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

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

From: Ian Abbott <abbotti@mev.co.uk>

commit 922b67c1ac53014d80649a961a2fde700cd065d8 upstream.

`labpc_common_detach()` is called by the comedi core to clean up if
either `labpc_attach()` (including the one in the "ni_labpc_cs" module)
or `labpc_attach_pci()` returns an error.  It assumes the `thisboard`
macro (expanding to `((struct labpc_board_struct *)dev->board_ptr)`) is
non-null.  This is a valid assumption if `labpc_attach()` fails, but not
if `labpc_attach_pci()` fails, leading to a possible NULL pointer
dereference.

Check `thisboard` at the top of `labpc_common_detach()` and return early
if it is `NULL`.  This is okay because the only other thing that could
have been allocated is `dev->private` and that is freed by the comedi
core, not by this function.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/staging/comedi/drivers/ni_labpc.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/drivers/staging/comedi/drivers/ni_labpc.c
+++ b/drivers/staging/comedi/drivers/ni_labpc.c

@@ -809,6 +809,8 @@ static int labpc_find_device(struct come
 
 void labpc_common_detach(struct comedi_device *dev)
 {
+	if (!thisboard)
+		return;
 	if (dev->subdevices)
 		subdev_8255_cleanup(dev, dev->subdevices + 2);
 #ifdef CONFIG_ISA_DMA_API