USB: xhci: Check URB's actual transfer buffer size.

Make sure that the amount of data the xHC says was transmitted is less
than or equal to the size of the requested transfer buffer. Before, if
the host controller erroneously reported that the number of bytes
untransferred was bigger than the buffer in the URB, urb->actual_length
could be set to a very large size.

Make sure urb->actual_length <= urb->transfer_buffer_length.

Signed-off-by: Sarah Sharp <[e-mail]>
Cc: stable <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/host/xhci-ring.c

···
 				td->urb->actual_length =
 					td->urb->transfer_buffer_length -
 					TRB_LEN(event->transfer_len);
-				if (td->urb->actual_length < 0) {
+				if (td->urb->transfer_buffer_length <
+						td->urb->actual_length) {
 					xhci_warn(xhci, "HC gave bad length "
 							"of %d bytes left\n",
 							TRB_LEN(event->transfer_len));
···
 td_cleanup:
 		/* Clean up the endpoint's TD list */
 		urb = td->urb;
+		/* Do one last check of the actual transfer length.
+		 * If the host controller said we transferred more data than
+		 * the buffer length, urb->actual_length will be a very big
+		 * number (since it's unsigned).  Play it safe and say we didn't
+		 * transfer anything.
+		 */
+		if (urb->actual_length > urb->transfer_buffer_length) {
+			xhci_warn(xhci, "URB transfer length is wrong, "
+					"xHC issue? req. len = %u, "
+					"act. len = %u\n",
+					urb->transfer_buffer_length,
+					urb->actual_length);
+			urb->actual_length = 0;
+		}
 		list_del(&td->td_list);
 		/* Was this TD slated to be cancelled but completed anyway? */
 		if (!list_empty(&td->cancelled_td_list)) {