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

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Message-ID: <51b8f03e-4dd3-6abc-235f-fca58ca4cd2e@huaweicloud.com>
Date: Wed, 18 Sep 2024 10:07:15 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: Zhu Yanjun <yanjun.zhu@...ux.dev>, Damien Le Moal <dlemoal@...nel.org>,
 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>,
 Chengming Zhou <zhouchengming@...edance.com>,
 John Garry <john.g.garry@...cle.com>,
 Shin'ichiro Kawasaki <shinichiro.kawasaki@....com>,
 linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
 lvc-project@...uxtesting.org, "yukuai (C)" <yukuai3@...wei.com>,
 "yangerkun@...wei.com" <yangerkun@...wei.com>
Subject: Re: [PATCH] nullb: Adjust device size calculation in null_alloc_dev()



在 2024/09/18 0:29, Zhu Yanjun 写道:
> 在 2024/9/17 15:24, Damien Le Moal 写道:
>> 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.
> 
> Because "unsigned long" on 32-bits architectures is 32 bit, so solution 
> 1 is to change the type "unsigned long" to u64, and the diff is as below:
> 
> diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c
> index 2f0431e42c49..27a453b3094d 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 = (u64)g_gb * 1024;
>          dev->completion_nsec = g_completion_nsec;
>          dev->submit_queues = g_submit_queues;
>          dev->prev_submit_queues = g_submit_queues;
> diff --git a/drivers/block/null_blk/null_blk.h 
> b/drivers/block/null_blk/null_blk.h
> index a7bb32f73ec3..e30c011909ad 100644
> --- a/drivers/block/null_blk/null_blk.h
> +++ b/drivers/block/null_blk/null_blk.h
> @@ -74,7 +74,7 @@ struct nullb_device {
>          bool need_zone_res_mgmt;
>          spinlock_t zone_res_lock;
> 
> -       unsigned long size; /* device size in MB */
> +       u64 size; /* device size in MB */

There is more, g_gb is GB, dev->size is MB, and dev->size will be used
later for inode size in bytes, and bdev size in sectors.

The max inode size is LONG_MAX, this is still more than UINT_MAX GB, so
it's right that set the device size by module params won't overflow.

However, take a look at setting the size through configfs, the max value
is ULONG_MAX MB, this will still overflow.

Thanks,
Kuai

>          unsigned long completion_nsec; /* time in ns to complete a 
> request */
>          unsigned long cache_size; /* disk cache size in MB */
>          unsigned long zone_size; /* zone size in MB if device is zoned */
> 
> I just built it and did not make tests.
> 
> Zhu Yanjun
> 
>>
>>>
>>>>       dev->completion_nsec = g_completion_nsec;
>>>>       dev->submit_queues = g_submit_queues;
>>>>       dev->prev_submit_queues = g_submit_queues;
>>>
>>
> 
> 
> .
>