[019/264] xhci-mem.c: Check for ring->first_seg != NULL

[Greg KH]

3.1-stable review patch.  If anyone has any objections, please let me know.

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

From: Kautuk Consul <consul.kautuk@xxxxxxxxx>

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@xxxxxxxxx>
Signed-off-by: Sarah Sharp <sarah.a.sharp@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 drivers/usb/host/xhci-mem.c |   22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

--- a/drivers/usb/host/xhci-mem.c
+++ b/drivers/usb/host/xhci-mem.c
@@ -112,18 +112,20 @@ void xhci_ring_free(struct xhci_hcd *xhc
 	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);
 }
 


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