[PATCH 3.16 332/370] net: mangle zero checksum in skb_checksum_help()

Ben Hutchings
2017-03-10T13:25:14Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 4f2e4ad56a65f3b7d64c258e373cb71e8d2499f4 ]

Sending zero checksum is ok for TCP, but not for UDP.

UDPv6 receiver should by default drop a frame with a 0 checksum,
and UDPv4 would not verify the checksum and might accept a corrupted
packet.

Simply replace such checksum by 0xffff, regardless of transport.

This error was caught on SIT tunnels, but seems generic.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Maciej Żenczykowski <maze@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Acked-by: Maciej Żenczykowski <maze@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
net/core/dev.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2282,7 +2282,7 @@ int skb_checksum_help(struct sk_buff *sk
goto out;
}

- *(__sum16 *)(skb->data + offset) = csum_fold(csum);
+ *(__sum16 *)(skb->data + offset) = csum_fold(csum) ?: CSUM_MANGLED_0;
out_set_summed:
skb->ip_summed = CHECKSUM_NONE;