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net: mangle zero checksum in skb_checksum_help()

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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>
This commit is contained in:
Eric Dumazet 2016-10-29 11:02:36 -07:00 committed by David S. Miller
parent e551c32d57
commit 4f2e4ad56a
1 changed files with 1 additions and 1 deletions
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2
net/core/dev.c
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@ -2484,7 +2484,7 @@ 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: