ubusd_monitor: fix possible null pointer dereference

This dereference could possibly happen if the calloc call fails as the
return value is unchecked. While at it refactor the code little bit to
make it easier to follow, use safe list iterator and provide return
value for ubusd_monitor_connect.

Signed-off-by: Petr Štetiar <ynezz@true.cz>

1 files changed, 30 insertions, 10 deletions

diff --git a/ubusd_monitor.c b/ubusd_monitor.c
index fcbc6a4..501e06d 100644
--- a/ubusd_monitor.c
+++ b/ubusd_monitor.c
@@ -29,7 +29,7 @@ ubusd_monitor_free(struct ubus_monitor *m)
 	free(m);
 }
 
-static void
+static bool
 ubusd_monitor_connect(struct ubus_client *cl, struct ubus_msg_buf *ub)
 {
 	struct ubus_monitor *m;
@@ -37,22 +37,40 @@ ubusd_monitor_connect(struct ubus_client *cl, struct ubus_msg_buf *ub)
 	ubusd_monitor_disconnect(cl);
 
 	m = calloc(1, sizeof(*m));
+	if (!m)
+		return false;
+
 	m->cl = cl;
 	list_add(&m->list, &monitors);
+
+	return true;
 }
 
-void
-ubusd_monitor_disconnect(struct ubus_client *cl)
+static struct ubus_monitor*
+ubusd_monitor_find(struct ubus_client *cl)
 {
-	struct ubus_monitor *m;
+	struct ubus_monitor *m, *tmp;
 
-	list_for_each_entry(m, &monitors, list) {
+	list_for_each_entry_safe(m, tmp, &monitors, list) {
 		if (m->cl != cl)
 			continue;
 
-		ubusd_monitor_free(m);
-		return;
+		return m;
 	}
+
+	return NULL;
+}
+
+void
+ubusd_monitor_disconnect(struct ubus_client *cl)
+{
+	struct ubus_monitor *m;
+
+	m = ubusd_monitor_find(cl);
+	if (!m)
+		return;
+
+	ubusd_monitor_free(m);
 }
 
 void
@@ -92,13 +110,15 @@ ubusd_monitor_recv(struct ubus_client *cl, struct ubus_msg_buf *ub,
 		return UBUS_STATUS_PERMISSION_DENIED;
 
 	if (!strcmp(method, "add")) {
-		ubusd_monitor_connect(cl, ub);
-		return 0;
+		if (!ubusd_monitor_connect(cl, ub))
+			return UBUS_STATUS_UNKNOWN_ERROR;
+
+		return UBUS_STATUS_OK;
 	}
 
 	if (!strcmp(method, "remove")) {
 		ubusd_monitor_disconnect(cl);
-		return 0;
+		return UBUS_STATUS_OK;
 	}
 
 	return UBUS_STATUS_METHOD_NOT_FOUND;