Willem de Bruijn 31c2e4926f udp: do not expect udp headers in recv cmsg IP_CMSG_CHECKSUM ...

On udp sockets, recv cmsg IP_CMSG_CHECKSUM returns a checksum over
the packet payload. Since commit e6afc8ace6 pulled the headers,
taking skb->data as the start of transport header is incorrect. Use
the transport header pointer.

Also, when peeking at an offset from the start of the packet, only
return a checksum from the start of the peeked data. Note that the
cmsg does not subtract a tail checkum when reading truncated data.

Fixes: e6afc8ace6 ("udp: remove headers from UDP packets before queueing")

Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2016-04-13 22:24:52 -04:00

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