[PATCH 4.14 56/80] staging: comedi: dt282x: fix a null pointer deref on interrupt

From: Greg Kroah-Hartman
Date: Wed Jul 17 2019 - 23:20:45 EST

From: Ian Abbott <abbotti@xxxxxxxxx>

commit b8336be66dec06bef518030a0df9847122053ec5 upstream.

The interrupt handler `dt282x_interrupt()` causes a null pointer
dereference for those supported boards that have no analog output
support. For these boards, `dev->write_subdev` will be `NULL` and
therefore the `s_ao` subdevice pointer variable will be `NULL`. In that
case, the following call near the end of the interrupt handler results
in a null pointer dereference:

comedi_handle_events(dev, s_ao);

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

(There are other uses of `s_ao` by the interrupt handler that may or may
not be reached depending on values of hardware registers. Trust that
they are reliable for now.)

commit 4f6f009b204f ("staging: comedi: dt282x: use comedi_handle_events()")
propagates an earlier error from
commit f21c74fa4cfe ("staging: comedi: dt282x: use cfc_handle_events()").

Fixes: 4f6f009b204f ("staging: comedi: dt282x: use comedi_handle_events()")
Cc: <stable@xxxxxxxxxxxxxxx> # v3.19+
Signed-off-by: Ian Abbott <abbotti@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

drivers/staging/comedi/drivers/dt282x.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/staging/comedi/drivers/dt282x.c
+++ b/drivers/staging/comedi/drivers/dt282x.c
@@ -566,7 +566,8 @@ static irqreturn_t dt282x_interrupt(int
comedi_handle_events(dev, s);
- comedi_handle_events(dev, s_ao);
+ if (s_ao)
+ comedi_handle_events(dev, s_ao);

return IRQ_RETVAL(handled);