batman-adv: Correct rcu refcounting for orig_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, 4 insertions, 2 deletions

diff --git a/net/batman-adv/originator.h b/net/batman-adv/originator.h
index b4b9a09259fd..3d7a39d4df0f 100644
--- a/net/batman-adv/originator.h
+++ b/net/batman-adv/originator.h
@@ -27,7 +27,7 @@
 int originator_init(struct bat_priv *bat_priv);
 void originator_free(struct bat_priv *bat_priv);
 void purge_orig_ref(struct bat_priv *bat_priv);
-void orig_node_free_ref(struct kref *refcount);
+void orig_node_free_ref(struct orig_node *orig_node);
 struct orig_node *get_orig_node(struct bat_priv *bat_priv, uint8_t *addr);
 struct neigh_node *create_neighbor(struct orig_node *orig_node,
                                    struct orig_node *orig_neigh_node,
@@ -88,8 +88,10 @@ static inline struct orig_node *orig_hash_find(struct bat_priv *bat_priv,
                 if (!compare_eth(orig_node, data))
                         continue;
 
+                if (!atomic_inc_not_zero(&orig_node->refcount))
+                        continue;
+
                 orig_node_tmp = orig_node;
-                kref_get(&orig_node_tmp->refcount);
                 break;
         }
         rcu_read_unlock();