[PATCH 03/11] comedi: dt2811: Fix sanity check in interrupt handler

[Ian Abbott]

The driver requests an interrupt handler for the device, after setting
device registers to disable interrupt generation.  The interrupt handler
should not be called prematurely unless the user-configured I/O port
base address and/or IRQ number are incorrect or the hardware is bad.

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 dev->read_subdev, 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/dt2811.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/comedi/drivers/dt2811.c b/drivers/comedi/drivers/dt2811.c
index bcc4b5ef48e8d..0438b8c90e441 100644
--- a/drivers/comedi/drivers/dt2811.c
+++ b/drivers/comedi/drivers/dt2811.c
@@ -193,13 +193,16 @@ static irqreturn_t dt2811_interrupt(int irq, void *d)
 {
 	struct comedi_device *dev = d;
 	struct comedi_subdevice *s = dev->read_subdev;
-	struct comedi_async *async = s->async;
-	struct comedi_cmd *cmd = &async->cmd;
+	struct comedi_async *async;
+	struct comedi_cmd *cmd;
 	unsigned int status;
 
 	if (!dev->attached)
 		return IRQ_NONE;
 
+	async = s->async;
+	cmd = &async->cmd;
+
 	status = inb(dev->iobase + DT2811_ADCSR_REG);
 
 	if (status & DT2811_ADCSR_ADERROR) {
-- 
2.53.0