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Date: Wed, 2 May 2012 18:06:01 +0400
From: Solar Designer <solar@...nwall.com>
To: john-dev@...ts.openwall.com
Subject: Re: wpapsk.h warnings

Lukas, magnum -

On Tue, May 01, 2012 at 11:57:05PM +0200, magnum wrote:
> I get these warnings when building. The first one looks like an actual
> bug to me, or maybe I misunderstand the code:
> 
> In file included from opencl_wpapsk_fmt.c:15:0:
> wpapsk.h: In function ???decode_hccap???:
> wpapsk.h:102:9: warning: array subscript is above array bounds
> [-Warray-bounds]
> 
> The array is char[6] but you write all the way to 118 * 3, no?

I looked into this yesterday.  The out-of-bounds writes look intentional
(I think they're still within the struct, although I did not verify
that), but there's assumption that they're permitted and that the struct
is packed.  We can only ensure the latter with specific compilers (such
as with gcc's __attribute__((packed)), which we'll need to specify),
although in practice I am not aware of cases of compilers inserting
padding between fields of type char.

I think it'd be best to rewrite this, maybe by using a union - one
sufficiently large array union'ed with a struct - although that still
depends on the struct being packed.

Alexander

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