Implement watching of nodes which don't exist.

Requires permission check every time event is generated.
Requires generalization of permissions: ask arbitrary number of
parents whether it's OK to tell about node (eg. watching
/dir/subdir/x when /dir is deleted: root permissions will now
determine whether we fire event).
Add test that we don't leak information on whether a file exists
or not.
Signed-off-by: Rusty Russel <rusty@rustcorp.com.au>
Signed-off-by: Christian Limpach <Christian.Limpach@cl.cam.ac.uk>

1 files changed, 13 insertions, 4 deletions

diff --git a/tools/xenstore/xenstored_watch.c b/tools/xenstore/xenstored_watch.c
index 1c42b72ced..a2727e46e4 100644
--- a/tools/xenstore/xenstored_watch.c
+++ b/tools/xenstore/xenstored_watch.c
@@ -95,10 +95,19 @@ static int destroy_watch_event(void *_event)
 	return 0;
 }
 
-static void add_event(struct watch *watch, const char *node)
+static void add_event(struct connection *conn,
+		      struct watch *watch, const char *node)
 {
 	struct watch_event *event;
 
+	/* Check read permission: no permission, no watch event.
+	 * If it doesn't exist, we need permission to read parent.
+	 */
+	if (!check_node_perms(conn, node, XS_PERM_READ|XS_PERM_ENOENT_OK)) {
+		fprintf(stderr, "No permission for %s\n", node);
+		return;
+	}
+
 	if (watch->relative_path) {
 		node += strlen(watch->relative_path);
 		if (*node == '/') /* Could be "" */
@@ -132,9 +141,9 @@ void fire_watches(struct connection *conn, const char *node, bool recurse)
 
 		list_for_each_entry(watch, &i->watches, list) {
 			if (is_child(node, watch->node))
-				add_event(watch, node);
+				add_event(i, watch, node);
 			else if (recurse && is_child(watch->node, node))
-				add_event(watch, watch->node);
+				add_event(i, watch, watch->node);
 			else
 				continue;
 			/* If connection not doing anything, queue this. */
@@ -206,7 +215,7 @@ void do_watch(struct connection *conn, struct buffered_data *in)
 
 	relative = !strstarts(vec[0], "/");
 	vec[0] = canonicalize(conn, vec[0]);
-	if (!check_node_perms(conn, vec[0], XS_PERM_READ)) {
+	if (!is_valid_nodename(vec[0])) {
 		send_error(conn, errno);
 		return;
 	}