netdev - Re: [PATCH] fib_trie: remove potential out of bound access

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Message-ID: <1375743656.4457.48.camel@edumazet-glaptop>
Date:	Mon, 05 Aug 2013 16:00:56 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Stephen Hemminger <stephen@...workplumber.org>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Andrey Konovalov <andreyknvl@...gle.com>,
	Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH] fib_trie: remove potential out of bound access

On Mon, 2013-08-05 at 15:41 -0700, Stephen Hemminger wrote:
> On Mon, 05 Aug 2013 11:18:49 -0700
> Eric Dumazet <eric.dumazet@...il.com> wrote:
> 
> > From: Eric Dumazet <edumazet@...gle.com>
> > 
> > AddressSanitizer [1] dynamic checker pointed a potential
> > out of bound access in leaf_walk_rcu()
> > 
> > We could allocate one more slot in tnode_new() to leave the prefetch()
> > in-place but it looks not worth the pain.
> > 
> > Bug added in commit 82cfbb008572b ("[IPV4] fib_trie: iterator recode")
> > 
> > [1] :
> > https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForKernel
> > 
> > Reported-by: Andrey Konovalov <andreyknvl@...gle.com>
> > Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> > Cc: Dmitry Vyukov <dvyukov@...gle.com>
> 
> Isn't prefetch supposed to always be safe, even out of bounds; even prefetch(NULL).
> Although I really doubt prefetch helps in in this code anyway.


prefetch(...) was not the problem here.

The problem was X = array[N]   with N being >= size(array)



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