From ca4ef4574f1ee5252e2cd365f8f5d5bafd048f32 Mon Sep 17 00:00:00 2001 From: Paolo Abeni Date: Tue, 21 Feb 2017 09:33:18 +0100 Subject: 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 Signed-off-by: Paolo Abeni Acked-by: Eric Dumazet Signed-off-by: David S. Miller --- net/ipv4/ip_sockglue.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c index ce1386a..ebd953b 100644 --- a/net/ipv4/ip_sockglue.c +++ b/net/ipv4/ip_sockglue.c @@ -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); } -- cgit v1.1