linux-kernel - Re: [PATCH 1/1] mtd: mtdoops: fix for a potential memory leak in mtdoops_notify

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Date:	Mon, 12 Aug 2013 14:26:50 -0300
From:	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>
To:	Nilanjan Roychowdhury <nilanjan.roychowdhury@...il.com>
Cc:	David Woodhouse <dwmw2@...radead.org>,
	linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] mtd: mtdoops: fix for a potential memory leak in
 mtdoops_notify_remove

On Sun, Aug 11, 2013 at 01:11:48PM -0700, Nilanjan Roychowdhury wrote:
> we are allocating cxt->oops_page_used using vmalloc in mtdoops_notify_add for
> every mtd_info addition but not freeing it in mtdoops_notify_remove
> 
> Signed-off-by: Nilanjan Roychowdhury <nilanjan.roychowdhury@...il.com>
> ---
>  drivers/mtd/mtdoops.c |    1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/mtd/mtdoops.c b/drivers/mtd/mtdoops.c
> index 97bb8f6..02f49aa 100644
> --- a/drivers/mtd/mtdoops.c
> +++ b/drivers/mtd/mtdoops.c
> @@ -386,6 +386,7 @@ static void mtdoops_notify_remove(struct mtd_info *mtd)
>  	cxt->mtd = NULL;
>  	flush_work(&cxt->work_erase);
>  	flush_work(&cxt->work_write);
> +	vfree(cxt->oops_page_used);
>  }
>  
> -- 
> 1.7.9.5
> 

Have you tested this patch doing an unregister/module remove cycle?

I'm not entirely sure, but I *think* you must also remove the
vfree(cxt->oops_page_used); at mtdoops_exit(). Otherwise,
you might call vfree() twice, the second time on a garbage pointer.

The reason for this is that the unregister_mtd_user(&mtdoops_notifier);
call in mtdoops_exit() will call the .remove callback (causing the first
vfree() with this patch) and then call vfree() for the second time, explicitly.
-- 
Ezequiel García, Free Electrons
Embedded Linux, Kernel and Android Engineering
http://free-electrons.com
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