batman-adv: Use kref_get for _batadv_update_route

_batadv_update_route requires that the caller already has a valid reference
for neigh_node. It is therefore not possible that it has an reference
counter of 0 and was still given to this function

The kref_get function instead WARNs (with debug information) when the
reference counter would still be 0. This makes a bug in batman-adv better
visible because kref_get_unless_zero would have ignored this problem.
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Antonio Quartulli <a@unstable.cc>

net/batman-adv/routing.c

@@ -100,10 +100,6 @@ static void _batadv_update_route(struct batadv_priv *bat_priv,
 	if (curr_router)
 		batadv_neigh_node_put(curr_router);
 
-	/* increase refcount of new best neighbor */
-	if (neigh_node && !kref_get_unless_zero(&neigh_node->refcount))
-		neigh_node = NULL;
-
 	spin_lock_bh(&orig_node->neigh_list_lock);
 	/* curr_router used earlier may not be the current orig_ifinfo->router
 	 * anymore because it was dereferenced outside of the neigh_list_lock
@@ -114,6 +110,10 @@ static void _batadv_update_route(struct batadv_priv *bat_priv,
 	 */
 	curr_router = rcu_dereference_protected(orig_ifinfo->router, true);
 
+	/* increase refcount of new best neighbor */
+	if (neigh_node)
+		kref_get(&neigh_node->refcount);
+
 	rcu_assign_pointer(orig_ifinfo->router, neigh_node);
 	spin_unlock_bh(&orig_node->neigh_list_lock);
 	batadv_orig_ifinfo_put(orig_ifinfo);