USB: uas: Ensure we only bind to a UAS interface

While all existing UAS devices use alternate interface 1, this is not
guaranteed, and it has caused confusion with people trying to bind the
uas driver to non-uas devices.

Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/storage/uas.c

@@ -582,6 +582,34 @@ static struct usb_device_id uas_usb_ids[] = {
 };
 MODULE_DEVICE_TABLE(usb, uas_usb_ids);
 
+static int uas_is_interface(struct usb_host_interface *intf)
+{
+	return (intf->desc.bInterfaceClass == USB_CLASS_MASS_STORAGE &&
+		intf->desc.bInterfaceSubClass == USB_SC_SCSI &&
+		intf->desc.bInterfaceProtocol == USB_PR_UAS);
+}
+
+static int uas_switch_interface(struct usb_device *udev,
+						struct usb_interface *intf)
+{
+	int i;
+
+	if (uas_is_interface(intf->cur_altsetting))
+		return 0;
+
+	for (i = 0; i < intf->num_altsetting; i++) {
+		struct usb_host_interface *alt = &intf->altsetting[i];
+		if (alt == intf->cur_altsetting)
+			continue;
+		if (uas_is_interface(alt))
+			return usb_set_interface(udev,
+						alt->desc.bInterfaceNumber,
+						alt->desc.bAlternateSetting);
+	}
+
+	return -ENODEV;
+}
+
 static void uas_configure_endpoints(struct uas_dev_info *devinfo)
 {
 	struct usb_host_endpoint *eps[4] = { };
@@ -655,13 +683,8 @@ static int uas_probe(struct usb_interface *intf, const struct usb_device_id *id)
 	struct uas_dev_info *devinfo;
 	struct usb_device *udev = interface_to_usbdev(intf);
 
-	if (id->bInterfaceProtocol == 0x50) {
-		int ifnum = intf->cur_altsetting->desc.bInterfaceNumber;
-/* XXX: Shouldn't assume that 1 is the alternative we want */
-		int ret = usb_set_interface(udev, ifnum, 1);
-		if (ret)
-			return -ENODEV;
-	}
+	if (uas_switch_interface(udev, intf))
+		return -ENODEV;
 
 	devinfo = kmalloc(sizeof(struct uas_dev_info), GFP_KERNEL);
 	if (!devinfo)