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

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Date:	Fri, 07 Jun 2013 11:40:26 +0200
From:	Jerome Marchand <jmarchan@...hat.com>
To:	Minchan Kim <minchan@...nel.org>
CC:	Jiang Liu <liuj97@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Nitin Gupta <ngupta@...are.org>,
	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 06/07/2013 10:09 AM, Minchan Kim wrote:
> 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?

I shall think so.

Jerome

> 
>>  		return 0;
>> -	}
>>  
>>  	/* I/O request is valid */
>>  	return 1;
>> -- 
>> 1.8.1.2
>>
>> --
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> 

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