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

From: Willem de Bruijn
Date: Sat Jul 09 2016 - 09:06:16 EST

On Sat, Jul 9, 2016 at 6:43 AM, Michal Kubecek <mkubecek@xxxxxxx> 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
>> >>>
>> >>>
>> >>>Fixes: e6afc8ace6dd ("udp: remove headers from UDP packets before queueing")
>> >>>Reported-by: Marco Grassi <marco.gra@xxxxxxxxx>
>> >>>Signed-off-by: Michal Kubecek <mkubecek@xxxxxxx>
>> >>>---
>> >>Acked-by: Eric Dumazet <edumazet@xxxxxxxxxx>
>> >
>> >this is incomplete fix. Please do not apply. See discussion at security@kernel
>> 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@xxxxxxxxxx>

Thanks, Michal.