[ 3.5.yuz extended stable ] Patch "xhci: Fix potential NULL ptr deref in command cancellation." has been added to staging queue

Herton Ronaldo Krzesinski herton.krzesinski at canonical.com
Thu Nov 22 04:50:22 UTC 2012

This is a note to let you know that I have just added a patch titled

    xhci: Fix potential NULL ptr deref in command cancellation.

to the linux-3.5.y-queue branch of the 3.5.yuz extended stable tree 
which can be found at:


If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.yuz tree, see



>From 025cc33e2f19b4430ca17fdb555031574a2d500d Mon Sep 17 00:00:00 2001
From: Sarah Sharp <sarah.a.sharp at linux.intel.com>
Date: Tue, 16 Oct 2012 13:17:43 -0700
Subject: [PATCH] xhci: Fix potential NULL ptr deref in command cancellation.

commit 43a09f7fb01fa1e091416a2aa49b6c666458c1ee upstream.

The command cancellation code doesn't check whether find_trb_seg()
couldn't find the segment that contains the TRB to be canceled.  This
could cause a NULL pointer deference later in the function when next_trb
is called.  It's unlikely to happen unless something is wrong with the
command ring pointers, so add some debugging in case it happens.

This patch should be backported to stable kernels as old as 3.0, that
contain the commit b63f4053cc8aa22a98e3f9a97845afe6c15d0a0d "xHCI:
handle command after aborting the command ring".

Signed-off-by: Sarah Sharp <sarah.a.sharp at linux.intel.com>
Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski at canonical.com>
 drivers/usb/host/xhci-ring.c |   11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
index 47b6bb6..755858e 100644
--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -1228,6 +1228,17 @@ static void xhci_cmd_to_noop(struct xhci_hcd *xhci, struct xhci_cd *cur_cd)
 	cur_seg = find_trb_seg(xhci->cmd_ring->first_seg,
 			xhci->cmd_ring->dequeue, &cycle_state);

+	if (!cur_seg) {
+		xhci_warn(xhci, "Command ring mismatch, dequeue = %p %llx (dma)\n",
+				xhci->cmd_ring->dequeue,
+				(unsigned long long)
+				xhci_trb_virt_to_dma(xhci->cmd_ring->deq_seg,
+					xhci->cmd_ring->dequeue));
+		xhci_debug_ring(xhci, xhci->cmd_ring);
+		xhci_dbg_ring_ptrs(xhci, xhci->cmd_ring);
+		return;
+	}
 	/* find the command trb matched by cd from command ring */
 	for (cmd_trb = xhci->cmd_ring->dequeue;
 			cmd_trb != xhci->cmd_ring->enqueue;

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