linux-kernel - Re: [RFC PATCH v1 6/8] zram: avoid access beyond the zram device

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Message-ID: <51ADE87F.9080303@redhat.com>
Date:	Tue, 04 Jun 2013 15:15:43 +0200
From:	Jerome Marchand <jmarchan@...hat.com>
To:	Jiang Liu <liuj97@...il.com>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Nitin Gupta <ngupta@...are.org>,
	Minchan Kim <minchan@...nel.org>,
	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 6/8] zram: avoid access beyond the zram device

On 06/03/2013 05:42 PM, Jiang Liu wrote:
> Function valid_io_request() should verify the entire request doesn't
> exceed the zram device, otherwise it will cause invalid memory access.
> 
> Signed-off-by: Jiang Liu <jiang.liu@...wei.com>
> ---
>  drivers/staging/zram/zram_drv.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
> index 66cf28a..64b51b9 100644
> --- a/drivers/staging/zram/zram_drv.c
> +++ b/drivers/staging/zram/zram_drv.c
> @@ -428,6 +428,10 @@ static inline int valid_io_request(struct zram *zram, struct bio *bio)
>  		return 0;
>  	}
>  
> +	if (unlikely((bio->bi_sector << SECTOR_SHIFT) + bio->bi_size >=
> +		     zram->disksize))
> +		return 0;
> +

This test make the first line of previous test redundant. Why not just
update it like the following:

-		(bio->bi_sector >= (zram->disksize >> SECTOR_SHIFT)) ||
+		((bio->bi_sector << SECTOR_SHIFT) + bio->bi_size >=
+			zram->disksize)) ||


Jerome

>  	/* I/O request is valid */
>  	return 1;
>  }
> 

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