keys: Garbage collect keys for which the domain has been removed

If a key operation domain (such as a network namespace) has been removed
then attempt to garbage collect all the keys that use it.

Signed-off-by: David Howells <dhowells@redhat.com>
diff --git a/security/keys/keyring.c b/security/keys/keyring.c
index 0da8fa2..d3c86fd 100644
--- a/security/keys/keyring.c
+++ b/security/keys/keyring.c
@@ -241,6 +241,21 @@ bool key_put_tag(struct key_tag *tag)
 	return false;
 }
 
+/**
+ * key_remove_domain - Kill off a key domain and gc its keys
+ * @domain_tag: The domain tag to release.
+ *
+ * This marks a domain tag as being dead and releases a ref on it.  If that
+ * wasn't the last reference, the garbage collector is poked to try and delete
+ * all keys that were in the domain.
+ */
+void key_remove_domain(struct key_tag *domain_tag)
+{
+	domain_tag->removed = true;
+	if (!key_put_tag(domain_tag))
+		key_schedule_gc_links();
+}
+
 /*
  * Build the next index key chunk.
  *