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udp: do not expect udp headers in recv cmsg IP_CMSG_CHECKSUM

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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>
This commit is contained in:
Willem de Bruijn 2016-04-07 18:12:59 -04:00 committed by David S. Miller
parent 9f9a45beaa
commit 31c2e4926f
2 changed files with 3 additions and 2 deletions
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3
net/ipv4/ip_sockglue.c
View File

@ -106,7 +106,8 @@ static void ip_cmsg_recv_checksum(struct msghdr *msg, struct sk_buff *skb,
return;
if (offset != 0)
csum = csum_sub(csum, csum_partial(skb->data, offset, 0));
csum = csum_sub(csum, csum_partial(skb_transport_header(skb),
offset, 0));
put_cmsg(msg, SOL_IP, IP_CHECKSUM, sizeof(__wsum), &csum);
}

2
net/ipv4/udp.c
View File

@ -1375,7 +1375,7 @@ try_again:
*addr_len = sizeof(*sin);
}
if (inet->cmsg_flags)
ip_cmsg_recv_offset(msg, skb, sizeof(struct udphdr));
ip_cmsg_recv_offset(msg, skb, sizeof(struct udphdr) + off);
err = copied;
if (flags & MSG_TRUNC)