[PATCH net] 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().

Fixes: d39d938c8228 ("ipv6: Introduce udpv6_send_skb()")
Signed-off-by: Subash Abhinov Kasiviswanathan <redacted>
---
 net/ipv6/udp.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index e2ecfb1..40d7234 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c

@@ -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 <redacted>
Date: Wed, 13 Sep 2017 19:30:51 -0600

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().

Fixes: d39d938c8228 ("ipv6: Introduce udpv6_send_skb()")
Signed-off-by: Subash Abhinov Kasiviswanathan <redacted>

Good catch, applied and queued up for -stable.