fscrypt: fix keyring memory leak on mount failure

Commit d7e7b9af104c ("fscrypt: stop using keyrings subsystem for
fscrypt_master_key") moved the keyring destruction from __put_super() to
generic_shutdown_super() so that the filesystem's block device(s) are
still available.  Unfortunately, this causes a memory leak in the case
where a mount is attempted with the test_dummy_encryption mount option,
but the mount fails after the option has already been processed.

To fix this, attempt the keyring destruction in both places.

Reported-by: syzbot+104c2a89561289cec13e@syzkaller.appspotmail.com
Fixes: d7e7b9af104c ("fscrypt: stop using keyrings subsystem for fscrypt_master_key")
Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Link: https://lore.kernel.org/r/20221011213838.209879-1-ebiggers@kernel.org

1 files changed, 11 insertions, 6 deletions

diff --git a/fs/crypto/keyring.c b/fs/crypto/keyring.c
index 1cca09aa43f8..2a24b1f0ae68 100644
--- a/fs/crypto/keyring.c
+++ b/fs/crypto/keyring.c
@@ -205,14 +205,19 @@ static int allocate_filesystem_keyring(struct super_block *sb)
 }
 
 /*
- * This is called at unmount time to release all encryption keys that have been
- * added to the filesystem, along with the keyring that contains them.
+ * Release all encryption keys that have been added to the filesystem, along
+ * with the keyring that contains them.
  *
- * Note that besides clearing and freeing memory, this might need to evict keys
- * from the keyslots of an inline crypto engine.  Therefore, this must be called
- * while the filesystem's underlying block device(s) are still available.
+ * This is called at unmount time.  The filesystem's underlying block device(s)
+ * are still available at this time; this is important because after user file
+ * accesses have been allowed, this function may need to evict keys from the
+ * keyslots of an inline crypto engine, which requires the block device(s).
+ *
+ * This is also called when the super_block is being freed.  This is needed to
+ * avoid a memory leak if mounting fails after the "test_dummy_encryption"
+ * option was processed, as in that case the unmount-time call isn't made.
  */
-void fscrypt_sb_delete(struct super_block *sb)
+void fscrypt_destroy_keyring(struct super_block *sb)
 {
 	struct fscrypt_keyring *keyring = sb->s_master_keys;
 	size_t i;