Patch "ip: fix IP_CHECKSUM handling" has been added to the 4.9-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    ip: fix IP_CHECKSUM handling

to the 4.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     ip-fix-ip_checksum-handling.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From foo@baz Thu Feb 23 21:13:05 CET 2017
From: Paolo Abeni <pabeni@redhat.com>
Date: Tue, 21 Feb 2017 09:33:18 +0100
Subject: ip: fix IP_CHECKSUM handling

From: Paolo Abeni <pabeni@redhat.com>


[ Upstream commit ca4ef4574f1ee5252e2cd365f8f5d5bafd048f32 ]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/ipv4/ip_sockglue.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -105,10 +105,10 @@ static void ip_cmsg_recv_checksum(struct
 	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);
 }


Patches currently in stable-queue which might be from pabeni@redhat.com are

queue-4.9/ip-fix-ip_checksum-handling.patch
queue-4.9/vxlan-fix-oops-in-dev_fill_metadata_dst.patch