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

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Date:	Tue, 1 Feb 2011 11:24:18 +0100
From:	Steffen Klassert <steffen.klassert@...unet.com>
To:	Dave Hansen <dave@...ux.vnet.ibm.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] flex_array: Change behaviour on zero size allocations

On Mon, Jan 31, 2011 at 08:31:37AM -0800, Dave Hansen wrote:
> 
> I think this still has some of the issues of the earlier patch.  The
> zero-size check needs to be moved after the ->total_nr_elements check.
> Otherwise, this won't produce any errors:
> 
> 	fa = flex_array_alloc(0, 100, GFP_KERNEL);
> 	flex_array_put(fa, 1001, ptr, GFP_KERNEL);
> 
> > @@ -284,6 +297,8 @@ void *flex_array_get(struct flex_array *fa, unsigned int element_nr)
> >         int part_nr = fa_element_to_part_nr(fa, element_nr);
> >         struct flex_array_part *part;
> > 
> > +       if (!fa->total_nr_elements || !fa->element_size)
> > +               return NULL;
> >         if (element_nr >= fa->total_nr_elements)
> >                 return NULL;
> >         if (elements_fit_in_base(fa))
> 
> Do you really need to check fa->total_nr_elements both for zero and
> against element_nr?  Seems a but superfluous to me.
> 

Both objections are correct, I'll send an updated patch.

Steffen
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