Re: [PATCH net] ip: fix IP_CHECKSUM handling
From: Stephen Hemminger <stephen@networkplumber.org>
Date: 2017-02-20 17:23:28
On Mon, 20 Feb 2017 17:55:39 +0100 Paolo Abeni [off-list ref] wrote:
quoted hunk ↗ jump to hunk
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. Fixes: ad6f939ab193 ("ip: Add offset parameter to ip_cmsg_recv") Reported-by: Andrey Konovalov <redacted> Signed-off-by: Paolo Abeni <pabeni@redhat.com> --- net/ipv4/ip_sockglue.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c index 9000117..d88bbe2 100644 --- a/net/ipv4/ip_sockglue.c +++ b/net/ipv4/ip_sockglue.c@@ -112,14 +112,15 @@ static void ip_cmsg_recv_checksum(struct msghdr *msg, struct sk_buff *skb, int tlen, int offset) { __wsum csum = skb->csum; + int tend_off; 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) { + tend_off = skb_transport_offset(skb) + tlen; + csum = csum_sub(csum, skb_checksum(skb, tend_off, offset, 0)); + }
If you need to add a local variable (tend_off) then please make its scope
as tight as possible. i.e.
if (offset != 0) {
int tend_off = skb_transport_offset(skb) + tlen;