Merge tag 'fscrypt-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/fscrypt

Pull fscrypt updates from Ted Ts'o:
 "Lots of cleanups, mostly courtesy by Eric Biggers"

* tag 'fscrypt-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/fscrypt:
  fscrypt: lock mutex before checking for bounce page pool
  fscrypt: add a documentation file for filesystem-level encryption
  ext4: switch to fscrypt_prepare_setattr()
  ext4: switch to fscrypt_prepare_lookup()
  ext4: switch to fscrypt_prepare_rename()
  ext4: switch to fscrypt_prepare_link()
  ext4: switch to fscrypt_file_open()
  fscrypt: new helper function - fscrypt_prepare_setattr()
  fscrypt: new helper function - fscrypt_prepare_lookup()
  fscrypt: new helper function - fscrypt_prepare_rename()
  fscrypt: new helper function - fscrypt_prepare_link()
  fscrypt: new helper function - fscrypt_file_open()
  fscrypt: new helper function - fscrypt_require_key()
  fscrypt: remove unneeded empty fscrypt_operations structs
  fscrypt: remove ->is_encrypted()
  fscrypt: switch from ->is_encrypted() to IS_ENCRYPTED()
  fs, fscrypt: add an S_ENCRYPTED inode flag
  fscrypt: clean up include file mess

Documentation/filesystems/fscrypt.rst

+=====================================
+Filesystem-level encryption (fscrypt)
+=====================================
+
+Introduction
+============
+
+fscrypt is a library which filesystems can hook into to support
+transparent encryption of files and directories.
+
+Note: "fscrypt" in this document refers to the kernel-level portion,
+implemented in ``fs/crypto/``, as opposed to the userspace tool
+`fscrypt <https://github.com/google/fscrypt>`_.  This document only
+covers the kernel-level portion.  For command-line examples of how to
+use encryption, see the documentation for the userspace tool `fscrypt
+<https://github.com/google/fscrypt>`_.  Also, it is recommended to use
+the fscrypt userspace tool, or other existing userspace tools such as
+`fscryptctl <https://github.com/google/fscryptctl>`_ or `Android's key
+management system
+<https://source.android.com/security/encryption/file-based>`_, over
+using the kernel's API directly.  Using existing tools reduces the
+chance of introducing your own security bugs.  (Nevertheless, for
+completeness this documentation covers the kernel's API anyway.)
+
+Unlike dm-crypt, fscrypt operates at the filesystem level rather than
+at the block device level.  This allows it to encrypt different files
+with different keys and to have unencrypted files on the same
+filesystem.  This is useful for multi-user systems where each user's
+data-at-rest needs to be cryptographically isolated from the others.
+However, except for filenames, fscrypt does not encrypt filesystem
+metadata.
+
+Unlike eCryptfs, which is a stacked filesystem, fscrypt is integrated
+directly into supported filesystems --- currently ext4, F2FS, and
+UBIFS.  This allows encrypted files to be read and written without
+caching both the decrypted and encrypted pages in the pagecache,
+thereby nearly halving the memory used and bringing it in line with
+unencrypted files.  Similarly, half as many dentries and inodes are
+needed.  eCryptfs also limits encrypted filenames to 143 bytes,
+causing application compatibility issues; fscrypt allows the full 255
+bytes (NAME_MAX).  Finally, unlike eCryptfs, the fscrypt API can be
+used by unprivileged users, with no need to mount anything.
+
+fscrypt does not support encrypting files in-place.  Instead, it
+supports marking an empty directory as encrypted.  Then, after
+userspace provides the key, all regular files, directories, and
+symbolic links created in that directory tree are transparently
+encrypted.
+
+Threat model
+============
+
+Offline attacks
+---------------
+
+Provided that userspace chooses a strong encryption key, fscrypt
+protects the confidentiality of file contents and filenames in the
+event of a single point-in-time permanent offline compromise of the
+block device content.  fscrypt does not protect the confidentiality of
+non-filename metadata, e.g. file sizes, file permissions, file
+timestamps, and extended attributes.  Also, the existence and location
+of holes (unallocated blocks which logically contain all zeroes) in
+files is not protected.
+
+fscrypt is not guaranteed to protect confidentiality or authenticity
+if an attacker is able to manipulate the filesystem offline prior to
+an authorized user later accessing the filesystem.
+
+Online attacks
+--------------
+
+fscrypt (and storage encryption in general) can only provide limited
+protection, if any at all, against online attacks.  In detail:
+
+fscrypt is only resistant to side-channel attacks, such as timing or
+electromagnetic attacks, to the extent that the underlying Linux
+Cryptographic API algorithms are.  If a vulnerable algorithm is used,
+such as a table-based implementation of AES, it may be possible for an
+attacker to mount a side channel attack against the online system.
+Side channel attacks may also be mounted against applications
+consuming decrypted data.
+
+After an encryption key has been provided, fscrypt is not designed to
+hide the plaintext file contents or filenames from other users on the
+same system, regardless of the visibility of the keyring key.
+Instead, existing access control mechanisms such as file mode bits,
+POSIX ACLs, LSMs, or mount namespaces should be used for this purpose.
+Also note that as long as the encryption keys are *anywhere* in
+memory, an online attacker can necessarily compromise them by mounting
+a physical attack or by exploiting any kernel security vulnerability
+which provides an arbitrary memory read primitive.
+
+While it is ostensibly possible to "evict" keys from the system,
+recently accessed encrypted files will remain accessible at least
+until the filesystem is unmounted or the VFS caches are dropped, e.g.
+using ``echo 2 > /proc/sys/vm/drop_caches``.  Even after that, if the
+RAM is compromised before being powered off, it will likely still be
+possible to recover portions of the plaintext file contents, if not
+some of the encryption keys as well.  (Since Linux v4.12, all
+in-kernel keys related to fscrypt are sanitized before being freed.
+However, userspace would need to do its part as well.)
+
+Currently, fscrypt does not prevent a user from maliciously providing
+an incorrect key for another user's existing encrypted files.  A
+protection against this is planned.
+
+Key hierarchy
+=============
+
+Master Keys
+-----------
+
+Each encrypted directory tree is protected by a *master key*.  Master
+keys can be up to 64 bytes long, and must be at least as long as the
+greater of the key length needed by the contents and filenames
+encryption modes being used.  For example, if AES-256-XTS is used for
+contents encryption, the master key must be 64 bytes (512 bits).  Note
+that the XTS mode is defined to require a key twice as long as that
+required by the underlying block cipher.
+
+To "unlock" an encrypted directory tree, userspace must provide the
+appropriate master key.  There can be any number of master keys, each
+of which protects any number of directory trees on any number of
+filesystems.
+
+Userspace should generate master keys either using a cryptographically
+secure random number generator, or by using a KDF (Key Derivation
+Function).  Note that whenever a KDF is used to "stretch" a
+lower-entropy secret such as a passphrase, it is critical that a KDF
+designed for this purpose be used, such as scrypt, PBKDF2, or Argon2.
+
+Per-file keys
+-------------
+
+Master keys are not used to encrypt file contents or names directly.
+Instead, a unique key is derived for each encrypted file, including
+each regular file, directory, and symbolic link.  This has several
+advantages:
+
+- In cryptosystems, the same key material should never be used for
+  different purposes.  Using the master key as both an XTS key for
+  contents encryption and as a CTS-CBC key for filenames encryption
+  would violate this rule.
+- Per-file keys simplify the choice of IVs (Initialization Vectors)
+  for contents encryption.  Without per-file keys, to ensure IV
+  uniqueness both the inode and logical block number would need to be
+  encoded in the IVs.  This would make it impossible to renumber
+  inodes, which e.g. ``resize2fs`` can do when resizing an ext4
+  filesystem.  With per-file keys, it is sufficient to encode just the
+  logical block number in the IVs.
+- Per-file keys strengthen the encryption of filenames, where IVs are
+  reused out of necessity.  With a unique key per directory, IV reuse
+  is limited to within a single directory.
+- Per-file keys allow individual files to be securely erased simply by
+  securely erasing their keys.  (Not yet implemented.)
+
+A KDF (Key Derivation Function) is used to derive per-file keys from
+the master key.  This is done instead of wrapping a randomly-generated
+key for each file because it reduces the size of the encryption xattr,
+which for some filesystems makes the xattr more likely to fit in-line
+in the filesystem's inode table.  With a KDF, only a 16-byte nonce is
+required --- long enough to make key reuse extremely unlikely.  A
+wrapped key, on the other hand, would need to be up to 64 bytes ---
+the length of an AES-256-XTS key.  Furthermore, currently there is no
+requirement to support unlocking a file with multiple alternative
+master keys or to support rotating master keys.  Instead, the master
+keys may be wrapped in userspace, e.g. as done by the `fscrypt
+<https://github.com/google/fscrypt>`_ tool.
+
+The current KDF encrypts the master key using the 16-byte nonce as an
+AES-128-ECB key.  The output is used as the derived key.  If the
+output is longer than needed, then it is truncated to the needed
+length.  Truncation is the norm for directories and symlinks, since
+those use the CTS-CBC encryption mode which requires a key half as
+long as that required by the XTS encryption mode.
+
+Note: this KDF meets the primary security requirement, which is to
+produce unique derived keys that preserve the entropy of the master
+key, assuming that the master key is already a good pseudorandom key.
+However, it is nonstandard and has some problems such as being
+reversible, so it is generally considered to be a mistake!  It may be
+replaced with HKDF or another more standard KDF in the future.
+
+Encryption modes and usage
+==========================
+
+fscrypt allows one encryption mode to be specified for file contents
+and one encryption mode to be specified for filenames.  Different
+directory trees are permitted to use different encryption modes.
+Currently, the following pairs of encryption modes are supported:
+
+- AES-256-XTS for contents and AES-256-CTS-CBC for filenames
+- AES-128-CBC for contents and AES-128-CTS-CBC for filenames
+
+It is strongly recommended to use AES-256-XTS for contents encryption.
+AES-128-CBC was added only for low-powered embedded devices with
+crypto accelerators such as CAAM or CESA that do not support XTS.
+
+New encryption modes can be added relatively easily, without changes
+to individual filesystems.  However, authenticated encryption (AE)
+modes are not currently supported because of the difficulty of dealing
+with ciphertext expansion.
+
+For file contents, each filesystem block is encrypted independently.
+Currently, only the case where the filesystem block size is equal to
+the system's page size (usually 4096 bytes) is supported.  With the
+XTS mode of operation (recommended), the logical block number within
+the file is used as the IV.  With the CBC mode of operation (not
+recommended), ESSIV is used; specifically, the IV for CBC is the
+logical block number encrypted with AES-256, where the AES-256 key is
+the SHA-256 hash of the inode's data encryption key.
+
+For filenames, the full filename is encrypted at once.  Because of the
+requirements to retain support for efficient directory lookups and
+filenames of up to 255 bytes, a constant initialization vector (IV) is
+used.  However, each encrypted directory uses a unique key, which
+limits IV reuse to within a single directory.  Note that IV reuse in
+the context of CTS-CBC encryption means that when the original
+filenames share a common prefix at least as long as the cipher block
+size (16 bytes for AES), the corresponding encrypted filenames will
+also share a common prefix.  This is undesirable; it may be fixed in
+the future by switching to an encryption mode that is a strong
+pseudorandom permutation on arbitrary-length messages, e.g. the HEH
+(Hash-Encrypt-Hash) mode.
+
+Since filenames are encrypted with the CTS-CBC mode of operation, the
+plaintext and ciphertext filenames need not be multiples of the AES
+block size, i.e. 16 bytes.  However, the minimum size that can be
+encrypted is 16 bytes, so shorter filenames are NUL-padded to 16 bytes
+before being encrypted.  In addition, to reduce leakage of filename
+lengths via their ciphertexts, all filenames are NUL-padded to the
+next 4, 8, 16, or 32-byte boundary (configurable).  32 is recommended
+since this provides the best confidentiality, at the cost of making
+directory entries consume slightly more space.  Note that since NUL
+(``\0``) is not otherwise a valid character in filenames, the padding
+will never produce duplicate plaintexts.
+
+Symbolic link targets are considered a type of filename and are
+encrypted in the same way as filenames in directory entries.  Each
+symlink also uses a unique key; hence, the hardcoded IV is not a
+problem for symlinks.
+
+User API
+========
+
+Setting an encryption policy
+----------------------------
+
+The FS_IOC_SET_ENCRYPTION_POLICY ioctl sets an encryption policy on an
+empty directory or verifies that a directory or regular file already
+has the specified encryption policy.  It takes in a pointer to a
+:c:type:`struct fscrypt_policy`, defined as follows::
+
+    #define FS_KEY_DESCRIPTOR_SIZE  8
+
+    struct fscrypt_policy {
+            __u8 version;
+            __u8 contents_encryption_mode;
+            __u8 filenames_encryption_mode;
+            __u8 flags;
+            __u8 master_key_descriptor[FS_KEY_DESCRIPTOR_SIZE];
+    };
+
+This structure must be initialized as follows:
+
+- ``version`` must be 0.
+
+- ``contents_encryption_mode`` and ``filenames_encryption_mode`` must
+  be set to constants from ``<linux/fs.h>`` which identify the
+  encryption modes to use.  If unsure, use
+  FS_ENCRYPTION_MODE_AES_256_XTS (1) for ``contents_encryption_mode``
+  and FS_ENCRYPTION_MODE_AES_256_CTS (4) for
+  ``filenames_encryption_mode``.
+
+- ``flags`` must be set to a value from ``<linux/fs.h>`` which
+  identifies the amount of NUL-padding to use when encrypting
+  filenames.  If unsure, use FS_POLICY_FLAGS_PAD_32 (0x3).
+
+- ``master_key_descriptor`` specifies how to find the master key in
+  the keyring; see `Adding keys`_.  It is up to userspace to choose a
+  unique ``master_key_descriptor`` for each master key.  The e4crypt
+  and fscrypt tools use the first 8 bytes of
+  ``SHA-512(SHA-512(master_key))``, but this particular scheme is not
+  required.  Also, the master key need not be in the keyring yet when
+  FS_IOC_SET_ENCRYPTION_POLICY is executed.  However, it must be added
+  before any files can be created in the encrypted directory.
+
+If the file is not yet encrypted, then FS_IOC_SET_ENCRYPTION_POLICY
+verifies that the file is an empty directory.  If so, the specified
+encryption policy is assigned to the directory, turning it into an
+encrypted directory.  After that, and after providing the
+corresponding master key as described in `Adding keys`_, all regular
+files, directories (recursively), and symlinks created in the
+directory will be encrypted, inheriting the same encryption policy.
+The filenames in the directory's entries will be encrypted as well.
+
+Alternatively, if the file is already encrypted, then
+FS_IOC_SET_ENCRYPTION_POLICY validates that the specified encryption
+policy exactly matches the actual one.  If they match, then the ioctl
+returns 0.  Otherwise, it fails with EEXIST.  This works on both
+regular files and directories, including nonempty directories.
+
+Note that the ext4 filesystem does not allow the root directory to be
+encrypted, even if it is empty.  Users who want to encrypt an entire
+filesystem with one key should consider using dm-crypt instead.
+
+FS_IOC_SET_ENCRYPTION_POLICY can fail with the following errors:
+
+- ``EACCES``: the file is not owned by the process's uid, nor does the
+  process have the CAP_FOWNER capability in a namespace with the file
+  owner's uid mapped
+- ``EEXIST``: the file is already encrypted with an encryption policy
+  different from the one specified
+- ``EINVAL``: an invalid encryption policy was specified (invalid
+  version, mode(s), or flags)
+- ``ENOTDIR``: the file is unencrypted and is a regular file, not a
+  directory
+- ``ENOTEMPTY``: the file is unencrypted and is a nonempty directory
+- ``ENOTTY``: this type of filesystem does not implement encryption
+- ``EOPNOTSUPP``: the kernel was not configured with encryption
+  support for this filesystem, or the filesystem superblock has not
+  had encryption enabled on it.  (For example, to use encryption on an
+  ext4 filesystem, CONFIG_EXT4_ENCRYPTION must be enabled in the
+  kernel config, and the superblock must have had the "encrypt"
+  feature flag enabled using ``tune2fs -O encrypt`` or ``mkfs.ext4 -O
+  encrypt``.)
+- ``EPERM``: this directory may not be encrypted, e.g. because it is
+  the root directory of an ext4 filesystem
+- ``EROFS``: the filesystem is readonly
+
+Getting an encryption policy
+----------------------------
+
+The FS_IOC_GET_ENCRYPTION_POLICY ioctl retrieves the :c:type:`struct
+fscrypt_policy`, if any, for a directory or regular file.  See above
+for the struct definition.  No additional permissions are required
+beyond the ability to open the file.
+
+FS_IOC_GET_ENCRYPTION_POLICY can fail with the following errors:
+
+- ``EINVAL``: the file is encrypted, but it uses an unrecognized
+  encryption context format
+- ``ENODATA``: the file is not encrypted
+- ``ENOTTY``: this type of filesystem does not implement encryption
+- ``EOPNOTSUPP``: the kernel was not configured with encryption
+  support for this filesystem
+
+Note: if you only need to know whether a file is encrypted or not, on
+most filesystems it is also possible to use the FS_IOC_GETFLAGS ioctl
+and check for FS_ENCRYPT_FL, or to use the statx() system call and
+check for STATX_ATTR_ENCRYPTED in stx_attributes.
+
+Getting the per-filesystem salt
+-------------------------------
+
+Some filesystems, such as ext4 and F2FS, also support the deprecated
+ioctl FS_IOC_GET_ENCRYPTION_PWSALT.  This ioctl retrieves a randomly
+generated 16-byte value stored in the filesystem superblock.  This
+value is intended to used as a salt when deriving an encryption key
+from a passphrase or other low-entropy user credential.
+
+FS_IOC_GET_ENCRYPTION_PWSALT is deprecated.  Instead, prefer to
+generate and manage any needed salt(s) in userspace.
+
+Adding keys
+-----------
+
+To provide a master key, userspace must add it to an appropriate
+keyring using the add_key() system call (see:
+``Documentation/security/keys/core.rst``).  The key type must be
+"logon"; keys of this type are kept in kernel memory and cannot be
+read back by userspace.  The key description must be "fscrypt:"
+followed by the 16-character lower case hex representation of the
+``master_key_descriptor`` that was set in the encryption policy.  The
+key payload must conform to the following structure::
+
+    #define FS_MAX_KEY_SIZE 64
+
+    struct fscrypt_key {
+            u32 mode;
+            u8 raw[FS_MAX_KEY_SIZE];
+            u32 size;
+    };
+
+``mode`` is ignored; just set it to 0.  The actual key is provided in
+``raw`` with ``size`` indicating its size in bytes.  That is, the
+bytes ``raw[0..size-1]`` (inclusive) are the actual key.
+
+The key description prefix "fscrypt:" may alternatively be replaced
+with a filesystem-specific prefix such as "ext4:".  However, the
+filesystem-specific prefixes are deprecated and should not be used in
+new programs.
+
+There are several different types of keyrings in which encryption keys
+may be placed, such as a session keyring, a user session keyring, or a
+user keyring.  Each key must be placed in a keyring that is "attached"
+to all processes that might need to access files encrypted with it, in
+the sense that request_key() will find the key.  Generally, if only
+processes belonging to a specific user need to access a given
+encrypted directory and no session keyring has been installed, then
+that directory's key should be placed in that user's user session
+keyring or user keyring.  Otherwise, a session keyring should be
+installed if needed, and the key should be linked into that session
+keyring, or in a keyring linked into that session keyring.
+
+Note: introducing the complex visibility semantics of keyrings here
+was arguably a mistake --- especially given that by design, after any
+process successfully opens an encrypted file (thereby setting up the
+per-file key), possessing the keyring key is not actually required for
+any process to read/write the file until its in-memory inode is
+evicted.  In the future there probably should be a way to provide keys
+directly to the filesystem instead, which would make the intended
+semantics clearer.
+
+Access semantics
+================
+
+With the key
+------------
+
+With the encryption key, encrypted regular files, directories, and
+symlinks behave very similarly to their unencrypted counterparts ---
+after all, the encryption is intended to be transparent.  However,
+astute users may notice some differences in behavior:
+
+- Unencrypted files, or files encrypted with a different encryption
+  policy (i.e. different key, modes, or flags), cannot be renamed or
+  linked into an encrypted directory; see `Encryption policy
+  enforcement`_.  Attempts to do so will fail with EPERM.  However,
+  encrypted files can be renamed within an encrypted directory, or
+  into an unencrypted directory.
+
+- Direct I/O is not supported on encrypted files.  Attempts to use
+  direct I/O on such files will fall back to buffered I/O.
+
+- The fallocate operations FALLOC_FL_COLLAPSE_RANGE,
+  FALLOC_FL_INSERT_RANGE, and FALLOC_FL_ZERO_RANGE are not supported
+  on encrypted files and will fail with EOPNOTSUPP.
+
+- Online defragmentation of encrypted files is not supported.  The
+  EXT4_IOC_MOVE_EXT and F2FS_IOC_MOVE_RANGE ioctls will fail with
+  EOPNOTSUPP.
+
+- The ext4 filesystem does not support data journaling with encrypted
+  regular files.  It will fall back to ordered data mode instead.
+
+- DAX (Direct Access) is not supported on encrypted files.
+
+- The st_size of an encrypted symlink will not necessarily give the
+  length of the symlink target as required by POSIX.  It will actually
+  give the length of the ciphertext, which may be slightly longer than
+  the plaintext due to the NUL-padding.
+
+Note that mmap *is* supported.  This is possible because the pagecache
+for an encrypted file contains the plaintext, not the ciphertext.
+
+Without the key
+---------------
+
+Some filesystem operations may be performed on encrypted regular
+files, directories, and symlinks even before their encryption key has
+been provided:
+
+- File metadata may be read, e.g. using stat().
+
+- Directories may be listed, in which case the filenames will be
+  listed in an encoded form derived from their ciphertext.  The
+  current encoding algorithm is described in `Filename hashing and
+  encoding`_.  The algorithm is subject to change, but it is
+  guaranteed that the presented filenames will be no longer than
+  NAME_MAX bytes, will not contain the ``/`` or ``\0`` characters, and
+  will uniquely identify directory entries.
+
+  The ``.`` and ``..`` directory entries are special.  They are always
+  present and are not encrypted or encoded.
+
+- Files may be deleted.  That is, nondirectory files may be deleted
+  with unlink() as usual, and empty directories may be deleted with
+  rmdir() as usual.  Therefore, ``rm`` and ``rm -r`` will work as
+  expected.
+
+- Symlink targets may be read and followed, but they will be presented
+  in encrypted form, similar to filenames in directories.  Hence, they
+  are unlikely to point to anywhere useful.
+
+Without the key, regular files cannot be opened or truncated.
+Attempts to do so will fail with ENOKEY.  This implies that any
+regular file operations that require a file descriptor, such as
+read(), write(), mmap(), fallocate(), and ioctl(), are also forbidden.
+
+Also without the key, files of any type (including directories) cannot
+be created or linked into an encrypted directory, nor can a name in an
+encrypted directory be the source or target of a rename, nor can an
+O_TMPFILE temporary file be created in an encrypted directory.  All
+such operations will fail with ENOKEY.
+
+It is not currently possible to backup and restore encrypted files
+without the encryption key.  This would require special APIs which
+have not yet been implemented.
+
+Encryption policy enforcement
+=============================
+
+After an encryption policy has been set on a directory, all regular
+files, directories, and symbolic links created in that directory
+(recursively) will inherit that encryption policy.  Special files ---
+that is, named pipes, device nodes, and UNIX domain sockets --- will
+not be encrypted.
+
+Except for those special files, it is forbidden to have unencrypted
+files, or files encrypted with a different encryption policy, in an
+encrypted directory tree.  Attempts to link or rename such a file into
+an encrypted directory will fail with EPERM.  This is also enforced
+during ->lookup() to provide limited protection against offline
+attacks that try to disable or downgrade encryption in known locations
+where applications may later write sensitive data.  It is recommended
+that systems implementing a form of "verified boot" take advantage of
+this by validating all top-level encryption policies prior to access.
+
+Implementation details
+======================
+
+Encryption context
+------------------
+
+An encryption policy is represented on-disk by a :c:type:`struct
+fscrypt_context`.  It is up to individual filesystems to decide where
+to store it, but normally it would be stored in a hidden extended
+attribute.  It should *not* be exposed by the xattr-related system
+calls such as getxattr() and setxattr() because of the special
+semantics of the encryption xattr.  (In particular, there would be
+much confusion if an encryption policy were to be added to or removed
+from anything other than an empty directory.)  The struct is defined
+as follows::
+
+    #define FS_KEY_DESCRIPTOR_SIZE  8
+    #define FS_KEY_DERIVATION_NONCE_SIZE 16
+
+    struct fscrypt_context {
+            u8 format;
+            u8 contents_encryption_mode;
+            u8 filenames_encryption_mode;
+            u8 flags;
+            u8 master_key_descriptor[FS_KEY_DESCRIPTOR_SIZE];
+            u8 nonce[FS_KEY_DERIVATION_NONCE_SIZE];
+    };
+
+Note that :c:type:`struct fscrypt_context` contains the same
+information as :c:type:`struct fscrypt_policy` (see `Setting an
+encryption policy`_), except that :c:type:`struct fscrypt_context`
+also contains a nonce.  The nonce is randomly generated by the kernel
+and is used to derive the inode's encryption key as described in
+`Per-file keys`_.
+
+Data path changes
+-----------------
+
+For the read path (->readpage()) of regular files, filesystems can
+read the ciphertext into the page cache and decrypt it in-place.  The
+page lock must be held until decryption has finished, to prevent the
+page from becoming visible to userspace prematurely.
+
+For the write path (->writepage()) of regular files, filesystems
+cannot encrypt data in-place in the page cache, since the cached
+plaintext must be preserved.  Instead, filesystems must encrypt into a
+temporary buffer or "bounce page", then write out the temporary
+buffer.  Some filesystems, such as UBIFS, already use temporary
+buffers regardless of encryption.  Other filesystems, such as ext4 and
+F2FS, have to allocate bounce pages specially for encryption.
+
+Filename hashing and encoding
+-----------------------------
+
+Modern filesystems accelerate directory lookups by using indexed
+directories.  An indexed directory is organized as a tree keyed by
+filename hashes.  When a ->lookup() is requested, the filesystem
+normally hashes the filename being looked up so that it can quickly
+find the corresponding directory entry, if any.
+
+With encryption, lookups must be supported and efficient both with and
+without the encryption key.  Clearly, it would not work to hash the
+plaintext filenames, since the plaintext filenames are unavailable
+without the key.  (Hashing the plaintext filenames would also make it
+impossible for the filesystem's fsck tool to optimize encrypted
+directories.)  Instead, filesystems hash the ciphertext filenames,
+i.e. the bytes actually stored on-disk in the directory entries.  When
+asked to do a ->lookup() with the key, the filesystem just encrypts
+the user-supplied name to get the ciphertext.
+
+Lookups without the key are more complicated.  The raw ciphertext may
+contain the ``\0`` and ``/`` characters, which are illegal in
+filenames.  Therefore, readdir() must base64-encode the ciphertext for
+presentation.  For most filenames, this works fine; on ->lookup(), the
+filesystem just base64-decodes the user-supplied name to get back to
+the raw ciphertext.
+
+However, for very long filenames, base64 encoding would cause the
+filename length to exceed NAME_MAX.  To prevent this, readdir()
+actually presents long filenames in an abbreviated form which encodes
+a strong "hash" of the ciphertext filename, along with the optional
+filesystem-specific hash(es) needed for directory lookups.  This
+allows the filesystem to still, with a high degree of confidence, map
+the filename given in ->lookup() back to a particular directory entry
+that was previously listed by readdir().  See :c:type:`struct
+fscrypt_digested_name` in the source for more details.
+
+Note that the precise way that filenames are presented to userspace
+without the key is subject to change in the future.  It is only meant
+as a way to temporarily present valid filenames so that commands like
+``rm -r`` work as expected on encrypted directories.

Documentation/filesystems/index.rst

@@ -315,3 +315,14 @@ exported for use by modules.
    :internal:
 
 .. kernel-doc:: fs/pipe.c
+
+Encryption API
+==============
+
+A library which filesystems can hook into to support transparent
+encryption of files and directories.
+
+.. toctree::
+    :maxdepth: 2
+
+    fscrypt

MAINTAINERS

@@ -5664,6 +5664,7 @@ T:	git git://git.kernel.org/pub/scm/linux/kernel/git/tytso/fscrypt.git
 S:	Supported
 F:	fs/crypto/
 F:	include/linux/fscrypt*.h
+F:	Documentation/filesystems/fscrypt.rst
 
 FUJITSU FR-V (FRV) PORT
 S:	Orphan

fs/crypto/Makefile

 obj-$(CONFIG_FS_ENCRYPTION)	+= fscrypto.o
 
-fscrypto-y := crypto.o fname.o policy.o keyinfo.o
+fscrypto-y := crypto.o fname.o hooks.o keyinfo.o policy.o
 fscrypto-$(CONFIG_BLOCK) += bio.o

fs/crypto/crypto.c

@@ -320,7 +320,7 @@ static int fscrypt_d_revalidate(struct dentry *dentry, unsigned int flags)
 		return -ECHILD;
 
 	dir = dget_parent(dentry);
-	if (!d_inode(dir)->i_sb->s_cop->is_encrypted(d_inode(dir))) {
+	if (!IS_ENCRYPTED(d_inode(dir))) {
 		dput(dir);
 		return 0;
 	}
@@ -390,11 +390,8 @@ int fscrypt_initialize(unsigned int cop_flags)
 {
 	int i, res = -ENOMEM;
 
-	/*
-	 * No need to allocate a bounce page pool if there already is one or
-	 * this FS won't use it.
-	 */
-	if (cop_flags & FS_CFLG_OWN_PAGES || fscrypt_bounce_page_pool)
+	/* No need to allocate a bounce page pool if this FS won't use it. */
+	if (cop_flags & FS_CFLG_OWN_PAGES)
 		return 0;
 
 	mutex_lock(&fscrypt_init_mutex);

fs/crypto/fname.c

@@ -359,8 +359,7 @@ int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname,
 	memset(fname, 0, sizeof(struct fscrypt_name));
 	fname->usr_fname = iname;
 
-	if (!dir->i_sb->s_cop->is_encrypted(dir) ||
-				fscrypt_is_dot_dotdot(iname)) {
+	if (!IS_ENCRYPTED(dir) || fscrypt_is_dot_dotdot(iname)) {
 		fname->disk_name.name = (unsigned char *)iname->name;
 		fname->disk_name.len = iname->len;
 		return 0;

fs/crypto/fscrypt_private.h

@@ -12,7 +12,8 @@
 #ifndef _FSCRYPT_PRIVATE_H
 #define _FSCRYPT_PRIVATE_H
 
-#include <linux/fscrypt_supp.h>
+#define __FS_HAS_ENCRYPTION 1
+#include <linux/fscrypt.h>
 #include <crypto/hash.h>
 
 /* Encryption parameters */

fs/crypto/hooks.c

+/*
+ * fs/crypto/hooks.c
+ *
+ * Encryption hooks for higher-level filesystem operations.
+ */
+
+#include <linux/ratelimit.h>
+#include "fscrypt_private.h"
+
+/**
+ * fscrypt_file_open - prepare to open a possibly-encrypted regular file
+ * @inode: the inode being opened
+ * @filp: the struct file being set up
+ *
+ * Currently, an encrypted regular file can only be opened if its encryption key
+ * is available; access to the raw encrypted contents is not supported.
+ * Therefore, we first set up the inode's encryption key (if not already done)
+ * and return an error if it's unavailable.
+ *
+ * We also verify that if the parent directory (from the path via which the file
+ * is being opened) is encrypted, then the inode being opened uses the same
+ * encryption policy.  This is needed as part of the enforcement that all files
+ * in an encrypted directory tree use the same encryption policy, as a
+ * protection against certain types of offline attacks.  Note that this check is
+ * needed even when opening an *unencrypted* file, since it's forbidden to have
+ * an unencrypted file in an encrypted directory.
+ *
+ * Return: 0 on success, -ENOKEY if the key is missing, or another -errno code
+ */
+int fscrypt_file_open(struct inode *inode, struct file *filp)
+{
+	int err;
+	struct dentry *dir;
+
+	err = fscrypt_require_key(inode);
+	if (err)
+		return err;
+
+	dir = dget_parent(file_dentry(filp));
+	if (IS_ENCRYPTED(d_inode(dir)) &&
+	    !fscrypt_has_permitted_context(d_inode(dir), inode)) {
+		pr_warn_ratelimited("fscrypt: inconsistent encryption contexts: %lu/%lu",
+				    d_inode(dir)->i_ino, inode->i_ino);
+		err = -EPERM;
+	}
+	dput(dir);
+	return err;
+}
+EXPORT_SYMBOL_GPL(fscrypt_file_open);
+
+int __fscrypt_prepare_link(struct inode *inode, struct inode *dir)
+{
+	int err;
+
+	err = fscrypt_require_key(dir);
+	if (err)
+		return err;
+
+	if (!fscrypt_has_permitted_context(dir, inode))
+		return -EPERM;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(__fscrypt_prepare_link);
+
+int __fscrypt_prepare_rename(struct inode *old_dir, struct dentry *old_dentry,
+			     struct inode *new_dir, struct dentry *new_dentry,
+			     unsigned int flags)
+{
+	int err;
+
+	err = fscrypt_require_key(old_dir);
+	if (err)
+		return err;
+
+	err = fscrypt_require_key(new_dir);
+	if (err)
+		return err;
+
+	if (old_dir != new_dir) {
+		if (IS_ENCRYPTED(new_dir) &&
+		    !fscrypt_has_permitted_context(new_dir,
+						   d_inode(old_dentry)))
+			return -EPERM;
+
+		if ((flags & RENAME_EXCHANGE) &&
+		    IS_ENCRYPTED(old_dir) &&
+		    !fscrypt_has_permitted_context(old_dir,
+						   d_inode(new_dentry)))
+			return -EPERM;
+	}
+	return 0;
+}
+EXPORT_SYMBOL_GPL(__fscrypt_prepare_rename);
+
+int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry)
+{
+	int err = fscrypt_get_encryption_info(dir);
+
+	if (err)
+		return err;
+
+	if (fscrypt_has_encryption_key(dir)) {
+		spin_lock(&dentry->d_lock);
+		dentry->d_flags |= DCACHE_ENCRYPTED_WITH_KEY;
+		spin_unlock(&dentry->d_lock);
+	}
+
+	d_set_d_op(dentry, &fscrypt_d_ops);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(__fscrypt_prepare_lookup);

fs/crypto/keyinfo.c

@@ -259,7 +259,7 @@ int fscrypt_get_encryption_info(struct inode *inode)
 	res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
 	if (res < 0) {
 		if (!fscrypt_dummy_context_enabled(inode) ||
-		    inode->i_sb->s_cop->is_encrypted(inode))
+		    IS_ENCRYPTED(inode))
 			return res;
 		/* Fake up a context for an unencrypted directory */
 		memset(&ctx, 0, sizeof(ctx));

fs/crypto/policy.c

@@ -110,7 +110,7 @@ int fscrypt_ioctl_get_policy(struct file *filp, void __user *arg)
 	struct fscrypt_policy policy;
 	int res;
 
-	if (!inode->i_sb->s_cop->is_encrypted(inode))
+	if (!IS_ENCRYPTED(inode))
 		return -ENODATA;
 
 	res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
@@ -167,11 +167,11 @@ int fscrypt_has_permitted_context(struct inode *parent, struct inode *child)
 		return 1;
 
 	/* No restrictions if the parent directory is unencrypted */
-	if (!cops->is_encrypted(parent))
+	if (!IS_ENCRYPTED(parent))
 		return 1;
 
 	/* Encrypted directories must not contain unencrypted files */
-	if (!cops->is_encrypted(child))
+	if (!IS_ENCRYPTED(child))
 		return 0;
 
 	/*

fs/ext4/ext4.h

@@ -34,17 +34,15 @@
 #include <linux/percpu_counter.h>
 #include <linux/ratelimit.h>
 #include <crypto/hash.h>
-#ifdef CONFIG_EXT4_FS_ENCRYPTION
-#include <linux/fscrypt_supp.h>
-#else
-#include <linux/fscrypt_notsupp.h>
-#endif
 #include <linux/falloc.h>
 #include <linux/percpu-rwsem.h>
 #ifdef __KERNEL__
 #include <linux/compat.h>
 #endif
 
+#define __FS_HAS_ENCRYPTION IS_ENABLED(CONFIG_EXT4_FS_ENCRYPTION)
+#include <linux/fscrypt.h>
+
 /*
  * The fourth extended filesystem constants/structures
  */

fs/ext4/file.c

@@ -365,7 +365,6 @@ static int ext4_file_open(struct inode * inode, struct file * filp)
 	struct super_block *sb = inode->i_sb;
 	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
 	struct vfsmount *mnt = filp->f_path.mnt;
-	struct dentry *dir;
 	struct path path;
 	char buf[64], *cp;
 	int ret;
@@ -405,25 +404,11 @@ static int ext4_file_open(struct inode * inode, struct file * filp)
 			ext4_journal_stop(handle);
 		}
 	}
-	if (ext4_encrypted_inode(inode)) {
-		ret = fscrypt_get_encryption_info(inode);
-		if (ret)
-			return -EACCES;
-		if (!fscrypt_has_encryption_key(inode))
-			return -ENOKEY;
-	}
 
-	dir = dget_parent(file_dentry(filp));
-	if (ext4_encrypted_inode(d_inode(dir)) &&
-			!fscrypt_has_permitted_context(d_inode(dir), inode)) {
-		ext4_warning(inode->i_sb,
-			     "Inconsistent encryption contexts: %lu/%lu",
-			     (unsigned long) d_inode(dir)->i_ino,
-			     (unsigned long) inode->i_ino);
-		dput(dir);
-		return -EPERM;
-	}
-	dput(dir);
+	ret = fscrypt_file_open(inode, filp);
+	if (ret)
+		return ret;
+
 	/*
 	 * Set up the jbd2_inode if we are opening the inode for
 	 * writing and the journal is present

fs/ext4/inode.c

@@ -4590,10 +4590,13 @@ void ext4_set_inode_flags(struct inode *inode)
 		new_fl |= S_DIRSYNC;
 	if (test_opt(inode->i_sb, DAX) && S_ISREG(inode->i_mode) &&
 	    !ext4_should_journal_data(inode) && !ext4_has_inline_data(inode) &&
-	    !ext4_encrypted_inode(inode))
+	    !(flags & EXT4_ENCRYPT_FL))
 		new_fl |= S_DAX;
+	if (flags & EXT4_ENCRYPT_FL)
+		new_fl |= S_ENCRYPTED;
 	inode_set_flags(inode, new_fl,
-			S_SYNC|S_APPEND|S_IMMUTABLE|S_NOATIME|S_DIRSYNC|S_DAX);
+			S_SYNC|S_APPEND|S_IMMUTABLE|S_NOATIME|S_DIRSYNC|S_DAX|
+			S_ENCRYPTED);
 }
 
 static blkcnt_t ext4_inode_blocks(struct ext4_inode *raw_inode,
@@ -5309,6 +5312,10 @@ int ext4_setattr(struct dentry *dentry, struct iattr *attr)
 	if (error)
 		return error;
 
+	error = fscrypt_prepare_setattr(dentry, attr);
+	if (error)
+		return error;
+
 	if (is_quota_modification(inode, attr)) {
 		error = dquot_initialize(inode);
 		if (error)
@@ -5354,14 +5361,6 @@ int ext4_setattr(struct dentry *dentry, struct iattr *attr)
 		loff_t oldsize = inode->i_size;
 		int shrink = (attr->ia_size <= inode->i_size);
 
-		if (ext4_encrypted_inode(inode)) {
-			error = fscrypt_get_encryption_info(inode);
-			if (error)
-				return error;
-			if (!fscrypt_has_encryption_key(inode))
-				return -ENOKEY;
-		}
-
 		if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))) {
 			struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
 

fs/ext4/namei.c

@@ -1539,24 +1539,14 @@ static struct dentry *ext4_lookup(struct inode *dir, struct dentry *dentry, unsi
 	struct inode *inode;
 	struct ext4_dir_entry_2 *de;
 	struct buffer_head *bh;
+	int err;
 
-	if (ext4_encrypted_inode(dir)) {
-		int res = fscrypt_get_encryption_info(dir);
-
-		/*
-		 * DCACHE_ENCRYPTED_WITH_KEY is set if the dentry is
-		 * created while the directory was encrypted and we
-		 * have access to the key.
-		 */
-		if (fscrypt_has_encryption_key(dir))
-			fscrypt_set_encrypted_dentry(dentry);
-		fscrypt_set_d_op(dentry);
-		if (res && res != -ENOKEY)
-			return ERR_PTR(res);
-	}
+	err = fscrypt_prepare_lookup(dir, dentry, flags);
+	if (err)
+		return ERR_PTR(err);
 
-       if (dentry->d_name.len > EXT4_NAME_LEN)
-	       return ERR_PTR(-ENAMETOOLONG);
+	if (dentry->d_name.len > EXT4_NAME_LEN)
+		return ERR_PTR(-ENAMETOOLONG);
 
 	bh = ext4_find_entry(dir, &dentry->d_name, &de, NULL);
 	if (IS_ERR(bh))
@@ -3222,9 +3212,10 @@ static int ext4_link(struct dentry *old_dentry,
 
 	if (inode->i_nlink >= EXT4_LINK_MAX)
 		return -EMLINK;
-	if (ext4_encrypted_inode(dir) &&
-			!fscrypt_has_permitted_context(dir, inode))
-		return -EPERM;
+
+	err = fscrypt_prepare_link(old_dentry, dir, dentry);
+	if (err)
+		return err;
 
        if ((ext4_test_inode_flag(dir, EXT4_INODE_PROJINHERIT)) &&
 	   (!projid_eq(EXT4_I(dir)->i_projid,
@@ -3516,12 +3507,6 @@ static int ext4_rename(struct inode *old_dir, struct dentry *old_dentry,
 			EXT4_I(old_dentry->d_inode)->i_projid)))
 		return -EXDEV;
 
-	if ((ext4_encrypted_inode(old_dir) &&
-	     !fscrypt_has_encryption_key(old_dir)) ||
-	    (ext4_encrypted_inode(new_dir) &&
-	     !fscrypt_has_encryption_key(new_dir)))
-		return -ENOKEY;
-
 	retval = dquot_initialize(old.dir);
 	if (retval)
 		return retval;
@@ -3550,13 +3535,6 @@ static int ext4_rename(struct inode *old_dir, struct dentry *old_dentry,
 	if (!old.bh || le32_to_cpu(old.de->inode) != old.inode->i_ino)
 		goto end_rename;
 
-	if ((old.dir != new.dir) &&
-	    ext4_encrypted_inode(new.dir) &&
-	    !fscrypt_has_permitted_context(new.dir, old.inode)) {
-		retval = -EPERM;
-		goto end_rename;
-	}
-
 	new.bh = ext4_find_entry(new.dir, &new.dentry->d_name,
 				 &new.de, &new.inlined);
 	if (IS_ERR(new.bh)) {
@@ -3722,19 +3700,6 @@ static int ext4_cross_rename(struct inode *old_dir, struct dentry *old_dentry,
 	int retval;
 	struct timespec ctime;
 
-	if ((ext4_encrypted_inode(old_dir) &&
-	     !fscrypt_has_encryption_key(old_dir)) ||
-	    (ext4_encrypted_inode(new_dir) &&
-	     !fscrypt_has_encryption_key(new_dir)))
-		return -ENOKEY;
-
-	if ((ext4_encrypted_inode(old_dir) ||
-	     ext4_encrypted_inode(new_dir)) &&
-	    (old_dir != new_dir) &&
-	    (!fscrypt_has_permitted_context(new_dir, old.inode) ||
-	     !fscrypt_has_permitted_context(old_dir, new.inode)))
-		return -EPERM;
-
 	if ((ext4_test_inode_flag(new_dir, EXT4_INODE_PROJINHERIT) &&
 	     !projid_eq(EXT4_I(new_dir)->i_projid,
 			EXT4_I(old_dentry->d_inode)->i_projid)) ||
@@ -3861,12 +3826,19 @@ static int ext4_rename2(struct inode *old_dir, struct dentry *old_dentry,
 			struct inode *new_dir, struct dentry *new_dentry,
 			unsigned int flags)
 {
+	int err;
+
 	if (unlikely(ext4_forced_shutdown(EXT4_SB(old_dir->i_sb))))
 		return -EIO;
 
 	if (flags & ~(RENAME_NOREPLACE | RENAME_EXCHANGE | RENAME_WHITEOUT))
 		return -EINVAL;
 
+	err = fscrypt_prepare_rename(old_dir, old_dentry, new_dir, new_dentry,
+				     flags);
+	if (err)
+		return err;
+
 	if (flags & RENAME_EXCHANGE) {
 		return ext4_cross_rename(old_dir, old_dentry,
 					 new_dir, new_dentry);

fs/ext4/super.c

@@ -1181,7 +1181,8 @@ static int ext4_set_context(struct inode *inode, const void *ctx, size_t len,
 			ext4_clear_inode_state(inode,
 					EXT4_STATE_MAY_INLINE_DATA);
 			/*
-			 * Update inode->i_flags - e.g. S_DAX may get disabled
+			 * Update inode->i_flags - S_ENCRYPTED will be enabled,
+			 * S_DAX may be disabled
 			 */
 			ext4_set_inode_flags(inode);
 		}
@@ -1206,7 +1207,10 @@ static int ext4_set_context(struct inode *inode, const void *ctx, size_t len,
 				    ctx, len, 0);
 	if (!res) {
 		ext4_set_inode_flag(inode, EXT4_INODE_ENCRYPT);
-		/* Update inode->i_flags - e.g. S_DAX may get disabled */
+		/*
+		 * Update inode->i_flags - S_ENCRYPTED will be enabled,
+		 * S_DAX may be disabled
+		 */
 		ext4_set_inode_flags(inode);
 		res = ext4_mark_inode_dirty(handle, inode);
 		if (res)
@@ -1237,14 +1241,9 @@ static const struct fscrypt_operations ext4_cryptops = {
 	.get_context		= ext4_get_context,
 	.set_context		= ext4_set_context,
 	.dummy_context		= ext4_dummy_context,
-	.is_encrypted		= ext4_encrypted_inode,
 	.empty_dir		= ext4_empty_dir,
 	.max_namelen		= ext4_max_namelen,
 };
-#else
-static const struct fscrypt_operations ext4_cryptops = {
-	.is_encrypted		= ext4_encrypted_inode,
-};
 #endif
 
 #ifdef CONFIG_QUOTA
@@ -3996,7 +3995,9 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 	sb->s_op = &ext4_sops;
 	sb->s_export_op = &ext4_export_ops;
 	sb->s_xattr = ext4_xattr_handlers;
+#ifdef CONFIG_EXT4_FS_ENCRYPTION
 	sb->s_cop = &ext4_cryptops;
+#endif
 #ifdef CONFIG_QUOTA
 	sb->dq_op = &ext4_quota_operations;
 	if (ext4_has_feature_quota(sb))

fs/f2fs/f2fs.h

@@ -23,13 +23,11 @@
 #include <linux/bio.h>
 #include <linux/blkdev.h>
 #include <linux/quotaops.h>
-#ifdef CONFIG_F2FS_FS_ENCRYPTION
-#include <linux/fscrypt_supp.h>
-#else
-#include <linux/fscrypt_notsupp.h>
-#endif
 #include <crypto/hash.h>
 
+#define __FS_HAS_ENCRYPTION IS_ENABLED(CONFIG_F2FS_FS_ENCRYPTION)
+#include <linux/fscrypt.h>
+
 #ifdef CONFIG_F2FS_CHECK_FS
 #define f2fs_bug_on(sbi, condition)	BUG_ON(condition)
 #else
@@ -2949,6 +2947,7 @@ static inline void f2fs_set_encrypted_inode(struct inode *inode)
 {
 #ifdef CONFIG_F2FS_FS_ENCRYPTION
 	file_set_encrypt(inode);
+	inode->i_flags |= S_ENCRYPTED;
 #endif
 }
 

fs/f2fs/inode.c

@@ -43,8 +43,11 @@ void f2fs_set_inode_flags(struct inode *inode)
 		new_fl |= S_NOATIME;
 	if (flags & FS_DIRSYNC_FL)
 		new_fl |= S_DIRSYNC;
+	if (f2fs_encrypted_inode(inode))
+		new_fl |= S_ENCRYPTED;
 	inode_set_flags(inode, new_fl,
-			S_SYNC|S_APPEND|S_IMMUTABLE|S_NOATIME|S_DIRSYNC);
+			S_SYNC|S_APPEND|S_IMMUTABLE|S_NOATIME|S_DIRSYNC|
+			S_ENCRYPTED);
 }
 
 static void __get_inode_rdev(struct inode *inode, struct f2fs_inode *ri)

fs/f2fs/super.c

@@ -1594,14 +1594,9 @@ static const struct fscrypt_operations f2fs_cryptops = {
 	.key_prefix	= "f2fs:",
 	.get_context	= f2fs_get_context,
 	.set_context	= f2fs_set_context,
-	.is_encrypted	= f2fs_encrypted_inode,
 	.empty_dir	= f2fs_empty_dir,
 	.max_namelen	= f2fs_max_namelen,
 };
-#else
-static const struct fscrypt_operations f2fs_cryptops = {
-	.is_encrypted	= f2fs_encrypted_inode,
-};
 #endif
 
 static struct inode *f2fs_nfs_get_inode(struct super_block *sb,
@@ -2320,7 +2315,9 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
 #endif
 
 	sb->s_op = &f2fs_sops;
+#ifdef CONFIG_F2FS_FS_ENCRYPTION
 	sb->s_cop = &f2fs_cryptops;
+#endif
 	sb->s_xattr = f2fs_xattr_handlers;
 	sb->s_export_op = &f2fs_export_ops;
 	sb->s_magic = F2FS_SUPER_MAGIC;

fs/ubifs/crypto.c

@@ -88,7 +88,6 @@ const struct fscrypt_operations ubifs_crypt_operations = {
 	.key_prefix		= "ubifs:",
 	.get_context		= ubifs_crypt_get_context,
 	.set_context		= ubifs_crypt_set_context,
-	.is_encrypted		= __ubifs_crypt_is_encrypted,
 	.empty_dir		= ubifs_crypt_empty_dir,
 	.max_namelen		= ubifs_crypt_max_namelen,
 };

fs/ubifs/ioctl.c

@@ -38,7 +38,8 @@ void ubifs_set_inode_flags(struct inode *inode)
 {
 	unsigned int flags = ubifs_inode(inode)->flags;
 
-	inode->i_flags &= ~(S_SYNC | S_APPEND | S_IMMUTABLE | S_DIRSYNC);
+	inode->i_flags &= ~(S_SYNC | S_APPEND | S_IMMUTABLE | S_DIRSYNC |
+			    S_ENCRYPTED);
 	if (flags & UBIFS_SYNC_FL)
 		inode->i_flags |= S_SYNC;
 	if (flags & UBIFS_APPEND_FL)
@@ -47,6 +48,8 @@ void ubifs_set_inode_flags(struct inode *inode)
 		inode->i_flags |= S_IMMUTABLE;
 	if (flags & UBIFS_DIRSYNC_FL)
 		inode->i_flags |= S_DIRSYNC;
+	if (flags & UBIFS_CRYPT_FL)
+		inode->i_flags |= S_ENCRYPTED;
 }
 
 /*

fs/ubifs/super.c

@@ -2007,12 +2007,6 @@ static struct ubifs_info *alloc_ubifs_info(struct ubi_volume_desc *ubi)
 	return c;
 }
 
-#ifndef CONFIG_UBIFS_FS_ENCRYPTION
-const struct fscrypt_operations ubifs_crypt_operations = {
-	.is_encrypted		= __ubifs_crypt_is_encrypted,
-};
-#endif
-
 static int ubifs_fill_super(struct super_block *sb, void *data, int silent)
 {
 	struct ubifs_info *c = sb->s_fs_info;
@@ -2055,7 +2049,9 @@ static int ubifs_fill_super(struct super_block *sb, void *data, int silent)
 		sb->s_maxbytes = c->max_inode_sz = MAX_LFS_FILESIZE;
 	sb->s_op = &ubifs_super_operations;
 	sb->s_xattr = ubifs_xattr_handlers;
+#ifdef CONFIG_UBIFS_FS_ENCRYPTION
 	sb->s_cop = &ubifs_crypt_operations;
+#endif
 
 	mutex_lock(&c->umount_mutex);
 	err = mount_ubifs(c);

fs/ubifs/ubifs.h

@@ -38,12 +38,11 @@
 #include <linux/backing-dev.h>
 #include <linux/security.h>
 #include <linux/xattr.h>
-#ifdef CONFIG_UBIFS_FS_ENCRYPTION
-#include <linux/fscrypt_supp.h>
-#else
-#include <linux/fscrypt_notsupp.h>
-#endif
 #include <linux/random.h>
+
+#define __FS_HAS_ENCRYPTION IS_ENABLED(CONFIG_UBIFS_FS_ENCRYPTION)
+#include <linux/fscrypt.h>
+
 #include "ubifs-media.h"
 
 /* Version of this UBIFS implementation */
@@ -1835,18 +1834,13 @@ int ubifs_decrypt(const struct inode *inode, struct ubifs_data_node *dn,
 
 extern const struct fscrypt_operations ubifs_crypt_operations;
 
-static inline bool __ubifs_crypt_is_encrypted(struct inode *inode)
+static inline bool ubifs_crypt_is_encrypted(const struct inode *inode)
 {
-	struct ubifs_inode *ui = ubifs_inode(inode);
+	const struct ubifs_inode *ui = ubifs_inode(inode);
 
 	return ui->flags & UBIFS_CRYPT_FL;
 }
 
-static inline bool ubifs_crypt_is_encrypted(const struct inode *inode)
-{
-	return __ubifs_crypt_is_encrypted((struct inode *)inode);
-}
-
 /* Normal UBIFS messages */
 __printf(2, 3)
 void ubifs_msg(const struct ubifs_info *c, const char *fmt, ...);

fs/ubifs/xattr.c

@@ -170,6 +170,7 @@ static int create_xattr(struct ubifs_info *c, struct inode *host,
 	err = ubifs_jnl_update(c, host, nm, inode, 0, 1);
 	if (err)
 		goto out_cancel;
+	ubifs_set_inode_flags(host);
 	mutex_unlock(&host_ui->ui_mutex);
 
 	ubifs_release_budget(c, &req);

include/linux/fs.h

@@ -1854,6 +1854,7 @@ struct super_operations {
 #else
 #define S_DAX		0	/* Make all the DAX code disappear */
 #endif
+#define S_ENCRYPTED	16384	/* Encrypted file (using fs/crypto/) */
 
 /*
  * Note that nosuid etc flags are inode-specific: setting some file-system
@@ -1893,6 +1894,7 @@ static inline bool sb_rdonly(const struct super_block *sb) { return sb->s_flags
 #define IS_AUTOMOUNT(inode)	((inode)->i_flags & S_AUTOMOUNT)
 #define IS_NOSEC(inode)		((inode)->i_flags & S_NOSEC)
 #define IS_DAX(inode)		((inode)->i_flags & S_DAX)
+#define IS_ENCRYPTED(inode)	((inode)->i_flags & S_ENCRYPTED)
 
 #define IS_WHITEOUT(inode)	(S_ISCHR(inode->i_mode) && \
 				 (inode)->i_rdev == WHITEOUT_DEV)

include/linux/fscrypt_common.h → include/linux/fscrypt.h

 /* SPDX-License-Identifier: GPL-2.0 */
 /*
- * fscrypt_common.h: common declarations for per-file encryption
+ * fscrypt.h: declarations for per-file encryption
+ *
+ * Filesystems that implement per-file encryption include this header
+ * file with the __FS_HAS_ENCRYPTION set according to whether that filesystem
+ * is being built with encryption support or not.
  *
  * Copyright (C) 2015, Google, Inc.
  *
  * Written by Michael Halcrow, 2015.
  * Modified by Jaegeuk Kim, 2015.
  */
-
-#ifndef _LINUX_FSCRYPT_COMMON_H
-#define _LINUX_FSCRYPT_COMMON_H
+#ifndef _LINUX_FSCRYPT_H
+#define _LINUX_FSCRYPT_H
 
 #include <linux/key.h>
 #include <linux/fs.h>
@@ -79,7 +82,6 @@ struct fscrypt_operations {
 	int (*get_context)(struct inode *, void *, size_t);
 	int (*set_context)(struct inode *, const void *, size_t, void *);
 	bool (*dummy_context)(struct inode *);
-	bool (*is_encrypted)(struct inode *);
 	bool (*empty_dir)(struct inode *);
 	unsigned (*max_namelen)(struct inode *);
 };
@@ -120,23 +122,173 @@ static inline bool fscrypt_is_dot_dotdot(const struct qstr *str)
 	return false;
 }
 
+#if __FS_HAS_ENCRYPTION
+
 static inline struct page *fscrypt_control_page(struct page *page)
 {
-#if IS_ENABLED(CONFIG_FS_ENCRYPTION)
 	return ((struct fscrypt_ctx *)page_private(page))->w.control_page;
-#else
+}
+
+static inline bool fscrypt_has_encryption_key(const struct inode *inode)
+{
+	return (inode->i_crypt_info != NULL);
+}
+
+#include <linux/fscrypt_supp.h>
+
+#else /* !__FS_HAS_ENCRYPTION */
+
+static inline struct page *fscrypt_control_page(struct page *page)
+{
 	WARN_ON_ONCE(1);
 	return ERR_PTR(-EINVAL);
-#endif
 }
 
-static inline int fscrypt_has_encryption_key(const struct inode *inode)
+static inline bool fscrypt_has_encryption_key(const struct inode *inode)
 {
-#if IS_ENABLED(CONFIG_FS_ENCRYPTION)
-	return (inode->i_crypt_info != NULL);
-#else
 	return 0;
-#endif
 }
 
-#endif	/* _LINUX_FSCRYPT_COMMON_H */
+#include <linux/fscrypt_notsupp.h>
+#endif /* __FS_HAS_ENCRYPTION */
+
+/**
+ * fscrypt_require_key - require an inode's encryption key
+ * @inode: the inode we need the key for
+ *
+ * If the inode is encrypted, set up its encryption key if not already done.
+ * Then require that the key be present and return -ENOKEY otherwise.
+ *
+ * No locks are needed, and the key will live as long as the struct inode --- so
+ * it won't go away from under you.
+ *
+ * Return: 0 on success, -ENOKEY if the key is missing, or another -errno code
+ * if a problem occurred while setting up the encryption key.
+ */
+static inline int fscrypt_require_key(struct inode *inode)
+{
+	if (IS_ENCRYPTED(inode)) {
+		int err = fscrypt_get_encryption_info(inode);
+
+		if (err)
+			return err;
+		if (!fscrypt_has_encryption_key(inode))
+			return -ENOKEY;
+	}
+	return 0;
+}
+
+/**
+ * fscrypt_prepare_link - prepare to link an inode into a possibly-encrypted directory
+ * @old_dentry: an existing dentry for the inode being linked
+ * @dir: the target directory
+ * @dentry: negative dentry for the target filename
+ *
+ * A new link can only be added to an encrypted directory if the directory's
+ * encryption key is available --- since otherwise we'd have no way to encrypt
+ * the filename.  Therefore, we first set up the directory's encryption key (if
+ * not already done) and return an error if it's unavailable.
+ *
+ * We also verify that the link will not violate the constraint that all files
+ * in an encrypted directory tree use the same encryption policy.
+ *
+ * Return: 0 on success, -ENOKEY if the directory's encryption key is missing,
+ * -EPERM if the link would result in an inconsistent encryption policy, or
+ * another -errno code.
+ */
+static inline int fscrypt_prepare_link(struct dentry *old_dentry,
+				       struct inode *dir,
+				       struct dentry *dentry)
+{
+	if (IS_ENCRYPTED(dir))
+		return __fscrypt_prepare_link(d_inode(old_dentry), dir);
+	return 0;
+}
+
+/**
+ * fscrypt_prepare_rename - prepare for a rename between possibly-encrypted directories
+ * @old_dir: source directory
+ * @old_dentry: dentry for source file
+ * @new_dir: target directory
+ * @new_dentry: dentry for target location (may be negative unless exchanging)
+ * @flags: rename flags (we care at least about %RENAME_EXCHANGE)
+ *
+ * Prepare for ->rename() where the source and/or target directories may be
+ * encrypted.  A new link can only be added to an encrypted directory if the
+ * directory's encryption key is available --- since otherwise we'd have no way
+ * to encrypt the filename.  A rename to an existing name, on the other hand,
+ * *is* cryptographically possible without the key.  However, we take the more
+ * conservative approach and just forbid all no-key renames.
+ *
+ * We also verify that the rename will not violate the constraint that all files
+ * in an encrypted directory tree use the same encryption policy.
+ *
+ * Return: 0 on success, -ENOKEY if an encryption key is missing, -EPERM if the
+ * rename would cause inconsistent encryption policies, or another -errno code.
+ */
+static inline int fscrypt_prepare_rename(struct inode *old_dir,
+					 struct dentry *old_dentry,
+					 struct inode *new_dir,
+					 struct dentry *new_dentry,
+					 unsigned int flags)
+{
+	if (IS_ENCRYPTED(old_dir) || IS_ENCRYPTED(new_dir))
+		return __fscrypt_prepare_rename(old_dir, old_dentry,
+						new_dir, new_dentry, flags);
+	return 0;
+}
+
+/**
+ * fscrypt_prepare_lookup - prepare to lookup a name in a possibly-encrypted directory
+ * @dir: directory being searched
+ * @dentry: filename being looked up
+ * @flags: lookup flags
+ *
+ * Prepare for ->lookup() in a directory which may be encrypted.  Lookups can be
+ * done with or without the directory's encryption key; without the key,
+ * filenames are presented in encrypted form.  Therefore, we'll try to set up
+ * the directory's encryption key, but even without it the lookup can continue.
+ *
+ * To allow invalidating stale dentries if the directory's encryption key is
+ * added later, we also install a custom ->d_revalidate() method and use the
+ * DCACHE_ENCRYPTED_WITH_KEY flag to indicate whether a given dentry is a
+ * plaintext name (flag set) or a ciphertext name (flag cleared).
+ *
+ * Return: 0 on success, -errno if a problem occurred while setting up the
+ * encryption key
+ */
+static inline int fscrypt_prepare_lookup(struct inode *dir,
+					 struct dentry *dentry,
+					 unsigned int flags)
+{
+	if (IS_ENCRYPTED(dir))
+		return __fscrypt_prepare_lookup(dir, dentry);
+	return 0;
+}
+
+/**
+ * fscrypt_prepare_setattr - prepare to change a possibly-encrypted inode's attributes
+ * @dentry: dentry through which the inode is being changed
+ * @attr: attributes to change
+ *
+ * Prepare for ->setattr() on a possibly-encrypted inode.  On an encrypted file,
+ * most attribute changes are allowed even without the encryption key.  However,
+ * without the encryption key we do have to forbid truncates.  This is needed
+ * because the size being truncated to may not be a multiple of the filesystem
+ * block size, and in that case we'd have to decrypt the final block, zero the
+ * portion past i_size, and re-encrypt it.  (We *could* allow truncating to a
+ * filesystem block boundary, but it's simpler to just forbid all truncates ---
+ * and we already forbid all other contents modifications without the key.)
+ *
+ * Return: 0 on success, -ENOKEY if the key is missing, or another -errno code
+ * if a problem occurred while setting up the encryption key.
+ */
+static inline int fscrypt_prepare_setattr(struct dentry *dentry,
+					  struct iattr *attr)
+{
+	if (attr->ia_valid & ATTR_SIZE)
+		return fscrypt_require_key(d_inode(dentry));
+	return 0;
+}
+
+#endif	/* _LINUX_FSCRYPT_H */

include/linux/fscrypt_notsupp.h

@@ -4,13 +4,16 @@
  *
  * This stubs out the fscrypt functions for filesystems configured without
  * encryption support.
+ *
+ * Do not include this file directly. Use fscrypt.h instead!
  */
+#ifndef _LINUX_FSCRYPT_H
+#error "Incorrect include of linux/fscrypt_notsupp.h!"
+#endif
 
 #ifndef _LINUX_FSCRYPT_NOTSUPP_H
 #define _LINUX_FSCRYPT_NOTSUPP_H
 
-#include <linux/fscrypt_common.h>
-
 /* crypto.c */
 static inline struct fscrypt_ctx *fscrypt_get_ctx(const struct inode *inode,
 						  gfp_t gfp_flags)
@@ -98,7 +101,7 @@ static inline int fscrypt_setup_filename(struct inode *dir,
 					 const struct qstr *iname,
 					 int lookup, struct fscrypt_name *fname)
 {
-	if (dir->i_sb->s_cop->is_encrypted(dir))
+	if (IS_ENCRYPTED(dir))
 		return -EOPNOTSUPP;
 
 	memset(fname, 0, sizeof(struct fscrypt_name));
@@ -175,4 +178,34 @@ static inline int fscrypt_zeroout_range(const struct inode *inode, pgoff_t lblk,
 	return -EOPNOTSUPP;
 }
 
+/* hooks.c */
+
+static inline int fscrypt_file_open(struct inode *inode, struct file *filp)
+{
+	if (IS_ENCRYPTED(inode))
+		return -EOPNOTSUPP;
+	return 0;
+}
+
+static inline int __fscrypt_prepare_link(struct inode *inode,
+					 struct inode *dir)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline int __fscrypt_prepare_rename(struct inode *old_dir,
+					   struct dentry *old_dentry,
+					   struct inode *new_dir,
+					   struct dentry *new_dentry,
+					   unsigned int flags)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline int __fscrypt_prepare_lookup(struct inode *dir,
+					   struct dentry *dentry)
+{
+	return -EOPNOTSUPP;
+}
+
 #endif	/* _LINUX_FSCRYPT_NOTSUPP_H */

include/linux/fscrypt_supp.h

@@ -2,14 +2,15 @@
 /*
  * fscrypt_supp.h
  *
- * This is included by filesystems configured with encryption support.
+ * Do not include this file directly. Use fscrypt.h instead!
  */
+#ifndef _LINUX_FSCRYPT_H
+#error "Incorrect include of linux/fscrypt_supp.h!"
+#endif
 
 #ifndef _LINUX_FSCRYPT_SUPP_H
 #define _LINUX_FSCRYPT_SUPP_H
 
-#include <linux/fscrypt_common.h>
-
 /* crypto.c */
 extern struct kmem_cache *fscrypt_info_cachep;
 extern struct fscrypt_ctx *fscrypt_get_ctx(const struct inode *, gfp_t);
@@ -143,4 +144,14 @@ extern void fscrypt_pullback_bio_page(struct page **, bool);
 extern int fscrypt_zeroout_range(const struct inode *, pgoff_t, sector_t,
 				 unsigned int);
 
+/* hooks.c */
+extern int fscrypt_file_open(struct inode *inode, struct file *filp);
+extern int __fscrypt_prepare_link(struct inode *inode, struct inode *dir);
+extern int __fscrypt_prepare_rename(struct inode *old_dir,
+				    struct dentry *old_dentry,
+				    struct inode *new_dir,
+				    struct dentry *new_dentry,
+				    unsigned int flags);
+extern int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry);
+
 #endif	/* _LINUX_FSCRYPT_SUPP_H */