[PATCH 3.16 181/192] netvsc: fix incorrect receive checksum offloading

[Ben Hutchings]

3.16.49-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Stephen Hemminger <sthemmin@xxxxxxxxxxxxx>

commit e52fed7177f74382f742c27de2cc5314790aebb6 upstream.

The Hyper-V netvsc driver was looking at the incorrect status bits
in the checksum info. It was setting the receive checksum unnecessary
flag based on the IP header checksum being correct. The checksum
flag is skb is about TCP and UDP checksum status. Because of this
bug, any packet received with bad TCP checksum would be passed
up the stack and to the application causing data corruption.
The problem is reproducible via netcat and netem.

This had a side effect of not doing receive checksum offload
on IPv6. The driver was also also always doing checksum offload
independent of the checksum setting done via ethtool.

Signed-off-by: Stephen Hemminger <sthemmin@xxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/net/hyperv/netvsc_drv.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

--- a/drivers/net/hyperv/netvsc_drv.c
+++ b/drivers/net/hyperv/netvsc_drv.c
@@ -643,15 +643,18 @@ int netvsc_recv_callback(struct hv_devic
 		packet->total_data_buflen);
 
 	skb->protocol = eth_type_trans(skb, net);
-	if (csum_info) {
-		/* We only look at the IP checksum here.
-		 * Should we be dropping the packet if checksum
-		 * failed? How do we deal with other checksums - TCP/UDP?
-		 */
-		if (csum_info->receive.ip_checksum_succeeded)
+
+	/* skb is already created with CHECKSUM_NONE */
+	skb_checksum_none_assert(skb);
+
+	/*
+	 * In Linux, the IP checksum is always checked.
+	 * Do L4 checksum offload if enabled and present.
+	 */
+	if (csum_info && (net->features & NETIF_F_RXCSUM)) {
+		if (csum_info->receive.tcp_checksum_succeeded ||
+		    csum_info->receive.udp_checksum_succeeded)
 			skb->ip_summed = CHECKSUM_UNNECESSARY;
-		else
-			skb->ip_summed = CHECKSUM_NONE;
 	}
 
 	if (packet->vlan_tci & VLAN_TAG_PRESENT)