Commit ca4ef457 authored Feb 21, 2017 by Paolo Abeni Committed by David S. Miller Feb 21, 2017

ip: fix IP_CHECKSUM handling



The skbs processed by ip_cmsg_recv() are not guaranteed to
be linear e.g. when sending UDP packets over loopback with
MSGMORE.
Using csum_partial() on [potentially] the whole skb len
is dangerous; instead be on the safe side and use skb_checksum().

Thanks to syzkaller team to detect the issue and provide the
reproducer.

v1 -> v2:
 - move the variable declaration in a tighter scope

Fixes: ad6f939a ("ip: Add offset parameter to ip_cmsg_recv")
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 8dcd81a9

net/ipv4/ip_sockglue.c

+4 −4

Original line number	Diff line number	Diff line
		@@ -116,10 +116,10 @@ static void ip_cmsg_recv_checksum(struct msghdr msg, struct sk_buff skb,
		if (skb->ip_summed != CHECKSUM_COMPLETE)
		return;

		if (offset != 0)
		csum = csum_sub(csum,
		csum_partial(skb_transport_header(skb) + tlen,
		offset, 0));
		if (offset != 0) {
		int tend_off = skb_transport_offset(skb) + tlen;
		csum = csum_sub(csum, skb_checksum(skb, tend_off, offset, 0));
		}

		put_cmsg(msg, SOL_IP, IP_CHECKSUM, sizeof(__wsum), &csum);
		}