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From:   Zheng Hacker <hackerzheng666@gmail.com>
Date:   Thu, 13 Apr 2023 16:09:15 +0800
Message-ID: <CAJedcCxT0ggGbVSQnqpcYcN=5gahUOEwGWZrP4P1Lz29A8Smqg@mail.gmail.com>
Subject: Re: [PATCH v3] usbip: vudc: Fix use after free bug in vudc_remove due
 to race condition
To:     Shuah Khan <skhan@linuxfoundation.org>
Cc:     Zheng Wang <zyytlz.wz@163.com>, valentina.manea.m@gmail.com,
        gregkh@linuxfoundation.org, linux-usb@vger.kernel.org,
        linux-kernel@vger.kernel.org, 1395428693sheep@gmail.com,
        alex000young@gmail.com
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Friendly ping about the issue.
Sorry that I couldn't make test about the driver.

Thanks,
Zheng

Zheng Hacker <hackerzheng666@gmail.com> =E4=BA=8E2023=E5=B9=B43=E6=9C=8818=
=E6=97=A5=E5=91=A8=E5=85=AD 15:39=E5=86=99=E9=81=93=EF=BC=9A
>
> Shuah Khan <skhan@linuxfoundation.org> =E4=BA=8E2023=E5=B9=B43=E6=9C=8818=
=E6=97=A5=E5=91=A8=E5=85=AD 06:53=E5=86=99=E9=81=93=EF=BC=9A
> >
> > 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 neve=
r
> > > happen. But the attacker can directly unplug the usb to trigger the r=
emove
> > > 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 posit=
ive.
> >
> > 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.
>
> Best regads,
> Zheng
>
> > thanks,
> > -- Shuah