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

[Zheng Hacker]

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.
>
> Best regads,
> Zheng
>
> > thanks,
> > -- Shuah