       └── s1d3
+ * │           ├── f1
+ * │           └── f2
+ * ├── s2d1
+ * │   ├── f1
+ * │   └── s2d2
+ * │       ├── f1
+ * │       ├── f2
+ * │       └── s1d3
+ * │           ├── f1
+ * │           └── f2
+ * └── s3d1
+ *     └── s3d2
+ *         └── s3d3
+ */
+
+TEST_F_FORK(layout1_bind, no_restriction)
+{
+	ASSERT_EQ(0, test_open(dir_s1d1, O_RDONLY));
+	ASSERT_EQ(0, test_open(file1_s1d1, O_RDONLY));
+	ASSERT_EQ(0, test_open(dir_s1d2, O_RDONLY));
+	ASSERT_EQ(0, test_open(file1_s1d2, O_RDONLY));
+	ASSERT_EQ(0, test_open(dir_s1d3, O_RDONLY));
+	ASSERT_EQ(0, test_open(file1_s1d3, O_RDONLY));
+
+	ASSERT_EQ(0, test_open(dir_s2d1, O_RDONLY));
+	ASSERT_EQ(0, test_open(file1_s2d1, O_RDONLY));
+	ASSERT_EQ(0, test_open(dir_s2d2, O_RDONLY));
+	ASSERT_EQ(0, test_open(file1_s2d2, O_RDONLY));
+	ASSERT_EQ(ENOENT, test_open(dir_s2d3, O_RDONLY));
+	ASSERT_EQ(ENOENT, test_open(file1_s2d3, O_RDONLY));
+
+	ASSERT_EQ(0, test_open(bind_dir_s1d3, O_RDONLY));
+	ASSERT_EQ(0, test_open(bind_file1_s1d3, O_RDONLY));
+
+	ASSERT_EQ(0, test_open(dir_s3d1, O_RDONLY));
+}
+
+TEST_F_FORK(layout1_bind, same_content_same_file)
+{
+	/*
+	 * Sets access right on parent directories of both source and
+	 * destination mount points.
+	 */
+	const struct rule layer1_parent[] = {
+		{
+			.path = dir_s1d1,
+			.access = ACCESS_RO,
+		},
+		{
+			.path = dir_s2d1,
+			.access = ACCESS_RW,
+		},
+		{}
+	};
+	/*
+	 * Sets access rights on the same bind-mounted directories.  The result
+	 * should be ACCESS_RW for both directories, but not both hierarchies
+	 * because of the first layer.
+	 */
+	const struct rule layer2_mount_point[] = {
+		{
+			.path = dir_s1d2,
+			.access = LANDLOCK_ACCESS_FS_READ_FILE,
+		},
+		{
+			.path = dir_s2d2,
+			.access = ACCESS_RW,
+		},
+		{}
+	};
+	/* Only allow read-access to the s1d3 hierarchies. */
+	const struct rule layer3_source[] = {
+		{
+			.path = dir_s1d3,
+			.access = LANDLOCK_ACCESS_FS_READ_FILE,
+		},
+		{}
+	};
+	/* Removes all access rights. */
+	const struct rule layer4_destination[] = {
+		{
+			.path = bind_file1_s1d3,
+			.access = LANDLOCK_ACCESS_FS_WRITE_FILE,
+		},
+		{}
+	};
+	int ruleset_fd;
+
+	/* Sets rules for the parent directories. */
+	ruleset_fd = create_ruleset(_metadata, ACCESS_RW, layer1_parent);
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/* Checks source hierarchy. */
+	ASSERT_EQ(0, test_open(file1_s1d1, O_RDONLY));
+	ASSERT_EQ(EACCES, test_open(file1_s1d1, O_WRONLY));
+	ASSERT_EQ(0, test_open(dir_s1d1, O_RDONLY | O_DIRECTORY));
+
+	ASSERT_EQ(0, test_open(file1_s1d2, O_RDONLY));
+	ASSERT_EQ(EACCES, test_open(file1_s1d2, O_WRONLY));
+	ASSERT_EQ(0, test_open(dir_s1d2, O_RDONLY | O_DIRECTORY));
+
+	/* Checks destination hierarchy. */
+	ASSERT_EQ(0, test_open(file1_s2d1, O_RDWR));
+	ASSERT_EQ(0, test_open(dir_s2d1, O_RDONLY | O_DIRECTORY));
+
+	ASSERT_EQ(0, test_open(file1_s2d2, O_RDWR));
+	ASSERT_EQ(0, test_open(dir_s2d2, O_RDONLY | O_DIRECTORY));
+
+	/* Sets rules for the mount points. */
+	ruleset_fd = create_ruleset(_metadata, ACCESS_RW, layer2_mount_point);
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/* Checks source hierarchy. */
+	ASSERT_EQ(EACCES, test_open(file1_s1d1, O_RDONLY));
+	ASSERT_EQ(EACCES, test_open(file1_s1d1, O_WRONLY));
+	ASSERT_EQ(EACCES, test_open(dir_s1d1, O_RDONLY | O_DIRECTORY));
+
+	ASSERT_EQ(0, test_open(file1_s1d2, O_RDONLY));
+	ASSERT_EQ(EACCES, test_open(file1_s1d2, O_WRONLY));
+	ASSERT_EQ(0, test_open(dir_s1d2, O_RDONLY | O_DIRECTORY));
+
+	/* Checks destination hierarchy. */
+	ASSERT_EQ(EACCES, test_open(file1_s2d1, O_RDONLY));
+	ASSERT_EQ(EACCES, test_open(file1_s2d1, O_WRONLY));
+	ASSERT_EQ(EACCES, test_open(dir_s2d1, O_RDONLY | O_DIRECTORY));
+
+	ASSERT_EQ(0, test_open(file1_s2d2, O_RDWR));
+	ASSERT_EQ(0, test_open(dir_s2d2, O_RDONLY | O_DIRECTORY));
+	ASSERT_EQ(0, test_open(bind_dir_s1d3, O_RDONLY | O_DIRECTORY));
+
+	/* Sets a (shared) rule only on the source. */
+	ruleset_fd = create_ruleset(_metadata, ACCESS_RW, layer3_source);
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/* Checks source hierarchy. */
+	ASSERT_EQ(EACCES, test_open(file1_s1d2, O_RDONLY));
+	ASSERT_EQ(EACCES, test_open(file1_s1d2, O_WRONLY));
+	ASSERT_EQ(EACCES, test_open(dir_s1d2, O_RDONLY | O_DIRECTORY));
+
+	ASSERT_EQ(0, test_open(file1_s1d3, O_RDONLY));
+	ASSERT_EQ(EACCES, test_open(file1_s1d3, O_WRONLY));
+	ASSERT_EQ(EACCES, test_open(dir_s1d3, O_RDONLY | O_DIRECTORY));
+
+	/* Checks destination hierarchy. */
+	ASSERT_EQ(EACCES, test_open(file1_s2d2, O_RDONLY));
+	ASSERT_EQ(EACCES, test_open(file1_s2d2, O_WRONLY));
+	ASSERT_EQ(EACCES, test_open(dir_s2d2, O_RDONLY | O_DIRECTORY));
+
+	ASSERT_EQ(0, test_open(bind_file1_s1d3, O_RDONLY));
+	ASSERT_EQ(EACCES, test_open(bind_file1_s1d3, O_WRONLY));
+	ASSERT_EQ(EACCES, test_open(bind_dir_s1d3, O_RDONLY | O_DIRECTORY));
+
+	/* Sets a (shared) rule only on the destination. */
+	ruleset_fd = create_ruleset(_metadata, ACCESS_RW, layer4_destination);
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/* Checks source hierarchy. */
+	ASSERT_EQ(EACCES, test_open(file1_s1d3, O_RDONLY));
+	ASSERT_EQ(EACCES, test_open(file1_s1d3, O_WRONLY));
+
+	/* Checks destination hierarchy. */
+	ASSERT_EQ(EACCES, test_open(bind_file1_s1d3, O_RDONLY));
+	ASSERT_EQ(EACCES, test_open(bind_file1_s1d3, O_WRONLY));
+}
+
+#define LOWER_BASE	TMP_DIR "/lower"
+#define LOWER_DATA	LOWER_BASE "/data"
+static const char lower_fl1[] = LOWER_DATA "/fl1";
+static const char lower_dl1[] = LOWER_DATA "/dl1";
+static const char lower_dl1_fl2[] = LOWER_DATA "/dl1/fl2";
+static const char lower_fo1[] = LOWER_DATA "/fo1";
+static const char lower_do1[] = LOWER_DATA "/do1";
+static const char lower_do1_fo2[] = LOWER_DATA "/do1/fo2";
+static const char lower_do1_fl3[] = LOWER_DATA "/do1/fl3";
+
+static const char (*lower_base_files[])[] = {
+	&lower_fl1,
+	&lower_fo1,
+	NULL
+};
+static const char (*lower_base_directories[])[] = {
+	&lower_dl1,
+	&lower_do1,
+	NULL
+};
+static const char (*lower_sub_files[])[] = {
+	&lower_dl1_fl2,
+	&lower_do1_fo2,
+	&lower_do1_fl3,
+	NULL
+};
+
+#define UPPER_BASE	TMP_DIR "/upper"
+#define UPPER_DATA	UPPER_BASE "/data"
+#define UPPER_WORK	UPPER_BASE "/work"
+static const char upper_fu1[] = UPPER_DATA "/fu1";
+static const char upper_du1[] = UPPER_DATA "/du1";
+static const char upper_du1_fu2[] = UPPER_DATA "/du1/fu2";
+static const char upper_fo1[] = UPPER_DATA "/fo1";
+static const char upper_do1[] = UPPER_DATA "/do1";
+static const char upper_do1_fo2[] = UPPER_DATA "/do1/fo2";
+static const char upper_do1_fu3[] = UPPER_DATA "/do1/fu3";
+
+static const char (*upper_base_files[])[] = {
+	&upper_fu1,
+	&upper_fo1,
+	NULL
+};
+static const char (*upper_base_directories[])[] = {
+	&upper_du1,
+	&upper_do1,
+	NULL
+};
+static const char (*upper_sub_files[])[] = {
+	&upper_du1_fu2,
+	&upper_do1_fo2,
+	&upper_do1_fu3,
+	NULL
+};
+
+#define MERGE_BASE	TMP_DIR "/merge"
+#define MERGE_DATA	MERGE_BASE "/data"
+static const char merge_fl1[] = MERGE_DATA "/fl1";
+static const char merge_dl1[] = MERGE_DATA "/dl1";
+static const char merge_dl1_fl2[] = MERGE_DATA "/dl1/fl2";
+static const char merge_fu1[] = MERGE_DATA "/fu1";
+static const char merge_du1[] = MERGE_DATA "/du1";
+static const char merge_du1_fu2[] = MERGE_DATA "/du1/fu2";
+static const char merge_fo1[] = MERGE_DATA "/fo1";
+static const char merge_do1[] = MERGE_DATA "/do1";
+static const char merge_do1_fo2[] = MERGE_DATA "/do1/fo2";
+static const char merge_do1_fl3[] = MERGE_DATA "/do1/fl3";
+static const char merge_do1_fu3[] = MERGE_DATA "/do1/fu3";
+
+static const char (*merge_base_files[])[] = {
+	&merge_fl1,
+	&merge_fu1,
+	&merge_fo1,
+	NULL
+};
+static const char (*merge_base_directories[])[] = {
+	&merge_dl1,
+	&merge_du1,
+	&merge_do1,
+	NULL
+};
+static const char (*merge_sub_files[])[] = {
+	&merge_dl1_fl2,
+	&merge_du1_fu2,
+	&merge_do1_fo2,
+	&merge_do1_fl3,
+	&merge_do1_fu3,
+	NULL
+};
+
+/*
+ * layout2_overlay hierarchy:
+ *
+ * tmp
+ * ├── lower
+ * │   └── data
+ * │       ├── dl1
+ * │       │   └── fl2
+ * │       ├── do1
+ * │       │   ├── fl3
+ * │       │   └── fo2
+ * │       ├── fl1
+ * │       └── fo1
+ * ├── merge
+ * │   └── data
+ * │       ├── dl1
+ * │       │   └── fl2
+ * │       ├── do1
+ * │       │   ├── fl3
+ * │       │   ├── fo2
+ * │       │   └── fu3
+ * │       ├── du1
+ * │       │   └── fu2
+ * │       ├── fl1
+ * │       ├── fo1
+ * │       └── fu1
+ * └── upper
+ *     ├── data
+ *     │   ├── do1
+ *     │   │   ├── fo2
+ *     │   │   └── fu3
+ *     │   ├── du1
+ *     │   │   └── fu2
+ *     │   ├── fo1
+ *     │   └── fu1
+ *     └── work
+ *         └── work
+ */
+
+FIXTURE(layout2_overlay) {
+};
+
+FIXTURE_SETUP(layout2_overlay)
+{
+	prepare_layout(_metadata);
+
+	create_directory(_metadata, LOWER_BASE);
+	set_cap(_metadata, CAP_SYS_ADMIN);
+	/* Creates tmpfs mount points to get deterministic overlayfs. */
+	ASSERT_EQ(0, mount("tmp", LOWER_BASE, "tmpfs", 0, "size=4m,mode=700"));
+	clear_cap(_metadata, CAP_SYS_ADMIN);
+	create_file(_metadata, lower_fl1);
+	create_file(_metadata, lower_dl1_fl2);
+	create_file(_metadata, lower_fo1);
+	create_file(_metadata, lower_do1_fo2);
+	create_file(_metadata, lower_do1_fl3);
+
+	create_directory(_metadata, UPPER_BASE);
+	set_cap(_metadata, CAP_SYS_ADMIN);
+	ASSERT_EQ(0, mount("tmp", UPPER_BASE, "tmpfs", 0, "size=4m,mode=700"));
+	clear_cap(_metadata, CAP_SYS_ADMIN);
+	create_file(_metadata, upper_fu1);
+	create_file(_metadata, upper_du1_fu2);
+	create_file(_metadata, upper_fo1);
+	create_file(_metadata, upper_do1_fo2);
+	create_file(_metadata, upper_do1_fu3);
+	ASSERT_EQ(0, mkdir(UPPER_WORK, 0700));
+
+	create_directory(_metadata, MERGE_DATA);
+	set_cap(_metadata, CAP_SYS_ADMIN);
+	set_cap(_metadata, CAP_DAC_OVERRIDE);
+	ASSERT_EQ(0, mount("overlay", MERGE_DATA, "overlay", 0,
+				"lowerdir=" LOWER_DATA
+				",upperdir=" UPPER_DATA
+				",workdir=" UPPER_WORK));
+	clear_cap(_metadata, CAP_DAC_OVERRIDE);
+	clear_cap(_metadata, CAP_SYS_ADMIN);
+}
+
+FIXTURE_TEARDOWN(layout2_overlay)
+{
+	EXPECT_EQ(0, remove_path(lower_do1_fl3));
+	EXPECT_EQ(0, remove_path(lower_dl1_fl2));
+	EXPECT_EQ(0, remove_path(lower_fl1));
+	EXPECT_EQ(0, remove_path(lower_do1_fo2));
+	EXPECT_EQ(0, remove_path(lower_fo1));
+	set_cap(_metadata, CAP_SYS_ADMIN);
+	EXPECT_EQ(0, umount(LOWER_BASE));
+	clear_cap(_metadata, CAP_SYS_ADMIN);
+	EXPECT_EQ(0, remove_path(LOWER_BASE));
+
+	EXPECT_EQ(0, remove_path(upper_do1_fu3));
+	EXPECT_EQ(0, remove_path(upper_du1_fu2));
+	EXPECT_EQ(0, remove_path(upper_fu1));
+	EXPECT_EQ(0, remove_path(upper_do1_fo2));
+	EXPECT_EQ(0, remove_path(upper_fo1));
+	EXPECT_EQ(0, remove_path(UPPER_WORK "/work"));
+	set_cap(_metadata, CAP_SYS_ADMIN);
+	EXPECT_EQ(0, umount(UPPER_BASE));
+	clear_cap(_metadata, CAP_SYS_ADMIN);
+	EXPECT_EQ(0, remove_path(UPPER_BASE));
+
+	set_cap(_metadata, CAP_SYS_ADMIN);
+	EXPECT_EQ(0, umount(MERGE_DATA));
+	clear_cap(_metadata, CAP_SYS_ADMIN);
+	EXPECT_EQ(0, remove_path(MERGE_DATA));
+
+	cleanup_layout(_metadata);
+}
+
+TEST_F_FORK(layout2_overlay, no_restriction)
+{
+	ASSERT_EQ(0, test_open(lower_fl1, O_RDONLY));
+	ASSERT_EQ(0, test_open(lower_dl1, O_RDONLY));
+	ASSERT_EQ(0, test_open(lower_dl1_fl2, O_RDONLY));
+	ASSERT_EQ(0, test_open(lower_fo1, O_RDONLY));
+	ASSERT_EQ(0, test_open(lower_do1, O_RDONLY));
+	ASSERT_EQ(0, test_open(lower_do1_fo2, O_RDONLY));
+	ASSERT_EQ(0, test_open(lower_do1_fl3, O_RDONLY));
+
+	ASSERT_EQ(0, test_open(upper_fu1, O_RDONLY));
+	ASSERT_EQ(0, test_open(upper_du1, O_RDONLY));
+	ASSERT_EQ(0, test_open(upper_du1_fu2, O_RDONLY));
+	ASSERT_EQ(0, test_open(upper_fo1, O_RDONLY));
+	ASSERT_EQ(0, test_open(upper_do1, O_RDONLY));
+	ASSERT_EQ(0, test_open(upper_do1_fo2, O_RDONLY));
+	ASSERT_EQ(0, test_open(upper_do1_fu3, O_RDONLY));
+
+	ASSERT_EQ(0, test_open(merge_fl1, O_RDONLY));
+	ASSERT_EQ(0, test_open(merge_dl1, O_RDONLY));
+	ASSERT_EQ(0, test_open(merge_dl1_fl2, O_RDONLY));
+	ASSERT_EQ(0, test_open(merge_fu1, O_RDONLY));
+	ASSERT_EQ(0, test_open(merge_du1, O_RDONLY));
+	ASSERT_EQ(0, test_open(merge_du1_fu2, O_RDONLY));
+	ASSERT_EQ(0, test_open(merge_fo1, O_RDONLY));
+	ASSERT_EQ(0, test_open(merge_do1, O_RDONLY));
+	ASSERT_EQ(0, test_open(merge_do1_fo2, O_RDONLY));
+	ASSERT_EQ(0, test_open(merge_do1_fl3, O_RDONLY));
+	ASSERT_EQ(0, test_open(merge_do1_fu3, O_RDONLY));
+}
+
+#define for_each_path(path_list, path_entry, i)			\
+	for (i = 0, path_entry = *path_list[i]; path_list[i];	\
+			path_entry = *path_list[++i])
+
+TEST_F_FORK(layout2_overlay, same_content_different_file)
+{
+	/* Sets access right on parent directories of both layers. */
+	const struct rule layer1_base[] = {
+		{
+			.path = LOWER_BASE,
+			.access = LANDLOCK_ACCESS_FS_READ_FILE,
+		},
+		{
+			.path = UPPER_BASE,
+			.access = LANDLOCK_ACCESS_FS_READ_FILE,
+		},
+		{
+			.path = MERGE_BASE,
+			.access = ACCESS_RW,
+		},
+		{}
+	};
+	const struct rule layer2_data[] = {
+		{
+			.path = LOWER_DATA,
+			.access = LANDLOCK_ACCESS_FS_READ_FILE,
+		},
+		{
+			.path = UPPER_DATA,
+			.access = LANDLOCK_ACCESS_FS_READ_FILE,
+		},
+		{
+			.path = MERGE_DATA,
+			.access = ACCESS_RW,
+		},
+		{}
+	};
+	/* Sets access right on directories inside both layers. */
+	const struct rule layer3_subdirs[] = {
+		{
+			.path = lower_dl1,
+			.access = LANDLOCK_ACCESS_FS_READ_FILE,
+		},
+		{
+			.path = lower_do1,
+			.access = LANDLOCK_ACCESS_FS_READ_FILE,
+		},
+		{
+			.path = upper_du1,
+			.access = LANDLOCK_ACCESS_FS_READ_FILE,
+		},
+		{
+			.path = upper_do1,
+			.access = LANDLOCK_ACCESS_FS_READ_FILE,
+		},
+		{
+			.path = merge_dl1,
+			.access = ACCESS_RW,
+		},
+		{
+			.path = merge_du1,
+			.access = ACCESS_RW,
+		},
+		{
+			.path = merge_do1,
+			.access = ACCESS_RW,
+		},
+		{}
+	};
+	/* Tighten access rights to the files. */
+	const struct rule layer4_files[] = {
+		{
+			.path = lower_dl1_fl2,
+			.access = LANDLOCK_ACCESS_FS_READ_FILE,
+		},
+		{
+			.path = lower_do1_fo2,
+			.access = LANDLOCK_ACCESS_FS_READ_FILE,
+		},
+		{
+			.path = lower_do1_fl3,
+			.access = LANDLOCK_ACCESS_FS_READ_FILE,
+		},
+		{
+			.path = upper_du1_fu2,
+			.access = LANDLOCK_ACCESS_FS_READ_FILE,
+		},
+		{
+			.path = upper_do1_fo2,
+			.access = LANDLOCK_ACCESS_FS_READ_FILE,
+		},
+		{
+			.path = upper_do1_fu3,
+			.access = LANDLOCK_ACCESS_FS_READ_FILE,
+		},
+		{
+			.path = merge_dl1_fl2,
+			.access = LANDLOCK_ACCESS_FS_READ_FILE |
+				LANDLOCK_ACCESS_FS_WRITE_FILE,
+		},
+		{
+			.path = merge_du1_fu2,
+			.access = LANDLOCK_ACCESS_FS_READ_FILE |
+				LANDLOCK_ACCESS_FS_WRITE_FILE,
+		},
+		{
+			.path = merge_do1_fo2,
+			.access = LANDLOCK_ACCESS_FS_READ_FILE |
+				LANDLOCK_ACCESS_FS_WRITE_FILE,
+		},
+		{
+			.path = merge_do1_fl3,
+			.access = LANDLOCK_ACCESS_FS_READ_FILE |
+				LANDLOCK_ACCESS_FS_WRITE_FILE,
+		},
+		{
+			.path = merge_do1_fu3,
+			.access = LANDLOCK_ACCESS_FS_READ_FILE |
+				LANDLOCK_ACCESS_FS_WRITE_FILE,
+		},
+		{}
+	};
+	const struct rule layer5_merge_only[] = {
+		{
+			.path = MERGE_DATA,
+			.access = LANDLOCK_ACCESS_FS_READ_FILE |
+				LANDLOCK_ACCESS_FS_WRITE_FILE,
+		},
+		{}
+	};
+	int ruleset_fd;
+	size_t i;
+	const char *path_entry;
+
+	/* Sets rules on base directories (i.e. outside overlay scope). */
+	ruleset_fd = create_ruleset(_metadata, ACCESS_RW, layer1_base);
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/* Checks lower layer. */
+	for_each_path(lower_base_files, path_entry, i) {
+		ASSERT_EQ(0, test_open(path_entry, O_RDONLY));
+		ASSERT_EQ(EACCES, test_open(path_entry, O_WRONLY));
+	}
+	for_each_path(lower_base_directories, path_entry, i) {
+		ASSERT_EQ(EACCES, test_open(path_entry, O_RDONLY | O_DIRECTORY));
+	}
+	for_each_path(lower_sub_files, path_entry, i) {
+		ASSERT_EQ(0, test_open(path_entry, O_RDONLY));
+		ASSERT_EQ(EACCES, test_open(path_entry, O_WRONLY));
+	}
+	/* Checks upper layer. */
+	for_each_path(upper_base_files, path_entry, i) {
+		ASSERT_EQ(0, test_open(path_entry, O_RDONLY));
+		ASSERT_EQ(EACCES, test_open(path_entry, O_WRONLY));
+	}
+	for_each_path(upper_base_directories, path_entry, i) {
+		ASSERT_EQ(EACCES, test_open(path_entry, O_RDONLY | O_DIRECTORY));
+	}
+	for_each_path(upper_sub_files, path_entry, i) {
+		ASSERT_EQ(0, test_open(path_entry, O_RDONLY));
+		ASSERT_EQ(EACCES, test_open(path_entry, O_WRONLY));
+	}
+	/*
+	 * Checks that access rights are independent from the lower and upper
+	 * layers: write access to upper files viewed through the merge point
+	 * is still allowed, and write access to lower file viewed (and copied)
+	 * through the merge point is still allowed.
+	 */
+	for_each_path(merge_base_files, path_entry, i) {
+		ASSERT_EQ(0, test_open(path_entry, O_RDWR));
+	}
+	for_each_path(merge_base_directories, path_entry, i) {
+		ASSERT_EQ(0, test_open(path_entry, O_RDONLY | O_DIRECTORY));
+	}
+	for_each_path(merge_sub_files, path_entry, i) {
+		ASSERT_EQ(0, test_open(path_entry, O_RDWR));
+	}
+
+	/* Sets rules on data directories (i.e. inside overlay scope). */
+	ruleset_fd = create_ruleset(_metadata, ACCESS_RW, layer2_data);
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/* Checks merge. */
+	for_each_path(merge_base_files, path_entry, i) {
+		ASSERT_EQ(0, test_open(path_entry, O_RDWR));
+	}
+	for_each_path(merge_base_directories, path_entry, i) {
+		ASSERT_EQ(0, test_open(path_entry, O_RDONLY | O_DIRECTORY));
+	}
+	for_each_path(merge_sub_files, path_entry, i) {
+		ASSERT_EQ(0, test_open(path_entry, O_RDWR));
+	}
+
+	/* Same checks with tighter rules. */
+	ruleset_fd = create_ruleset(_metadata, ACCESS_RW, layer3_subdirs);
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/* Checks changes for lower layer. */
+	for_each_path(lower_base_files, path_entry, i) {
+		ASSERT_EQ(EACCES, test_open(path_entry, O_RDONLY));
+	}
+	/* Checks changes for upper layer. */
+	for_each_path(upper_base_files, path_entry, i) {
+		ASSERT_EQ(EACCES, test_open(path_entry, O_RDONLY));
+	}
+	/* Checks all merge accesses. */
+	for_each_path(merge_base_files, path_entry, i) {
+		ASSERT_EQ(EACCES, test_open(path_entry, O_RDWR));
+	}
+	for_each_path(merge_base_directories, path_entry, i) {
+		ASSERT_EQ(0, test_open(path_entry, O_RDONLY | O_DIRECTORY));
+	}
+	for_each_path(merge_sub_files, path_entry, i) {
+		ASSERT_EQ(0, test_open(path_entry, O_RDWR));
+	}
+
+	/* Sets rules directly on overlayed files. */
+	ruleset_fd = create_ruleset(_metadata, ACCESS_RW, layer4_files);
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/* Checks unchanged accesses on lower layer. */
+	for_each_path(lower_sub_files, path_entry, i) {
+		ASSERT_EQ(0, test_open(path_entry, O_RDONLY));
+		ASSERT_EQ(EACCES, test_open(path_entry, O_WRONLY));
+	}
+	/* Checks unchanged accesses on upper layer. */
+	for_each_path(upper_sub_files, path_entry, i) {
+		ASSERT_EQ(0, test_open(path_entry, O_RDONLY));
+		ASSERT_EQ(EACCES, test_open(path_entry, O_WRONLY));
+	}
+	/* Checks all merge accesses. */
+	for_each_path(merge_base_files, path_entry, i) {
+		ASSERT_EQ(EACCES, test_open(path_entry, O_RDWR));
+	}
+	for_each_path(merge_base_directories, path_entry, i) {
+		ASSERT_EQ(EACCES, test_open(path_entry, O_RDONLY | O_DIRECTORY));
+	}
+	for_each_path(merge_sub_files, path_entry, i) {
+		ASSERT_EQ(0, test_open(path_entry, O_RDWR));
+	}
+
+	/* Only allowes access to the merge hierarchy. */
+	ruleset_fd = create_ruleset(_metadata, ACCESS_RW, layer5_merge_only);
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/* Checks new accesses on lower layer. */
+	for_each_path(lower_sub_files, path_entry, i) {
+		ASSERT_EQ(EACCES, test_open(path_entry, O_RDONLY));
+	}
+	/* Checks new accesses on upper layer. */
+	for_each_path(upper_sub_files, path_entry, i) {
+		ASSERT_EQ(EACCES, test_open(path_entry, O_RDONLY));
+	}
+	/* Checks all merge accesses. */
+	for_each_path(merge_base_files, path_entry, i) {
+		ASSERT_EQ(EACCES, test_open(path_entry, O_RDWR));
+	}
+	for_each_path(merge_base_directories, path_entry, i) {
+		ASSERT_EQ(EACCES, test_open(path_entry, O_RDONLY | O_DIRECTORY));
+	}
+	for_each_path(merge_sub_files, path_entry, i) {
+		ASSERT_EQ(0, test_open(path_entry, O_RDWR));
+	}
+}
+
+TEST_HARNESS_MAIN

tools/testing/selftests/landlock/ptrace_test.c

+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Landlock tests - Ptrace
+ *
+ * Copyright © 2017-2020 Mickaël Salaün <mic@digikod.net>
+ * Copyright © 2019-2020 ANSSI
+ */
+
+#define _GNU_SOURCE
+#include <errno.h>
+#include <fcntl.h>
+#include <linux/landlock.h>
+#include <signal.h>
+#include <sys/prctl.h>
+#include <sys/ptrace.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include "common.h"
+
+static void create_domain(struct __test_metadata *const _metadata)
+{
+	int ruleset_fd;
+	struct landlock_ruleset_attr ruleset_attr = {
+		.handled_access_fs = LANDLOCK_ACCESS_FS_MAKE_BLOCK,
+	};
+
+	ruleset_fd = landlock_create_ruleset(&ruleset_attr,
+			sizeof(ruleset_attr), 0);
+	EXPECT_LE(0, ruleset_fd) {
+		TH_LOG("Failed to create a ruleset: %s", strerror(errno));
+	}
+	EXPECT_EQ(0, prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0));
+	EXPECT_EQ(0, landlock_restrict_self(ruleset_fd, 0));
+	EXPECT_EQ(0, close(ruleset_fd));
+}
+
+static int test_ptrace_read(const pid_t pid)
+{
+	static const char path_template[] = "/proc/%d/environ";
+	char procenv_path[sizeof(path_template) + 10];
+	int procenv_path_size, fd;
+
+	procenv_path_size = snprintf(procenv_path, sizeof(procenv_path),
+			path_template, pid);
+	if (procenv_path_size >= sizeof(procenv_path))
+		return E2BIG;
+
+	fd = open(procenv_path, O_RDONLY | O_CLOEXEC);
+	if (fd < 0)
+		return errno;
+	/*
+	 * Mixing error codes from close(2) and open(2) should not lead to any
+	 * (access type) confusion for this test.
+	 */
+	if (close(fd) != 0)
+		return errno;
+	return 0;
+}
+
+FIXTURE(hierarchy) { };
+
+FIXTURE_VARIANT(hierarchy) {
+	const bool domain_both;
+	const bool domain_parent;
+	const bool domain_child;
+};
+
+/*
+ * Test multiple tracing combinations between a parent process P1 and a child
+ * process P2.
+ *
+ * Yama's scoped ptrace is presumed disabled.  If enabled, this optional
+ * restriction is enforced in addition to any Landlock check, which means that
+ * all P2 requests to trace P1 would be denied.
+ */
+
+/*
+ *        No domain
+ *
+ *   P1-.               P1 -> P2 : allow
+ *       \              P2 -> P1 : allow
+ *        'P2
+ */
+FIXTURE_VARIANT_ADD(hierarchy, allow_without_domain) {
+	.domain_both = false,
+	.domain_parent = false,
+	.domain_child = false,
+};
+
+/*
+ *        Child domain
+ *
+ *   P1--.              P1 -> P2 : allow
+ *        \             P2 -> P1 : deny
+ *        .'-----.
+ *        |  P2  |
+ *        '------'
+ */
+FIXTURE_VARIANT_ADD(hierarchy, allow_with_one_domain) {
+	.domain_both = false,
+	.domain_parent = false,
+	.domain_child = true,
+};
+
+/*
+ *        Parent domain
+ * .------.
+ * |  P1  --.           P1 -> P2 : deny
+ * '------'  \          P2 -> P1 : allow
+ *            '
+ *            P2
+ */
+FIXTURE_VARIANT_ADD(hierarchy, deny_with_parent_domain) {
+	.domain_both = false,
+	.domain_parent = true,
+	.domain_child = false,
+};
+
+/*
+ *        Parent + child domain (siblings)
+ * .------.
+ * |  P1  ---.          P1 -> P2 : deny
+ * '------'   \         P2 -> P1 : deny
+ *         .---'--.
+ *         |  P2  |
+ *         '------'
+ */
+FIXTURE_VARIANT_ADD(hierarchy, deny_with_sibling_domain) {
+	.domain_both = false,
+	.domain_parent = true,
+	.domain_child = true,
+};
+
+/*
+ *         Same domain (inherited)
+ * .-------------.
+ * | P1----.     |      P1 -> P2 : allow
+ * |        \    |      P2 -> P1 : allow
+ * |         '   |
+ * |         P2  |
+ * '-------------'
+ */
+FIXTURE_VARIANT_ADD(hierarchy, allow_sibling_domain) {
+	.domain_both = true,
+	.domain_parent = false,
+	.domain_child = false,
+};
+
+/*
+ *         Inherited + child domain
+ * .-----------------.
+ * |  P1----.        |  P1 -> P2 : allow
+ * |         \       |  P2 -> P1 : deny
+ * |        .-'----. |
+ * |        |  P2  | |
+ * |        '------' |
+ * '-----------------'
+ */
+FIXTURE_VARIANT_ADD(hierarchy, allow_with_nested_domain) {
+	.domain_both = true,
+	.domain_parent = false,
+	.domain_child = true,
+};
+
+/*
+ *         Inherited + parent domain
+ * .-----------------.
+ * |.------.         |  P1 -> P2 : deny
+ * ||  P1  ----.     |  P2 -> P1 : allow
+ * |'------'    \    |
+ * |             '   |
+ * |             P2  |
+ * '-----------------'
+ */
+FIXTURE_VARIANT_ADD(hierarchy, deny_with_nested_and_parent_domain) {
+	.domain_both = true,
+	.domain_parent = true,
+	.domain_child = false,
+};
+
+/*
+ *         Inherited + parent and child domain (siblings)
+ * .-----------------.
+ * | .------.        |  P1 -> P2 : deny
+ * | |  P1  .        |  P2 -> P1 : deny
+ * | '------'\       |
+ * |          \      |
+ * |        .--'---. |
+ * |        |  P2  | |
+ * |        '------' |
+ * '-----------------'
+ */
+FIXTURE_VARIANT_ADD(hierarchy, deny_with_forked_domain) {
+	.domain_both = true,
+	.domain_parent = true,
+	.domain_child = true,
+};
+
+FIXTURE_SETUP(hierarchy)
+{ }
+
+FIXTURE_TEARDOWN(hierarchy)
+{ }
+
+/* Test PTRACE_TRACEME and PTRACE_ATTACH for parent and child. */
+TEST_F(hierarchy, trace)
+{
+	pid_t child, parent;
+	int status, err_proc_read;
+	int pipe_child[2], pipe_parent[2];
+	char buf_parent;
+	long ret;
+
+	/*
+	 * Removes all effective and permitted capabilities to not interfere
+	 * with cap_ptrace_access_check() in case of PTRACE_MODE_FSCREDS.
+	 */
+	drop_caps(_metadata);
+
+	parent = getpid();
+	ASSERT_EQ(0, pipe2(pipe_child, O_CLOEXEC));
+	ASSERT_EQ(0, pipe2(pipe_parent, O_CLOEXEC));
+	if (variant->domain_both) {
+		create_domain(_metadata);
+		if (!_metadata->passed)
+			/* Aborts before forking. */
+			return;
+	}
+
+	child = fork();
+	ASSERT_LE(0, child);
+	if (child == 0) {
+		char buf_child;
+
+		ASSERT_EQ(0, close(pipe_parent[1]));
+		ASSERT_EQ(0, close(pipe_child[0]));
+		if (variant->domain_child)
+			create_domain(_metadata);
+
+		/* Waits for the parent to be in a domain, if any. */
+		ASSERT_EQ(1, read(pipe_parent[0], &buf_child, 1));
+
+		/* Tests PTRACE_ATTACH and PTRACE_MODE_READ on the parent. */
+		err_proc_read = test_ptrace_read(parent);
+		ret = ptrace(PTRACE_ATTACH, parent, NULL, 0);
+		if (variant->domain_child) {
+			EXPECT_EQ(-1, ret);
+			EXPECT_EQ(EPERM, errno);
+			EXPECT_EQ(EACCES, err_proc_read);
+		} else {
+			EXPECT_EQ(0, ret);
+			EXPECT_EQ(0, err_proc_read);
+		}
+		if (ret == 0) {
+			ASSERT_EQ(parent, waitpid(parent, &status, 0));
+			ASSERT_EQ(1, WIFSTOPPED(status));
+			ASSERT_EQ(0, ptrace(PTRACE_DETACH, parent, NULL, 0));
+		}
+
+		/* Tests child PTRACE_TRACEME. */
+		ret = ptrace(PTRACE_TRACEME);
+		if (variant->domain_parent) {
+			EXPECT_EQ(-1, ret);
+			EXPECT_EQ(EPERM, errno);
+		} else {
+			EXPECT_EQ(0, ret);
+		}
+
+		/*
+		 * Signals that the PTRACE_ATTACH test is done and the
+		 * PTRACE_TRACEME test is ongoing.
+		 */
+		ASSERT_EQ(1, write(pipe_child[1], ".", 1));
+
+		if (!variant->domain_parent) {
+			ASSERT_EQ(0, raise(SIGSTOP));
+		}
+
+		/* Waits for the parent PTRACE_ATTACH test. */
+		ASSERT_EQ(1, read(pipe_parent[0], &buf_child, 1));
+		_exit(_metadata->passed ? EXIT_SUCCESS : EXIT_FAILURE);
+		return;
+	}
+
+	ASSERT_EQ(0, close(pipe_child[1]));
+	ASSERT_EQ(0, close(pipe_parent[0]));
+	if (variant->domain_parent)
+		create_domain(_metadata);
+
+	/* Signals that the parent is in a domain, if any. */
+	ASSERT_EQ(1, write(pipe_parent[1], ".", 1));
+
+	/*
+	 * Waits for the child to test PTRACE_ATTACH on the parent and start
+	 * testing PTRACE_TRACEME.
+	 */
+	ASSERT_EQ(1, read(pipe_child[0], &buf_parent, 1));
+
+	/* Tests child PTRACE_TRACEME. */
+	if (!variant->domain_parent) {
+		ASSERT_EQ(child, waitpid(child, &status, 0));
+		ASSERT_EQ(1, WIFSTOPPED(status));
+		ASSERT_EQ(0, ptrace(PTRACE_DETACH, child, NULL, 0));
+	} else {
+		/* The child should not be traced by the parent. */
+		EXPECT_EQ(-1, ptrace(PTRACE_DETACH, child, NULL, 0));
+		EXPECT_EQ(ESRCH, errno);
+	}
+
+	/* Tests PTRACE_ATTACH and PTRACE_MODE_READ on the child. */
+	err_proc_read = test_ptrace_read(child);
+	ret = ptrace(PTRACE_ATTACH, child, NULL, 0);
+	if (variant->domain_parent) {
+		EXPECT_EQ(-1, ret);
+		EXPECT_EQ(EPERM, errno);
+		EXPECT_EQ(EACCES, err_proc_read);
+	} else {
+		EXPECT_EQ(0, ret);
+		EXPECT_EQ(0, err_proc_read);
+	}
+	if (ret == 0) {
+		ASSERT_EQ(child, waitpid(child, &status, 0));
+		ASSERT_EQ(1, WIFSTOPPED(status));
+		ASSERT_EQ(0, ptrace(PTRACE_DETACH, child, NULL, 0));
+	}
+
+	/* Signals that the parent PTRACE_ATTACH test is done. */
+	ASSERT_EQ(1, write(pipe_parent[1], ".", 1));
+	ASSERT_EQ(child, waitpid(child, &status, 0));
+	if (WIFSIGNALED(status) || !WIFEXITED(status) ||
+			WEXITSTATUS(status) != EXIT_SUCCESS)
+		_metadata->passed = 0;
+}
+
+TEST_HARNESS_MAIN

tools/testing/selftests/landlock/true.c

+// SPDX-License-Identifier: GPL-2.0
+int main(void)
+{
+	return 0;
+}