USB: composite: Fix bug: low byte of w_index is the usb interface number not the whole 2 bytes of w_index

In some usb gadget driver, for example usb audio class device, the high
byte of w_index is the entity id and low byte is the interface number.
If we use the 2 bytes of w_index as the array number, we will get a
wrong pointer or NULL pointer.

This patch fixes this issue.

Signed-off-by: Bryan Wu <cooloney@kernel.org>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/gadget/composite.c

@@ -683,6 +683,7 @@ composite_setup(struct usb_gadget *gadget, const struct usb_ctrlrequest *ctrl)
 	struct usb_request		*req = cdev->req;
 	int				value = -EOPNOTSUPP;
 	u16				w_index = le16_to_cpu(ctrl->wIndex);
+	u8				intf = w_index & 0xFF;
 	u16				w_value = le16_to_cpu(ctrl->wValue);
 	u16				w_length = le16_to_cpu(ctrl->wLength);
 	struct usb_function		*f = NULL;
@@ -769,7 +770,7 @@ composite_setup(struct usb_gadget *gadget, const struct usb_ctrlrequest *ctrl)
 			goto unknown;
 		if (!cdev->config || w_index >= MAX_CONFIG_INTERFACES)
 			break;
-		f = cdev->config->interface[w_index];
+		f = cdev->config->interface[intf];
 		if (!f)
 			break;
 		if (w_value && !f->set_alt)
@@ -781,7 +782,7 @@ composite_setup(struct usb_gadget *gadget, const struct usb_ctrlrequest *ctrl)
 			goto unknown;
 		if (!cdev->config || w_index >= MAX_CONFIG_INTERFACES)
 			break;
-		f = cdev->config->interface[w_index];
+		f = cdev->config->interface[intf];
 		if (!f)
 			break;
 		/* lots of interfaces only need altsetting zero... */
@@ -808,7 +809,7 @@ unknown:
 		 */
 		if ((ctrl->bRequestType & USB_RECIP_MASK)
 				== USB_RECIP_INTERFACE) {
-			f = cdev->config->interface[w_index];
+			f = cdev->config->interface[intf];
 			if (f && f->setup)
 				value = f->setup(f, ctrl);
 			else