To mitigate some types of offline attacks, filesystem encryption is
designed to enforce that all files in an encrypted directory tree use
the same encryption policy (i.e. the same encryption context excluding
the nonce). However, the fscrypt_has_permitted_context() function which
enforces this relies on comparing struct fscrypt_info's, which are only
available when we have the encryption keys. This can cause two
incorrect behaviors:
1. If we have the parent directory's key but not the child's key, or
vice versa, then fscrypt_has_permitted_context() returned false,
causing applications to see EPERM or ENOKEY. This is incorrect if
the encryption contexts are in fact consistent. Although we'd
normally have either both keys or neither key in that case since the
master_key_descriptors would be the same, this is not guaranteed
because keys can be added or removed from keyrings at any time.
2. If we have neither the parent's key nor the child's key, then
fscrypt_has_permitted_context() returned true, causing applications
to see no error (or else an error for some other reason). This is
incorrect if the encryption contexts are in fact inconsistent, since
in that case we should deny access.
To fix this, retrieve and compare the fscrypt_contexts if we are unable
to set up both fscrypt_infos.
While this slightly hurts performance when accessing an encrypted
directory tree without the key, this isn't a case we really need to be
optimizing for; access *with* the key is much more important.
Furthermore, the performance hit is barely noticeable given that we are
already retrieving the fscrypt_context and doing two keyring searches in
fscrypt_get_encryption_info(). If we ever actually wanted to optimize
this case we might start by caching the fscrypt_contexts.
Cc: stable@vger.kernel.org # 4.0+
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
The functions in fs/crypto/*.c are only called by filesystems configured
with encryption support. Since the ->get_context(), ->set_context(),
and ->empty_dir() operations are always provided in that case (and must
be, otherwise there would be no way to get/set encryption policies, or
in the case of ->get_context() even access encrypted files at all),
there is no need to check for these operations being NULL and we can
remove these unneeded checks.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
The only use of the ->prepare_context() fscrypt operation was to allow
ext4 to evict inline data from the inode before ->set_context().
However, there is no reason why this cannot be done as simply the first
step in ->set_context(), and in fact it makes more sense to do it that
way because then the policy modes and flags get validated before any
real work is done. Therefore, merge ext4_prepare_context() into
ext4_set_context(), and remove ->prepare_context().
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Currently, the test_dummy_encryption ext4 mount option, which exists
only to test encrypted I/O paths with xfstests, overrides all
per-inode encryption keys with a fixed key.
This change minimizes test_dummy_encryption-specific code path changes
by supplying a fake context for directories which are not encrypted
for use when creating new directories, files, or symlinks. This
allows us to properly exercise the keyring lookup, derivation, and
context inheritance code paths.
Before mounting a file system using test_dummy_encryption, userspace
must execute the following shell commands:
mode='\x00\x00\x00\x00'
raw="$(printf ""\\\\x%02x"" $(seq 0 63))"
if lscpu | grep "Byte Order" | grep -q Little ; then
size='\x40\x00\x00\x00'
else
size='\x00\x00\x00\x40'
fi
key="${mode}${raw}${size}"
keyctl new_session
echo -n -e "${key}" | keyctl padd logon fscrypt:4242424242424242 @s
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
It was possible for the ->get_context() operation to fail with a
specific error code, which was then not returned to the caller of
FS_IOC_SET_ENCRYPTION_POLICY or FS_IOC_GET_ENCRYPTION_POLICY. Make sure
to pass through these error codes. Also reorganize the code so that
->get_context() only needs to be called one time when setting an
encryption policy, and handle contexts of unrecognized sizes more
appropriately.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Several warning messages were not rate limited and were user-triggerable
from FS_IOC_SET_ENCRYPTION_POLICY. These shouldn't really have been
there in the first place, but either way they aren't as useful now that
the error codes have been improved. So just remove them.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
As part of an effort to clean up fscrypt-related error codes, make
FS_IOC_SET_ENCRYPTION_POLICY fail with EEXIST when the file already uses
a different encryption policy. This is more descriptive than EINVAL,
which was ambiguous with some of the other error cases.
I am not aware of any users who might be relying on the previous error
code of EINVAL, which was never documented anywhere.
This failure case will be exercised by an xfstest.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
As part of an effort to clean up fscrypt-related error codes, make
FS_IOC_SET_ENCRYPTION_POLICY fail with ENOTDIR when the file descriptor
does not refer to a directory. This is more descriptive than EINVAL,
which was ambiguous with some of the other error cases.
I am not aware of any users who might be relying on the previous error
code of EINVAL, which was never documented anywhere, and in some buggy
kernels did not exist at all as the S_ISDIR() check was missing.
This failure case will be exercised by an xfstest.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Attempting to link a device node, named pipe, or socket file into an
encrypted directory through rename(2) or link(2) always failed with
EPERM. This happened because fscrypt_has_permitted_context() saw that
the file was unencrypted and forbid creating the link. This behavior
was unexpected because such files are never encrypted; only regular
files, directories, and symlinks can be encrypted.
To fix this, make fscrypt_has_permitted_context() always return true on
special files.
This will be covered by a test in my encryption xfstests patchset.
Fixes: 9bd8212f98 ("ext4 crypto: add encryption policy and password salt support")
Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Richard Weinberger <richard@nod.at>
Cc: stable@vger.kernel.org
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Multiple bugs were recently fixed in the "set encryption policy" ioctl.
To make it clear that fscrypt_process_policy() and fscrypt_get_policy()
implement ioctls and therefore their implementations must take standard
security and correctness precautions, rename them to
fscrypt_ioctl_set_policy() and fscrypt_ioctl_get_policy(). Make the
latter take in a struct file * to make it consistent with the former.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
i_rwsem needs to be acquired while setting an encryption policy so that
concurrent calls to FS_IOC_SET_ENCRYPTION_POLICY are correctly
serialized (especially the ->get_context() + ->set_context() pair), and
so that new files cannot be created in the directory during or after the
->empty_dir() check.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Richard Weinberger <richard@nod.at>
Cc: stable@vger.kernel.org
Since setting an encryption policy requires writing metadata to the
filesystem, it should be guarded by mnt_want_write/mnt_drop_write.
Otherwise, a user could cause a write to a frozen or readonly
filesystem. This was handled correctly by f2fs but not by ext4. Make
fscrypt_process_policy() handle it rather than relying on the filesystem
to get it right.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Cc: stable@vger.kernel.org # 4.1+; check fs/{ext4,f2fs}
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Acked-by: Jaegeuk Kim <jaegeuk@kernel.org>
The FS_IOC_SET_ENCRYPTION_POLICY ioctl allowed setting an encryption
policy on nondirectory files. This was unintentional, and in the case
of nonempty regular files did not behave as expected because existing
data was not actually encrypted by the ioctl.
In the case of ext4, the user could also trigger filesystem errors in
->empty_dir(), e.g. due to mismatched "directory" checksums when the
kernel incorrectly tried to interpret a regular file as a directory.
This bug affected ext4 with kernels v4.8-rc1 or later and f2fs with
kernels v4.6 and later. It appears that older kernels only permitted
directories and that the check was accidentally lost during the
refactoring to share the file encryption code between ext4 and f2fs.
This patch restores the !S_ISDIR() check that was present in older
kernels.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
On an ext4 or f2fs filesystem with file encryption supported, a user
could set an encryption policy on any empty directory(*) to which they
had readonly access. This is obviously problematic, since such a
directory might be owned by another user and the new encryption policy
would prevent that other user from creating files in their own directory
(for example).
Fix this by requiring inode_owner_or_capable() permission to set an
encryption policy. This means that either the caller must own the file,
or the caller must have the capability CAP_FOWNER.
(*) Or also on any regular file, for f2fs v4.6 and later and ext4
v4.8-rc1 and later; a separate bug fix is coming for that.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Cc: stable@vger.kernel.org # 4.1+; check fs/{ext4,f2fs}
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This patch adds the renamed functions moved from the f2fs crypto files.
1. definitions for per-file encryption used by ext4 and f2fs.
2. crypto.c for encrypt/decrypt functions
a. IO preparation:
- fscrypt_get_ctx / fscrypt_release_ctx
b. before IOs:
- fscrypt_encrypt_page
- fscrypt_decrypt_page
- fscrypt_zeroout_range
c. after IOs:
- fscrypt_decrypt_bio_pages
- fscrypt_pullback_bio_page
- fscrypt_restore_control_page
3. policy.c supporting context management.
a. For ioctls:
- fscrypt_process_policy
- fscrypt_get_policy
b. For context permission
- fscrypt_has_permitted_context
- fscrypt_inherit_context
4. keyinfo.c to handle permissions
- fscrypt_get_encryption_info
- fscrypt_free_encryption_info
5. fname.c to support filename encryption
a. general wrapper functions
- fscrypt_fname_disk_to_usr
- fscrypt_fname_usr_to_disk
- fscrypt_setup_filename
- fscrypt_free_filename
b. specific filename handling functions
- fscrypt_fname_alloc_buffer
- fscrypt_fname_free_buffer
6. Makefile and Kconfig
Cc: Al Viro <viro@ftp.linux.org.uk>
Signed-off-by: Michael Halcrow <mhalcrow@google.com>
Signed-off-by: Ildar Muslukhov <ildarm@google.com>
Signed-off-by: Uday Savagaonkar <savagaon@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Eric Biggers
Theodore Ts'o
Jaegeuk Kim