KEYS: Flag dead keys to induce EKEYREVOKED [try #6]

Set the KEY_FLAG_DEAD flag on keys for which the type has been removed.  This
causes the key_permission() function to return EKEYREVOKED in response to
various commands.  It does not, however, prevent unlinking or clearing of
keyrings from detaching the key.
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: James Morris <jmorris@namei.org>

security/keys/key.c

@@ -956,8 +956,10 @@ void unregister_key_type(struct key_type *ktype)
 	for (_n = rb_first(&key_serial_tree); _n; _n = rb_next(_n)) {
 		key = rb_entry(_n, struct key, serial_node);
 
-		if (key->type == ktype)
+		if (key->type == ktype) {
 			key->type = &key_type_dead;
+			set_bit(KEY_FLAG_DEAD, &key->flags);
+		}
 	}
 
 	spin_unlock(&key_serial_lock);