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

[Shuah Khan <skhan@linuxfoundation.org>]

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.

> 
> Fixes: b6a0ca111867 ("usbip: vudc: Add UDC specific ops")
> Signed-off-by: Zheng Wang <zyytlz.wz@163.com>
> ---
> v2:
> - add more details about how the bug was found suggested by Shuah
> ---
>   drivers/usb/usbip/vudc_dev.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/usb/usbip/vudc_dev.c b/drivers/usb/usbip/vudc_dev.c
> index 2bc428f2e261..33d0991755bb 100644
> --- a/drivers/usb/usbip/vudc_dev.c
> +++ b/drivers/usb/usbip/vudc_dev.c
> @@ -633,6 +633,7 @@ int vudc_remove(struct platform_device *pdev)
>   {
>   	struct vudc *udc = platform_get_drvdata(pdev);
>   
> +	timer_shutdown_sync(&udc->timer);
>   	usb_del_gadget_udc(&udc->gadget);
>   	cleanup_vudc_hw(udc);
>   	kfree(udc);

thanks,
-- Shuah