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

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Date:   Fri, 14 Apr 2023 10:33:35 +0800
From:   Zheng Hacker <hackerzheng666@...il.com>
To:     Shuah Khan <skhan@...uxfoundation.org>
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
Subject: Re: [PATCH v3] usbip: vudc: Fix use after free bug in vudc_remove due
 to race condition

Hi Shuah,

I got it. I'll try it.

Best regards,
Zheng

Shuah Khan <skhan@...uxfoundation.org> 于2023年4月14日周五 02:01写道：
>
> 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
>