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Date:   Thu, 9 Mar 2017 15:47:16 +1100
From:   Jonathan Maxwell <jmaxwell37@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     gerrit@....abdn.ac.uk, David Miller <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        kuznet <kuznet@....inr.ac.ru>, jmorris <jmorris@...ei.org>,
        yoshfuji <yoshfuji@...ux-ipv6.org>, kaber <kaber@...sh.net>,
        Neal Cardwell <ncardwell@...gle.com>, dccp@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jon Maxwell <jmaxwell@...hat.com>,
        Eric Garver <egarver@...hat.com>,
        Hannes Sowa <hsowa@...hat.com>
Subject: Re: [PATCH net] dccp/tcp: fix routing redirect race

On Thu, Mar 9, 2017 at 3:40 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Thu, 2017-03-09 at 14:42 +1100, Jonathan Maxwell wrote:
>> Sorry let me resend in plain text mode.
>>
>> On Thu, Mar 9, 2017 at 1:10 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>> > On Thu, 2017-03-09 at 12:15 +1100, Jon Maxwell wrote:
>> >> We have seen a few incidents lately where a dst_enty has been freed
>> >> with a dangling TCP socket reference (sk->sk_dst_cache) pointing to that
>> >> dst_entry. If the conditions/timings are right a crash then ensues when the
>> >> freed dst_entry is referenced later on. A Common crashing back trace is:
>> >
>> > Very nice catch !
>> >
>>
>> Thanks Eric.
>>
>> > Don't we have a similar issue for IPv6 ?
>> >
>> >
>>
>> Good point.
>>
>> We checked and as far as we can tell IPv6 does not invalidate the route.
>> So it should be safer.
>
> Simply doing :
>
> __sk_dst_check(sk, np->dst_cookie);
>
> is racy, even before calling dst->ops->redirect(dst, sk, skb);
>
> (if socket is owned by user)
>
>
>

Okay, I will add a similar patch for IPv6 to also protect from that.

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