Re: [PATCH 2/2] usbip: block SET_INTERFACE for isoc alt settings

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, Jul 01, 2026 at 12:18:26PM +0200, Sascha Grunert wrote:
> USB/IP cannot forward isochronous transfers. When the client activates
> an alt setting with isoc endpoints, the transfers fail with -EPROTO and
> the resulting usb_clear_halt cascade disconnects the device.
> 
> Intercept SET_INTERFACE in tweak_set_interface_cmd() and fake success
> when the target alt setting contains isoc endpoints, keeping the device
> at alt 0.
> 
> Tested with a Turtle Beach Velocity One Flight yoke (10f5:7001)
> forwarded to a VM via USB/IP, which previously disconnect-looped every
> few seconds and now stays connected.
> 
> Cc: stable@vger.kernel.org
> Signed-off-by: Sascha Grunert <sgrunert@redhat.com>

What commit id does this fix?

> ---
>  drivers/usb/usbip/stub_rx.c | 36 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 36 insertions(+)
> 
> diff --git a/drivers/usb/usbip/stub_rx.c b/drivers/usb/usbip/stub_rx.c
> index d0e3d3f..f323b48 100644
> --- a/drivers/usb/usbip/stub_rx.c
> +++ b/drivers/usb/usbip/stub_rx.c
> @@ -100,6 +100,28 @@ static int tweak_clear_halt_cmd(struct urb *urb)
>  	return ret;
>  }
>  
> +static bool altsetting_has_isoc(struct usb_device *udev, __u16 interface,
> +				__u16 alternate)
> +{
> +	struct usb_interface *intf;
> +	struct usb_host_interface *alt;
> +	int i;
> +
> +	intf = usb_ifnum_to_if(udev, interface);
> +	if (!intf)
> +		return false;
> +
> +	alt = usb_altnum_to_altsetting(intf, alternate);
> +	if (!alt)
> +		return false;
> +
> +	for (i = 0; i < alt->desc.bNumEndpoints; i++) {
> +		if (usb_endpoint_xfer_isoc(&alt->endpoint[i].desc))
> +			return true;
> +	}
> +	return false;
> +}
> +
>  static int tweak_set_interface_cmd(struct urb *urb)
>  {
>  	struct usb_ctrlrequest *req;
> @@ -111,6 +133,20 @@ static int tweak_set_interface_cmd(struct urb *urb)
>  	alternate = le16_to_cpu(req->wValue);
>  	interface = le16_to_cpu(req->wIndex);
>  
> +	/*
> +	 * USB/IP cannot forward isochronous transfers.  If the requested
> +	 * alt setting activates isochronous endpoints, pretend the switch
> +	 * succeeded without touching the device.  This prevents the
> +	 * cascade of failed isoc URBs that leads to a device disconnect.
> +	 */
> +	if (alternate != 0 && altsetting_has_isoc(urb->dev, interface,
> +						  alternate)) {
> +		dev_info(&urb->dev->dev,
> +			 "usb_set_interface blocked: inf %u alt %u (isoc)\n",
> +			 interface, alternate);

Why is this not an error?  And if a user sees this, what can they do
about it?

> +		return 0;

Why isn't this an error?

thanks,

greg k-h