usbip: prevent bind loops on devices attached to vhci_hcd

usbip host binds to devices attached to vhci_hcd on the same server
when user does attach over localhost or specifies the server as the
remote.

usbip attach -r localhost -b busid
or
usbip attach -r servername (or server IP)

Unbind followed by bind works, however device is left in a bad state with
accesses via the attached busid result in errors and system hangs during
shutdown.

Fix it to check and bail out if the device is already attached to vhci_hcd.

Cc: [e-mail]
Signed-off-by: Shuah Khan <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

tools/usb/usbip/src/usbip_bind.c

···
 	int rc;
 	struct udev *udev;
 	struct udev_device *dev;
+	const char *devpath;
 
 	/* Check whether the device with this bus ID exists. */
 	udev = udev_new();
···
 		err("device with the specified bus ID does not exist");
 		return -1;
 	}
+	devpath = udev_device_get_devpath(dev);
 	udev_unref(udev);
+
+	/* If the device is already attached to vhci_hcd - bail out */
+	if (strstr(devpath, USBIP_VHCI_DRV_NAME)) {
+		err("bind loop detected: device: %s is attached to %s\n",
+		    devpath, USBIP_VHCI_DRV_NAME);
+		return -1;
+	}
 
 	rc = unbind_other(busid);
 	if (rc == UNBIND_ST_FAILED) {