From ca4ef4574f1ee5252e2cd365f8f5d5bafd048f32 Mon Sep 17 00:00:00 2001
From: Paolo Abeni <pabeni@redhat.com>
Date: Tue, 21 Feb 2017 09:33:18 +0100
Subject: [PATCH] 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>
---
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 ce1386a67e243..ebd953bc5607f 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);
}
--
2.30.2