netdev - Re: Bug in net/ipv6/ip6_fib.c:fib6_dump

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Message-ID: <CAATkVEyaocRcYJnfuQmGFAySBerQsXY44JDi4zjveP7TZNmu7Q@mail.gmail.com>
Date:	Fri, 22 Jun 2012 17:12:07 -0400
From:	Debabrata Banerjee <dbavatar@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Josh Hunt <johunt@...mai.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"kaber@...sh.net" <kaber@...sh.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"yoshfuji@...ux-ipv6.org" <yoshfuji@...ux-ipv6.org>,
	"jmorris@...ei.org" <jmorris@...ei.org>,
	"pekkas@...core.fi" <pekkas@...core.fi>,
	"kuznet@....inr.ac.ru" <kuznet@....inr.ac.ru>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Bug in net/ipv6/ip6_fib.c:fib6_dump_table()

On Fri, Jun 22, 2012 at 2:13 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Fri, 2012-06-22 at 08:44 -0500, Josh Hunt wrote:
>
>> Ahh. That makes sense and is what Alexey said before I just didn't put
>> it all together. So we are OK reverting this patch? I cannot find a path
>> where the walker's pointers are updated without the tb6_lock write_lock.
>>
>
> There was a bug somewhere, not sure we want to NULL dereference again.
>

As you identified, the tree seems to be protected by tb6_lock. I
couldn't find a race by inspection either. If this is not the root of
the problem, how would this patch fix it? So I think it does nothing.
We are attempting to reproduce that crash to prove it, but like Gao
feng I don't think we will see it.

My current favorite theory is that inet6_dump_fib was called with a
NULL func in callback. This looks like the approximate area of the
crash, but it's impossible to say without more information from
Patrick McHardy.
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