[ 52/54] staging: comedi: amplc_pc236: fix invalid register access during detach

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

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

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

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

commit aaeb61a97b7159ebe30b18a422d04eeabfa8790b upstream.

`pc236_detach()` is called by the comedi core if it attempted to attach
a device and failed.  `pc236_detach()` calls `pc236_intr_disable()` if
the comedi device private data pointer (`devpriv`) is non-null.  This
test is insufficient as `pc236_intr_disable()` accesses hardware
registers and the attach routine may have failed before it has saved
their I/O base addresses.

Fix it by checking `dev->iobase` is non-zero before calling
`pc236_intr_disable()` as that means the I/O base addresses have been
saved and the hardware registers can be accessed.  It also implies the
comedi device private data pointer is valid, so there is no need to
check it.

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

---
 drivers/staging/comedi/drivers/amplc_pc236.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/staging/comedi/drivers/amplc_pc236.c
+++ b/drivers/staging/comedi/drivers/amplc_pc236.c
@@ -468,7 +468,7 @@ static int pc236_detach(struct comedi_de
 {
 	printk(KERN_DEBUG "comedi%d: %s: detach\n", dev->minor,
 	       PC236_DRIVER_NAME);
-	if (devpriv)
+	if (dev->iobase)
 		pc236_intr_disable(dev);
 
 	if (dev->irq)