Re: [PATCH v3] usbip: vudc: Fix use after free bug in vudc_remove due to race condition

[Shuah Khan]

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@xxxxxxxxx> 于2023年3月18日周六 15:39写道：
> > Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx> 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