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

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Date:	Tue, 04 Jun 2013 23:09:49 +0800
From:	Jiang Liu <liuj97@...il.com>
To:	Jerome Marchand <jmarchan@...hat.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 Tue 04 Jun 2013 09:15:43 PM CST, Jerome Marchand wrote:
> 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
Hi Jerome,
         I think the test "bio->bi_sector >= (zram->disksize >> 
SECTOR_SHIFT)" is still
needed to protect "(bio->bi_sector << SECTOR_SHIFT) + bio->bi_size" 
from wrapping
around.
Regards!
Gerry

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


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