linux-kernel - Re: [PATCH v7 1/3] Staging: zram: Fix access of NULL pointer

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Date:	Wed, 30 Oct 2013 11:42:07 +0100
From:	Jerome Marchand <jmarchan@...hat.com>
To:	Rashika Kheria <rashika.kheria@...il.com>
CC:	opw-kernel@...glegroups.com, Minchan Kim <minchan@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiang Liu <jiang.liu@...wei.com>,
	Nitin Gupta <ngupta@...are.org>,
	Jerome Marchand <jmarchand@...hat.com>,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v7 1/3] Staging: zram: Fix access of NULL pointer

On 10/30/2013 12:10 AM, Rashika Kheria wrote:
> This patch fixes the bug in reset_store caused by accessing NULL pointer.
> 
> The bdev gets its value from bdget_disk() which could fail when memory
> pressure is severe and hence can return NULL because allocation of
> inode in bdget could fail.
> 
> Hence, this patch introduces a check for bdev to prevent reference to a
> NULL pointer in the later part of the code. It also removes unnecessary
> check of bdev for fsync_bdev().
> 
> Cc: stable@...r.kernel.org
> Signed-off-by: Rashika Kheria <rashika.kheria@...il.com>
Acked-by: Jerome Marchand <jmarchan@...hat.com>

> ---
> 
> This patch fixes the following issues of the previous revision-
> Better Description
> 
>  drivers/staging/zram/zram_drv.c |    6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
> index 2c4ed52..d640a8f 100644
> --- a/drivers/staging/zram/zram_drv.c
> +++ b/drivers/staging/zram/zram_drv.c
> @@ -648,6 +648,9 @@ static ssize_t reset_store(struct device *dev,
>  	zram = dev_to_zram(dev);
>  	bdev = bdget_disk(zram->disk, 0);
>  
> +	if (!bdev)
> +		return -EBUSY;
> +
>  	/* Do not reset an active device! */
>  	if (bdev->bd_holders)
>  		return -EBUSY;
> @@ -660,8 +663,7 @@ static ssize_t reset_store(struct device *dev,
>  		return -EINVAL;
>  
>  	/* Make sure all pending I/O is finished */
> -	if (bdev)
> -		fsync_bdev(bdev);
> +	fsync_bdev(bdev);
>  
>  	zram_reset_device(zram, true);
>  	return len;
> 

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