batman-adv: increase orig refcount when storing ref in gw_node

A pointer to the orig_node representing a bat-gateway is
stored in the gw_node->orig_node member, but the refcount
for such orig_node is never increased.
This leads to memory faults when gw_node->orig_node is accessed
and the originator has already been freed.

Fix this by increasing the refcount on gw_node creation
and decreasing it on gw_node free.

Signed-off-by: Antonio Quartulli <antonio@open-mesh.com>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>

net/batman-adv/gateway_client.c

@@ -42,8 +42,10 @@
 
 static void batadv_gw_node_free_ref(struct batadv_gw_node *gw_node)
 {
-	if (atomic_dec_and_test(&gw_node->refcount))
+	if (atomic_dec_and_test(&gw_node->refcount)) {
+		batadv_orig_node_free_ref(gw_node->orig_node);
 		kfree_rcu(gw_node, rcu);
+	}
 }
 
 static struct batadv_gw_node *
@@ -406,10 +408,15 @@ static void batadv_gw_node_add(struct batadv_priv *bat_priv,
 	if (gateway->bandwidth_down == 0)
 		return;
 
-	gw_node = kzalloc(sizeof(*gw_node), GFP_ATOMIC);
-	if (!gw_node)
+	if (!atomic_inc_not_zero(&orig_node->refcount))
 		return;
 
+	gw_node = kzalloc(sizeof(*gw_node), GFP_ATOMIC);
+	if (!gw_node) {
+		batadv_orig_node_free_ref(orig_node);
+		return;
+	}
+
 	INIT_HLIST_NODE(&gw_node->list);
 	gw_node->orig_node = orig_node;
 	atomic_set(&gw_node->refcount, 1);