From 250fb892d3915f81a04f4eee2f8abe2e88718faa Mon Sep 17 00:00:00 2001
From: Hans Petter Selasky <hselasky@FreeBSD.org>
Date: Wed, 30 Jan 2013 07:48:43 +0000
Subject: [PATCH] Add missing NULL pointer check.

Reported by:	Lars Engels
MFC after:	1 week
---
 sys/dev/usb/controller/xhci.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/sys/dev/usb/controller/xhci.c b/sys/dev/usb/controller/xhci.c
index c62f7815eaf..2a06ea2cfb9 100644
--- a/sys/dev/usb/controller/xhci.c
+++ b/sys/dev/usb/controller/xhci.c
@@ -886,6 +886,12 @@ xhci_check_transfer(struct xhci_softc *sc, struct xhci_trb *trb)
 			 * a short packet also makes the transfer done
 			 */
 			if (td->remainder > 0) {
+				if (td->alt_next == NULL) {
+					DPRINTF("short TD has no "
+					    "alternate next\n");
+					xhci_generic_done(xfer);
+					break;
+				}
 				DPRINTF("TD has short pkt\n");
 				if (xfer->flags_int.short_frames_ok ||
 				    xfer->flags_int.isochronous_xfr ||