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| -rw-r--r-- | Documentation/filesystems/fscrypt.rst | 610 | ||||
| -rw-r--r-- | Documentation/filesystems/index.rst | 11 | ||||
| -rw-r--r-- | MAINTAINERS | 1 | ||||
| -rw-r--r-- | fs/crypto/Makefile | 2 | ||||
| -rw-r--r-- | fs/crypto/crypto.c | 9 | ||||
| -rw-r--r-- | fs/crypto/fname.c | 3 | ||||
| -rw-r--r-- | fs/crypto/fscrypt_private.h | 3 | ||||
| -rw-r--r-- | fs/crypto/hooks.c | 112 | ||||
| -rw-r--r-- | fs/crypto/keyinfo.c | 2 | ||||
| -rw-r--r-- | fs/crypto/policy.c | 6 | ||||
| -rw-r--r-- | fs/ext4/ext4.h | 8 | ||||
| -rw-r--r-- | fs/ext4/file.c | 23 | ||||
| -rw-r--r-- | fs/ext4/inode.c | 19 | ||||
| -rw-r--r-- | fs/ext4/namei.c | 62 | ||||
| -rw-r--r-- | fs/ext4/super.c | 15 | ||||
| -rw-r--r-- | fs/f2fs/f2fs.h | 9 | ||||
| -rw-r--r-- | fs/f2fs/inode.c | 5 | ||||
| -rw-r--r-- | fs/f2fs/super.c | 7 | ||||
| -rw-r--r-- | fs/ubifs/crypto.c | 1 | ||||
| -rw-r--r-- | fs/ubifs/ioctl.c | 5 | ||||
| -rw-r--r-- | fs/ubifs/super.c | 8 | ||||
| -rw-r--r-- | fs/ubifs/ubifs.h | 18 | ||||
| -rw-r--r-- | fs/ubifs/xattr.c | 1 | ||||
| -rw-r--r-- | include/linux/fs.h | 2 | ||||
| -rw-r--r-- | include/linux/fscrypt.h | 294 | ||||
| -rw-r--r-- | include/linux/fscrypt_common.h | 142 | ||||
| -rw-r--r-- | include/linux/fscrypt_notsupp.h | 39 | ||||
| -rw-r--r-- | include/linux/fscrypt_supp.h | 17 |
28 files changed, 1155 insertions, 279 deletions
diff --git a/Documentation/filesystems/fscrypt.rst b/Documentation/filesystems/fscrypt.rst new file mode 100644 index 000000000000..776ddc655f79 --- /dev/null +++ b/Documentation/filesystems/fscrypt.rst @@ -0,0 +1,610 @@ +===================================== +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. diff --git a/Documentation/filesystems/index.rst b/Documentation/filesystems/index.rst index 256e10eedba4..53b89d0edc15 100644 --- a/Documentation/filesystems/index.rst +++ b/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 diff --git a/MAINTAINERS b/MAINTAINERS index 9a9343a24528..e372994747b7 100644 --- a/MAINTAINERS +++ b/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 diff --git a/fs/crypto/Makefile b/fs/crypto/Makefile index 9f6607f17b53..cb496989a6b6 100644 --- a/fs/crypto/Makefile +++ b/fs/crypto/Makefile @@ -1,4 +1,4 @@ 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 diff --git a/fs/crypto/crypto.c b/fs/crypto/crypto.c index 80a3cada53de..732a786cce9d 100644 --- a/fs/crypto/crypto.c +++ b/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); diff --git a/fs/crypto/fname.c b/fs/crypto/fname.c index 0b94cd2b3222..305541bcd108 100644 --- a/fs/crypto/fname.c +++ b/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; diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h index e54e602b473f..c0b4f5597e1a 100644 --- a/fs/crypto/fscrypt_private.h +++ b/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 */ diff --git a/fs/crypto/hooks.c b/fs/crypto/hooks.c new file mode 100644 index 000000000000..9f5fb2eb9cf7 --- /dev/null +++ b/fs/crypto/hooks.c @@ -0,0 +1,112 @@ +/* + * 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); diff --git a/fs/crypto/keyinfo.c b/fs/crypto/keyinfo.c index 4486b3eecc27..5e6e846f5a24 100644 --- a/fs/crypto/keyinfo.c +++ b/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)); diff --git a/fs/crypto/policy.c b/fs/crypto/policy.c index a120649beeca..c6d431a5cce9 100644 --- a/fs/crypto/policy.c +++ b/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; /* diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h index 58a0304566db..27f38bb5046d 100644 --- a/fs/ext4/ext4.h +++ b/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 */ diff --git a/fs/ext4/file.c b/fs/ext4/file.c index 5cb9aa3ad249..b937078bcff3 100644 --- a/fs/ext4/file.c +++ b/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 diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index 90afeb7293a6..168a1b499cdf 100644 --- a/fs/ext4/inode.c +++ b/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); diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c index bd48a8d83961..798b3ac680db 100644 --- a/fs/ext4/namei.c +++ b/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); diff --git a/fs/ext4/super.c b/fs/ext4/super.c index b0915b734a38..e2557711a11c 100644 --- a/fs/ext4/super.c +++ b/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 @@ retry: 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)) diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h index 4b4a72f392be..115204fdefcc 100644 --- a/fs/f2fs/f2fs.h +++ b/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 } diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c index 50c88e37ed66..53fb08810ee9 100644 --- a/fs/f2fs/inode.c +++ b/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) diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c index 933c3d529e65..97e03c637e90 100644 --- a/fs/f2fs/super.c +++ b/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 @@ try_onemore: #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; diff --git a/fs/ubifs/crypto.c b/fs/ubifs/crypto.c index 16a5d5c82073..616a688f5d8f 100644 --- a/fs/ubifs/crypto.c +++ b/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, }; diff --git a/fs/ubifs/ioctl.c b/fs/ubifs/ioctl.c index fdc311246807..0164bcc827f8 100644 --- a/fs/ubifs/ioctl.c +++ b/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; } /* diff --git a/fs/ubifs/super.c b/fs/ubifs/super.c index 5496b17b959c..7503e7cdf870 100644 --- a/fs/ubifs/super.c +++ b/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); diff --git a/fs/ubifs/ubifs.h b/fs/ubifs/ubifs.h index cd43651f1731..63c7468147eb 100644 --- a/fs/ubifs/ubifs.h +++ b/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, ...); diff --git a/fs/ubifs/xattr.c b/fs/ubifs/xattr.c index c13eae819cbc..5ddc89d564fd 100644 --- a/fs/ubifs/xattr.c +++ b/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); diff --git a/include/linux/fs.h b/include/linux/fs.h index e1f75a3b4af5..269086440071 100644 --- a/include/linux/fs.h +++ b/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) diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h new file mode 100644 index 000000000000..08b4b40c5aa8 --- /dev/null +++ b/include/linux/fscrypt.h @@ -0,0 +1,294 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * 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_H +#define _LINUX_FSCRYPT_H + +#include <linux/key.h> +#include <linux/fs.h> +#include <linux/mm.h> +#include <linux/bio.h> +#include <linux/dcache.h> +#include <crypto/skcipher.h> +#include <uapi/linux/fs.h> + +#define FS_CRYPTO_BLOCK_SIZE 16 + +struct fscrypt_info; + +struct fscrypt_ctx { + union { + struct { + struct page *bounce_page; /* Ciphertext page */ + struct page *control_page; /* Original page */ + } w; + struct { + struct bio *bio; + struct work_struct work; + } r; + struct list_head free_list; /* Free list */ + }; + u8 flags; /* Flags */ +}; + +/** + * For encrypted symlinks, the ciphertext length is stored at the beginning + * of the string in little-endian format. + */ +struct fscrypt_symlink_data { + __le16 len; + char encrypted_path[1]; +} __packed; + +struct fscrypt_str { + unsigned char *name; + u32 len; +}; + +struct fscrypt_name { + const struct qstr *usr_fname; + struct fscrypt_str disk_name; + u32 hash; + u32 minor_hash; + struct fscrypt_str crypto_buf; +}; + +#define FSTR_INIT(n, l) { .name = n, .len = l } +#define FSTR_TO_QSTR(f) QSTR_INIT((f)->name, (f)->len) +#define fname_name(p) ((p)->disk_name.name) +#define fname_len(p) ((p)->disk_name.len) + +/* + * fscrypt superblock flags + */ +#define FS_CFLG_OWN_PAGES (1U << 1) + +/* + * crypto opertions for filesystems + */ +struct fscrypt_operations { + unsigned int flags; + const char *key_prefix; + int (*get_context)(struct inode *, void *, size_t); + int (*set_context)(struct inode *, const void *, size_t, void *); + bool (*dummy_context)(struct inode *); + bool (*empty_dir)(struct inode *); + unsigned (*max_namelen)(struct inode *); +}; + +/* Maximum value for the third parameter of fscrypt_operations.set_context(). */ +#define FSCRYPT_SET_CONTEXT_MAX_SIZE 28 + +static inline bool fscrypt_dummy_context_enabled(struct inode *inode) +{ + if (inode->i_sb->s_cop->dummy_context && + inode->i_sb->s_cop->dummy_context(inode)) + return true; + return false; +} + +static inline bool fscrypt_valid_enc_modes(u32 contents_mode, + u32 filenames_mode) +{ + if (contents_mode == FS_ENCRYPTION_MODE_AES_128_CBC && + filenames_mode == FS_ENCRYPTION_MODE_AES_128_CTS) + return true; + + if (contents_mode == FS_ENCRYPTION_MODE_AES_256_XTS && + filenames_mode == FS_ENCRYPTION_MODE_AES_256_CTS) + return true; + + return false; +} + +static inline bool fscrypt_is_dot_dotdot(const struct qstr *str) +{ + if (str->len == 1 && str->name[0] == '.') + return true; + + if (str->len == 2 && str->name[0] == '.' && str->name[1] == '.') + return true; + + return false; +} + +#if __FS_HAS_ENCRYPTION + +static inline struct page *fscrypt_control_page(struct page *page) +{ + return ((struct fscrypt_ctx *)page_private(page))->w.control_page; +} + +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); +} + +static inline bool fscrypt_has_encryption_key(const struct inode *inode) +{ + return 0; +} + +#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 */ diff --git a/include/linux/fscrypt_common.h b/include/linux/fscrypt_common.h deleted file mode 100644 index 854d724978fa..000000000000 --- a/include/linux/fscrypt_common.h +++ /dev/null @@ -1,142 +0,0 @@ -/* SPDX-License-Identifier: GPL-2.0 */ -/* - * fscrypt_common.h: common declarations for per-file encryption - * - * 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 - -#include <linux/key.h> -#include <linux/fs.h> -#include <linux/mm.h> -#include <linux/bio.h> -#include <linux/dcache.h> -#include <crypto/skcipher.h> -#include <uapi/linux/fs.h> - -#define FS_CRYPTO_BLOCK_SIZE 16 - -struct fscrypt_info; - -struct fscrypt_ctx { - union { - struct { - struct page *bounce_page; /* Ciphertext page */ - struct page *control_page; /* Original page */ - } w; - struct { - struct bio *bio; - struct work_struct work; - } r; - struct list_head free_list; /* Free list */ - }; - u8 flags; /* Flags */ -}; - -/** - * For encrypted symlinks, the ciphertext length is stored at the beginning - * of the string in little-endian format. - */ -struct fscrypt_symlink_data { - __le16 len; - char encrypted_path[1]; -} __packed; - -struct fscrypt_str { - unsigned char *name; - u32 len; -}; - -struct fscrypt_name { - const struct qstr *usr_fname; - struct fscrypt_str disk_name; - u32 hash; - u32 minor_hash; - struct fscrypt_str crypto_buf; -}; - -#define FSTR_INIT(n, l) { .name = n, .len = l } -#define FSTR_TO_QSTR(f) QSTR_INIT((f)->name, (f)->len) -#define fname_name(p) ((p)->disk_name.name) -#define fname_len(p) ((p)->disk_name.len) - -/* - * fscrypt superblock flags - */ -#define FS_CFLG_OWN_PAGES (1U << 1) - -/* - * crypto opertions for filesystems - */ -struct fscrypt_operations { - unsigned int flags; - const char *key_prefix; - 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 *); -}; - -/* Maximum value for the third parameter of fscrypt_operations.set_context(). */ -#define FSCRYPT_SET_CONTEXT_MAX_SIZE 28 - -static inline bool fscrypt_dummy_context_enabled(struct inode *inode) -{ - if (inode->i_sb->s_cop->dummy_context && - inode->i_sb->s_cop->dummy_context(inode)) - return true; - return false; -} - -static inline bool fscrypt_valid_enc_modes(u32 contents_mode, - u32 filenames_mode) -{ - if (contents_mode == FS_ENCRYPTION_MODE_AES_128_CBC && - filenames_mode == FS_ENCRYPTION_MODE_AES_128_CTS) - return true; - - if (contents_mode == FS_ENCRYPTION_MODE_AES_256_XTS && - filenames_mode == FS_ENCRYPTION_MODE_AES_256_CTS) - return true; - - return false; -} - -static inline bool fscrypt_is_dot_dotdot(const struct qstr *str) -{ - if (str->len == 1 && str->name[0] == '.') - return true; - - if (str->len == 2 && str->name[0] == '.' && str->name[1] == '.') - return true; - - return false; -} - -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 - WARN_ON_ONCE(1); - return ERR_PTR(-EINVAL); -#endif -} - -static inline int 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 */ diff --git a/include/linux/fscrypt_notsupp.h b/include/linux/fscrypt_notsupp.h index 19609ceea350..63e58808519a 100644 --- a/include/linux/fscrypt_notsupp.h +++ b/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 */ diff --git a/include/linux/fscrypt_supp.h b/include/linux/fscrypt_supp.h index 5153dce22f09..cf9e9fc02f0a 100644 --- a/include/linux/fscrypt_supp.h +++ b/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 */ |