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, 13 insertions, 8 deletions

diff --git a/net/batman-adv/originator.c b/net/batman-adv/originator.c
index bdcb399329d..a70debebfc5 100644
--- a/net/batman-adv/originator.c
+++ b/net/batman-adv/originator.c
@@ -102,13 +102,13 @@ struct neigh_node *create_neighbor(struct orig_node *orig_node,
 	return neigh_node;
 }
 
-void orig_node_free_ref(struct kref *refcount)
+static void orig_node_free_rcu(struct rcu_head *rcu)
 {
 	struct hlist_node *node, *node_tmp;
 	struct neigh_node *neigh_node, *tmp_neigh_node;
 	struct orig_node *orig_node;
 
-	orig_node = container_of(refcount, struct orig_node, refcount);
+	orig_node = container_of(rcu, struct orig_node, rcu);
 
 	spin_lock_bh(&orig_node->neigh_list_lock);
 
@@ -137,6 +137,12 @@ void orig_node_free_ref(struct kref *refcount)
 	kfree(orig_node);
 }
 
+void orig_node_free_ref(struct orig_node *orig_node)
+{
+	if (atomic_dec_and_test(&orig_node->refcount))
+		call_rcu(&orig_node->rcu, orig_node_free_rcu);
+}
+
 void originator_free(struct bat_priv *bat_priv)
 {
 	struct hashtable_t *hash = bat_priv->orig_hash;
@@ -163,7 +169,7 @@ void originator_free(struct bat_priv *bat_priv)
 					  head, hash_entry) {
 
 			hlist_del_rcu(node);
-			kref_put(&orig_node->refcount, orig_node_free_ref);
+			orig_node_free_ref(orig_node);
 		}
 		spin_unlock_bh(list_lock);
 	}
@@ -196,7 +202,9 @@ struct orig_node *get_orig_node(struct bat_priv *bat_priv, uint8_t *addr)
 	spin_lock_init(&orig_node->ogm_cnt_lock);
 	spin_lock_init(&orig_node->bcast_seqno_lock);
 	spin_lock_init(&orig_node->neigh_list_lock);
-	kref_init(&orig_node->refcount);
+
+	/* extra reference for return */
+	atomic_set(&orig_node->refcount, 2);
 
 	orig_node->bat_priv = bat_priv;
 	memcpy(orig_node->orig, addr, ETH_ALEN);
@@ -229,8 +237,6 @@ struct orig_node *get_orig_node(struct bat_priv *bat_priv, uint8_t *addr)
 	if (hash_added < 0)
 		goto free_bcast_own_sum;
 
-	/* extra reference for return */
-	kref_get(&orig_node->refcount);
 	return orig_node;
 free_bcast_own_sum:
 	kfree(orig_node->bcast_own_sum);
@@ -348,8 +354,7 @@ static void _purge_orig(struct bat_priv *bat_priv)
 				if (orig_node->gw_flags)
 					gw_node_delete(bat_priv, orig_node);
 				hlist_del_rcu(node);
-				kref_put(&orig_node->refcount,
-					 orig_node_free_ref);
+				orig_node_free_ref(orig_node);
 				continue;
 			}