linux-kernel - Re: [PATCH v2] usbip: vudc: Fix use after free bug in vudc

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Message-ID: <ZBNpf5X+y26+eKYf@kroah.com>
Date:   Thu, 16 Mar 2023 20:09:51 +0100
From:   "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
To:     Zheng Hacker <hackerzheng666@...il.com>
Cc:     Shuah Khan <skhan@...uxfoundation.org>,
        Zheng Wang <zyytlz.wz@....com>,
        "valentina.manea.m@...il.com" <valentina.manea.m@...il.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "1395428693sheep@...il.com" <1395428693sheep@...il.com>,
        "alex000young@...il.com" <alex000young@...il.com>
Subject: Re: [PATCH v2] usbip: vudc: Fix use after free bug in vudc_remove
 due to race condition

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@...uxfoundation.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