linux-kernel - Re: [PATCH net] udp: prevent bugcheck if filter truncates packet too much

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Date:	Sat, 9 Jul 2016 09:05:23 -0400
From:	Willem de Bruijn <willemb@...gle.com>
To:	Michal Kubecek <mkubecek@...e.cz>
Cc:	Daniel Borkmann <daniel@...earbox.net>,
	Alexei Starovoitov <alexei.starovoitov@...il.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	samanthakumar <samanthakumar@...gle.com>,
	Marco Grassi <marco.gra@...il.com>,
	Network Development <netdev@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>
Subject: Re: [PATCH net] udp: prevent bugcheck if filter truncates packet too much

On Sat, Jul 9, 2016 at 6:43 AM, Michal Kubecek <mkubecek@...e.cz> wrote:
> On Sat, Jul 09, 2016 at 11:48:49AM +0200, Daniel Borkmann wrote:
>> On 07/09/2016 02:20 AM, Alexei Starovoitov wrote:
>> >On Sat, Jul 09, 2016 at 01:31:40AM +0200, Eric Dumazet wrote:
>> >>On Fri, 2016-07-08 at 17:52 +0200, Michal Kubecek wrote:
>> >>>If socket filter truncates an udp packet below the length of UDP header
>> >>>in udpv6_queue_rcv_skb() or udp_queue_rcv_skb(), it will trigger a
>> >>>BUG_ON in skb_pull_rcsum(). This BUG_ON (and therefore a system crash if
>> >>>kernel is configured that way) can be easily enforced by an unprivileged
>> >>>user which was reported as CVE-2016-6162. For a reproducer, see
>> >>>http://seclists.org/oss-sec/2016/q3/8
>> >>>
>> >>>Fixes: e6afc8ace6dd ("udp: remove headers from UDP packets before queueing")
>> >>>Reported-by: Marco Grassi <marco.gra@...il.com>
>> >>>Signed-off-by: Michal Kubecek <mkubecek@...e.cz>
>> >>>---
>
>> >>Acked-by: Eric Dumazet <edumazet@...gle.com>
>> >
>> >this is incomplete fix. Please do not apply. See discussion at security@...nel
>>
>> Ohh well, didn't see it earlier before starting the discussion at security@...
>>
>> I'm okay if we take this for now as a quick band aid and find a better
>> way how to deal with the underlying issue long-term so that it's
>> /guaranteed/ that it doesn't bite us any further in such fragile ways.
>
> Agreed. As rc7 is due in a day or two, rushing a complex and intrusive
> solution in might be too risky.

Acked-by: Willem de Bruijn <willemb@...gle.com>

Thanks, Michal.