net: mvneta: fix race condition in mvneta_tx()

[ Upstream commit 5f478b41 ]

mvneta_tx() dereferences skb to get skb->len too late,
as hardware might have completed the transmit and TX completion
could have freed the skb from another cpu.

Fixes: 71f6d1b3 ("net: mvneta: replace Tx timer with a real interrupt")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>

drivers/net/ethernet/marvell/mvneta.c

@@ -1524,6 +1524,7 @@ static int mvneta_tx(struct sk_buff *skb, struct net_device *dev)
 	struct mvneta_tx_queue *txq = &pp->txqs[txq_id];
 	struct mvneta_tx_desc *tx_desc;
 	struct netdev_queue *nq;
+	int len = skb->len;
 	int frags = 0;
 	u32 tx_cmd;
 
@@ -1584,7 +1585,7 @@ static int mvneta_tx(struct sk_buff *skb, struct net_device *dev)
 	if (frags > 0) {
 		u64_stats_update_begin(&pp->tx_stats.syncp);
 		pp->tx_stats.packets++;
-		pp->tx_stats.bytes += skb->len;
+		pp->tx_stats.bytes += len;
 		u64_stats_update_end(&pp->tx_stats.syncp);
 
 	} else {