diff -pur linux-3.4.18.orig/drivers/usb/host/xen-usbback/usbback.c linux-3.4.18/drivers/usb/host/xen-usbback/usbback.c
--- linux-3.4.18.orig/drivers/usb/host/xen-usbback/usbback.c	2012-11-20 00:03:57.562663987 +0100
+++ linux-3.4.18/drivers/usb/host/xen-usbback/usbback.c	2012-12-09 16:16:36.395197677 +0100
@@ -582,6 +582,8 @@
 		break;
 	}
 
+	urb->transfer_flags &= ~(URB_FREE_BUFFER);
+
 	if (req->buffer_length) {
 		urb->transfer_dma = pending_req->transfer_dma;
 		urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
diff -pur linux-3.4.18.orig/drivers/usb/host/xen-usbfront.c linux-3.4.18/drivers/usb/host/xen-usbfront.c