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

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

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

commit ee280d134f2e05e0172369a53fbe202dbfc527fa upstream.

`das08_detach()` is called by the comedi core to clean up if either
`das08_attach()` or `das08_attach_pci()` returns an error.  It sets
`thisboard` to the return value of `comedi_board(dev)` and assumes it is
non-null.  This is a valid assumption if `das08_attach()` fails, but not
if `das08_attach_pci()` fails, leading to a possible NULL pointer
dereference.

Check `thisboard` at the top of `das08_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/das08.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/drivers/staging/comedi/drivers/das08.c
+++ b/drivers/staging/comedi/drivers/das08.c

@@ -1028,6 +1028,8 @@ static void __maybe_unused das08_detach(
 	const struct das08_board_struct *thisboard = comedi_board(dev);
 	struct das08_private_struct *devpriv = dev->private;
 
+	if (!thisboard)
+		return;
 	das08_common_detach(dev);
 	if (IS_ENABLED(CONFIG_COMEDI_DAS08_ISA) &&
 	    (thisboard->bustype == isa || thisboard->bustype == pc104)) {