Commit 31c2e492 authored Apr 07, 2016 by Willem de Bruijn Committed by David S. Miller Apr 13, 2016

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 e6afc8ac 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: e6afc8ac ("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>

parent 9f9a45be

net/ipv4/ip_sockglue.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -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);
		}

net/ipv4/udp.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -1375,7 +1375,7 @@ int udp_recvmsg(struct sock sk, struct msghdr msg, size_t len, int noblock,
		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)