keys: ensure that ->match_free() is called in request_key_and_link()

If check_cached_key() returns a non-NULL value, we still need to call
key_type::match_free() to undo key_type::match_preparse().

Fixes: 7743c48e ("keys: Cache result of request_key*() temporarily in task_struct")
Signed-off-by: NEric Biggers <ebiggers@google.com>
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

security/keys/request_key.c

@@ -595,7 +595,7 @@ struct key *request_key_and_link(struct key_type *type,
 
 	key = check_cached_key(&ctx);
 	if (key)
-		return key;
+		goto error_free;
 
 	/* search all the process keyrings for a key */
 	rcu_read_lock();