Re: [PATCH] nullb: Adjust device size calculation in null_alloc_dev()

[Zhu Yanjun <yanjun.zhu@linux.dev>]

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@t-argos.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 */
         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;
>>
>