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    Subject[PATCH 3.16 332/370] net: mangle zero checksum in skb_checksum_help()
    3.16.42-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    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;
    out:
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