hyperv: Fix a bug in netvsc_start_xmit()

[ Upstream commit dedb845d ]

After the packet is successfully sent, we should not touch the skb
as it may have been freed. This patch is based on the work done by
Long Li <longli@microsoft.com>.

In this version of the patch I have fixed issues pointed out by David.
David, please queue this up for stable.
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Tested-by: Long Li <longli@microsoft.com>
Tested-by: Sitsofe Wheeler <sitsofe@yahoo.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/net/hyperv/netvsc_drv.c

@@ -138,6 +138,7 @@ static int netvsc_start_xmit(struct sk_buff *skb, struct net_device *net)
 	struct hv_netvsc_packet *packet;
 	int ret;
 	unsigned int i, num_pages, npg_data;
+	u32 skb_length = skb->len;
 
 	/* Add multipages for skb->data and additional 2 for RNDIS */
 	npg_data = (((unsigned long)skb->data + skb_headlen(skb) - 1)
@@ -208,7 +209,7 @@ static int netvsc_start_xmit(struct sk_buff *skb, struct net_device *net)
 	ret = rndis_filter_send(net_device_ctx->device_ctx,
 				  packet);
 	if (ret == 0) {
-		net->stats.tx_bytes += skb->len;
+		net->stats.tx_bytes += skb_length;
 		net->stats.tx_packets++;
 	} else {
 		kfree(packet);