batman-adv: Prevent duplicated gateway_node entry

commit dff9bc42ab0b2d38c5e90ddd79b238fed5b4c7ad upstream.

The function batadv_gw_node_add is responsible for adding new gw_node to
the gateway_list. It is expecting that the caller already checked that
there is not already an entry with the same key or not.

But the lock for the list is only held when the list is really modified.
This could lead to duplicated entries because another context could create
an entry with the same key between the check and the list manipulation.

The check and the manipulation of the list must therefore be in the same
locked code section.

Fixes: c6c8fea29769 ("net: Add batman-adv meshing protocol")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Acked-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/net/batman-adv/gateway_client.c b/net/batman-adv/gateway_client.c
index b22ba87b6b22506ab581620a2434504e69fb7d3a..5f8e972e465eb0812e437acae8908a5bc3278e7d 100644 (file)
--- a/net/batman-adv/gateway_client.c
+++ b/net/batman-adv/gateway_client.c
@@ -27,6 +27,7 @@
 #include <linux/ipv6.h>
 #include <linux/udp.h>
 #include <linux/if_vlan.h>
+#include <linux/lockdep.h>
 
 /* These are the offsets of the "hw type" and "hw address length" in the dhcp
  * packet starting at the beginning of the dhcp header
@@ -398,6 +399,9 @@ out:
  * @bat_priv: the bat priv with all the soft interface information
  * @orig_node: originator announcing gateway capabilities
  * @gateway: announced bandwidth information
+ *
+ * Has to be called with the appropriate locks being acquired
+ * (gw.list_lock).
  */
 static void batadv_gw_node_add(struct batadv_priv *bat_priv,
                               struct batadv_orig_node *orig_node,
@@ -405,6 +409,8 @@ static void batadv_gw_node_add(struct batadv_priv *bat_priv,
 {
        struct batadv_gw_node *gw_node;
 
+       lockdep_assert_held(&bat_priv->gw.list_lock);
+
        if (gateway->bandwidth_down == 0)
                return;
 
@@ -421,9 +427,7 @@ static void batadv_gw_node_add(struct batadv_priv *bat_priv,
        gw_node->orig_node = orig_node;
        atomic_set(&gw_node->refcount, 1);
 
-       spin_lock_bh(&bat_priv->gw.list_lock);
        hlist_add_head_rcu(&gw_node->list, &bat_priv->gw.list);
-       spin_unlock_bh(&bat_priv->gw.list_lock);
 
        batadv_dbg(BATADV_DBG_BATMAN, bat_priv,
                   "Found new gateway %pM -> gw bandwidth: %u.%u/%u.%u MBit\n",
@@ -479,11 +483,14 @@ void batadv_gw_node_update(struct batadv_priv *bat_priv,
 {
        struct batadv_gw_node *gw_node, *curr_gw = NULL;
 
+       spin_lock_bh(&bat_priv->gw.list_lock);
        gw_node = batadv_gw_node_get(bat_priv, orig_node);
        if (!gw_node) {
                batadv_gw_node_add(bat_priv, orig_node, gateway);
+               spin_unlock_bh(&bat_priv->gw.list_lock);
                goto out;
        }
+       spin_unlock_bh(&bat_priv->gw.list_lock);
 
        if ((gw_node->bandwidth_down == ntohl(gateway->bandwidth_down)) &&
            (gw_node->bandwidth_up == ntohl(gateway->bandwidth_up)))