linux-kernel - Re: [RFC PATCH v1 2/8] zram: avoid invalid memory access in zram

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Message-ID: <20130604090309.GB28551@blaptop>
Date:	Tue, 4 Jun 2013 18:03:09 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Jiang Liu <liuj97@...il.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Nitin Gupta <ngupta@...are.org>,
	Jerome Marchand <jmarchan@...hat.com>,
	Yijing Wang <wangyijing@...wei.com>,
	Jiang Liu <jiang.liu@...wei.com>, devel@...verdev.osuosl.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v1 2/8] zram: avoid invalid memory access in
 zram_exit()

On Mon, Jun 03, 2013 at 11:42:14PM +0800, Jiang Liu wrote:
> Memory for zram->disk object may have already been freed after returning
> from destroy_device(zram), then it's unsafe for zram_reset_device(zram)
> to access zram->disk again.
> 
> Fix it by holding an extra reference to zram->disk before calling
> destroy_device(zram).
> 
> Signed-off-by: Jiang Liu <jiang.liu@...wei.com>
> ---
>  drivers/staging/zram/zram_drv.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
> index e34e3fe..ee6b67d 100644
> --- a/drivers/staging/zram/zram_drv.c
> +++ b/drivers/staging/zram/zram_drv.c
> @@ -727,8 +727,10 @@ static void __exit zram_exit(void)
>  	for (i = 0; i < num_devices; i++) {
>  		zram = &zram_devices[i];
>  
> +		get_disk(zram->disk);
>  		destroy_device(zram);
>  		zram_reset_device(zram);
> +		put_disk(zram->disk);

Can't we simple reverse calling order of above two functions?

        zram_reset_device(zram);
        destroy_device(zram);

-- 
Kind regards,
Minchan Kim
--
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