linux-kernel - Re: [PATCH v3] usbip: vudc: Fix use after free bug in vudc

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Date:   Sat, 18 Mar 2023 15:39:22 +0800
From:   Zheng Hacker <hackerzheng666@...il.com>
To:     Shuah Khan <skhan@...uxfoundation.org>
Cc:     Zheng Wang <zyytlz.wz@....com>, valentina.manea.m@...il.com,
        gregkh@...uxfoundation.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, 1395428693sheep@...il.com,
        alex000young@...il.com
Subject: Re: [PATCH v3] usbip: vudc: Fix use after free bug in vudc_remove due
 to race condition

Shuah Khan <skhan@...uxfoundation.org> 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