linux-kernel - Re: [PATCH] USB: gadget: udc: Fix use after free bug in udc_plat

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Date:   Thu, 23 Mar 2023 17:20:27 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Zheng Wang <zyytlz.wz@....com>
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        hackerzheng666@...il.com, 1395428693sheep@...il.com,
        alex000young@...il.com
Subject: Re: [PATCH] USB: gadget: udc: Fix use after free bug in
 udc_plat_remove due to race condition

On Fri, Mar 10, 2023 at 03:00:39PM +0800, Zheng Wang wrote:
> In udc_plat_probe, &udc->drd_work is bound with
> udc_drd_work. udc_drd_work may be called by
> usbd_connect_notify to start the work.
> 
> Besides, there is a invoking chain:
> udc_plat_probe
> ->udc_probe
> ->usb_add_gadget_udc_release
> ->usb_add_gadget
> 
> It will add a new gadget to the udc class driver
>  list. In usb_add_gadget, it uses usb_udc_release
>  as its release function, which will kfree(udc)
>  to when destroying the gadget.
> 
> If we remove the module which will call udc_plat_remove
>   to make cleanup, there may be a unfinished work.
> The possible sequence is as follows:
> 
> Fix it by finishing the work before cleanup in the udc_plat_remove
> 
> Fixes: 1b9f35adb0ff ("usb: gadget: udc: Add Synopsys UDC Platform driver")
> Signed-off-by: Zheng Wang <zyytlz.wz@....com>
> ---
>  drivers/usb/gadget/udc/snps_udc_plat.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/usb/gadget/udc/snps_udc_plat.c b/drivers/usb/gadget/udc/snps_udc_plat.c
> index 8bbb89c80348..6228e178cc0a 100644
> --- a/drivers/usb/gadget/udc/snps_udc_plat.c
> +++ b/drivers/usb/gadget/udc/snps_udc_plat.c
> @@ -230,6 +230,7 @@ static int udc_plat_remove(struct platform_device *pdev)
>  	struct udc *dev;
>  
>  	dev = platform_get_drvdata(pdev);
> +	cancel_delayed_work_sync(&dev->drd_work);
>  
>  	usb_del_gadget_udc(&dev->gadget);
>  	/* gadget driver must not be registered */
> -- 
> 2.25.1
> 

Please test this to verify that it actually works.

thanks,

greg k-h