keys: Grant Link permission to possessers of request_key auth keys

Grant Link permission to the possessers of request_key authentication keys,
thereby allowing a daemon that is servicing upcalls to arrange things such
that only the necessary auth key is passed to the actual service program
and not all the daemon's pending auth keys.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: James Morris <jamorris@linux.microsoft.com>

security/keys/request_key_auth.c

@@ -204,7 +204,7 @@ struct key *request_key_auth_new(struct key *target, const char *op,
 
 	authkey = key_alloc(&key_type_request_key_auth, desc,
 			    cred->fsuid, cred->fsgid, cred,
-			    KEY_POS_VIEW | KEY_POS_READ | KEY_POS_SEARCH |
+			    KEY_POS_VIEW | KEY_POS_READ | KEY_POS_SEARCH | KEY_POS_LINK |
 			    KEY_USR_VIEW, KEY_ALLOC_NOT_IN_QUOTA, NULL);
 	if (IS_ERR(authkey)) {
 		ret = PTR_ERR(authkey);