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

[Eric Dumazet <eric.dumazet@gmail.com>]

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@gmail.com> wrote:
> 
> > From: Eric Dumazet <edumazet@google.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@google.com>
> > Signed-off-by: Eric Dumazet <edumazet@google.com>
> > Cc: Dmitry Vyukov <dvyukov@google.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)