batman-adv: Add missing refcnt for last_candidate

commit 936523441bb64cdc9a5b263e8fd2782e70313a57 upstream.

batadv_find_router dereferences last_bonding_candidate from
orig_node without making sure that it has a valid reference. This reference
has to be retrieved by increasing the reference counter while holding
neigh_list_lock. The lock is required to avoid that
batadv_last_bonding_replace removes the current last_bonding_candidate,
reduces the reference counter and maybe destroys the object in this
process.

Fixes: f3b3d9018975 ("batman-adv: add bonding again")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
[bwh: Backported to 3.16:
 - s/kref_get/atomic_inc/
 - s/_put/_free_ref/]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/net/batman-adv/routing.c b/net/batman-adv/routing.c
index a2df39054b355676f6e8d91cbd089ba4dda4197f..34c20cc0670c9773d21ab0b49c2d73a7759a316a 100644 (file)
--- a/net/batman-adv/routing.c
+++ b/net/batman-adv/routing.c
@@ -424,6 +424,29 @@ static int batadv_check_unicast_packet(struct batadv_priv *bat_priv,
        return 0;
 }
 
+/**
+ * batadv_last_bonding_get - Get last_bonding_candidate of orig_node
+ * @orig_node: originator node whose last bonding candidate should be retrieved
+ *
+ * Return: last bonding candidate of router or NULL if not found
+ *
+ * The object is returned with refcounter increased by 1.
+ */
+static struct batadv_orig_ifinfo *
+batadv_last_bonding_get(struct batadv_orig_node *orig_node)
+{
+       struct batadv_orig_ifinfo *last_bonding_candidate;
+
+       spin_lock_bh(&orig_node->neigh_list_lock);
+       last_bonding_candidate = orig_node->last_bonding_candidate;
+
+       if (last_bonding_candidate)
+               atomic_inc(&last_bonding_candidate->refcount);
+       spin_unlock_bh(&orig_node->neigh_list_lock);
+
+       return last_bonding_candidate;
+}
+
 /**
  * batadv_last_bonding_replace - Replace last_bonding_candidate of orig_node
  * @orig_node: originator node whose bonding candidates should be replaced
@@ -492,7 +515,7 @@ batadv_find_router(struct batadv_priv *bat_priv,
         * router - obviously there are no other candidates.
         */
        rcu_read_lock();
-       last_candidate = orig_node->last_bonding_candidate;
+       last_candidate = batadv_last_bonding_get(orig_node);
        if (last_candidate)
                last_cand_router = rcu_dereference(last_candidate->router);
 
@@ -584,6 +607,9 @@ next:
                batadv_orig_ifinfo_free_ref(next_candidate);
        }
 
+       if (last_candidate)
+               batadv_orig_ifinfo_free_ref(last_candidate);
+
        return router;
 }