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From:   Ben Hutchings <ben@decadent.org.uk>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
CC:     akpm@linux-foundation.org, "Sven Eckelmann" <sven@narfation.org>,
        "Simon Wunderlich" <sw@simonwunderlich.de>,
        "Marek Lindner" <mareklindner@neomailbox.ch>
Date:   Sun, 09 Dec 2018 21:50:33 +0000
Message-ID: <lsq.1544392233.389632344@decadent.org.uk>
Subject: [PATCH 3.16 213/328] batman-adv: Prevent duplicated gateway_node
 entry
In-Reply-To: <lsq.1544392232.713909046@decadent.org.uk>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

3.16.62-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Sven Eckelmann <sven@narfation.org>

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>
---
 net/batman-adv/gateway_client.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

--- 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 ba
 {
 	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 ba
 	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
 {
 	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)))