netdev - Re: Potential out-of-bounds access in ip6_finish

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Date:	Sat, 21 Sep 2013 17:14:57 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Dmitry Vyukov <dvyukov@...gle.com>, yoshfuji@...ux-ipv6.org,
	netdev@...r.kernel.org, Paul Turner <pjt@...gle.com>,
	Andrey Konovalov <andreyknvl@...gle.com>,
	Kostya Serebryany <kcc@...gle.com>,
	Tom Herbert <therbert@...gle.com>
Subject: Re: Potential out-of-bounds access in ip6_finish_output2

On Wed, Sep 18, 2013 at 12:48:51AM +0200, Hannes Frederic Sowa wrote:
> On Mon, Sep 16, 2013 at 10:13:10PM -0700, Dmitry Vyukov wrote:
> > I am working on AddressSanitizer -- a tool that detects use-after-free
> > and out-of-bounds bugs
> > (https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForKernel).
> > 
> > I've got a dozen of reports in ip6_finish_output2. Below are 2 of
> > them. They are always followed by kernel crash. Unfortunately I don't
> > have a reproducer because I am using trinity fuzzer. I would
> > appreciate if somebody familiar with the code look at sources and
> > maybe spot the bug.
> 
> Thanks for the report!
> 
> I tried reproducing the bug and hit some other bugs nearby. I'll try to fix
> them, but this could take some time.

I fixed the first bug I encountered with trinity here:
http://patchwork.ozlabs.org/patch/276835/

The main cause of this bug has nothing to do with raw sockets, so I first
thought they are not related. But I left my machine run trinity while
I was sleeping and did not see any other splats (I added some manually
range checks in ip6_append_data). So maybe your bug happend because the
premature exit in the dontfrag check without resetting cork->length. Maybe
you could give this patch a try? I'll have a second look later today.

Thanks,

  Hannes

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