staging: comedi: amplc_pci230: fix null pointer deref on interrupt

BugLink: https://bugs.launchpad.net/bugs/1839036
commit 7379e6baeddf580d01feca650ec1ad508b6ea8ee upstream.

The interrupt handler `pci230_interrupt()` causes a null pointer
dereference for a PCI260 card.  There is no analog output subdevice for
a PCI260.  The `dev->write_subdev` subdevice pointer and therefore the
`s_ao` subdevice pointer variable will be `NULL` for a PCI260.  The
following call near the end of the interrupt handler results in the null
pointer dereference for a PCI260:

	comedi_handle_events(dev, s_ao);

Fix it by only calling the above function if `s_ao` is valid.

Note that the other uses of `s_ao` in the calls
`pci230_handle_ao_nofifo(dev, s_ao);` and `pci230_handle_ao_fifo(dev,
s_ao);` will never be reached for a PCI260, so they are safe.

Fixes: 39064f23284c ("staging: comedi: amplc_pci230: use comedi_handle_events()")
Cc: <stable@vger.kernel.org> # v3.19+
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/drivers/staging/comedi/drivers/amplc_pci230.c b/drivers/staging/comedi/drivers/amplc_pci230.c
index 48c7890c30071ea62b615d596d2d3ab1917ef498..2b0b757dc626bb785ea3c88f02a094404f387d32 100644 (file)
--- a/drivers/staging/comedi/drivers/amplc_pci230.c
+++ b/drivers/staging/comedi/drivers/amplc_pci230.c
@@ -2339,7 +2339,8 @@ static irqreturn_t pci230_interrupt(int irq, void *d)
        devpriv->intr_running = false;
        spin_unlock_irqrestore(&devpriv->isr_spinlock, irqflags);
 
-       comedi_handle_events(dev, s_ao);
+       if (s_ao)
+               comedi_handle_events(dev, s_ao);
        comedi_handle_events(dev, s_ai);
 
        return IRQ_HANDLED;