net: mangle zero checksum in skb_checksum_help()
authorEric Dumazet <edumazet@google.com>
Sat, 29 Oct 2016 18:02:36 +0000 (11:02 -0700)
committerBen Hutchings <ben@decadent.org.uk>
Thu, 16 Mar 2017 02:18:53 +0000 (02:18 +0000)
[ 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 ┼╗enczykowski <maze@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Acked-by: Maciej ┼╗enczykowski <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

index 91018eb..164958d 100644 (file)
@@ -1918,7 +1918,7 @@ int skb_checksum_help(struct sk_buff *skb)
                        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;
 out: