From: Eric Biggers <ebiggers@xxxxxxxxxx>
IV_INO_LBLK_* exist only because of hardware limitations, and currently
the only known use case for them involves AES-256-XTS. Therefore, for
now only allow them in combination with AES-256-XTS. This way we don't
have to worry about them being combined with other encryption modes.
(To be clear, combining IV_INO_LBLK_* with other encryption modes
*should* work just fine. It's just not being tested, so we can't be
100% sure it works. So with no known use case, it's best to disallow it
for now, just like we don't allow other weird combinations like
AES-256-XTS contents encryption with Adiantum filenames encryption.)
This can be relaxed later if a use case for other combinations arises.
Fixes: b103fb7653ff ("fscrypt: add support for IV_INO_LBLK_64 policies")
Fixes: e3b1078bedd3 ("fscrypt: add support for IV_INO_LBLK_32 policies")
Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
---
fs/crypto/policy.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)
diff --git a/fs/crypto/policy.c b/fs/crypto/policy.c
index 8a8ad0e44bb8..8e667aadf271 100644
--- a/fs/crypto/policy.c
+++ b/fs/crypto/policy.c
@@ -77,6 +77,20 @@ static bool supported_iv_ino_lblk_policy(const struct fscrypt_policy_v2 *policy,
struct super_block *sb = inode->i_sb;
int ino_bits = 64, lblk_bits = 64;
+ /*
+ * IV_INO_LBLK_* exist only because of hardware limitations, and
+ * currently the only known use case for them involves AES-256-XTS.
+ * That's also all we test currently. For these reasons, for now only
+ * allow AES-256-XTS here. This can be relaxed later if a use case for
+ * IV_INO_LBLK_* with other encryption modes arises.
+ */
+ if (policy->contents_encryption_mode != FSCRYPT_MODE_AES_256_XTS) {
+ fscrypt_warn(inode,
+ "Can't use %s policy with contents mode other than AES-256-XTS",
+ type);
+ return false;
+ }
+
/*
* It's unsafe to include inode numbers in the IVs if the filesystem can
* potentially renumber inodes, e.g. via filesystem shrinking.
--
2.27.0
