batman-adv: avoid potential race condition when adding a new neighbour

When adding a new neighbour it is important to atomically
perform the following:
- check if the neighbour already exists
- append the neighbour to the proper list

If the two operations are not performed in an atomic context
it is possible that two concurrent insertions add the same
neighbour twice.

Signed-off-by: Antonio Quartulli <antonio@open-mesh.com>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>

1 files changed, 16 insertions, 6 deletions

diff --git a/net/batman-adv/bat_iv_ogm.c b/net/batman-adv/bat_iv_ogm.c
index 512159bf607f..094ae7ca50a0 100644
--- a/net/batman-adv/bat_iv_ogm.c
+++ b/net/batman-adv/bat_iv_ogm.c
@@ -266,7 +266,7 @@ batadv_iv_ogm_neigh_new(struct batadv_hard_iface *hard_iface,
 			struct batadv_orig_node *orig_neigh)
 {
 	struct batadv_priv *bat_priv = netdev_priv(hard_iface->soft_iface);
-	struct batadv_neigh_node *neigh_node;
+	struct batadv_neigh_node *neigh_node, *tmp_neigh_node;
 
 	neigh_node = batadv_neigh_node_new(hard_iface, neigh_addr, orig_node);
 	if (!neigh_node)
@@ -281,14 +281,24 @@ batadv_iv_ogm_neigh_new(struct batadv_hard_iface *hard_iface,
 	neigh_node->orig_node = orig_neigh;
 	neigh_node->if_incoming = hard_iface;
 
-	batadv_dbg(BATADV_DBG_BATMAN, bat_priv,
-		   "Creating new neighbor %pM for orig_node %pM on interface %s\n",
-		   neigh_addr, orig_node->orig, hard_iface->net_dev->name);
-
 	spin_lock_bh(&orig_node->neigh_list_lock);
-	hlist_add_head_rcu(&neigh_node->list, &orig_node->neigh_list);
+	tmp_neigh_node = batadv_neigh_node_get(orig_node, hard_iface,
+					       neigh_addr);
+	if (!tmp_neigh_node) {
+		hlist_add_head_rcu(&neigh_node->list, &orig_node->neigh_list);
+	} else {
+		kfree(neigh_node);
+		batadv_hardif_free_ref(hard_iface);
+		neigh_node = tmp_neigh_node;
+	}
 	spin_unlock_bh(&orig_node->neigh_list_lock);
 
+	if (!tmp_neigh_node)
+		batadv_dbg(BATADV_DBG_BATMAN, bat_priv,
+			   "Creating new neighbor %pM for orig_node %pM on interface %s\n",
+			   neigh_addr, orig_node->orig,
+			   hard_iface->net_dev->name);
+
 out:
 	return neigh_node;
 }