linux-kernel - Re: [PATCH] block: Fix minor range check in device_add

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Date:   Mon, 30 Oct 2023 17:32:09 +0800
From:   zhongjinghua <zhongjinghua@...wei.com>
To:     Yu Kuai <yukuai1@...weicloud.com>,
        zhongjinghua <zhongjinghua@...weicloud.com>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        <axboe@...nel.dk>
CC:     <linux-block@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <yi.zhang@...wei.com>, "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH] block: Fix minor range check in device_add_disk()


在 2023/10/30 17:26, Yu Kuai 写道:
> Hi,
>
> 在 2023/10/26 16:52, zhongjinghua 写道:
>>
>> 在 2023/10/25 18:06, Tetsuo Handa 写道:
>>> On 2023/10/25 17:46, Zhong Jinghua wrote:
>>>> Checks added in patch:
>>>> commit e338924bd05d ("block: check minor range in device_add_disk()")
>>>> ignore the problem of first_minore < 0 and disk->minors < 0.
>>> What is the problem of first_minor < 0 or disk->minors < 0 ?
>>> Are negative values legal/illegal ?
>>
>> These two values are used as the secondary device number and the 
>> maximum number of partitions, which is illegal if negative. Then 
>> first_minore and disk->minors are signed numbers, and the sum may be 
>> less than MINORMASK to bypass the check.
>
> Let me complement it, first_minor and minors can be set by driver, and
> driver allow set them throuhh ioctl/sysfs from user parameters, for
> example:
>
> If user pass in -1, and each disk support 8 partitions, driver will
> usually set:
>
> disk->first_minor = -1 * 8 = -8;
> disk->minors = 8;
>
> Then first_minor + minors = 0, then the following condition can't detect
> this case:
>
> if (disk->first_minor + disk->minors > MINORMASK + 1)
>
> By the way, we never limit how first_minor and minors is set by driver,
> and it's illegal if driver set first_minor = -4, and minors = 8.
>
> Thanks,
> Kuai
>
>>
>> .
>>
>
Kuai, Thank for your explanation.

Jinghua