Message-ID: <d05ae776-ee19-2ce0-c06b-9825e5cbea82@linuxfoundation.org>
Date:   Fri, 17 Mar 2023 16:53:07 -0600
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Subject: Re: [PATCH v3] usbip: vudc: Fix use after free bug in vudc_remove due
 to race condition
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To:     Zheng Wang <zyytlz.wz@163.com>, valentina.manea.m@gmail.com
Cc:     gregkh@linuxfoundation.org, linux-usb@vger.kernel.org,
        linux-kernel@vger.kernel.org, hackerzheng666@gmail.com,
        1395428693sheep@gmail.com, alex000young@gmail.com,
        Shuah Khan <skhan@linuxfoundation.org>
References: <20230317100954.2626573-1-zyytlz.wz@163.com>
From:   Shuah Khan <skhan@linuxfoundation.org>
In-Reply-To: <20230317100954.2626573-1-zyytlz.wz@163.com>
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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?

thanks,
-- Shuah