linux/fs/crypto
Eric Biggers ac4acb1f4b fscrypt: handle test_dummy_encryption in more logical way
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 ed318a6cc0 ("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>
2020-09-22 06:48:49 -07:00
..
bio.c fscrypt: add inline encryption support 2020-07-08 10:29:30 -07:00
crypto.c fscrypt: adjust logging for in-creation inodes 2020-09-22 06:48:38 -07:00
fname.c fscrypt: handle test_dummy_encryption in more logical way 2020-09-22 06:48:49 -07:00
fscrypt_private.h fscrypt: handle test_dummy_encryption in more logical way 2020-09-22 06:48:49 -07:00
hkdf.c fscrypt: use crypto_shash_tfm_digest() 2020-05-08 15:32:14 +10:00
hooks.c fscrypt: handle test_dummy_encryption in more logical way 2020-09-22 06:48:49 -07:00
inline_crypt.c fscrypt: stop pretending that key setup is nofs-safe 2020-09-22 06:48:42 -07:00
Kconfig fscrypt: switch fscrypt_do_sha256() to use the SHA-256 library 2020-07-21 16:02:13 -07:00
keyring.c fscrypt: adjust logging for in-creation inodes 2020-09-22 06:48:38 -07:00
keysetup_v1.c fscrypt: stop pretending that key setup is nofs-safe 2020-09-22 06:48:42 -07:00
keysetup.c fscrypt: handle test_dummy_encryption in more logical way 2020-09-22 06:48:49 -07:00
Makefile fscrypt: add inline encryption support 2020-07-08 10:29:30 -07:00
policy.c fscrypt: handle test_dummy_encryption in more logical way 2020-09-22 06:48:49 -07:00