batman-adv: fix backbone_gw refcount on queue_work() failure

The backbone_gw refcounter is to be decreased by the queued work and
currently is never decreased if the queue_work() call fails.
Fix by checking the queue_work() return value and decrease refcount
if necessary.

Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>

net/batman-adv/bridge_loop_avoidance.c

@@ -1772,6 +1772,7 @@ batadv_bla_loopdetect_check(struct batadv_priv *bat_priv, struct sk_buff *skb,
 {
 	struct batadv_bla_backbone_gw *backbone_gw;
 	struct ethhdr *ethhdr;
+	bool ret;
 
 	ethhdr = eth_hdr(skb);
 
@@ -1795,8 +1796,13 @@ batadv_bla_loopdetect_check(struct batadv_priv *bat_priv, struct sk_buff *skb,
 	if (unlikely(!backbone_gw))
 		return true;
 
-	queue_work(batadv_event_workqueue, &backbone_gw->report_work);
-	/* backbone_gw is unreferenced in the report work function function */
+	ret = queue_work(batadv_event_workqueue, &backbone_gw->report_work);
+
+	/* backbone_gw is unreferenced in the report work function function
+	 * if queue_work() call was successful
+	 */
+	if (!ret)
+		batadv_backbone_gw_put(backbone_gw);
 
 	return true;
 }