linux-kernel - Re: [PATCH 1/5] tmpfs: fix oops on mounts with mpol=default

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Message-Id: <1268835371.4773.40.camel@useless.americas.hpqcorp.net>
Date:	Wed, 17 Mar 2010 10:16:11 -0400
From:	Lee Schermerhorn <Lee.Schermerhorn@...com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, kiran@...lex86.org,
	cl@...ux-foundation.org, hugh.dickins@...cali.co.uk, mel@....ul.ie,
	stable@...nel.org, linux-mm <linux-mm@...ck.org>,
	akpm@...ux-foundation.org
Subject: Re: [PATCH 1/5] tmpfs: fix oops on mounts with mpol=default

On Tue, 2010-03-16 at 14:49 +0900, KOSAKI Motohiro wrote:
> ChangeLog from Ravikiran's original one
>   - Fix the patch description. the problem is in mount, not only remount.
>   - Skip mpol_new() simply, instead adding NULL check.
> 
> 
> =========================
> From: Ravikiran G Thirumalai <kiran@...lex86.org>
> 
> Fix an 'oops' when a tmpfs mount point is mounted with the mpol=default
> mempolicy.
> 
> Upon remounting a tmpfs mount point with 'mpol=default' option, the
> mount code crashed with a null pointer dereference.  The initial
> problem report was on 2.6.27, but the problem exists in mainline
> 2.6.34-rc as well.  On examining the code, we see that mpol_new returns
> NULL if default mempolicy was requested.  This 'NULL' mempolicy is
> accessed to store the node mask resulting in oops.
> 
> The following patch fixes it.
> 
> Signed-off-by: Ravikiran Thirumalai <kiran@...lex86.org>
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> Cc: Christoph Lameter <cl@...ux-foundation.org>
> Cc: Mel Gorman <mel@....ul.ie>
> Cc: Lee Schermerhorn <lee.schermerhorn@...com>
> Cc: Hugh Dickins <hugh.dickins@...cali.co.uk>
> Cc: <stable@...nel.org>

Acked-by: Lee Schermerhorn <lee.schermerhorn@...com>

> ---
>  mm/mempolicy.c |    9 +++++++--
>  1 files changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index bda230e..25a0c0f 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -2213,10 +2213,15 @@ int mpol_parse_str(char *str, struct mempolicy **mpol, int no_context)
>  			goto out;
>  		mode = MPOL_PREFERRED;
>  		break;
> -
> +	case MPOL_DEFAULT:
> +		/*
> +		 * Insist on a empty nodelist
> +		 */
> +		if (!nodelist)
> +			err = 0;
> +		goto out;
>  	/*
>  	 * case MPOL_BIND:    mpol_new() enforces non-empty nodemask.
> -	 * case MPOL_DEFAULT: mpol_new() enforces empty nodemask, ignores flags.
>  	 */
>  	}
>  

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