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Date: Wed, 30 Oct 2013 11:42:07 +0100
From: Jerome Marchand <jmarchan@redhat.com>
MIME-Version: 1.0
To: Rashika Kheria <rashika.kheria@gmail.com>
CC: opw-kernel@googlegroups.com, Minchan Kim <minchan@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Jiang Liu <jiang.liu@huawei.com>,
	Nitin Gupta <ngupta@vflare.org>,
	Jerome Marchand <jmarchand@redhat.com>,
	linux-kernel@vger.kernel.org, stable@vger.kernel.org
Subject: Re: [PATCH v7 1/3] Staging: zram: Fix access of NULL pointer
References: <20131019110539.GA25167@gmail.com> <cc16130b4e23207971139eff313a4ec71f51c187.1383087326.git.rashika.kheria@gmail.com>
In-Reply-To: <cc16130b4e23207971139eff313a4ec71f51c187.1383087326.git.rashika.kheria@gmail.com>
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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@vger.kernel.org
> Signed-off-by: Rashika Kheria <rashika.kheria@gmail.com>
Acked-by: Jerome Marchand <jmarchan@redhat.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;
>