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

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Date:	Tue, 22 Apr 2014 14:00:06 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Alexey Preobrazhensky <preobr@...gle.com>
Cc:	netdev@...r.kernel.org, Kostya Serebryany <kcc@...gle.com>,
	Dmitry Vyukov <dvyukov@...gle.com>, yoshfuji@...ux-ipv6.org,
	maze@...gle.com, edumazet@...gle.com, brutus@...gle.com
Subject: Re: Potential out-of-bounds access in ip6_finish_output2

On Mon, Apr 21, 2014 at 05:22:05PM +0400, Alexey Preobrazhensky wrote:
> Hi,
> 
> I’m working on AddressSanitizer[1] -- a tool that detects
> use-after-free and out-of-bounds bugs in kernel.
> 
> I’ve encountered a heap-buffer-overflow in ip6_finish_output2 in linux
> kernel 3.14 (revision 455c6fdbd219161bd09b1165f11699d6d73de11c). A
> similar problem was reported earlier[2] and resulted in a patch[3],
> but we’ve hit this report again, so it seems the issue weren’t fixed,
> or there is another issue. The offending code in
> include/net/neighbour.h:401 is:
> 
> do {
>         seq = read_seqbegin(&hh->hh_lock);
>         hh_len = hh->hh_len;
>         if (likely(hh_len <= HH_DATA_MOD)) {
>                 /* this is inlined by gcc */
> /* 401: */    memcpy(skb->data - HH_DATA_MOD, hh->hh_data, HH_DATA_MOD);
>         } else {
>                 int hh_alen = HH_DATA_ALIGN(hh_len);
> 
>                 memcpy(skb->data - hh_alen, hh->hh_data, hh_alen);
>         }
> } while (read_seqretry(&hh->hh_lock, seq));
> 
> This heap-buffer-overflow was triggered under trinity syscall fuzzer,
> so there is no reproducer. The report is followed by crash (included).
> 
> It would be great if someone familiar with the code took time to look
> into this report.

Thanks for the report!

By only looking at the report I doubt it is the same problem. I still have a
lot of mails to catch up but hope that I can audit the code in the next days.

Thanks,

  Hannes

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