netdev - Possible problem with e6afc8ac ("udp: remove headers from UDP packets before queueing")

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Date:	Wed, 1 Jun 2016 15:01:05 -0400
From:	Paul Moore <paul@...l-moore.com>
To:	samanthakumar@...gle.com
Cc:	netdev@...r.kernel.org, linux-security-module@...r.kernel.org,
	selinux@...ho.nsa.gov
Subject: Possible problem with e6afc8ac ("udp: remove headers from UDP packets
 before queueing")

Hello,

I'm currently trying to debug a problem with 4.7-rc1 and labeled
networking over UDP.  I'm having some difficulty with the latest
4.7-rc1 builds on my test system at the moment so I haven't been able
to concisely identify the problem, but looking through the commits in
4.7-rc1 I think there may be a problem with the following:

  commit e6afc8ace6dd5cef5e812f26c72579da8806f5ac
  Author: samanthakumar <samanthakumar@...gle.com>
  Date:   Tue Apr 5 12:41:15 2016 -0400

   udp: remove headers from UDP packets before queueing

   Remove UDP transport headers before queueing packets for reception.
   This change simplifies a follow-up patch to add MSG_PEEK support.

   Signed-off-by: Sam Kumar <samanthakumar@...gle.com>
   Signed-off-by: Willem de Bruijn <willemb@...gle.com>
   Signed-off-by: David S. Miller <davem@...emloft.net>

... it appears that this commit changes things so that sk_filter() is
only called when sk->sk_filter is not NULL.  While this is fine for
the traditional socket filter case, it causes problems with LSMs that
make use of security_sock_rcv_skb() to enforce per-packet access
controls.

Hopefully I'll get 4.7-rc1 booting soon and I can do a proper
bisection test around this patch, but I wanted to mention this now in
case others are seeing the same problem.

-- 
paul moore
www.paul-moore.com