netdev - Re: [PATCH net] dccp/tcp: fix routing redirect race

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Message-ID: <1489034454.28631.21.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Wed, 08 Mar 2017 20:40:54 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Jonathan Maxwell <jmaxwell37@...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, 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)