linux-kernel - [PATCH AUTOSEL 4.18 09/58] batman-adv: Prevent duplicated gateway

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Message-Id: <20181008152523.70705-9-sashal@kernel.org>
Date:   Mon,  8 Oct 2018 11:24:34 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     stable@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Sven Eckelmann <sven@...fation.org>,
        Simon Wunderlich <sw@...onwunderlich.de>,
        Sasha Levin <alexander.levin@...rosoft.com>
Subject: [PATCH AUTOSEL 4.18 09/58] batman-adv: Prevent duplicated gateway_node entry

From: Sven Eckelmann <sven@...fation.org>

[ Upstream commit dff9bc42ab0b2d38c5e90ddd79b238fed5b4c7ad ]

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@...fation.org>
Acked-by: Marek Lindner <mareklindner@...mailbox.ch>
Signed-off-by: Simon Wunderlich <sw@...onwunderlich.de>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
---
 net/batman-adv/gateway_client.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/net/batman-adv/gateway_client.c b/net/batman-adv/gateway_client.c
index 8b198ee798c9..140c61a3f1ec 100644
--- a/net/batman-adv/gateway_client.c
+++ b/net/batman-adv/gateway_client.c
@@ -32,6 +32,7 @@
 #include <linux/kernel.h>
 #include <linux/kref.h>
 #include <linux/list.h>
+#include <linux/lockdep.h>
 #include <linux/netdevice.h>
 #include <linux/netlink.h>
 #include <linux/rculist.h>
@@ -348,6 +349,9 @@ void batadv_gw_check_election(struct batadv_priv *bat_priv,
  * @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,
@@ -355,6 +359,8 @@ 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;
 
@@ -369,10 +375,8 @@ static void batadv_gw_node_add(struct batadv_priv *bat_priv,
 	gw_node->bandwidth_down = ntohl(gateway->bandwidth_down);
 	gw_node->bandwidth_up = ntohl(gateway->bandwidth_up);
 
-	spin_lock_bh(&bat_priv->gw.list_lock);
 	kref_get(&gw_node->refcount);
 	hlist_add_head_rcu(&gw_node->list, &bat_priv->gw.gateway_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",
@@ -428,11 +432,14 @@ 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))
-- 
2.17.1