scene: ensure node cannot be reparented below itself

types/wlr_scene.c

@@ -138,6 +138,13 @@ void wlr_scene_node_reparent(struct wlr_scene_node *node,
 	if (node->parent == new_parent) {
 		return;
 	}
+	/* Ensure that a node cannot become its own ancestor */
+	for (struct wlr_scene_node *ancestor = new_parent; ancestor != NULL;
+			ancestor = ancestor->parent) {
+		if (ancestor == node) {
+			return;
+		}
+	}
 
 	wl_list_remove(&node->state.link);