batman-adv: use neigh_node's orig_node only as id

The orig_node member of struct batadv_neigh_node is no longer used in
B.A.T.M.A.N. IV. But batadv_neigh_node_create() is still storing it.
Only batadv_v_ogm_route_update() uses it to check if we route toward
it - not needing the data stored in the batadv_orig_node object itself,
but merely a pointer to identify the originator.

The field cannot hold a proper reference because that would create a
reference cycle, so it must never be dereferenced. Rename it to
orig_node_id and mark it __private to make any future attempt to
dereference it immediately noticeable.

Signed-off-by: Sven Eckelmann <sven@narfation.org>

Author: ecsv

net/batman-adv/bat_v_ogm.c

@@ -719,7 +719,7 @@ static bool batadv_v_ogm_route_update(struct batadv_priv *bat_priv,
 	 * don't route towards it
 	 */
 	router = batadv_orig_router_get(orig_node, if_outgoing);
-	if (router && router->orig_node != orig_node && !orig_neigh_router) {
+	if (router && ACCESS_PRIVATE(router, orig_node_id) != orig_node && !orig_neigh_router) {
 		batadv_dbg(BATADV_DBG_BATMAN, bat_priv,
 			   "Drop packet: OGM via unknown neighbor!\n");
 		goto out;

net/batman-adv/originator.c

@@ -693,9 +693,12 @@ batadv_neigh_node_create(struct batadv_orig_node *orig_node,
 	kref_get(&hard_iface->refcount);
 	ether_addr_copy(neigh_node->addr, neigh_addr);
 	neigh_node->if_incoming = hard_iface;
-	neigh_node->orig_node = orig_node;
 	neigh_node->last_seen = jiffies;
 
+#ifdef CONFIG_BATMAN_ADV_BATMAN_V
+	ACCESS_PRIVATE(neigh_node, orig_node_id) = orig_node;
+#endif
+
 	/* increment unique neighbor refcount */
 	kref_get(&hardif_neigh->refcount);
 	neigh_node->hardif_neigh = hardif_neigh;

net/batman-adv/types.h

@@ -663,8 +663,15 @@ struct batadv_neigh_node {
 	/** @list: list node for &batadv_orig_node.neigh_list */
 	struct hlist_node list;
 
-	/** @orig_node: pointer to corresponding orig_node */
-	struct batadv_orig_node *orig_node;
+#ifdef CONFIG_BATMAN_ADV_BATMAN_V
+	/**
+	 * @orig_node_id: pointer to corresponding orig_node. It must only be used
+	 * to identify the node but must NEVER be dereferenced. The reference counter
+	 * was not increased when this was assigned because it would otherwise create
+	 * a reference cycle.
+	 */
+	struct batadv_orig_node *__private orig_node_id;
+#endif
 
 	/** @addr: the MAC address of the neighboring interface */
 	u8 addr[ETH_ALEN];