ext4 crypto: add missing locking for keyring_key access

BugLink: http://bugs.launchpad.net/bugs/1540532

commit db7730e upstream.

Signed-off-by: Theodore Ts'o <[email protected]>
Signed-off-by: Kamal Mostafa <[email protected]>

Author: tytso

fs/ext4/crypto_key.c

@@ -213,9 +213,11 @@ int _ext4_get_encryption_info(struct inode *inode)
 		res = -ENOKEY;
 		goto out;
 	}
+	down_read(&keyring_key->sem);
 	ukp = ((struct user_key_payload *)keyring_key->payload.data);
 	if (ukp->datalen != sizeof(struct ext4_encryption_key)) {
 		res = -EINVAL;
+		up_read(&keyring_key->sem);
 		goto out;
 	}
 	master_key = (struct ext4_encryption_key *)ukp->data;
@@ -226,10 +228,12 @@ int _ext4_get_encryption_info(struct inode *inode)
 			    "ext4: key size incorrect: %d\n",
 			    master_key->size);
 		res = -ENOKEY;
+		up_read(&keyring_key->sem);
 		goto out;
 	}
 	res = ext4_derive_key_aes(ctx.nonce, master_key->raw,
 				  raw_key);
+	up_read(&keyring_key->sem);
 	if (res)
 		goto out;
 got_key: