- 10 Jun, 2020 1 commit
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Alexey Gladkov authored
syzbot found that proc_fill_super() fails before filling up sb->s_fs_info, deactivate_locked_super() will be called and sb->s_fs_info will be NULL. The proc_kill_sb() does not expect fs_info to be NULL which is wrong. Link: https://lore.kernel.org/lkml/0000000000002d7ca605a7b8b1c5@google.com Reported-by: syzbot+4abac52934a48af5ff19@syzkaller.appspotmail.com Fixes: fa10fed3 ("proc: allow to mount many instances of proc in one pid namespace") Signed-off-by:
Alexey Gladkov <gladkov.alexey@gmail.com> Signed-off-by:
Eric W. Biederman <ebiederm@xmission.com>
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- 19 May, 2020 1 commit
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Alexey Gladkov authored
syzbot found that touch /proc/testfile causes NULL pointer dereference at tomoyo_get_local_path() because inode of the dentry is NULL. Before c59f415a, Tomoyo received pid_ns from proc's s_fs_info directly. Since proc_pid_ns() can only work with inode, using it in the tomoyo_get_local_path() was wrong. To avoid creating more functions for getting proc_ns, change the argument type of the proc_pid_ns() function. Then, Tomoyo can use the existing super_block to get pid_ns. Link: https://lkml.kernel.org/r/0000000000002f0c7505a5b0e04c@google.com Link: https://lkml.kernel.org/r/20200518180738.2939611-1-gladkov.alexey@gmail.com Reported-by: syzbot+c1af344512918c61362c@syzkaller.appspotmail.com Fixes: c59f415a ("Use proc_pid_ns() to get pid_namespace from the proc superblock") Signed-off-by:
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- 30 Apr, 2020 3 commits
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Eric W. Biederman authored
The current posix-cpu-timer code uses pids when holding persistent references in timers. However the lookups from clock_id_t still return tasks that need to be converted into pids for use. This results in usage being pid->task->pid and that can race with release_task and de_thread. This can lead to some not wrong but surprising results. Surprising enough that Oleg and I both thought there were some bugs in the code for a while. This set of changes modifies the code to just lookup, verify, and return pids from the clockid_t lookups to remove those potentialy troublesome races. Eric W. Biederman (3): posix-cpu-timers: Extend rcu_read_lock removing task_struct references posix-cpu-timers: Replace cpu_timer_pid_type with clock_pid_type posix-cpu-timers: Replace __get_task_for_clock with pid_for_clock kernel/time/posix-cpu-timers.c | 102 ++++++++++++++++++----------------------- 1 file changed, 45 insertions(+), 57 deletions(-) Suggested-by:Oleg Nesterov <oleg@redhat.com> Signed-off-by:
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Oleg Nesterov authored
Starting from 2c470475 ("pids: Move the pgrp and session pid pointers from task_struct to signal_struct") __task_pid_nr_ns() doesn't dereference task->group_leader, we can remove the pid_alive() check. pid_nr_ns() has to check pid != NULL anyway, pid_alive() just adds the unnecessary confusion. Signed-off-by:
Christian Brauner <christian.brauner@ubuntu.com> Signed-off-by:
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Eric W. Biederman authored
With de_thread now calling exchange_tids has_group_leader_pid no longer makes any sense and is equivalent to calling thread_group_leader. As there are only 2 remaining users of has_group_leader_pid let's update the code and get rid of has_group_leader_pid. There is one extra patch to lookup_task that performs that unifies to code paths that become identical when has_group_leader_pid went away. Eric W. Biederman (4): posix-cpu-timer: Tidy up group_leader logic in lookup_task posix-cpu-timer: Unify the now redundant code in lookup_task exec: Remove BUG_ON(has_group_leader_pid) signal: Remove has_group_leader_pid fs/exec.c | 1 - include/linux/sched/signal.h | 11 ----------- kernel/time/posix-cpu-timers.c | 21 ++++++++------------- 3 files changed, 8 insertions(+), 25 deletions(-) Signed-off-by:
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- 29 Apr, 2020 3 commits
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Eric W. Biederman authored
Now that the codes store references to pids instead of referendes to tasks. Looking up a task for a clock instead of looking up a struct pid makes the code more difficult to verify it is correct than necessary. In posix_cpu_timers_create get_task_pid can race with release_task for threads and return a NULL pid. As put_pid and cpu_timer_task_rcu handle NULL pids just fine the code works without problems but it is an extra case to consider and keep in mind while verifying and modifying the code. There are races with de_thread to consider that only don't apply because thread clocks are only allowed for threads in the same thread_group. So instead of leaving a burden for people making modification to the code in the future return a rcu protected struct pid for the clock instead. The logic for __get_task_for_pid and lookup_task has been folded into the new function pid_for_clock with the only change being the logic has been modified from working on a task to working on a pid that will be returned. In posix_cpu_clock_get instead of calling pid_for_clock checking the result and then calling pid_task to get the task. The result of pid_for_clock is fed directly into pid_task. This is safe because pid_task handles NULL pids. As such an extra error check was unnecessary. Instead of hiding the flag that enables the special clock_gettime handling, I have made the 3 callers just pass the flag in themselves. That is less code and seems just as simple to work with as the wrapper functions. Historically the clock_gettime special case of allowing a process clock to be found by the thread id did not even exist [33ab0fec] but Thomas Gleixner reports that he has found code that uses that functionality [55e8c8eb]. Link: https://lkml.kernel.org/r/87zhaxqkwa.fsf@nanos.tec.linutronix.de/ Ref: 33ab0fec ("posix-timers: Consolidate posix_cpu_clock_get()") Ref: 55e8c8eb ("posix-cpu-timers: Store a reference to a pid not a task") Signed-off-by:
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Eric W. Biederman authored
Taking a clock and returning a pid_type is a more general and a superset of taking a timer and returning a pid_type. Perform this generalization so that future changes may use this code on clocks as well as timers. Signed-off-by: -
Eric W. Biederman authored
Now that the code stores of pid references it is no longer necessary or desirable to take a reference on task_struct in __get_task_for_clock. Instead extend the scope of rcu_read_lock and remove the reference counting on struct task_struct entirely. Signed-off-by:
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- 28 Apr, 2020 7 commits
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Eric W. Biederman authored
After the introduction of exchange_tids has_group_leader_pid is equivalent to thread_group_leader. After the last couple of cleanups has_group_leader_pid has no more callers. So remove the now unused and redundant has_group_leader_pid. Signed-off-by: -
Eric W. Biederman authored
With the introduction of exchange_tids thread_group_leader and has_group_leader_pid have become equivalent. Further at this point in the code a thread group has exactly two threads, the previous thread_group_leader that is waiting to be reaped and tsk. So we know it is impossible for tsk to be the thread_group_leader. This is also the last user of has_group_leader_pid so removing this check will allow has_group_leader_pid to be removed. So remove the "BUG_ON(has_group_leader_pid)" that will never fire. Signed-off-by: -
Eric W. Biederman authored
Now that both !thread paths through lookup_task call thread_group_leader, unify them into the single test at the end of lookup_task. This unification just makes it clear what is happening in the gettime special case of lookup_task. Signed-off-by: -
Eric W. Biederman authored
Replace has_group_leader_pid with thread_group_leader. Years ago Oleg suggested changing thread_group_leader to has_group_leader_pid to handle races. Looking at the code then and now I don't see how it ever helped. Especially as then the code really did need to be the thread_group_leader. Today it doesn't make a difference if thread_group_leader races with de_thread as the task returned from lookup_task in the non-thread case is just used to find values in task->signal. Since the races with de_thread have never been handled revert has_group_header_pid to thread_group_leader for clarity. Update the comment in lookup_task to remove implementation details that are no longer true and to mention task->signal instead of task->sighand, as the relevant cpu timer details are all in task->signal. Ref: 55e8c8eb ("posix-cpu-timers: Store a reference to a pid not a task") Ref: c0deae8c ("posix-cpu-timers: Rcu_read_lock/unlock protect find_task_by_vpid call") Signed-off-by:
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Eric W. Biederman authored
In the work to remove proc_mnt I noticed that we were calling proc_flush_task now proc_flush_pid possibly multiple times for the same pid because of how de_thread works. This is a bare minimal patchset to sort out de_thread, by introducing exchange_tids and the helper of exchange_tids hlists_swap_heads_rcu. The actual call of exchange_tids should be slowpath so I have prioritized readability over getting every last drop of performance. I have also read through a bunch of the code to see if I could find anything that would be affected by this change. Users of has_group_leader_pid were a good canidates. But I also looked at other cases that might have a pid->task->pid transition. I ignored other sources of races with de_thread and exec as those are preexisting. I found a close call with send_signals user of task_active_pid_ns, but all pids of a thread group are guaranteeds to be in the same pid namespace so there is not a problem. I found a few pieces of debugging code that do: task = pid_task(pid, PIDTYPE_PID); if (task) { printk("%u\n", task->pid); } But I can't see how we care if it happens at the wrong moment that task->pid might not match pid_nr(pid); Similarly because the code in posix-cpu-timers goes pid->task->pid it feels like there should be a problem. But as the code that works with PIDTYPE_PID is only available within the thread group, and as de_thread kills all of the other threads before it makes any changes of this kind the race can not happen. In short I don't think this change will introduce any regressions. Eric W. Biederman (2): rculist: Add hlists_swap_heads_rcu proc: Ensure we see the exit of each process tid exactly once fs/exec.c | 5 +---- include/linux/pid.h | 1 + include/linux/rculist.h | 21 +++++++++++++++++++++ kernel/pid.c | 19 +++++++++++++++++++ 4 files changed, 42 insertions(+), 4 deletions(-) Link: https://lore.kernel.org/lkml/87sggnajpv.fsf_-_@x220.int.ebiederm.org/Acked-by:Linus Torvalds <torvalds@linux-foundation.org> Acked-by:
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Eric W. Biederman authored
When the thread group leader changes during exec and the old leaders thread is reaped proc_flush_pid will flush the dentries for the entire process because the leader still has it's original pid. Fix this by exchanging the pids in an rcu safe manner, and wrapping the code to do that up in a helper exchange_tids. When I removed switch_exec_pids and introduced this behavior in d73d6529 ("[PATCH] pidhash: kill switch_exec_pids") there really was nothing that cared as flushing happened with the cached dentry and de_thread flushed both of them on exec. This lack of fully exchanging pids became a problem a few months later when I introduced 48e6484d ("[PATCH] proc: Rewrite the proc dentry flush on exit optimization"). Which overlooked the de_thread case was no longer swapping pids, and I was looking up proc dentries by task->pid. The current behavior isn't properly a bug as everything in proc will continue to work correctly just a little bit less efficiently. Fix this just so there are no little surprise corner cases waiting to bite people. -- Oleg points out this could be an issue in next_tgid in proc where has_group_leader_pid is called, and reording some of the assignments should fix that. -- Oleg points out this will break the 10 year old hack in __exit_signal.c > /* > * This can only happen if the caller is de_thread(). > * FIXME: this is the temporary hack, we should teach > * posix-cpu-timers to handle this case correctly. > */ > if (unlikely(has_group_leader_pid(tsk))) > posix_cpu_timers_exit_group(tsk); The code in next_tgid has been changed to use PIDTYPE_TGID, and the posix cpu timers code has been fixed so it does not need the 10 year old hack, so this should be safe to merge now. Link: https://lore.kernel.org/lkml/87h7x3ajll.fsf_-_@x220.int.ebiederm.org/Acked-by:
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Eric W. Biederman authored
Using the struct pid to refer to two tasks in de_thread was a clever idea and ultimately too clever, as it has lead to proc_flush_task being called inconsistently. To support rectifying this add hlists_swap_heads_rcu. An hlist primitive that just swaps the hlist heads of two lists. This is exactly what is needed for exchanging the pids of two tasks. Only consideration of correctness of the code has been given, as the caller is expected to be a slowpath. Link: https://lore.kernel.org/lkml/87mu6vajnq.fsf_-_@x220.int.ebiederm.org/Acked-by:
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- 24 Apr, 2020 4 commits
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Eric W. Biederman authored
Combine the pid_task and thes test has_group_leader_pid into a single dereference by using pid_task(PIDTYPE_TGID). This makes the code simpler and proof against needing to even think about any shenanigans that de_thread might get up to. Acked-by:
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Eric W. Biederman authored
Alexey Gladkov <gladkov.alexey@gmail.com> writes: Procfs modernization: --------------------- Historically procfs was always tied to pid namespaces, during pid namespace creation we internally create a procfs mount for it. However, this has the effect that all new procfs mounts are just a mirror of the internal one, any change, any mount option update, any new future introduction will propagate to all other procfs mounts that are in the same pid namespace. This may have solved several use cases in that time. However today we face new requirements, and making procfs able to support new private instances inside same pid namespace seems a major point. If we want to to introduce new features and security mechanisms we have to make sure first that we do not break existing usecases. Supporting private procfs instances will allow to support new features and behaviour without propagating it to all other procfs mounts. Today procfs is more of a burden especially to some Embedded, IoT, sandbox, container use cases. In user space we are over-mounting null or inaccessible files on top to hide files and information. If we want to hide pids we have to create PID namespaces otherwise mount options propagate to all other proc mounts, changing a mount option value in one mount will propagate to all other proc mounts. If we want to introduce new features, then they will propagate to all other mounts too, resulting either maybe new useful functionality or maybe breaking stuff. We have also to note that userspace should not workaround procfs, the kernel should just provide a sane simple interface. In this regard several developers and maintainers pointed out that there are problems with procfs and it has to be modernized: "Here's another one: split up and modernize /proc." by Andy Lutomirski [1] Discussion about kernel pointer leaks: "And yes, as Kees and Daniel mentioned, it's definitely not just dmesg. In fact, the primary things tend to be /proc and /sys, not dmesg itself." By Linus Torvalds [2] Lot of other areas in the kernel and filesystems have been updated to be able to support private instances, devpts is one major example [3]. Which will be used for: 1) Embedded systems and IoT: usually we have one supervisor for apps, we have some lightweight sandbox support, however if we create pid namespaces we have to manage all the processes inside too, where our goal is to be able to run a bunch of apps each one inside its own mount namespace, maybe use network namespaces for vlans setups, but right now we only want mount namespaces, without all the other complexity. We want procfs to behave more like a real file system, and block access to inodes that belong to other users. The 'hidepid=' will not work since it is a shared mount option. 2) Containers, sandboxes and Private instances of file systems - devpts case Historically, lot of file systems inside Linux kernel view when instantiated were just a mirror of an already created and mounted filesystem. This was the case of devpts filesystem, it seems at that time the requirements were to optimize things and reuse the same memory, etc. This design used to work but not anymore with today's containers, IoT, hostile environments and all the privacy challenges that Linux faces. In that regards, devpts was updated so that each new mounts is a total independent file system by the following patches: "devpts: Make each mount of devpts an independent filesystem" by Eric W. Biederman [3] [4] 3) Linux Security Modules have multiple ptrace paths inside some subsystems, however inside procfs, the implementation does not guarantee that the ptrace() check which triggers the security_ptrace_check() hook will always run. We have the 'hidepid' mount option that can be used to force the ptrace_may_access() check inside has_pid_permissions() to run. The problem is that 'hidepid' is per pid namespace and not attached to the mount point, any remount or modification of 'hidepid' will propagate to all other procfs mounts. This also does not allow to support Yama LSM easily in desktop and user sessions. Yama ptrace scope which restricts ptrace and some other syscalls to be allowed only on inferiors, can be updated to have a per-task context, where the context will be inherited during fork(), clone() and preserved across execve(). If we support multiple private procfs instances, then we may force the ptrace_may_access() on /proc/<pids>/ to always run inside that new procfs instances. This will allow to specifiy on user sessions if we should populate procfs with pids that the user can ptrace or not. By using Yama ptrace scope, some restricted users will only be able to see inferiors inside /proc, they won't even be able to see their other processes. Some software like Chromium, Firefox's crash handler, Wine and others are already using Yama to restrict which processes can be ptracable. With this change this will give the possibility to restrict /proc/<pids>/ but more importantly this will give desktop users a generic and usuable way to specifiy which users should see all processes and which user can not. Side notes: * This covers the lack of seccomp where it is not able to parse arguments, it is easy to install a seccomp filter on direct syscalls that operate on pids, however /proc/<pid>/ is a Linux ABI using filesystem syscalls. With this change all LSMs should be able to analyze open/read/write/close... on /proc/<pid>/ 4) This will allow to implement new features either in kernel or userspace without having to worry about procfs. In containers, sandboxes, etc we have workarounds to hide some /proc inodes, this should be supported natively without doing extra complex work, the kernel should be able to support sane options that work with today and future Linux use cases. 5) Creation of new superblock with all procfs options for each procfs mount will fix the ignoring of mount options. The problem is that the second mount of procfs in the same pid namespace ignores the mount options. The mount options are ignored without error until procfs is remounted. Before: proc /proc proc rw,relatime,hidepid=2 0 0 mount("proc", "/tmp/proc", "proc", 0, "hidepid=1") = 0 +++ exited with 0 +++ proc /proc proc rw,relatime,hidepid=2 0 0 proc /tmp/proc proc rw,relatime,hidepid=2 0 0 proc /proc proc rw,relatime,hidepid=1 0 0 proc /tmp/proc proc rw,relatime,hidepid=1 0 0 After: proc /proc proc rw,relatime,hidepid=ptraceable 0 0 proc /proc proc rw,relatime,hidepid=ptraceable 0 0 proc /tmp/proc proc rw,relatime,hidepid=invisible 0 0 Introduced changes: ------------------- Each mount of procfs creates a separate procfs instance with its own mount options. This series adds few new mount options: * New 'hidepid=ptraceable' or 'hidepid=4' mount option to show only ptraceable processes in the procfs. This allows to support lightweight sandboxes in Embedded Linux, also solves the case for LSM where now with this mount option, we make sure that they have a ptrace path in procfs. * 'subset=pid' that allows to hide non-pid inodes from procfs. It can be used in containers and sandboxes, as these are already trying to hide and block access to procfs inodes anyway. ChangeLog: ---------- * Rebase on top of v5.7-rc1. * Fix a resource leak if proc is not mounted or if proc is simply reconfigured. * Add few selftests. * After a discussion with Eric W. Biederman, the numerical values for hidepid parameter have been removed from uapi. * Remove proc_self and proc_thread_self from the pid_namespace struct. * I took into account the comment of Kees Cook. * Update Reviewed-by tags. * 'subset=pidfs' renamed to 'subset=pid' as suggested by Alexey Dobriyan. * Include Reviewed-by tags. * Rebase on top of Eric W. Biederman's procfs changes. * Add human readable values of 'hidepid' as suggested by Andy Lutomirski. * Started using RCU lock to clean dcache entries as suggested by Linus Torvalds. * 'pidonly=1' renamed to 'subset=pidfs' as suggested by Alexey Dobriyan. * HIDEPID_* moved to uapi/ as they are user interface to mount(). Suggested-by Alexey Dobriyan <adobriyan@gmail.com> * 'hidepid=' and 'gid=' mount options are moved from pid namespace to superblock. * 'newinstance' mount option removed as suggested by Eric W. Biederman. Mount of procfs always creates a new instance. * 'limit_pids' renamed to 'hidepid=3'. * I took into account the comment of Linus Torvalds [7]. * Documentation added. * Fixed a bug that caused a problem with the Fedora boot. * The 'pidonly' option is visible among the mount options. * Renamed mount options to 'newinstance' and 'pids=' Suggested-by:Andy Lutomirski <luto@kernel.org> * Fixed order of commit, Suggested-by: Andy Lutomirski <luto@kernel.org> * Many bug fixes. * Removed 'unshared' mount option and replaced it with 'limit_pids' which is attached to the current procfs mount. Suggested-by Andy Lutomirski <luto@kernel.org> * Do not fill dcache with pid entries that we can not ptrace. * Many bug fixes. References: ----------- [1] https://lists.linuxfoundation.org/pipermail/ksummit-discuss/2017-January/004215.html [2] http://www.openwall.com/lists/kernel-hardening/2017/10/05/5 [3] https://lwn.net/Articles/689539/ [4] http://lxr.free-electrons.com/source/Documentation/filesystems/devpts.txt?v=3.14 [5] https://lkml.org/lkml/2017/5/2/407 [6] https://lkml.org/lkml/2017/5/3/357 [7] https://lkml.org/lkml/2018/5/11/505 Alexey Gladkov (7): proc: rename struct proc_fs_info to proc_fs_opts proc: allow to mount many instances of proc in one pid namespace proc: instantiate only pids that we can ptrace on 'hidepid=4' mount option proc: add option to mount only a pids subset docs: proc: add documentation for "hidepid=4" and "subset=pid" options and new mount behavior proc: use human-readable values for hidepid proc: use named enums for better readability Documentation/filesystems/proc.rst | 92 +++++++++--- fs/proc/base.c | 48 +++++-- fs/proc/generic.c | 9 ++ fs/proc/inode.c | 30 +++- fs/proc/root.c | 131 +++++++++++++----- fs/proc/self.c | 6 +- fs/proc/thread_self.c | 6 +- fs/proc_namespace.c | 14 +- include/linux/pid_namespace.h | 12 -- include/linux/proc_fs.h | 30 +++- tools/testing/selftests/proc/.gitignore | 2 + tools/testing/selftests/proc/Makefile | 2 + .../selftests/proc/proc-fsconfig-hidepid.c | 50 +++++++ .../selftests/proc/proc-multiple-procfs.c | 48 +++++++ 14 files changed, 384 insertions(+), 96 deletions(-) create mode 100644 tools/testing/selftests/proc/proc-fsconfig-hidepid.c create mode 100644 tools/testing/selftests/proc/proc-multiple-procfs.c Link: https://lore.kernel.org/lkml/20200419141057.621356-1-gladkov.alexey@gmail.com/Signed-off-by:
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Alexey Gladkov authored
To get pid_namespace from the procfs superblock should be used a special helper. This will avoid errors when s_fs_info will change the type. Link: https://lore.kernel.org/lkml/20200423200316.164518-3-gladkov.alexey@gmail.com/ Link: https://lore.kernel.org/lkml/20200423112858.95820-1-gladkov.alexey@gmail.com/ Link: https://lore.kernel.org/lkml/06B50A1C-406F-4057-BFA8-3A7729EA7469@lca.pw/Signed-off-by:
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Eric W. Biederman authored
Oleg pointed out that in the unlikely event the kernel is compiled with CONFIG_PROC_FS unset that release_task will now leak the pid. Move the put_pid out of proc_flush_pid into release_task to fix this and to guarantee I don't make that mistake again. When possible it makes sense to keep get and put in the same function so it can easily been seen how they pair up. Fixes: 7bc3e6e5 ("proc: Use a list of inodes to flush from proc") Reported-by:
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- 22 Apr, 2020 7 commits
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Alexey Gladkov authored
Signed-off-by:
Alexey Dobriyan <adobriyan@gmail.com> Reviewed-by:
Kees Cook <keescook@chromium.org> Signed-off-by:
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Alexey Gladkov authored
The hidepid parameter values are becoming more and more and it becomes difficult to remember what each new magic number means. Backward compatibility is preserved since it is possible to specify numerical value for the hidepid parameter. This does not break the fsconfig since it is not possible to specify a numerical value through it. All numeric values are converted to a string. The type FSCONFIG_SET_BINARY cannot be used to indicate a numerical value. Selftest has been added to verify this behavior. Suggested-by:
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Alexey Gladkov authored
Signed-off-by:
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Alexey Gladkov authored
This allows to hide all files and directories in the procfs that are not related to tasks. Signed-off-by:
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Alexey Gladkov authored
If "hidepid=4" mount option is set then do not instantiate pids that we can not ptrace. "hidepid=4" means that procfs should only contain pids that the caller can ptrace. Signed-off-by:
Djalal Harouni <tixxdz@gmail.com> Signed-off-by:
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Alexey Gladkov authored
This patch allows to have multiple procfs instances inside the same pid namespace. The aim here is lightweight sandboxes, and to allow that we have to modernize procfs internals. 1) The main aim of this work is to have on embedded systems one supervisor for apps. Right now we have some lightweight sandbox support, however if we create pid namespacess we have to manages all the processes inside too, where our goal is to be able to run a bunch of apps each one inside its own mount namespace without being able to notice each other. We only want to use mount namespaces, and we want procfs to behave more like a real mount point. 2) Linux Security Modules have multiple ptrace paths inside some subsystems, however inside procfs, the implementation does not guarantee that the ptrace() check which triggers the security_ptrace_check() hook will always run. We have the 'hidepid' mount option that can be used to force the ptrace_may_access() check inside has_pid_permissions() to run. The problem is that 'hidepid' is per pid namespace and not attached to the mount point, any remount or modification of 'hidepid' will propagate to all other procfs mounts. This also does not allow to support Yama LSM easily in desktop and user sessions. Yama ptrace scope which restricts ptrace and some other syscalls to be allowed only on inferiors, can be updated to have a per-task context, where the context will be inherited during fork(), clone() and preserved across execve(). If we support multiple private procfs instances, then we may force the ptrace_may_access() on /proc/<pids>/ to always run inside that new procfs instances. This will allow to specifiy on user sessions if we should populate procfs with pids that the user can ptrace or not. By using Yama ptrace scope, some restricted users will only be able to see inferiors inside /proc, they won't even be able to see their other processes. Some software like Chromium, Firefox's crash handler, Wine and others are already using Yama to restrict which processes can be ptracable. With this change this will give the possibility to restrict /proc/<pids>/ but more importantly this will give desktop users a generic and usuable way to specifiy which users should see all processes and which users can not. Side notes: * This covers the lack of seccomp where it is not able to parse arguments, it is easy to install a seccomp filter on direct syscalls that operate on pids, however /proc/<pid>/ is a Linux ABI using filesystem syscalls. With this change LSMs should be able to analyze open/read/write/close... In the new patch set version I removed the 'newinstance' option as suggested by Eric W. Biederman. Selftest has been added to verify new behavior. Signed-off-by:
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Alexey Gladkov authored
Signed-off-by:
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- 21 Apr, 2020 1 commit
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Eric W. Biederman authored
Christof Meerwald <cmeerw@cmeerw.org> writes: > Hi, > > this is probably related to commit > 7a0cf094 (signal: Correct namespace > fixups of si_pid and si_uid). > > With a 5.6.5 kernel I am seeing SIGCHLD signals that don't include a > properly set si_pid field - this seems to happen for multi-threaded > child processes. > > A simple test program (based on the sample from the signalfd man page): > > #include <sys/signalfd.h> > #include <signal.h> > #include <unistd.h> > #include <spawn.h> > #include <stdlib.h> > #include <stdio.h> > > #define handle_error(msg) \ > do { perror(msg); exit(EXIT_FAILURE); } while (0) > > int main(int argc, char *argv[]) > { > sigset_t mask; > int sfd; > struct signalfd_siginfo fdsi; > ssize_t s; > > sigemptyset(&mask); > sigaddset(&mask, SIGCHLD); > > if (sigprocmask(SIG_BLOCK, &mask, NULL) == -1) > handle_error("sigprocmask"); > > pid_t chldpid; > char *chldargv[] = { "./sfdclient", NULL }; > posix_spawn(&chldpid, "./sfdclient", NULL, NULL, chldargv, NULL); > > sfd = signalfd(-1, &mask, 0); > if (sfd == -1) > handle_error("signalfd"); > > for (;;) { > s = read(sfd, &fdsi, sizeof(struct signalfd_siginfo)); > if (s != sizeof(struct signalfd_siginfo)) > handle_error("read"); > > if (fdsi.ssi_signo == SIGCHLD) { > printf("Got SIGCHLD %d %d %d %d\n", > fdsi.ssi_status, fdsi.ssi_code, > fdsi.ssi_uid, fdsi.ssi_pid); > return 0; > } else { > printf("Read unexpected signal\n"); > } > } > } > > > and a multi-threaded client to test with: > > #include <unistd.h> > #include <pthread.h> > > void *f(void *arg) > { > sleep(100); > } > > int main() > { > pthread_t t[8]; > > for (int i = 0; i != 8; ++i) > { > pthread_create(&t[i], NULL, f, NULL); > } > } > > I tried to do a bit of debugging and what seems to be happening is > that > > /* From an ancestor pid namespace? */ > if (!task_pid_nr_ns(current, task_active_pid_ns(t))) { > > fails inside task_pid_nr_ns because the check for "pid_alive" fails. > > This code seems to be called from do_notify_parent and there we > actually have "tsk != current" (I am assuming both are threads of the > current process?) I instrumented the code with a warning and received the following backtrace: > WARNING: CPU: 0 PID: 777 at kernel/pid.c:501 __task_pid_nr_ns.cold.6+0xc/0x15 > Modules linked in: > CPU: 0 PID: 777 Comm: sfdclient Not tainted 5.7.0-rc1userns+ #2924 > Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 > RIP: 0010:__task_pid_nr_ns.cold.6+0xc/0x15 > Code: ff 66 90 48 83 ec 08 89 7c 24 04 48 8d 7e 08 48 8d 74 24 04 e8 9a b6 44 00 48 83 c4 08 c3 48 c7 c7 59 9f ac 82 e8 c2 c4 04 00 <0f> 0b e9 3fd > RSP: 0018:ffffc9000042fbf8 EFLAGS: 00010046 > RAX: 000000000000000c RBX: 0000000000000000 RCX: ffffc9000042faf4 > RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffff81193d29 > RBP: ffffc9000042fc18 R08: 0000000000000000 R09: 0000000000000001 > R10: 000000100f938416 R11: 0000000000000309 R12: ffff8880b941c140 > R13: 0000000000000000 R14: 0000000000000000 R15: ffff8880b941c140 > FS: 0000000000000000(0000) GS:ffff8880bca00000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00007f2e8c0a32e0 CR3: 0000000002e10000 CR4: 00000000000006f0 > Call Trace: > send_signal+0x1c8/0x310 > do_notify_parent+0x50f/0x550 > release_task.part.21+0x4fd/0x620 > do_exit+0x6f6/0xaf0 > do_group_exit+0x42/0xb0 > get_signal+0x13b/0xbb0 > do_signal+0x2b/0x670 > ? __audit_syscall_exit+0x24d/0x2b0 > ? rcu_read_lock_sched_held+0x4d/0x60 > ? kfree+0x24c/0x2b0 > do_syscall_64+0x176/0x640 > ? trace_hardirqs_off_thunk+0x1a/0x1c > entry_SYSCALL_64_after_hwframe+0x49/0xb3 The immediate problem is as Christof noticed that "pid_alive(current) == false". This happens because do_notify_parent is called from the last thread to exit in a process after that thread has been reaped. The bigger issue is that do_notify_parent can be called from any process that manages to wait on a thread of a multi-threaded process from wait_task_zombie. So any logic based upon current for do_notify_parent is just nonsense, as current can be pretty much anything. So change do_notify_parent to call __send_signal directly. Inspecting the code it appears this problem has existed since the pid namespace support started handling this case in 2.6.30. This fix only backports to 7a0cf094 ("signal: Correct namespace fixups of si_pid and si_uid") where the problem logic was moved out of __send_signal and into send_signal. Cc: stable@vger.kernel.org Fixes: 6588c1e3 ("signals: SI_USER: Masquerade si_pid when crossing pid ns boundary") Ref: 921cf9f6 ("signals: protect cinit from unblocked SIG_DFL signals") Link: https://lore.kernel.org/lkml/20200419201336.GI22017@edge.cmeerw.net/Reported-by:
Christof Meerwald <cmeerw@cmeerw.org> Acked-by:
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- 16 Apr, 2020 1 commit
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Eric W. Biederman authored
syzbot writes: > KASAN: use-after-free Read in dput (2) > > proc_fill_super: allocate dentry failed > ================================================================== > BUG: KASAN: use-after-free in fast_dput fs/dcache.c:727 [inline] > BUG: KASAN: use-after-free in dput+0x53e/0xdf0 fs/dcache.c:846 > Read of size 4 at addr ffff88808a618cf0 by task syz-executor.0/8426 > > CPU: 0 PID: 8426 Comm: syz-executor.0 Not tainted 5.6.0-next-20200412-syzkaller #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > Call Trace: > __dump_stack lib/dump_stack.c:77 [inline] > dump_stack+0x188/0x20d lib/dump_stack.c:118 > print_address_description.constprop.0.cold+0xd3/0x315 mm/kasan/report.c:382 > __kasan_report.cold+0x35/0x4d mm/kasan/report.c:511 > kasan_report+0x33/0x50 mm/kasan/common.c:625 > fast_dput fs/dcache.c:727 [inline] > dput+0x53e/0xdf0 fs/dcache.c:846 > proc_kill_sb+0x73/0xf0 fs/proc/root.c:195 > deactivate_locked_super+0x8c/0xf0 fs/super.c:335 > vfs_get_super+0x258/0x2d0 fs/super.c:1212 > vfs_get_tree+0x89/0x2f0 fs/super.c:1547 > do_new_mount fs/namespace.c:2813 [inline] > do_mount+0x1306/0x1b30 fs/namespace.c:3138 > __do_sys_mount fs/namespace.c:3347 [inline] > __se_sys_mount fs/namespace.c:3324 [inline] > __x64_sys_mount+0x18f/0x230 fs/namespace.c:3324 > do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295 > entry_SYSCALL_64_after_hwframe+0x49/0xb3 > RIP: 0033:0x45c889 > Code: ad b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 > RSP: 002b:00007ffc1930ec48 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5 > RAX: ffffffffffffffda RBX: 0000000001324914 RCX: 000000000045c889 > RDX: 0000000020000140 RSI: 0000000020000040 RDI: 0000000000000000 > RBP: 000000000076bf00 R08: 0000000000000000 R09: 0000000000000000 > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000003 > R13: 0000000000000749 R14: 00000000004ca15a R15: 0000000000000013 Looking at the code now that it the internal mount of proc is no longer used it is possible to unmount proc. If proc is unmounted the fields of the pid namespace that were used for filesystem specific state are not reinitialized. Which means that proc_self and proc_thread_self can be pointers to already freed dentries. The reported user after free appears to be from mounting and unmounting proc followed by mounting proc again and using error injection to cause the new root dentry allocation to fail. This in turn results in proc_kill_sb running with proc_self and proc_thread_self still retaining their values from the previous mount of proc. Then calling dput on either proc_self of proc_thread_self will result in double put. Which KASAN sees as a use after free. Solve this by always reinitializing the filesystem state stored in the struct pid_namespace, when proc is unmounted. Reported-by: syzbot+72868dd424eb66c6b95f@syzkaller.appspotmail.com Acked-by:
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- 12 Apr, 2020 10 commits
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Linus Torvalds authored
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Linus Torvalds authored
This sorts the actual field names too, potentially causing even more chaos and confusion at merge time if you have edited the MAINTAINERS file. But the end result is a more consistent layout, and hopefully it's a one-time pain minimized by doing this just before the -rc1 release. This was entirely scripted: ./scripts/parse-maintainers.pl --input=MAINTAINERS --output=MAINTAINERS --order Requested-by:
Joe Perches <joe@perches.com> Signed-off-by:
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Linus Torvalds authored
They are all supposed to be sorted, but people who add new entries don't always know the alphabet. Plus sometimes the entry names get edited, and people don't then re-order the entry. Let's see how painful this will be for merging purposes (the MAINTAINERS file is often edited in various different trees), but Joe claims there's relatively few patches in -next that touch this, and doing it just before -rc1 is likely the best time. Fingers crossed. This was scripted with /scripts/parse-maintainers.pl --input=MAINTAINERS --output=MAINTAINERS but then I also ended up manually upper-casing a few entry names that stood out when looking at the end result. Requested-by:
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tipLinus Torvalds authored
Pull x86 fixes from Thomas Gleixner: "A set of three patches to fix the fallout of the newly added split lock detection feature. It addressed the case where a KVM guest triggers a split lock #AC and KVM reinjects it into the guest which is not prepared to handle it. Add proper sanity checks which prevent the unconditional injection into the guest and handles the #AC on the host side in the same way as user space detections are handled. Depending on the detection mode it either warns and disables detection for the task or kills the task if the mode is set to fatal" * tag 'x86-urgent-2020-04-12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: KVM: VMX: Extend VMXs #AC interceptor to handle split lock #AC in guest KVM: x86: Emulate split-lock access as a write in emulator x86/split_lock: Provide handle_guest_split_lock()
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tipLinus Torvalds authored
Pull time(keeping) updates from Thomas Gleixner: - Fix the time_for_children symlink in /proc/$PID/ so it properly reflects that it part of the 'time' namespace - Add the missing userns limit for the allowed number of time namespaces, which was half defined but the actual array member was not added. This went unnoticed as the array has an exessive empty member at the end but introduced a user visible regression as the output was corrupted. - Prevent further silent ucount corruption by adding a BUILD_BUG_ON() to catch half updated data. * tag 'timers-urgent-2020-04-12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: ucount: Make sure ucounts in /proc/sys/user don't regress again time/namespace: Add max_time_namespaces ucount time/namespace: Fix time_for_children symlink
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tipLinus Torvalds authored
Pull scheduler fixes/updates from Thomas Gleixner: - Deduplicate the average computations in the scheduler core and the fair class code. - Fix a raise between runtime distribution and assignement which can cause exceeding the quota by up to 70%. - Prevent negative results in the imbalanace calculation - Remove a stale warning in the workqueue code which can be triggered since the call site was moved out of preempt disabled code. It's a false positive. - Deduplicate the print macros for procfs - Add the ucmap values to the SCHED_DEBUG procfs output for completness * tag 'sched-urgent-2020-04-12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: sched/debug: Add task uclamp values to SCHED_DEBUG procfs sched/debug: Factor out printing formats into common macros sched/debug: Remove redundant macro define sched/core: Remove unused rq::last_load_update_tick workqueue: Remove the warning in wq_worker_sleeping() sched/fair: Fix negative imbalance in imbalance calculation sched/fair: Fix race between runtime distribution and assignment sched/fair: Align rq->avg_idle and rq->avg_scan_cost
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tipLinus Torvalds authored
Pull perf fixes from Thomas Gleixner: "Three fixes/updates for perf: - Fix the perf event cgroup tracking which tries to track the cgroup even for disabled events. - Add Ice Lake server support for uncore events - Disable pagefaults when retrieving the physical address in the sampling code" * tag 'perf-urgent-2020-04-12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: perf/core: Disable page faults when getting phys address perf/x86/intel/uncore: Add Ice Lake server uncore support perf/cgroup: Correct indirection in perf_less_group_idx() perf/core: Fix event cgroup tracking -
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tipLinus Torvalds authored
Pull locking fixes from Thomas Gleixner: "Three small fixes/updates for the locking core code: - Plug a task struct reference leak in the percpu rswem implementation. - Document the refcount interaction with PID_MAX_LIMIT - Improve the 'invalid wait context' data dump in lockdep so it contains all information which is required to decode the problem" * tag 'locking-urgent-2020-04-12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: locking/lockdep: Improve 'invalid wait context' splat locking/refcount: Document interaction with PID_MAX_LIMIT locking/percpu-rwsem: Fix a task_struct refcount -
git://git.samba.org/sfrench/cifs-2.6Linus Torvalds authored
Pull cifs fixes from Steve French: "Ten cifs/smb fixes: - five RDMA (smbdirect) related fixes - add experimental support for swap over SMB3 mounts - also a fix which improves performance of signed connections" * tag '5.7-rc-smb3-fixes-part2' of git://git.samba.org/sfrench/cifs-2.6: smb3: enable swap on SMB3 mounts smb3: change noisy error message to FYI smb3: smbdirect support can be configured by default cifs: smbd: Do not schedule work to send immediate packet on every receive cifs: smbd: Properly process errors on ib_post_send cifs: Allocate crypto structures on the fly for calculating signatures of incoming packets cifs: smbd: Update receive credits before sending and deal with credits roll back on failure before sending cifs: smbd: Check send queue size before posting a send cifs: smbd: Merge code to track pending packets cifs: ignore cached share root handle closing errors
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git://git.linux-nfs.org/projects/trondmy/linux-nfsLinus Torvalds authored
Pull NFS client bugfix from Trond Myklebust: "Fix an RCU read lock leakage in pnfs_alloc_ds_commits_list()" * tag 'nfs-for-5.7-2' of git://git.linux-nfs.org/projects/trondmy/linux-nfs: pNFS: Fix RCU lock leakage
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- 11 Apr, 2020 2 commits
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git://git.kernel.org/pub/scm/linux/kernel/git/lftan/nios2Linus Torvalds authored
Pull nios2 updates from Ley Foon Tan: - Remove nios2-dev@lists.rocketboards.org from MAINTAINERS - remove 'resetvalue' property - rename 'altr,gpio-bank-width' -> 'altr,ngpio' - enable the common clk subsystem on Nios2 * tag 'nios2-v5.7-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/lftan/nios2: MAINTAINERS: Remove nios2-dev@lists.rocketboards.org arch: nios2: remove 'resetvalue' property arch: nios2: rename 'altr,gpio-bank-width' -> 'altr,ngpio' arch: nios2: Enable the common clk subsystem on Nios2
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git://git.infradead.org/users/hch/dma-mappingLinus Torvalds authored
Pull dma-mapping fixes from Christoph Hellwig: - fix an integer truncation in dma_direct_get_required_mask (Kishon Vijay Abraham) - fix the display of dma mapping types (Grygorii Strashko) * tag 'dma-mapping-5.7-1' of git://git.infradead.org/users/hch/dma-mapping: dma-debug: fix displaying of dma allocation type dma-direct: fix data truncation in dma_direct_get_required_mask()
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