linux-kernel - Re: [PATCH] nullb: Adjust device size calculation in null_alloc

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Message-ID: <e1aad556-eab1-4ac4-aec3-1706e302cfb1@kernel.org>
Date: Tue, 17 Sep 2024 09:24:27 +0200
From: Damien Le Moal <dlemoal@...nel.org>
To: Aleksandr Mishin <amishin@...rgos.ru>, Shaohua Li <shli@...com>
Cc: Jens Axboe <axboe@...nel.dk>, Hannes Reinecke <hare@...e.de>,
 Johannes Thumshirn <johannes.thumshirn@....com>,
 Chaitanya Kulkarni <kch@...dia.com>, Zhu Yanjun <yanjun.zhu@...ux.dev>,
 Chengming Zhou <zhouchengming@...edance.com>,
 John Garry <john.g.garry@...cle.com>, Yu Kuai <yukuai3@...wei.com>,
 Shin'ichiro Kawasaki <shinichiro.kawasaki@....com>,
 linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
 lvc-project@...uxtesting.org
Subject: Re: [PATCH] nullb: Adjust device size calculation in null_alloc_dev()

On 2024/09/17 16:21, Damien Le Moal wrote:
> On 2024/09/17 16:07, Aleksandr Mishin wrote:
>> In null_alloc_dev() device size is a subject to overflow because 'g_gb'
>> (which is module parameter, may have any value and is not validated
>> anywhere) is not cast to a larger data type before performing arithmetic.
>>
>> Cast 'g_gb' to unsigned long to prevent overflow.
>>
>> Found by Linux Verification Center (linuxtesting.org) with SVACE.
>>
>> Fixes: 2984c8684f96 ("nullb: factor disk parameters")
>> Signed-off-by: Aleksandr Mishin <amishin@...rgos.ru>
>> ---
>>  drivers/block/null_blk/main.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c
>> index 2f0431e42c49..5edbf9c0aceb 100644
>> --- a/drivers/block/null_blk/main.c
>> +++ b/drivers/block/null_blk/main.c
>> @@ -762,7 +762,7 @@ static struct nullb_device *null_alloc_dev(void)
>>  		return NULL;
>>  	}
>>  
>> -	dev->size = g_gb * 1024;
>> +	dev->size = (unsigned long)g_gb * 1024;
> 
> This still does not prevent overflows... So what about doing a proper check ?

This still does not prevent overflows on 32-bits architectures.

> 
>>  	dev->completion_nsec = g_completion_nsec;
>>  	dev->submit_queues = g_submit_queues;
>>  	dev->prev_submit_queues = g_submit_queues;
> 

-- 
Damien Le Moal
Western Digital Research