linux-kernel - Re: [PATCH v3] usbip: vudc: Fix use after free bug in vudc

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Date:   Thu, 13 Apr 2023 12:01:43 -0600
From:   Shuah Khan <skhan@...uxfoundation.org>
To:     Zheng Hacker <hackerzheng666@...il.com>
Cc:     Zheng Wang <zyytlz.wz@....com>, valentina.manea.m@...il.com,
        gregkh@...uxfoundation.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, 1395428693sheep@...il.com,
        alex000young@...il.com, Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH v3] usbip: vudc: Fix use after free bug in vudc_remove due
 to race condition

On 4/13/23 02:09, Zheng Hacker wrote:
> Friendly ping about the issue.
> Sorry that I couldn't make test about the driver.
> 
> Thanks,
> Zheng
> 
> Zheng Hacker <hackerzheng666@...il.com> 于2023年3月18日周六 15:39写道：
>>
>> Shuah Khan <skhan@...uxfoundation.org> 于2023年3月18日周六 06:53写道：
>>>
>>> On 3/17/23 04:09, Zheng Wang wrote:
>>>> In vudc_probe, it calls init_vudc_hw, which bound &udc->timer with v_timer.
>>>>
>>>> When it calls usbip_sockfd_store, it will call v_start_timer to start the
>>>> timer work.
>>>>
>>>> When we call vudc_remove to remove the driver, theremay be a sequence as
>>>> follows:
>>>>
>>>> Fix it by shutdown the timer work before cleanup in vudc_remove.
>>>>
>>>> Note that removing a driver is a root-only operation, and should never
>>>> happen. But the attacker can directly unplug the usb to trigger the remove
>>>> function.
>>>>
>>>> CPU0                  CPU1
>>>>
>>>>                        |v_timer
>>>> vudc_remove          |
>>>> kfree(udc);          |
>>>> //free shost         |
>>>>                        |udc->gadget
>>>>                        |//use
>>>>
>>>> The udc might be removed before v_timer finished, and UAF happens.
>>>>
>>>> This bug was found by Codeql static analysis and might by false positive.
>>>
>>> This statement that this could be a false positive makes me hesitate
>>> taking this patch.
>>>
>>> What kind of testing have you done with this fix? Were you able to test
>>> the scenario of unplugging usb?
>>>
>>
>> Sorry I did't make a full test for I did't have the device. The
>> attacking scenario if based on other cases.
>>

Sorry. I really need for you test this and provide information on how
it was tested.

thanks,
-- Shuah