netdev - [patch net-next 7/7] mlxsw: Fix use-after-free bug in mlxsw_sx_port

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Date:	Thu,  6 Aug 2015 16:41:58 +0200
From:	Jiri Pirko <jiri@...nulli.us>
To:	netdev@...r.kernel.org
Cc:	davem@...emloft.net, idosch@...lanox.com, eladr@...lanox.com,
	ogerlitz@...lanox.com, Jiri Pirko <jiri@...lanox.com>
Subject: [patch net-next 7/7] mlxsw: Fix use-after-free bug in mlxsw_sx_port_xmit

From: Ido Schimmel <idosch@...lanox.com>

Store the length of the skb before transmitting it and use it for stats
instead of skb->len, since skb might have been freed already.

This issue was discovered using the Kernel Address sanitizer (KASan).

Signed-off-by: Ido Schimmel <idosch@...lanox.com>
Signed-off-by: Jiri Pirko <jiri@...lanox.com>
---
 drivers/net/ethernet/mellanox/mlxsw/switchx2.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/mellanox/mlxsw/switchx2.c b/drivers/net/ethernet/mellanox/mlxsw/switchx2.c
index fce9b45..3e52ee9 100644
--- a/drivers/net/ethernet/mellanox/mlxsw/switchx2.c
+++ b/drivers/net/ethernet/mellanox/mlxsw/switchx2.c
@@ -300,6 +300,7 @@ static netdev_tx_t mlxsw_sx_port_xmit(struct sk_buff *skb,
 		.local_port = mlxsw_sx_port->local_port,
 		.is_emad = false,
 	};
+	u64 len;
 	int err;
 
 	if (mlxsw_core_skb_transmit_busy(mlxsw_sx, &tx_info))
@@ -316,6 +317,7 @@ static netdev_tx_t mlxsw_sx_port_xmit(struct sk_buff *skb,
 		}
 	}
 	mlxsw_sx_txhdr_construct(skb, &tx_info);
+	len = skb->len;
 	/* Due to a race we might fail here because of a full queue. In that
 	 * unlikely case we simply drop the packet.
 	 */
@@ -325,7 +327,7 @@ static netdev_tx_t mlxsw_sx_port_xmit(struct sk_buff *skb,
 		pcpu_stats = this_cpu_ptr(mlxsw_sx_port->pcpu_stats);
 		u64_stats_update_begin(&pcpu_stats->syncp);
 		pcpu_stats->tx_packets++;
-		pcpu_stats->tx_bytes += skb->len;
+		pcpu_stats->tx_bytes += len;
 		u64_stats_update_end(&pcpu_stats->syncp);
 	} else {
 		this_cpu_inc(mlxsw_sx_port->pcpu_stats->tx_dropped);
-- 
1.9.3

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