Subject: Re: [PATCH -next V3] ubi: fix race condition between ctrl_cdev_ioctl
 and ubi_cdev_ioctl
To:     Richard Weinberger <richard@nod.at>
CC:     Miquel Raynal <miquel.raynal@bootlin.com>,
        Vignesh Raghavendra <vigneshr@ti.com>,
        linux-mtd <linux-mtd@lists.infradead.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        <yukuai3@huawei.com>, Hulk Robot <hulkci@huawei.com>,
        Baokun Li <libaokun1@huawei.com>
References: <20211105093022.1360601-1-libaokun1@huawei.com>
 <7e00eda5-3b35-6d3c-29fb-664b12cca6dd@huawei.com>
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From:   "libaokun (A)" <libaokun1@huawei.com>
Message-ID: <e36106b0-2f7d-c618-4915-476168d7fa7a@huawei.com>
Date:   Tue, 28 Dec 2021 20:40:17 +0800
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在 2021/12/24 5:06, Richard Weinberger 写道:
> ----- Ursprüngliche Mail -----
>> Von: "libaokun (A)" <libaokun1@huawei.com>
>> 在 2021/11/5 17:30, Baokun Li 写道:
>>
>> ping
> Thanks for your patience.
>   
>>> Hulk Robot reported a KASAN report about use-after-free:
> [...]
>
>>> The cause of this problem is that commit 714fb87e8bc0 make device
>>> "available" before it becomes accessible via sysfs. Therefore, we
>>> roll back the modification. We will fix the race condition between
>>> ubi device creation and udev by removing ubi_get_device in
>>> vol_attribute_show and dev_attribute_show.This avoids accessing
>>> uninitialized ubi_devices[ubi_num].
>>>
>>> ubi_get_device is used to prevent devices from being deleted during
>>> sysfs execution. However, now kernfs ensures that devices will not
>>> be deleted before all reference counting are released.
>>> The key process is shown in the following stack.
> ubi_get_device() in dev_attribute_show() is used to detect whether
> the ubi device got detached while the sysfs file is open.
>
> Hmm. I thought for sysfs this is not the case since sysfs does not implement
> a release() method. So kernfs_drain_open_files() will return early.
> But there is a good chance that I don't got all kernfs/sysfs details.
>
> Thanks,
> //richard
> .

Thank you for your review!

-- 
With Best Regards,
Baokun Li