mlxsw: Fix use-after-free bug in mlxsw_sx_port_xmit

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@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/ethernet/mellanox/mlxsw/switchx2.c b/drivers/net/ethernet/mellanox/mlxsw/switchx2.c
index fce9b45..3e52ee9 100644 (file)
--- 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);