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Subject: Re: [PATCH] block: Fix minor range check in device_add_disk()
To:     zhongjinghua <zhongjinghua@huaweicloud.com>,
        Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
        axboe@kernel.dk
Cc:     linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        zhongjinghua@huawei.com, yi.zhang@huawei.com,
        "yukuai (C)" <yukuai3@huawei.com>
References: <20231025084621.2338604-1-zhongjinghua@huaweicloud.com>
 <119b7314-10a9-4d62-b40f-19462dc68009@I-love.SAKURA.ne.jp>
 <26bafe93-345d-2696-8ee7-7d1baa0e7eb7@huaweicloud.com>
From:   Yu Kuai <yukuai1@huaweicloud.com>
Message-ID: <df52b8a2-dff1-3973-b2bf-ca915c3f44d3@huaweicloud.com>
Date:   Mon, 30 Oct 2023 17:26:51 +0800
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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

> 
> .
>