The legacy 'fscrypt_direct_keys' table caches master keys that are used
by v1 encryption policies that have FSCRYPT_POLICY_FLAG_DIRECT_KEY.
It's just a global table for all filesystems (since the keys can be
provided by the legacy process-subscribed keyrings mechanism, which
makes it difficult to reuse super_block::s_master_keys).
The entries in it ('struct fscrypt_direct_key') do contain a super_block
pointer, though, for passing to fscrypt_destroy_inline_crypt_key() when
the last inode that references the key is evicted.
However, when finding the fscrypt_direct_key for an inode, we weren't
actually comparing the super_block pointer. As a result, inodes with
different super_blocks could point to the same fscrypt_direct_key. That
could extend the lifetime of a fscrypt_direct_key beyond the
super_block it points to, causing a use-after-free later.
Fix this by creating distinct fscrypt_direct_key structs for distinct
super_block structs.
Note that this problem doesn't exist in the v2 policy equivalent
("per-mode keys"), since the data structures there are per super_block.
Fixes: 22e9947a4b2b ("fscrypt: stop holding extra request_queue references")
Cc: [email protected]
Signed-off-by: Eric Biggers <[email protected]>
---
fs/crypto/keysetup_v1.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/fs/crypto/keysetup_v1.c b/fs/crypto/keysetup_v1.c
index e6e527c73f167..7e3a58dc4b566 100644
--- a/fs/crypto/keysetup_v1.c
+++ b/fs/crypto/keysetup_v1.c
@@ -147,13 +147,19 @@ find_or_insert_direct_key(struct fscrypt_direct_key
*to_insert,
if (memcmp(ci->ci_policy.v1.master_key_descriptor,
dk->dk_descriptor, FSCRYPT_KEY_DESCRIPTOR_SIZE) != 0)
continue;
+ /* The sb is used at eviction time, so it must be the same. */
+ if (ci->ci_inode->i_sb != dk->dk_sb)
+ continue;
if (ci->ci_mode != dk->dk_mode)
continue;
if (!fscrypt_is_key_prepared(&dk->dk_key, ci))
continue;
if (crypto_memneq(raw_key, dk->dk_raw, ci->ci_mode->keysize))
continue;
- /* using existing tfm with same (descriptor, mode, raw_key) */
+ /*
+ * Use an existing prepared key with the same (descriptor, sb,
+ * mode, inlinecrypt, raw_key) combination.
+ */
refcount_inc(&dk->dk_refcount);
spin_unlock(&fscrypt_direct_keys_lock);
free_direct_key(to_insert);
base-commit: f2ec6312bf711369561bdcb22f8a63c0b118c479
--
2.55.0
