[PATCH 3.16 039/294] xhci: Fix NULL pointer dereference when cleaning up streams for removed host

[Ben Hutchings]

3.16.50-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Mathias Nyman <mathias.nyman@xxxxxxxxxxxxxxx>

commit 4b895868bb2da60a386a17cde3bf9ecbc70c79f4 upstream.

This off by one in stream_id indexing caused NULL pointer dereference and
soft lockup on machines with USB attached SCSI devices connected to a
hotpluggable xhci controller.

The code that cleans up pending URBs for dead hosts tried to dereference
a stream ring at the invalid stream_id 0.
ep->stream_info->stream_rings[0] doesn't point to a ring.

Start looping stream_id from 1 like in all the other places in the driver,
and check that the ring exists before trying to kill URBs on it.

Reported-by: rocko r <rockorequin@xxxxxxxxx>
Signed-off-by: Mathias Nyman <mathias.nyman@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/usb/host/xhci-ring.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -821,13 +821,16 @@ static void xhci_kill_endpoint_urbs(stru
 			(ep->ep_state & EP_GETTING_NO_STREAMS)) {
 		int stream_id;
 
-		for (stream_id = 0; stream_id < ep->stream_info->num_streams;
+		for (stream_id = 1; stream_id < ep->stream_info->num_streams;
 				stream_id++) {
+			ring = ep->stream_info->stream_rings[stream_id];
+			if (!ring)
+				continue;
+
 			xhci_dbg_trace(xhci, trace_xhci_dbg_cancel_urb,
 					"Killing URBs for slot ID %u, ep index %u, stream %u",
-					slot_id, ep_index, stream_id + 1);
-			xhci_kill_ring_urbs(xhci,
-					ep->stream_info->stream_rings[stream_id]);
+					slot_id, ep_index, stream_id);
+			xhci_kill_ring_urbs(xhci, ring);
 		}
 	} else {
 		ring = ep->ring;