linux-kernel - Re: [PATCH v3 05/10] zram: avoid access beyond the zram device

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Date:	Fri, 7 Jun 2013 17:09:45 +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>,
	Jiang Liu <jiang.liu@...wei.com>, devel@...verdev.osuosl.org,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v3 05/10] zram: avoid access beyond the zram device

On Fri, Jun 07, 2013 at 12:07:26AM +0800, Jiang Liu wrote:
> Function valid_io_request() should verify the entire request are within
> the zram device address range. Otherwise it may cause invalid memory
> access when accessing/modifying zram->meta->table[index] because the
> 'index' is out of range. Then it may access non-exist memory, randomly
> modify memory belong to other subsystems, which is hard to track down.
> 
> Signed-off-by: Jiang Liu <jiang.liu@...wei.com>
> Cc: stable@...r.kernel.org
> ---
>  drivers/staging/zram/zram_drv.c | 17 ++++++++++++-----
>  1 file changed, 12 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
> index 27ab824..9289217 100644
> --- a/drivers/staging/zram/zram_drv.c
> +++ b/drivers/staging/zram/zram_drv.c
> @@ -420,13 +420,20 @@ out:
>   */
>  static inline int valid_io_request(struct zram *zram, struct bio *bio)
>  {
> -	if (unlikely(
> -		(bio->bi_sector >= (zram->disksize >> SECTOR_SHIFT)) ||
> -		(bio->bi_sector & (ZRAM_SECTOR_PER_LOGICAL_BLOCK - 1)) ||
> -		(bio->bi_size & (ZRAM_LOGICAL_BLOCK_SIZE - 1)))) {
> +	u64 start, end, bound;
> +	
> +	/* unaligned request */
> +	if (unlikely(bio->bi_sector & (ZRAM_SECTOR_PER_LOGICAL_BLOCK - 1)))
> +		return 0;
> +	if (unlikely(bio->bi_size & (ZRAM_LOGICAL_BLOCK_SIZE - 1)))
> +		return 0;
>  
> +	start = bio->bi_sector;
> +	end = start + (bio->bi_size >> SECTOR_SHIFT);
> +	bound = zram->disksize >> SECTOR_SHIFT;
> +	/* out of range range */
> +	if (unlikely(start >= bound || end >= bound || start > end))

        if (end >= bound || start > end) isn't enough?

>  		return 0;
> -	}
>  
>  	/* I/O request is valid */
>  	return 1;
> -- 
> 1.8.1.2
> 
> --
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-- 
Kind regards,
Minchan Kim
--
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