linux-kernel - Re: [PATCH] - Fix slab corruption caused by alloc_cpumask_var

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Date:	Thu, 2 Apr 2009 23:42:19 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Jack Steiner <steiner@....com>
Cc:	akpm@...ux-foundation.org, rusty@...tcorp.com.au,
	sfr@...b.auug.org.au, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] - Fix slab corruption caused by
	alloc_cpumask_var_node()


* Jack Steiner <steiner@....com> wrote:

> Fix for slab corruption caused by alloc_cpumask_var_node() overwriting
> the tail end of an off-stack cpumask.
> 
> Signed-off-by: Jack Steiner <steiner@....com>
> Acked-by: Mike Travis <travis.sgi.com>
> 
> 
> ---
> 
> Corrruption was found in latest linux-next (4/1)
> 	v2.6.29-12081-g421a9f3
> 
> 
> 
>  lib/cpumask.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> Index: linux/lib/cpumask.c
> ===================================================================
> --- linux.orig/lib/cpumask.c	2009-04-02 15:30:05.000000000 -0500
> +++ linux/lib/cpumask.c	2009-04-02 15:57:44.000000000 -0500
> @@ -109,10 +109,10 @@ bool alloc_cpumask_var_node(cpumask_var_
>  #endif
>  	/* FIXME: Bandaid to save us from old primitives which go to NR_CPUS. */
>  	if (*mask) {
> +		unsigned char *ptr = (unsigned char *)cpumask_bits(*mask);
>  		unsigned int tail;
>  		tail = BITS_TO_LONGS(NR_CPUS - nr_cpumask_bits) * sizeof(long);
> -		memset(cpumask_bits(*mask) + cpumask_size() - tail,
> -		       0, tail);
> +		memset(ptr + cpumask_size() - tail, 0, tail);

Nice,

Acked-by: Ingo Molnar <mingo@...e.hu>

Note: it also needs a Cc: <stable@...nel.org> tag as v2.6.29 is 
affected by this bug too.

	Ingo
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