udpv6: Fix the checksum computation when HW checksum does not apply

While trying an ESP transport mode encryption for UDPv6 packets of datagram size 1436 with MTU 1500, checksum error was observed in the secondary fragment.

This error occurs due to the UDP payload checksum being missed out when computing the full checksum for these packets in udp6_hwcsum_outgoing().

---
 net/ipv6/udp.c | 1 +
 1 file changed, 1 insertion(+)

index e2ecfb1..40d7234 100644
@@ -1015,6 +1015,7 @@ static void udp6_hwcsum_outgoing(struct sock *sk, struct sk_buff *skb,
 		 */
 		offset = skb_transport_offset(skb);
 		skb->csum = skb_checksum(skb, offset, skb->len - offset, 0);
+		csum = skb->csum;
 
 		skb->ip_summed = CHECKSUM_NONE;
 

1.9.1

From: Subash Abhinov Kasiviswanathan <[email protected]>
Date: Wed, 13 Sep 2017 19:30:51 -0600

Good catch, applied and queued up for -stable.