[PATCH 11/11] comedi: quatech_daqp_cs: Fix sanity check in interrupt handler

[Ian Abbott]

The driver requests an interrupt handler for the device before it is
fully set up.

For safety, the interrupt handler checks the dev->attached flag to
ensure the device is fully set up, but it currently does that after
dereferencing the dev->read_dev pointer which may be NULL if
dev->attached is false.  Move the check to avoid the possible null
pointer dereference.

Signed-off-by: Ian Abbott <abbotti@xxxxxxxxx>
---
 drivers/comedi/drivers/quatech_daqp_cs.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/comedi/drivers/quatech_daqp_cs.c b/drivers/comedi/drivers/quatech_daqp_cs.c
index 2a76c75c513b8..d5e3e213e233b 100644
--- a/drivers/comedi/drivers/quatech_daqp_cs.c
+++ b/drivers/comedi/drivers/quatech_daqp_cs.c
@@ -211,13 +211,15 @@ static irqreturn_t daqp_interrupt(int irq, void *dev_id)
 {
 	struct comedi_device *dev = dev_id;
 	struct comedi_subdevice *s = dev->read_subdev;
-	struct comedi_cmd *cmd = &s->async->cmd;
+	struct comedi_cmd *cmd;
 	int loop_limit = 10000;
 	int status;
 
 	if (!dev->attached)
 		return IRQ_NONE;
 
+	cmd = &s->async->cmd;
+
 	status = inb(dev->iobase + DAQP_STATUS_REG);
 	if (!(status & DAQP_STATUS_EVENTS))
 		return IRQ_NONE;
-- 
2.53.0