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git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs
Pull f2fs updates from Jaegeuk Kim:
"In this round, we've made more work into per-file compression support.
For example, F2FS_IOC_GET | SET_COMPRESS_OPTION provides a way to
change the algorithm or cluster size per file. F2FS_IOC_COMPRESS |
DECOMPRESS_FILE provides a way to compress and decompress the existing
normal files manually.
There is also a new mount option, compress_mode=fs|user, which can
control who compresses the data.
Chao also added a checksum feature with a mount option so that
we are able to detect any corrupted cluster.
In addition, Daniel contributed casefolding with encryption patch,
which will be used for Android devices.
Summary:
Enhancements:
- add ioctls and mount option to manage per-file compression feature
- support casefolding with encryption
- support checksum for compressed cluster
- avoid IO starvation by replacing mutex with rwsem
- add sysfs, max_io_bytes, to control max bio size
Bug fixes:
- fix use-after-free issue when compression and fsverity are enabled
- fix consistency corruption during fault injection test
- fix data offset for lseek
- get rid of buffer_head which has 32bits limit in fiemap
- fix some bugs in multi-partitions support
- fix nat entry count calculation in shrinker
- fix some stat information
And, we've refactored some logics and fix minor bugs as well"
* tag 'f2fs-for-5.11-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs: (36 commits)
f2fs: compress: fix compression chksum
f2fs: fix shift-out-of-bounds in sanity_check_raw_super()
f2fs: fix race of pending_pages in decompression
f2fs: fix to account inline xattr correctly during recovery
f2fs: inline: fix wrong inline inode stat
f2fs: inline: correct comment in f2fs_recover_inline_data
f2fs: don't check PAGE_SIZE again in sanity_check_raw_super()
f2fs: convert to F2FS_*_INO macro
f2fs: introduce max_io_bytes, a sysfs entry, to limit bio size
f2fs: don't allow any writes on readonly mount
f2fs: avoid race condition for shrinker count
f2fs: add F2FS_IOC_DECOMPRESS_FILE and F2FS_IOC_COMPRESS_FILE
f2fs: add compress_mode mount option
f2fs: Remove unnecessary unlikely()
f2fs: init dirty_secmap incorrectly
f2fs: remove buffer_head which has 32bits limit
f2fs: fix wrong block count instead of bytes
f2fs: use new conversion functions between blks and bytes
f2fs: rename logical_to_blk and blk_to_logical
f2fs: fix kbytes written stat for multi-device case
...
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This shifts the responsibility of setting up dentry operations from
fscrypt to the individual filesystems, allowing them to have their own
operations while still setting fscrypt's d_revalidate as appropriate.
Most filesystems can just use generic_set_encrypted_ci_d_ops, unless
they have their own specific dentry operations as well. That operation
will set the minimal d_ops required under the circumstances.
Since the fscrypt d_ops are set later on, we must set all d_ops there,
since we cannot adjust those later on. This should not result in any
change in behavior.
Signed-off-by: Daniel Rosenberg <drosen@google.com>
Acked-by: Theodore Ts'o <tytso@mit.edu>
Acked-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
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Currently it's impossible to delete files that use an unsupported
encryption policy, as the kernel will just return an error when
performing any operation on the top-level encrypted directory, even just
a path lookup into the directory or opening the directory for readdir.
More specifically, this occurs in any of the following cases:
- The encryption context has an unrecognized version number. Current
kernels know about v1 and v2, but there could be more versions in the
future.
- The encryption context has unrecognized encryption modes
(FSCRYPT_MODE_*) or flags (FSCRYPT_POLICY_FLAG_*), an unrecognized
combination of modes, or reserved bits set.
- The encryption key has been added and the encryption modes are
recognized but aren't available in the crypto API -- for example, a
directory is encrypted with FSCRYPT_MODE_ADIANTUM but the kernel
doesn't have CONFIG_CRYPTO_ADIANTUM enabled.
It's desirable to return errors for most operations on files that use an
unsupported encryption policy, but the current behavior is too strict.
We need to allow enough to delete files, so that people can't be stuck
with undeletable files when downgrading kernel versions. That includes
allowing directories to be listed and allowing dentries to be looked up.
Fix this by modifying the key setup logic to treat an unsupported
encryption policy in the same way as "key unavailable" in the cases that
are required for a recursive delete to work: preparing for a readdir or
a dentry lookup, revalidating a dentry, or checking whether an inode has
the same encryption policy as its parent directory.
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Link: https://lore.kernel.org/r/20201203022041.230976-10-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Now that fscrypt_get_encryption_info() is only called from files in
fs/crypto/ (due to all key setup now being handled by higher-level
helper functions instead of directly by filesystems), unexport it and
move its declaration to fscrypt_private.h.
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Link: https://lore.kernel.org/r/20201203022041.230976-9-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
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fscrypt_require_key() is now only used by files in fs/crypto/. So
reduce its visibility to fscrypt_private.h. This is also a prerequsite
for unexporting fscrypt_get_encryption_info().
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Link: https://lore.kernel.org/r/20201203022041.230976-8-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
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The stated reasons for separating fscrypt_master_key::mk_secret_sem from
the standard semaphore contained in every 'struct key' no longer apply.
First, due to commit a992b20cd4ee ("fscrypt: add
fscrypt_prepare_new_inode() and fscrypt_set_context()"),
fscrypt_get_encryption_info() is no longer called from within a
filesystem transaction.
Second, due to commit d3ec10aa9581 ("KEYS: Don't write out to userspace
while holding key semaphore"), the semaphore for the "keyring" key type
no longer ranks above page faults.
That leaves performance as the only possible reason to keep the separate
mk_secret_sem. Specifically, having mk_secret_sem reduces the
contention between setup_file_encryption_key() and
FS_IOC_{ADD,REMOVE}_ENCRYPTION_KEY. However, these ioctls aren't
executed often, so this doesn't seem to be worth the extra complexity.
Therefore, simplify the locking design by just using key->sem instead of
mk_secret_sem.
Link: https://lore.kernel.org/r/20201117032626.320275-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
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There isn't really any valid reason to use __FSCRYPT_MODE_MAX or
FSCRYPT_POLICY_FLAGS_VALID in a userspace program. These constants are
only meant to be used by the kernel internally, and they are defined in
the UAPI header next to the mode numbers and flags only so that kernel
developers don't forget to update them when adding new modes or flags.
In https://lkml.kernel.org/r/20201005074133.1958633-2-satyat@google.com
there was an example of someone wanting to use __FSCRYPT_MODE_MAX in a
user program, and it was wrong because the program would have broken if
__FSCRYPT_MODE_MAX were ever increased. So having this definition
available is harmful. FSCRYPT_POLICY_FLAGS_VALID has the same problem.
So, remove these definitions from the UAPI header. Replace
FSCRYPT_POLICY_FLAGS_VALID with just listing the valid flags explicitly
in the one kernel function that needs it. Move __FSCRYPT_MODE_MAX to
fscrypt_private.h, remove the double underscores (which were only
present to discourage use by userspace), and add a BUILD_BUG_ON() and
comments to (hopefully) ensure it is kept in sync.
Keep the old name FS_POLICY_FLAGS_VALID, since it's been around for
longer and there's a greater chance that removing it would break source
compatibility with some program. Indeed, mtd-utils is using it in
an #ifdef, and removing it would introduce compiler warnings (about
FS_POLICY_FLAGS_PAD_* being redefined) into the mtd-utils build.
However, reduce its value to 0x07 so that it only includes the flags
with old names (the ones present before Linux 5.4), and try to make it
clear that it's now "frozen" and no new flags should be added to it.
Fixes: 2336d0deb2d4 ("fscrypt: use FSCRYPT_ prefix for uapi constants")
Cc: <stable@vger.kernel.org> # v5.4+
Link: https://lore.kernel.org/r/20201024005132.495952-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
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The behavior of the test_dummy_encryption mount option is that when a
new file (or directory or symlink) is created in an unencrypted
directory, it's automatically encrypted using a dummy encryption policy.
That's it; in particular, the encryption (or lack thereof) of existing
files (or directories or symlinks) doesn't change.
Unfortunately the implementation of test_dummy_encryption is a bit weird
and confusing. When test_dummy_encryption is enabled and a file is
being created in an unencrypted directory, we set up an encryption key
(->i_crypt_info) for the directory. This isn't actually used to do any
encryption, however, since the directory is still unencrypted! Instead,
->i_crypt_info is only used for inheriting the encryption policy.
One consequence of this is that the filesystem ends up providing a
"dummy context" (policy + nonce) instead of a "dummy policy". In
commit ed318a6cc0b6 ("fscrypt: support test_dummy_encryption=v2"), I
mistakenly thought this was required. However, actually the nonce only
ends up being used to derive a key that is never used.
Another consequence of this implementation is that it allows for
'inode->i_crypt_info != NULL && !IS_ENCRYPTED(inode)', which is an edge
case that can be forgotten about. For example, currently
FS_IOC_GET_ENCRYPTION_POLICY on an unencrypted directory may return the
dummy encryption policy when the filesystem is mounted with
test_dummy_encryption. That seems like the wrong thing to do, since
again, the directory itself is not actually encrypted.
Therefore, switch to a more logical and maintainable implementation
where the dummy encryption policy inheritance is done without setting up
keys for unencrypted directories. This involves:
- Adding a function fscrypt_policy_to_inherit() which returns the
encryption policy to inherit from a directory. This can be a real
policy, a dummy policy, or no policy.
- Replacing struct fscrypt_dummy_context, ->get_dummy_context(), etc.
with struct fscrypt_dummy_policy, ->get_dummy_policy(), etc.
- Making fscrypt_fname_encrypted_size() take an fscrypt_policy instead
of an inode.
Acked-by: Jaegeuk Kim <jaegeuk@kernel.org>
Acked-by: Jeff Layton <jlayton@kernel.org>
Link: https://lore.kernel.org/r/20200917041136.178600-13-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
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The fscrypt UAPI header defines fscrypt_policy to fscrypt_policy_v1,
for source compatibility with old userspace programs.
Internally, the kernel doesn't want that compatibility definition.
Instead, fscrypt_private.h #undefs it and re-defines it to a union.
That works for now. However, in order to add
fscrypt_operations::get_dummy_policy(), we'll need to forward declare
'union fscrypt_policy' in include/linux/fscrypt.h. That would cause
build errors because "fscrypt_policy" is used in ioctl numbers.
To avoid this, modify the UAPI header to make the fscrypt_policy
compatibility definition conditional on !__KERNEL__, and make the ioctls
use fscrypt_policy_v1 instead of fscrypt_policy.
Note that this doesn't change the actual ioctl numbers.
Acked-by: Jeff Layton <jlayton@kernel.org>
Link: https://lore.kernel.org/r/20200917041136.178600-11-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
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fscrypt_get_encryption_info() is intended to be GFP_NOFS-safe. But
actually it isn't, since it uses functions like crypto_alloc_skcipher()
which aren't GFP_NOFS-safe, even when called under memalloc_nofs_save().
Therefore it can deadlock when called from a context that needs
GFP_NOFS, e.g. during an ext4 transaction or between f2fs_lock_op() and
f2fs_unlock_op(). This happens when creating a new encrypted file.
We can't fix this by just not setting up the key for new inodes right
away, since new symlinks need their key to encrypt the symlink target.
So we need to set up the new inode's key before starting the
transaction. But just calling fscrypt_get_encryption_info() earlier
doesn't work, since it assumes the encryption context is already set,
and the encryption context can't be set until the transaction.
The recently proposed fscrypt support for the ceph filesystem
(https://lkml.kernel.org/linux-fscrypt/20200821182813.52570-1-jlayton@kernel.org/T/#u)
will have this same ordering problem too, since ceph will need to
encrypt new symlinks before setting their encryption context.
Finally, f2fs can deadlock when the filesystem is mounted with
'-o test_dummy_encryption' and a new file is created in an existing
unencrypted directory. Similarly, this is caused by holding too many
locks when calling fscrypt_get_encryption_info().
To solve all these problems, add new helper functions:
- fscrypt_prepare_new_inode() sets up a new inode's encryption key
(fscrypt_info), using the parent directory's encryption policy and a
new random nonce. It neither reads nor writes the encryption context.
- fscrypt_set_context() persists the encryption context of a new inode,
using the information from the fscrypt_info already in memory. This
replaces fscrypt_inherit_context().
Temporarily keep fscrypt_inherit_context() around until all filesystems
have been converted to use fscrypt_set_context().
Acked-by: Jeff Layton <jlayton@kernel.org>
Link: https://lore.kernel.org/r/20200917041136.178600-2-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Normally smp_store_release() or cmpxchg_release() is paired with
smp_load_acquire(). Sometimes smp_load_acquire() can be replaced with
the more lightweight READ_ONCE(). However, for this to be safe, all the
published memory must only be accessed in a way that involves the
pointer itself. This may not be the case if allocating the object also
involves initializing a static or global variable, for example.
fscrypt_prepared_key includes a pointer to a crypto_skcipher object,
which is internal to and is allocated by the crypto subsystem. By using
READ_ONCE() for it, we're relying on internal implementation details of
the crypto subsystem.
Remove this fragile assumption by using smp_load_acquire() instead.
(Note: I haven't seen any real-world problems here. This change is just
fixing the code to be guaranteed correct and less fragile.)
Fixes: 5fee36095cda ("fscrypt: add inline encryption support")
Cc: Satya Tangirala <satyat@google.com>
Link: https://lore.kernel.org/r/20200721225920.114347-3-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
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The name "FS_KEY_DERIVATION_NONCE_SIZE" is a bit outdated since due to
the addition of FSCRYPT_POLICY_FLAG_DIRECT_KEY, the file nonce may now
be used as a tweak instead of for key derivation. Also, we're now
prefixing the fscrypt constants with "FSCRYPT_" instead of "FS_".
Therefore, rename this constant to FSCRYPT_FILE_NONCE_SIZE.
Link: https://lore.kernel.org/r/20200708215722.147154-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Each HKDF context byte is associated with a specific format of the
remaining part of the application-specific info string. Add comments so
that it's easier to keep track of what these all are.
Link: https://lore.kernel.org/r/20200708215529.146890-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Add support for inline encryption to fs/crypto/. With "inline
encryption", the block layer handles the decryption/encryption as part
of the bio, instead of the filesystem doing the crypto itself via
Linux's crypto API. This model is needed in order to take advantage of
the inline encryption hardware present on most modern mobile SoCs.
To use inline encryption, the filesystem needs to be mounted with
'-o inlinecrypt'. Blk-crypto will then be used instead of the traditional
filesystem-layer crypto whenever possible to encrypt the contents
of any encrypted files in that filesystem. Fscrypt still provides the key
and IV to use, and the actual ciphertext on-disk is still the same;
therefore it's testable using the existing fscrypt ciphertext verification
tests.
Note that since blk-crypto has a fallback to Linux's crypto API, and
also supports all the encryption modes currently supported by fscrypt,
this feature is usable and testable even without actual inline
encryption hardware.
Per-filesystem changes will be needed to set encryption contexts when
submitting bios and to implement the 'inlinecrypt' mount option. This
patch just adds the common code.
Signed-off-by: Satya Tangirala <satyat@google.com>
Reviewed-by: Jaegeuk Kim <jaegeuk@kernel.org>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Link: https://lore.kernel.org/r/20200702015607.1215430-3-satyat@google.com
Co-developed-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
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The eMMC inline crypto standard will only specify 32 DUN bits (a.k.a. IV
bits), unlike UFS's 64. IV_INO_LBLK_64 is therefore not applicable, but
an encryption format which uses one key per policy and permits the
moving of encrypted file contents (as f2fs's garbage collector requires)
is still desirable.
To support such hardware, add a new encryption format IV_INO_LBLK_32
that makes the best use of the 32 bits: the IV is set to
'SipHash-2-4(inode_number) + file_logical_block_number mod 2^32', where
the SipHash key is derived from the fscrypt master key. We hash only
the inode number and not also the block number, because we need to
maintain contiguity of DUNs to merge bios.
Unlike with IV_INO_LBLK_64, with this format IV reuse is possible; this
is unavoidable given the size of the DUN. This means this format should
only be used where the requirements of the first paragraph apply.
However, the hash spreads out the IVs in the whole usable range, and the
use of a keyed hash makes it difficult for an attacker to determine
which files use which IVs.
Besides the above differences, this flag works like IV_INO_LBLK_64 in
that on ext4 it is only allowed if the stable_inodes feature has been
enabled to prevent inode numbers and the filesystem UUID from changing.
Link: https://lore.kernel.org/r/20200515204141.251098-1-ebiggers@kernel.org
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Paul Crowley <paulcrowley@google.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Currently, the test_dummy_encryption mount option (which is used for
encryption I/O testing with xfstests) uses v1 encryption policies, and
it relies on userspace inserting a test key into the session keyring.
We need test_dummy_encryption to support v2 encryption policies too.
Requiring userspace to add the test key doesn't work well with v2
policies, since v2 policies only support the filesystem keyring (not the
session keyring), and keys in the filesystem keyring are lost when the
filesystem is unmounted. Hooking all test code that unmounts and
re-mounts the filesystem would be difficult.
Instead, let's make the filesystem automatically add the test key to its
keyring when test_dummy_encryption is enabled.
That puts the responsibility for choosing the test key on the kernel.
We could just hard-code a key. But out of paranoia, let's first try
using a per-boot random key, to prevent this code from being misused.
A per-boot key will work as long as no one expects dummy-encrypted files
to remain accessible after a reboot. (gce-xfstests doesn't.)
Therefore, this patch adds a function fscrypt_add_test_dummy_key() which
implements the above. The next patch will use it.
Link: https://lore.kernel.org/r/20200512233251.118314-3-ebiggers@kernel.org
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Remove the unnecessary 'extern' keywords from function declarations.
This makes it so that we don't have a mix of both styles, so it won't be
ambiguous what to use in new fscrypt patches. This also makes the code
shorter and matches the 'checkpatch --strict' expectation.
Link: https://lore.kernel.org/r/20200511191358.53096-4-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Fix all kerneldoc warnings in fs/crypto/ and include/linux/fscrypt.h.
Most of these were due to missing documentation for function parameters.
Detected with:
scripts/kernel-doc -v -none fs/crypto/*.{c,h} include/linux/fscrypt.h
This cleanup makes it possible to check new patches for kerneldoc
warnings without having to filter out all the existing ones.
For consistency, also adjust some function "brief descriptions" to
include the parentheses and to wrap at 80 characters. (The latter
matches the checkpatch expectation.)
Link: https://lore.kernel.org/r/20200511191358.53096-2-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Add an ioctl FS_IOC_GET_ENCRYPTION_NONCE which retrieves the nonce from
an encrypted file or directory. The nonce is the 16-byte random value
stored in the inode's encryption xattr. It is normally used together
with the master key to derive the inode's actual encryption key.
The nonces are needed by automated tests that verify the correctness of
the ciphertext on-disk. Except for the IV_INO_LBLK_64 case, there's no
way to replicate a file's ciphertext without knowing that file's nonce.
The nonces aren't secret, and the existing ciphertext verification tests
in xfstests retrieve them from disk using debugfs or dump.f2fs. But in
environments that lack these debugging tools, getting the nonces by
manually parsing the filesystem structure would be very hard.
To make this important type of testing much easier, let's just add an
ioctl that retrieves the nonce.
Link: https://lore.kernel.org/r/20200314205052.93294-2-ebiggers@kernel.org
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Now that there's sometimes a second type of per-file key (the dirhash
key), clarify some function names, macros, and documentation that
specifically deal with per-file *encryption* keys.
Link: https://lore.kernel.org/r/20200120223201.241390-4-ebiggers@kernel.org
Reviewed-by: Daniel Rosenberg <drosen@google.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
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When we allow indexed directories to use both encryption and
casefolding, for the dirhash we can't just hash the ciphertext filenames
that are stored on-disk (as is done currently) because the dirhash must
be case insensitive, but the stored names are case-preserving. Nor can
we hash the plaintext names with an unkeyed hash (or a hash keyed with a
value stored on-disk like ext4's s_hash_seed), since that would leak
information about the names that encryption is meant to protect.
Instead, if we can accept a dirhash that's only computable when the
fscrypt key is available, we can hash the plaintext names with a keyed
hash using a secret key derived from the directory's fscrypt master key.
We'll use SipHash-2-4 for this purpose.
Prepare for this by deriving a SipHash key for each casefolded encrypted
directory. Make sure to handle deriving the key not only when setting
up the directory's fscrypt_info, but also in the case where the casefold
flag is enabled after the fscrypt_info was already set up. (We could
just always derive the key regardless of casefolding, but that would
introduce unnecessary overhead for people not using casefolding.)
Signed-off-by: Daniel Rosenberg <drosen@google.com>
[EB: improved commit message, updated fscrypt.rst, squashed with change
that avoids unnecessarily deriving the key, and many other cleanups]
Link: https://lore.kernel.org/r/20200120223201.241390-3-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
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fname_encrypt() is a global function, due to being used in both fname.c
and hooks.c. So it should be prefixed with "fscrypt_", like all the
other global functions in fs/crypto/.
Link: https://lore.kernel.org/r/20200120071736.45915-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
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fscrypt_is_direct_key_policy() is no longer used, so remove it.
Link: https://lore.kernel.org/r/20191209211829.239800-5-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
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fscrypt_valid_enc_modes() is only used by policy.c, so move it to there.
Also adjust the order of the checks to be more natural, matching the
numerical order of the constants and also keeping AES-256 (the
recommended default) first in the list.
No change in behavior.
Link: https://lore.kernel.org/r/20191209211829.239800-4-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
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FSCRYPT_POLICY_FLAG_DIRECT_KEY is currently only allowed with Adiantum
encryption. But FS_IOC_SET_ENCRYPTION_POLICY allowed it in combination
with other encryption modes, and an error wasn't reported until later
when the encrypted directory was actually used.
Fix it to report the error earlier by validating the correct use of the
DIRECT_KEY flag in fscrypt_supported_policy(), similar to how we
validate the IV_INO_LBLK_64 flag.
Link: https://lore.kernel.org/r/20191209211829.239800-3-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
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fscrypt_d_revalidate() and fscrypt_d_ops really belong in fname.c, since
they're specific to filenames encryption. crypto.c is for contents
encryption and general fs/crypto/ initialization and utilities.
Link: https://lore.kernel.org/r/20191209204359.228544-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Constify the struct inode parameter to fscrypt_fname_disk_to_usr() and
the other filename encryption functions so that users don't have to pass
in a non-const inode when they are dealing with a const one, as in [1].
[1] https://lkml.kernel.org/linux-ext4/20191203051049.44573-6-drosen@google.com/
Cc: Daniel Rosenberg <drosen@google.com>
Link: https://lore.kernel.org/r/20191215213947.9521-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Constify the struct fscrypt_hkdf parameter to fscrypt_hkdf_expand().
This makes it clearer that struct fscrypt_hkdf contains the key only,
not any per-request state.
Link: https://lore.kernel.org/r/20191209204054.227736-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Inline encryption hardware compliant with the UFS v2.1 standard or with
the upcoming version of the eMMC standard has the following properties:
(1) Per I/O request, the encryption key is specified by a previously
loaded keyslot. There might be only a small number of keyslots.
(2) Per I/O request, the starting IV is specified by a 64-bit "data unit
number" (DUN). IV bits 64-127 are assumed to be 0. The hardware
automatically increments the DUN for each "data unit" of
configurable size in the request, e.g. for each filesystem block.
Property (1) makes it inefficient to use the traditional fscrypt
per-file keys. Property (2) precludes the use of the existing
DIRECT_KEY fscrypt policy flag, which needs at least 192 IV bits.
Therefore, add a new fscrypt policy flag IV_INO_LBLK_64 which causes the
encryption to modified as follows:
- The encryption keys are derived from the master key, encryption mode
number, and filesystem UUID.
- The IVs are chosen as (inode_number << 32) | file_logical_block_num.
For filenames encryption, file_logical_block_num is 0.
Since the file nonces aren't used in the key derivation, many files may
share the same encryption key. This is much more efficient on the
target hardware. Including the inode number in the IVs and mixing the
filesystem UUID into the keys ensures that data in different files is
nevertheless still encrypted differently.
Additionally, limiting the inode and block numbers to 32 bits and
placing the block number in the low bits maintains compatibility with
the 64-bit DUN convention (property (2) above).
Since this scheme assumes that inode numbers are stable (which may
preclude filesystem shrinking) and that inode and file logical block
numbers are at most 32-bit, IV_INO_LBLK_64 will only be allowed on
filesystems that meet these constraints. These are acceptable
limitations for the cases where this format would actually be used.
Note that IV_INO_LBLK_64 is an on-disk format, not an implementation.
This patch just adds support for it using the existing filesystem layer
encryption. A later patch will add support for inline encryption.
Reviewed-by: Paul Crowley <paulcrowley@google.com>
Co-developed-by: Satya Tangirala <satyat@google.com>
Signed-off-by: Satya Tangirala <satyat@google.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
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The access to logged_impl_name is technically a data race, which tools
like KCSAN could complain about in the future. See:
https://github.com/google/ktsan/wiki/READ_ONCE-and-WRITE_ONCE
Fix by using xchg(), which also ensures that only one thread does the
logging.
This also required switching from bool to int, to avoid a build error on
the RISC-V architecture which doesn't implement xchg on bytes.
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Now that ext4 and f2fs implement their own post-read workflow that
supports both fscrypt and fsverity, the fscrypt-only workflow based
around struct fscrypt_ctx is no longer used. So remove the unused code.
This is based on a patch from Chandan Rajendra's "Consolidate FS read
I/O callbacks code" patchset, but rebased onto the latest kernel, folded
__fscrypt_decrypt_bio() into fscrypt_decrypt_bio(), cleaned up
fscrypt_initialize(), and updated the commit message.
Originally-from: Chandan Rajendra <chandan@linux.ibm.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Instead of open-coding the calculations for ESSIV handling, use an ESSIV
skcipher which does all of this under the hood. ESSIV was added to the
crypto API in v5.4.
This is based on a patch from Ard Biesheuvel, but reworked to apply
after all the fscrypt changes that went into v5.4.
Tested with 'kvm-xfstests -c ext4,f2fs -g encrypt', including the
ciphertext verification tests for v1 and v2 encryption policies.
Originally-from: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
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By looking up the master keys in a filesystem-level keyring rather than
in the calling processes' key hierarchy, it becomes possible for a user
to set an encryption policy which refers to some key they don't actually
know, then encrypt their files using that key. Cryptographically this
isn't much of a problem, but the semantics of this would be a bit weird.
Thus, enforce that a v2 encryption policy can only be set if the user
has previously added the key, or has capable(CAP_FOWNER).
We tolerate that this problem will continue to exist for v1 encryption
policies, however; there is no way around that.
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Allow the FS_IOC_ADD_ENCRYPTION_KEY and FS_IOC_REMOVE_ENCRYPTION_KEY
ioctls to be used by non-root users to add and remove encryption keys
from the filesystem-level crypto keyrings, subject to limitations.
Motivation: while privileged fscrypt key management is sufficient for
some users (e.g. Android and Chromium OS, where a privileged process
manages all keys), the old API by design also allows non-root users to
set up and use encrypted directories, and we don't want to regress on
that. Especially, we don't want to force users to continue using the
old API, running into the visibility mismatch between files and keyrings
and being unable to "lock" encrypted directories.
Intuitively, the ioctls have to be privileged since they manipulate
filesystem-level state. However, it's actually safe to make them
unprivileged if we very carefully enforce some specific limitations.
First, each key must be identified by a cryptographic hash so that a
user can't add the wrong key for another user's files. For v2
encryption policies, we use the key_identifier for this. v1 policies
don't have this, so managing keys for them remains privileged.
Second, each key a user adds is charged to their quota for the keyrings
service. Thus, a user can't exhaust memory by adding a huge number of
keys. By default each non-root user is allowed up to 200 keys; this can
be changed using the existing sysctl 'kernel.keys.maxkeys'.
Third, if multiple users add the same key, we keep track of those users
of the key (of which there remains a single copy), and won't really
remove the key, i.e. "lock" the encrypted files, until all those users
have removed it. This prevents denial of service attacks that would be
possible under simpler schemes, such allowing the first user who added a
key to remove it -- since that could be a malicious user who has
compromised the key. Of course, encryption keys should be kept secret,
but the idea is that using encryption should never be *less* secure than
not using encryption, even if your key was compromised.
We tolerate that a user will be unable to really remove a key, i.e.
unable to "lock" their encrypted files, if another user has added the
same key. But in a sense, this is actually a good thing because it will
avoid providing a false notion of security where a key appears to have
been removed when actually it's still in memory, available to any
attacker who compromises the operating system kernel.
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Add a new fscrypt policy version, "v2". It has the following changes
from the original policy version, which we call "v1" (*):
- Master keys (the user-provided encryption keys) are only ever used as
input to HKDF-SHA512. This is more flexible and less error-prone, and
it avoids the quirks and limitations of the AES-128-ECB based KDF.
Three classes of cryptographically isolated subkeys are defined:
- Per-file keys, like used in v1 policies except for the new KDF.
- Per-mode keys. These implement the semantics of the DIRECT_KEY
flag, which for v1 policies made the master key be used directly.
These are also planned to be used for inline encryption when
support for it is added.
- Key identifiers (see below).
- Each master key is identified by a 16-byte master_key_identifier,
which is derived from the key itself using HKDF-SHA512. This prevents
users from associating the wrong key with an encrypted file or
directory. This was easily possible with v1 policies, which
identified the key by an arbitrary 8-byte master_key_descriptor.
- The key must be provided in the filesystem-level keyring, not in a
process-subscribed keyring.
The following UAPI additions are made:
- The existing ioctl FS_IOC_SET_ENCRYPTION_POLICY can now be passed a
fscrypt_policy_v2 to set a v2 encryption policy. It's disambiguated
from fscrypt_policy/fscrypt_policy_v1 by the version code prefix.
- A new ioctl FS_IOC_GET_ENCRYPTION_POLICY_EX is added. It allows
getting the v1 or v2 encryption policy of an encrypted file or
directory. The existing FS_IOC_GET_ENCRYPTION_POLICY ioctl could not
be used because it did not have a way for userspace to indicate which
policy structure is expected. The new ioctl includes a size field, so
it is extensible to future fscrypt policy versions.
- The ioctls FS_IOC_ADD_ENCRYPTION_KEY, FS_IOC_REMOVE_ENCRYPTION_KEY,
and FS_IOC_GET_ENCRYPTION_KEY_STATUS now support managing keys for v2
encryption policies. Such keys are kept logically separate from keys
for v1 encryption policies, and are identified by 'identifier' rather
than by 'descriptor'. The 'identifier' need not be provided when
adding a key, since the kernel will calculate it anyway.
This patch temporarily keeps adding/removing v2 policy keys behind the
same permission check done for adding/removing v1 policy keys:
capable(CAP_SYS_ADMIN). However, the next patch will carefully take
advantage of the cryptographically secure master_key_identifier to allow
non-root users to add/remove v2 policy keys, thus providing a full
replacement for v1 policies.
(*) Actually, in the API fscrypt_policy::version is 0 while on-disk
fscrypt_context::format is 1. But I believe it makes the most sense
to advance both to '2' to have them be in sync, and to consider the
numbering to start at 1 except for the API quirk.
Reviewed-by: Paul Crowley <paulcrowley@google.com>
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Add an implementation of HKDF (RFC 5869) to fscrypt, for the purpose of
deriving additional key material from the fscrypt master keys for v2
encryption policies. HKDF is a key derivation function built on top of
HMAC. We choose SHA-512 for the underlying unkeyed hash, and use an
"hmac(sha512)" transform allocated from the crypto API.
We'll be using this to replace the AES-ECB based KDF currently used to
derive the per-file encryption keys. While the AES-ECB based KDF is
believed to meet the original security requirements, it is nonstandard
and has problems that don't exist in modern KDFs such as HKDF:
1. It's reversible. Given a derived key and nonce, an attacker can
easily compute the master key. This is okay if the master key and
derived keys are equally hard to compromise, but now we'd like to be
more robust against threats such as a derived key being compromised
through a timing attack, or a derived key for an in-use file being
compromised after the master key has already been removed.
2. It doesn't evenly distribute the entropy from the master key; each 16
input bytes only affects the corresponding 16 output bytes.
3. It isn't easily extensible to deriving other values or keys, such as
a public hash for securely identifying the key, or per-mode keys.
Per-mode keys will be immediately useful for Adiantum encryption, for
which fscrypt currently uses the master key directly, introducing
unnecessary usage constraints. Per-mode keys will also be useful for
hardware inline encryption, which is currently being worked on.
HKDF solves all the above problems.
Reviewed-by: Paul Crowley <paulcrowley@google.com>
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Add a new fscrypt ioctl, FS_IOC_REMOVE_ENCRYPTION_KEY. This ioctl
removes an encryption key that was added by FS_IOC_ADD_ENCRYPTION_KEY.
It wipes the secret key itself, then "locks" the encrypted files and
directories that had been unlocked using that key -- implemented by
evicting the relevant dentries and inodes from the VFS caches.
The problem this solves is that many fscrypt users want the ability to
remove encryption keys, causing the corresponding encrypted directories
to appear "locked" (presented in ciphertext form) again. Moreover,
users want removing an encryption key to *really* remove it, in the
sense that the removed keys cannot be recovered even if kernel memory is
compromised, e.g. by the exploit of a kernel security vulnerability or
by a physical attack. This is desirable after a user logs out of the
system, for example. In many cases users even already assume this to be
the case and are surprised to hear when it's not.
It is not sufficient to simply unlink the master key from the keyring
(or to revoke or invalidate it), since the actual encryption transform
objects are still pinned in memory by their inodes. Therefore, to
really remove a key we must also evict the relevant inodes.
Currently one workaround is to run 'sync && echo 2 >
/proc/sys/vm/drop_caches'. But, that evicts all unused inodes in the
system rather than just the inodes associated with the key being
removed, causing severe performance problems. Moreover, it requires
root privileges, so regular users can't "lock" their encrypted files.
Another workaround, used in Chromium OS kernels, is to add a new
VFS-level ioctl FS_IOC_DROP_CACHE which is a more restricted version of
drop_caches that operates on a single super_block. It does:
shrink_dcache_sb(sb);
invalidate_inodes(sb, false);
But it's still a hack. Yet, the major users of filesystem encryption
want this feature badly enough that they are actually using these hacks.
To properly solve the problem, start maintaining a list of the inodes
which have been "unlocked" using each master key. Originally this
wasn't possible because the kernel didn't keep track of in-use master
keys at all. But, with the ->s_master_keys keyring it is now possible.
Then, add an ioctl FS_IOC_REMOVE_ENCRYPTION_KEY. It finds the specified
master key in ->s_master_keys, then wipes the secret key itself, which
prevents any additional inodes from being unlocked with the key. Then,
it syncs the filesystem and evicts the inodes in the key's list. The
normal inode eviction code will free and wipe the per-file keys (in
->i_crypt_info). Note that freeing ->i_crypt_info without evicting the
inodes was also considered, but would have been racy.
Some inodes may still be in use when a master key is removed, and we
can't simply revoke random file descriptors, mmap's, etc. Thus, the
ioctl simply skips in-use inodes, and returns -EBUSY to indicate that
some inodes weren't evicted. The master key *secret* is still removed,
but the fscrypt_master_key struct remains to keep track of the remaining
inodes. Userspace can then retry the ioctl to evict the remaining
inodes. Alternatively, if userspace adds the key again, the refreshed
secret will be associated with the existing list of inodes so they
remain correctly tracked for future key removals.
The ioctl doesn't wipe pagecache pages. Thus, we tolerate that after a
kernel compromise some portions of plaintext file contents may still be
recoverable from memory. This can be solved by enabling page poisoning
system-wide, which security conscious users may choose to do. But it's
very difficult to solve otherwise, e.g. note that plaintext file
contents may have been read in other places than pagecache pages.
Like FS_IOC_ADD_ENCRYPTION_KEY, FS_IOC_REMOVE_ENCRYPTION_KEY is
initially restricted to privileged users only. This is sufficient for
some use cases, but not all. A later patch will relax this restriction,
but it will require introducing key hashes, among other changes.
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Add a new fscrypt ioctl, FS_IOC_ADD_ENCRYPTION_KEY. This ioctl adds an
encryption key to the filesystem's fscrypt keyring ->s_master_keys,
making any files encrypted with that key appear "unlocked".
Why we need this
~~~~~~~~~~~~~~~~
The main problem is that the "locked/unlocked" (ciphertext/plaintext)
status of encrypted files is global, but the fscrypt keys are not.
fscrypt only looks for keys in the keyring(s) the process accessing the
filesystem is subscribed to: the thread keyring, process keyring, and
session keyring, where the session keyring may contain the user keyring.
Therefore, userspace has to put fscrypt keys in the keyrings for
individual users or sessions. But this means that when a process with a
different keyring tries to access encrypted files, whether they appear
"unlocked" or not is nondeterministic. This is because it depends on
whether the files are currently present in the inode cache.
Fixing this by consistently providing each process its own view of the
filesystem depending on whether it has the key or not isn't feasible due
to how the VFS caches work. Furthermore, while sometimes users expect
this behavior, it is misguided for two reasons. First, it would be an
OS-level access control mechanism largely redundant with existing access
control mechanisms such as UNIX file permissions, ACLs, LSMs, etc.
Encryption is actually for protecting the data at rest.
Second, almost all users of fscrypt actually do need the keys to be
global. The largest users of fscrypt, Android and Chromium OS, achieve
this by having PID 1 create a "session keyring" that is inherited by
every process. This works, but it isn't scalable because it prevents
session keyrings from being used for any other purpose.
On general-purpose Linux distros, the 'fscrypt' userspace tool [1] can't
similarly abuse the session keyring, so to make 'sudo' work on all
systems it has to link all the user keyrings into root's user keyring
[2]. This is ugly and raises security concerns. Moreover it can't make
the keys available to system services, such as sshd trying to access the
user's '~/.ssh' directory (see [3], [4]) or NetworkManager trying to
read certificates from the user's home directory (see [5]); or to Docker
containers (see [6], [7]).
By having an API to add a key to the *filesystem* we'll be able to fix
the above bugs, remove userspace workarounds, and clearly express the
intended semantics: the locked/unlocked status of an encrypted directory
is global, and encryption is orthogonal to OS-level access control.
Why not use the add_key() syscall
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We use an ioctl for this API rather than the existing add_key() system
call because the ioctl gives us the flexibility needed to implement
fscrypt-specific semantics that will be introduced in later patches:
- Supporting key removal with the semantics such that the secret is
removed immediately and any unused inodes using the key are evicted;
also, the eviction of any in-use inodes can be retried.
- Calculating a key-dependent cryptographic identifier and returning it
to userspace.
- Allowing keys to be added and removed by non-root users, but only keys
for v2 encryption policies; and to prevent denial-of-service attacks,
users can only remove keys they themselves have added, and a key is
only really removed after all users who added it have removed it.
Trying to shoehorn these semantics into the keyrings syscalls would be
very difficult, whereas the ioctls make things much easier.
However, to reuse code the implementation still uses the keyrings
service internally. Thus we get lockless RCU-mode key lookups without
having to re-implement it, and the keys automatically show up in
/proc/keys for debugging purposes.
References:
[1] https://github.com/google/fscrypt
[2] https://goo.gl/55cCrI#heading=h.vf09isp98isb
[3] https://github.com/google/fscrypt/issues/111#issuecomment-444347939
[4] https://github.com/google/fscrypt/issues/116
[5] https://bugs.launchpad.net/ubuntu/+source/fscrypt/+bug/1770715
[6] https://github.com/google/fscrypt/issues/128
[7] https://askubuntu.com/questions/1130306/cannot-run-docker-on-an-encrypted-filesystem
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Rename keyinfo.c to keysetup.c since this better describes what the file
does (sets up the key), and it matches the new file keysetup_v1.c.
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
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In preparation for introducing v2 encryption policies which will find
and derive encryption keys differently from the current v1 encryption
policies, move the v1 policy-specific key setup code from keyinfo.c into
keysetup_v1.c.
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Do some more refactoring of the key setup code, in preparation for
introducing a filesystem-level keyring and v2 encryption policies:
- Now that ci_inode exists, don't pass around the inode unnecessarily.
- Define a function setup_file_encryption_key() which handles the crypto
key setup given an under-construction fscrypt_info. Don't pass the
fscrypt_context, since everything is in the fscrypt_info.
[This will be extended for v2 policies and the fs-level keyring.]
- Define a function fscrypt_set_derived_key() which sets the per-file
key, without depending on anything specific to v1 policies.
[This will also be used for v2 policies.]
- Define a function fscrypt_setup_v1_file_key() which takes the raw
master key, thus separating finding the key from using it.
[This will also be used if the key is found in the fs-level keyring.]
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
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In preparation for introducing a filesystem-level keyring which will
contain fscrypt master keys, rename the existing 'struct
fscrypt_master_key' to 'struct fscrypt_direct_key'. This is the
structure in the existing table of master keys that's maintained to
deduplicate the crypto transforms for v1 DIRECT_KEY policies.
I've chosen to keep this table as-is rather than make it automagically
add/remove the keys to/from the filesystem-level keyring, since that
would add a lot of extra complexity to the filesystem-level keyring.
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Add an inode back-pointer to 'struct fscrypt_info', such that
inode->i_crypt_info->ci_inode == inode.
This will be useful for:
1. Evicting the inodes when a fscrypt key is removed, since we'll track
the inodes using a given key by linking their fscrypt_infos together,
rather than the inodes directly. This avoids bloating 'struct inode'
with a new list_head.
2. Simplifying the per-file key setup, since the inode pointer won't
have to be passed around everywhere just in case something goes wrong
and it's needed for fscrypt_warn().
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Update fs/crypto/ to use the new names for the UAPI constants rather
than the old names, then make the old definitions conditional on
!__KERNEL__.
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Most of the warning and error messages in fs/crypto/ are for situations
related to a specific inode, not merely to a super_block. So to make
things easier, make fscrypt_msg() take an inode rather than a
super_block, and make it print the inode number.
Note: This is the same approach I'm taking for fsverity_msg().
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Since commit 643fa9612bf1 ("fscrypt: remove filesystem specific build
config option"), fs/crypto/ can no longer be built as a loadable module.
Thus it no longer needs a module_exit function, nor a MODULE_LICENSE.
So remove them, and change module_init to late_initcall.
Reviewed-by: Chandan Rajendra <chandan@linux.ibm.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
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fscrypt_do_page_crypto() only does a single encryption or decryption
operation, with a single logical block number (single IV). So it
actually operates on a filesystem block, not a "page" per se. To
reflect this, rename it to fscrypt_crypt_block().
Reviewed-by: Chandan Rajendra <chandan@linux.ibm.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Currently, bounce page handling for writes to encrypted files is
unnecessarily complicated. A fscrypt_ctx is allocated along with each
bounce page, page_private(bounce_page) points to this fscrypt_ctx, and
fscrypt_ctx::w::control_page points to the original pagecache page.
However, because writes don't use the fscrypt_ctx for anything else,
there's no reason why page_private(bounce_page) can't just point to the
original pagecache page directly.
Therefore, this patch makes this change. In the process, it also cleans
up the API exposed to filesystems that allows testing whether a page is
a bounce page, getting the pagecache page from a bounce page, and
freeing a bounce page.
Reviewed-by: Chandan Rajendra <chandan@linux.ibm.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
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In order to have a common code base for fscrypt "post read" processing
for all filesystems which support encryption, this commit removes
filesystem specific build config option (e.g. CONFIG_EXT4_FS_ENCRYPTION)
and replaces it with a build option (i.e. CONFIG_FS_ENCRYPTION) whose
value affects all the filesystems making use of fscrypt.
Reviewed-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Chandan Rajendra <chandan@linux.vnet.ibm.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Add support for the Adiantum encryption mode to fscrypt. Adiantum is a
tweakable, length-preserving encryption mode with security provably
reducible to that of XChaCha12 and AES-256, subject to a security bound.
It's also a true wide-block mode, unlike XTS. See the paper
"Adiantum: length-preserving encryption for entry-level processors"
(https://eprint.iacr.org/2018/720.pdf) for more details. Also see
commit 059c2a4d8e16 ("crypto: adiantum - add Adiantum support").
On sufficiently long messages, Adiantum's bottlenecks are XChaCha12 and
the NH hash function. These algorithms are fast even on processors
without dedicated crypto instructions. Adiantum makes it feasible to
enable storage encryption on low-end mobile devices that lack AES
instructions; currently such devices are unencrypted. On ARM Cortex-A7,
on 4096-byte messages Adiantum encryption is about 4 times faster than
AES-256-XTS encryption; decryption is about 5 times faster.
In fscrypt, Adiantum is suitable for encrypting both file contents and
names. With filenames, it fixes a known weakness: when two filenames in
a directory share a common prefix of >= 16 bytes, with CTS-CBC their
encrypted filenames share a common prefix too, leaking information.
Adiantum does not have this problem.
Since Adiantum also accepts long tweaks (IVs), it's also safe to use the
master key directly for Adiantum encryption rather than deriving
per-file keys, provided that the per-file nonce is included in the IVs
and the master key isn't used for any other encryption mode. This
configuration saves memory and improves performance. A new fscrypt
policy flag is added to allow users to opt-in to this configuration.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
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