Re: [PATCH 1/2] usb: gadget: uvc: replace mutex lock/unlock with scoped_guard in uvc_function_bind()

[Frank Li]

On Fri, Aug 21, 2026 at 04:22:36PM +0800, Xu Yang wrote:
> From: Xu Yang <xu.yang_2@xxxxxxx>
>
> Commit 68aa70648b62 ("usb: gadget: uvc: hold opts->lock across XU walks
> in uvc_function_bind") introduced an error_unlock label to release
> opts->lock on failure paths. The label is misplaced between the return
> statement and v4l2_error, causing it to fall through into v4l2_error
> and call v4l2_device_unregister() on a device that was never registered.
>
> Replace the manual mutex_lock/unlock pair and the error_unlock label
> with scoped_guard(mutex), removing the need for explicit lock cleanup on
> error paths.
>
> Fixes: 68aa70648b62 ("usb: gadget: uvc: hold opts->lock across XU walks in uvc_function_bind")
> Assisted-by: Claude:claude-sonnet-4.6
> Signed-off-by: Xu Yang <xu.yang_2@xxxxxxx>
> ---

Reviewed-by: Frank Li <Frank.Li@xxxxxxx>

>  drivers/usb/gadget/function/f_uvc.c | 80 +++++++++++++++++--------------------
>  1 file changed, 36 insertions(+), 44 deletions(-)
>
> diff --git a/drivers/usb/gadget/function/f_uvc.c b/drivers/usb/gadget/function/f_uvc.c
> index d1bf3ea75197..a4fb2790f4ff 100644
> --- a/drivers/usb/gadget/function/f_uvc.c
> +++ b/drivers/usb/gadget/function/f_uvc.c
> @@ -768,23 +768,17 @@ uvc_function_bind(struct usb_configuration *c, struct usb_function *f)
>  	uvc_hs_streaming_ep.bEndpointAddress = uvc->video.ep->address;
>  	uvc_ss_streaming_ep.bEndpointAddress = uvc->video.ep->address;
>
> -	/*
> -	 * Hold opts->lock across both the XU string-descriptor fixup below and
> -	 * the descriptor-copy block further down.  Without this, configfs
> -	 * uvcg_extension_drop() (which takes opts->lock) can race with the
> -	 * list_for_each_entry() walks here and inside uvc_copy_descriptors(),
> -	 * leading to a UAF on a freed struct uvcg_extension.  See
> -	 * drivers/usb/gadget/function/uvc_configfs.c::uvcg_extension_drop().
> -	 */
> -	mutex_lock(&opts->lock);
> -
>  	/*
>  	 * XUs can have an arbitrary string descriptor describing them. If they
> -	 * have one pick up the ID.
> +	 * have one pick up the ID. Hold opts->lock here to avoid race with configfs
> +	 * uvcg_extension_make() and uvcg_extension_drop().
>  	 */
> -	list_for_each_entry(xu, &opts->extension_units, list)
> -		if (xu->string_descriptor_index)
> -			xu->desc.iExtension = cdev->usb_strings[xu->string_descriptor_index].id;
> +	scoped_guard(mutex, &opts->lock) {
> +		list_for_each_entry(xu, &opts->extension_units, list)
> +			if (xu->string_descriptor_index)
> +				xu->desc.iExtension =
> +					cdev->usb_strings[xu->string_descriptor_index].id;
> +	}
>
>  	/*
>  	 * We attach the hard-coded defaults incase the user does not provide
> @@ -795,7 +789,7 @@ uvc_function_bind(struct usb_configuration *c, struct usb_function *f)
>  				 ARRAY_SIZE(uvc_en_us_strings));
>  	if (IS_ERR(us)) {
>  		ret = PTR_ERR(us);
> -		goto error_unlock;
> +		goto error;
>  	}
>
>  	uvc_iad.iFunction = opts->iad_index ? cdev->usb_strings[opts->iad_index].id :
> @@ -809,50 +803,50 @@ uvc_function_bind(struct usb_configuration *c, struct usb_function *f)
>
>  	/* Allocate interface IDs. */
>  	if ((ret = usb_interface_id(c, f)) < 0)
> -		goto error_unlock;
> +		goto error;
>  	uvc_iad.bFirstInterface = ret;
>  	uvc_control_intf.bInterfaceNumber = ret;
>  	uvc->control_intf = ret;
>  	opts->control_interface = ret;
>
>  	if ((ret = usb_interface_id(c, f)) < 0)
> -		goto error_unlock;
> +		goto error;
>  	uvc_streaming_intf_alt0.bInterfaceNumber = ret;
>  	uvc_streaming_intf_alt1.bInterfaceNumber = ret;
>  	uvc->streaming_intf = ret;
>  	opts->streaming_interface = ret;
>
>  	/* Copy descriptors */
> -	f->fs_descriptors = uvc_copy_descriptors(uvc, USB_SPEED_FULL);
> -	if (IS_ERR(f->fs_descriptors)) {
> -		ret = PTR_ERR(f->fs_descriptors);
> -		f->fs_descriptors = NULL;
> -		goto error_unlock;
> -	}
> +	scoped_guard(mutex, &opts->lock) {
> +		f->fs_descriptors = uvc_copy_descriptors(uvc, USB_SPEED_FULL);
> +		if (IS_ERR(f->fs_descriptors)) {
> +			ret = PTR_ERR(f->fs_descriptors);
> +			f->fs_descriptors = NULL;
> +			goto error;
> +		}
>
> -	f->hs_descriptors = uvc_copy_descriptors(uvc, USB_SPEED_HIGH);
> -	if (IS_ERR(f->hs_descriptors)) {
> -		ret = PTR_ERR(f->hs_descriptors);
> -		f->hs_descriptors = NULL;
> -		goto error_unlock;
> -	}
> +		f->hs_descriptors = uvc_copy_descriptors(uvc, USB_SPEED_HIGH);
> +		if (IS_ERR(f->hs_descriptors)) {
> +			ret = PTR_ERR(f->hs_descriptors);
> +			f->hs_descriptors = NULL;
> +			goto error;
> +		}
>
> -	f->ss_descriptors = uvc_copy_descriptors(uvc, USB_SPEED_SUPER);
> -	if (IS_ERR(f->ss_descriptors)) {
> -		ret = PTR_ERR(f->ss_descriptors);
> -		f->ss_descriptors = NULL;
> -		goto error_unlock;
> -	}
> +		f->ss_descriptors = uvc_copy_descriptors(uvc, USB_SPEED_SUPER);
> +		if (IS_ERR(f->ss_descriptors)) {
> +			ret = PTR_ERR(f->ss_descriptors);
> +			f->ss_descriptors = NULL;
> +			goto error;
> +		}
>
> -	f->ssp_descriptors = uvc_copy_descriptors(uvc, USB_SPEED_SUPER_PLUS);
> -	if (IS_ERR(f->ssp_descriptors)) {
> -		ret = PTR_ERR(f->ssp_descriptors);
> -		f->ssp_descriptors = NULL;
> -		goto error_unlock;
> +		f->ssp_descriptors = uvc_copy_descriptors(uvc, USB_SPEED_SUPER_PLUS);
> +		if (IS_ERR(f->ssp_descriptors)) {
> +			ret = PTR_ERR(f->ssp_descriptors);
> +			f->ssp_descriptors = NULL;
> +			goto error;
> +		}
>  	}
>
> -	mutex_unlock(&opts->lock);
> -
>  	/* Preallocate control endpoint request. */
>  	uvc->control_req = usb_ep_alloc_request(cdev->gadget->ep0, GFP_KERNEL);
>  	uvc->control_buf = kmalloc(UVC_MAX_REQUEST_SIZE, GFP_KERNEL);
> @@ -884,8 +878,6 @@ uvc_function_bind(struct usb_configuration *c, struct usb_function *f)
>
>  	return 0;
>
> -error_unlock:
> -	mutex_unlock(&opts->lock);
>  v4l2_error:
>  	v4l2_device_unregister(&uvc->v4l2_dev);
>  error:
>
> --
> 2.34.1
>
>