linux-kernel - Re: [PATCH v2] flex_array: Change behaviour on zero size allocations

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Date:	Tue, 08 Feb 2011 09:02:41 -0800
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	Steffen Klassert <steffen.klassert@...unet.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Eric Paris <eparis@...hat.com>, linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org
Subject: Re: [PATCH v2] flex_array: Change behaviour on zero size
 allocations

On Mon, 2011-02-07 at 13:29 +0100, Steffen Klassert wrote:
>  int flex_array_prealloc(struct flex_array *fa, unsigned int start,
> -                       unsigned int end, gfp_t flags)
> +                       unsigned int nr_elements, gfp_t flags)
>  {
>         int start_part;
>         int end_part;
>         int part_nr;
> +       unsigned int end;
>         struct flex_array_part *part;
> 
> -       if (start >= fa->total_nr_elements || end >= fa->total_nr_elements)
> +       if (!fa->total_nr_elements && !start)
> +               return 0;
> +       if (start >= fa->total_nr_elements)
> +               return -ENOSPC;
> +       if (!nr_elements)
> +               return 0;
> +
> +       end = start + nr_elements - 1;
> +
> +       if (end >= fa->total_nr_elements)
>                 return -ENOSPC;
> +       if (!fa->element_size)
> +               return 0; 

The rest of this patch looks good.  When you resend, you need to break
this up in to at least two patches: one to change 'end' to
'nr_elements' (or something else) and the one to handle zero-sized
elements and arrays.

I also think we need to remove the ability to do zero-sized elements.
Unless there's some new code that I'm missing, I don't see any of the
existing security policy code which would be able to do that.

-- Dave

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