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

[Sascha Grunert <sgrunert@redhat.com>]

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>
---
 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);
+		return 0;
+	}
+
 	usbip_dbg_stub_rx("set_interface: inf %u alt %u\n",
 			  interface, alternate);
 
-- 
2.52.0