linux-kernel - [v2.6.34-stable 065/165] xhci-mem.c: Check for ring->first

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Date:	Wed, 15 Aug 2012 15:46:49 -0400
From:	Paul Gortmaker <paul.gortmaker@...driver.com>
To:	<stable@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC:	Kautuk Consul <consul.kautuk@...il.com>,
	Sarah Sharp <sarah.a.sharp@...ux.intel.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Paul Gortmaker <paul.gortmaker@...driver.com>
Subject: [v2.6.34-stable 065/165] xhci-mem.c: Check for ring->first_seg != NULL

From: Kautuk Consul <consul.kautuk@...il.com>

                   -------------------
    This is a commit scheduled for the next v2.6.34 longterm release.
    http://git.kernel.org/?p=linux/kernel/git/paulg/longterm-queue-2.6.34.git
    If you see a problem with using this for longterm, please comment.
                   -------------------

commit 0e6c7f746ea99089fb3263709075c20485a479ae upstream.

There are 2 situations wherein the xhci_ring* might not get freed:
- When xhci_ring_alloc() -> xhci_segment_alloc() returns NULL and
  we goto the fail: label in xhci_ring_alloc. In this case, the ring
  will not get kfreed.
- When the num_segs argument to xhci_ring_alloc is passed as 0 and
  we try to free the rung after that.
  ( This doesn't really happen as of now in the code but we seem to
    be entertaining num_segs=0 in xhci_ring_alloc )

This should be backported to kernels as old as 2.6.31.

Signed-off-by: Kautuk Consul <consul.kautuk@...il.com>
Signed-off-by: Sarah Sharp <sarah.a.sharp@...ux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>
Signed-off-by: Paul Gortmaker <paul.gortmaker@...driver.com>
---
 drivers/usb/host/xhci-mem.c | 22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
index 727ac40..31cf540 100644
--- a/drivers/usb/host/xhci-mem.c
+++ b/drivers/usb/host/xhci-mem.c
@@ -111,18 +111,20 @@ void xhci_ring_free(struct xhci_hcd *xhci, struct xhci_ring *ring)
 	struct xhci_segment *seg;
 	struct xhci_segment *first_seg;
 
-	if (!ring || !ring->first_seg)
+	if (!ring)
 		return;
-	first_seg = ring->first_seg;
-	seg = first_seg->next;
-	xhci_dbg(xhci, "Freeing ring at %p\n", ring);
-	while (seg != first_seg) {
-		struct xhci_segment *next = seg->next;
-		xhci_segment_free(xhci, seg);
-		seg = next;
+	if (ring->first_seg) {
+		first_seg = ring->first_seg;
+		seg = first_seg->next;
+		xhci_dbg(xhci, "Freeing ring at %p\n", ring);
+		while (seg != first_seg) {
+			struct xhci_segment *next = seg->next;
+			xhci_segment_free(xhci, seg);
+			seg = next;
+		}
+		xhci_segment_free(xhci, first_seg);
+		ring->first_seg = NULL;
 	}
-	xhci_segment_free(xhci, first_seg);
-	ring->first_seg = NULL;
 	kfree(ring);
 }
 
-- 
1.7.12.rc2

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