Code: static void ip_cmsg_recv_checksum(struct msghdr *msg, struct sk_buff *skb,
				  int tlen, int offset)
{
	__wsum csum = skb->csum;

 	if (skb->ip_summed != CHECKSUM_COMPLETE)
 		return;
 
	if (offset != 0)
		csum = csum_sub(csum,
				csum_partial(skb_transport_header(skb) + tlen,
					     offset, 0));
 
 	put_cmsg(msg, SOL_IP, IP_CHECKSUM, sizeof(__wsum), &csum);
 }

Vulnerability Type: DoS 
CWE ID: CWE-125
Summary: The ip_cmsg_recv_checksum function in net/ipv4/ip_sockglue.c in the Linux kernel before 4.10.1 has incorrect expectations about skb data layout, which allows local users to cause a denial of service (buffer over-read) or possibly have unspecified other impact via crafted system calls, as demonstrated by use of the MSG_MORE flag in conjunction with loopback UDP transmission.
Commit Message: 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: ad6f939ab193 ("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>