KEYS: don't revoke uninstantiated key in request_key_auth_new()

If key_instantiate_and_link() were to fail (which fortunately isn't
possible currently), the call to key_revoke(authkey) would crash with a
NULL pointer dereference in request_key_auth_revoke() because the key
has not yet been instantiated.

Fix this by removing the call to key_revoke().  key_put() is sufficient,
as it's not possible for an uninstantiated authkey to have been used for
anything yet.

Fixes: b5f545c880 ("[PATCH] keys: Permit running process to instantiate keys")
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>

security/keys/request_key_auth.c

@@ -220,7 +220,6 @@ struct key *request_key_auth_new(struct key *target, const void *callout_info,
 	return authkey;
 
 error_put_authkey:
-	key_revoke(authkey);
 	key_put(authkey);
 error_free_rka:
 	free_request_key_auth(rka);