batman-adv: Fix reference counting of hardif_neigh_node object for neigh_node

The batadv_neigh_node was specific to a batadv_hardif_neigh_node and held
an implicit reference to it. But this reference was never stored in form of
a pointer in the batadv_neigh_node itself. Instead
batadv_neigh_node_release depends on a consistent state of
hard_iface->neigh_list and that batadv_hardif_neigh_get always returns the
batadv_hardif_neigh_node object which it has a reference for. But
batadv_hardif_neigh_get cannot guarantee that because it is working only
with rcu_read_lock on this list. It can therefore happen that a neigh_addr
is in this list twice or that batadv_hardif_neigh_get cannot find the
batadv_hardif_neigh_node for an neigh_addr due to some other list
operations taking place at the same time.

Instead add a batadv_hardif_neigh_node pointer directly in
batadv_neigh_node which will be used for the reference counter decremented
on release of batadv_neigh_node.

Fixes: cef63419f7db ("batman-adv: add list of unique single hop neighbors per hard-interface")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Antonio Quartulli <a@unstable.cc>

1 files changed, 2 insertions, 0 deletions

diff --git a/net/batman-adv/types.h b/net/batman-adv/types.h
index 65afd090ab3e..1e47fbe8bb7b 100644
--- a/net/batman-adv/types.h
+++ b/net/batman-adv/types.h
@@ -433,6 +433,7 @@ struct batadv_hardif_neigh_node {
  * @ifinfo_lock: lock protecting private ifinfo members and list
  * @if_incoming: pointer to incoming hard-interface
  * @last_seen: when last packet via this neighbor was received
+ * @hardif_neigh: hardif_neigh of this neighbor
  * @refcount: number of contexts the object is used
  * @rcu: struct used for freeing in an RCU-safe manner
  */
@@ -444,6 +445,7 @@ struct batadv_neigh_node {
 	spinlock_t ifinfo_lock;	/* protects ifinfo_list and its members */
 	struct batadv_hard_iface *if_incoming;
 	unsigned long last_seen;
+	struct batadv_hardif_neigh_node *hardif_neigh;
 	struct kref refcount;
 	struct rcu_head rcu;
 };