batman-adv: Correct rcu refcounting for neigh_node

It might be possible that 2 threads access the same data in the same
rcu grace period. The first thread calls call_rcu() to decrement the
refcount and free the data while the second thread increases the
refcount to use the data. To avoid this race condition all refcount
operations have to be atomic.

Reported-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Marek Lindner <lindner_marek@yahoo.de>

1 files changed, 8 insertions, 18 deletions

diff --git a/net/batman-adv/originator.c b/net/batman-adv/originator.c
index a85eadca6b2d..61299da82c6b 100644
--- a/net/batman-adv/originator.c
+++ b/net/batman-adv/originator.c
@@ -59,28 +59,18 @@ err:
         return 0;
 }
 
-void neigh_node_free_ref(struct kref *refcount)
-{
-        struct neigh_node *neigh_node;
-
-        neigh_node = container_of(refcount, struct neigh_node, refcount);
-        kfree(neigh_node);
-}
-
 static void neigh_node_free_rcu(struct rcu_head *rcu)
 {
         struct neigh_node *neigh_node;
 
         neigh_node = container_of(rcu, struct neigh_node, rcu);
-        kref_put(&neigh_node->refcount, neigh_node_free_ref);
+        kfree(neigh_node);
 }
 
-void neigh_node_free_rcu_bond(struct rcu_head *rcu)
+void neigh_node_free_ref(struct neigh_node *neigh_node)
 {
-        struct neigh_node *neigh_node;
-
-        neigh_node = container_of(rcu, struct neigh_node, rcu_bond);
-        kref_put(&neigh_node->refcount, neigh_node_free_ref);
+        if (atomic_dec_and_test(&neigh_node->refcount))
+                call_rcu(&neigh_node->rcu, neigh_node_free_rcu);
 }
 
 struct neigh_node *create_neighbor(struct orig_node *orig_node,
@@ -104,7 +94,7 @@ struct neigh_node *create_neighbor(struct orig_node *orig_node,
         memcpy(neigh_node->addr, neigh, ETH_ALEN);
         neigh_node->orig_node = orig_neigh_node;
         neigh_node->if_incoming = if_incoming;
-        kref_init(&neigh_node->refcount);
+        atomic_set(&neigh_node->refcount, 1);
 
         spin_lock_bh(&orig_node->neigh_list_lock);
         hlist_add_head_rcu(&neigh_node->list, &orig_node->neigh_list);
@@ -126,14 +116,14 @@ void orig_node_free_ref(struct kref *refcount)
         list_for_each_entry_safe(neigh_node, tmp_neigh_node,
                                  &orig_node->bond_list, bonding_list) {
                 list_del_rcu(&neigh_node->bonding_list);
-                call_rcu(&neigh_node->rcu_bond, neigh_node_free_rcu_bond);
+                neigh_node_free_ref(neigh_node);
         }
 
         /* for all neighbors towards this originator ... */
         hlist_for_each_entry_safe(neigh_node, node, node_tmp,
                                   &orig_node->neigh_list, list) {
                 hlist_del_rcu(&neigh_node->list);
-                call_rcu(&neigh_node->rcu, neigh_node_free_rcu);
+                neigh_node_free_ref(neigh_node);
         }
 
         spin_unlock_bh(&orig_node->neigh_list_lock);
@@ -315,7 +305,7 @@ static bool purge_orig_neighbors(struct bat_priv *bat_priv,
 
                         hlist_del_rcu(&neigh_node->list);
                         bonding_candidate_del(orig_node, neigh_node);
-                        call_rcu(&neigh_node->rcu, neigh_node_free_rcu);
+                        neigh_node_free_ref(neigh_node);
                 } else {
                         if ((!*best_neigh_node) ||
                             (neigh_node->tq_avg > (*best_neigh_node)->tq_avg))