tools/xenstore: fire watches only when removing a specific node

Instead of firing all watches for removing a subtree in one go, do so
only when the related node is being removed.

The watches for the top-most node being removed include all watches
including that node, while watches for nodes below that are only fired
if they are matching exactly. This avoids firing any watch more than
once when removing a subtree.

This is part of XSA-115.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Julien Grall <jgrall@amazon.com>
Reviewed-by: Paul Durrant <paul@xen.org>

tools/xenstore/xenstored_core.c

@@ -1118,8 +1118,8 @@ static void delete_child(struct connection *conn,
 	corrupt(conn, "Can't find child '%s' in %s", childname, node->name);
 }
 
-static int delete_node(struct connection *conn, struct node *parent,
-		       struct node *node)
+static int delete_node(struct connection *conn, const void *ctx,
+		       struct node *parent, struct node *node)
 {
 	char *name;
 
@@ -1131,7 +1131,7 @@ static int delete_node(struct connection *conn, struct node *parent,
 				       node->children);
 		child = name ? read_node(conn, node, name) : NULL;
 		if (child) {
-			if (delete_node(conn, node, child))
+			if (delete_node(conn, ctx, node, child))
 				return errno;
 		} else {
 			trace("delete_node: Error deleting child '%s/%s'!\n",
@@ -1143,6 +1143,7 @@ static int delete_node(struct connection *conn, struct node *parent,
 		talloc_free(name);
 	}
 
+	fire_watches(conn, ctx, node->name, true);
 	delete_node_single(conn, node);
 	delete_child(conn, parent, basename(node->name));
 	talloc_free(node);
@@ -1172,8 +1173,8 @@ static int _rm(struct connection *conn, const void *ctx, struct node *node,
 	 * This fine as we are single threaded and the next possible read will
 	 * be handled only after the node has been really removed.
 	 */
-	fire_watches(conn, ctx, name, true);
-	return delete_node(conn, parent, node);
+	fire_watches(conn, ctx, name, false);
+	return delete_node(conn, ctx, parent, node);
 }
 
 

tools/xenstore/xenstored_watch.c

@@ -122,7 +122,7 @@ static void add_event(struct connection *conn,
  * Temporary memory allocations are done with ctx.
  */
 void fire_watches(struct connection *conn, const void *ctx, const char *name,
-		  bool recurse)
+		  bool exact)
 {
 	struct connection *i;
 	struct watch *watch;
@@ -134,10 +134,13 @@ void fire_watches(struct connection *conn, const void *ctx, const char *name,
 	/* Create an event for each watch. */
 	list_for_each_entry(i, &connections, list) {
 		list_for_each_entry(watch, &i->watches, list) {
-			if (is_child(name, watch->node))
-				add_event(i, ctx, watch, name);
-			else if (recurse && is_child(watch->node, name))
-				add_event(i, ctx, watch, watch->node);
+			if (exact) {
+				if (streq(name, watch->node))
+					add_event(i, ctx, watch, name);
+			} else {
+				if (is_child(name, watch->node))
+					add_event(i, ctx, watch, name);
+			}
 		}
 	}
 }

tools/xenstore/xenstored_watch.h

@@ -24,9 +24,9 @@
 int do_watch(struct connection *conn, struct buffered_data *in);
 int do_unwatch(struct connection *conn, struct buffered_data *in);
 
-/* Fire all watches: recurse means all the children are affected (ie. rm). */
+/* Fire all watches: !exact means all the children are affected (ie. rm). */
 void fire_watches(struct connection *conn, const void *tmp, const char *name,
-		  bool recurse);
+		  bool exact);
 
 void conn_delete_all_watches(struct connection *conn);