Re: [PATCH v2] usbip: vudc: Fix use after free bug in vudc_remove due to race condition

["gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>]

On Fri, Mar 17, 2023 at 02:27:05AM +0800, Zheng Hacker wrote:
> 在 2023年3月17日星期五，Shuah Khan <skhan@linuxfoundation.org> 写道：
> 
> > On 3/16/23 12:09, 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.
> >>
> >> CPU0                  CPU1
> >>
> >>                       |v_timer
> >> vudc_remove          |
> >> kfree(udc);          |
> >> //free shost         |
> >>                       |udc->gadget
> >>                       |//use
> >>
> >> This bug was found by static analysis.
> >>
> >
> > Tell me which static analysis tool did you use to find this and
> > the output from the tool.
> 
> 
>      This is found by codeql，the rule is complicated. It     finally found
> there is no timer stop behavior in remove function.

When using tools like this, you are required to follow the rules in
Documentation/process/researcher-guidelines.rst

Please do so here.

thanks,

greg k-h