[PATCH 04/11] comedi: ni_at_a2150: 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 various pointers which may be NULL if dev->attached is
false.  Move the check to avoid the possible null pointer dereferences.

Signed-off-by: Ian Abbott <abbotti@xxxxxxxxx>
---
 drivers/comedi/drivers/ni_at_a2150.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/drivers/comedi/drivers/ni_at_a2150.c b/drivers/comedi/drivers/ni_at_a2150.c
index 44221c928e327..86629b495fedc 100644
--- a/drivers/comedi/drivers/ni_at_a2150.c
+++ b/drivers/comedi/drivers/ni_at_a2150.c
@@ -132,11 +132,11 @@ static irqreturn_t a2150_interrupt(int irq, void *d)
 	struct comedi_device *dev = d;
 	struct a2150_private *devpriv = dev->private;
 	struct comedi_isadma *dma = devpriv->dma;
-	struct comedi_isadma_desc *desc = &dma->desc[0];
+	struct comedi_isadma_desc *desc;
 	struct comedi_subdevice *s = dev->read_subdev;
-	struct comedi_async *async = s->async;
-	struct comedi_cmd *cmd = &async->cmd;
-	unsigned short *buf = desc->virt_addr;
+	struct comedi_async *async;
+	struct comedi_cmd *cmd;
+	unsigned short *buf;
 	unsigned int max_points, num_points, residue, leftover;
 	unsigned short dpnt;
 	int status;
@@ -145,6 +145,11 @@ static irqreturn_t a2150_interrupt(int irq, void *d)
 	if (!dev->attached)
 		return IRQ_HANDLED;
 
+	desc = &dma->desc[0];
+	async = s->async;
+	cmd = &async->cmd;
+	buf = desc->virt_addr;
+
 	status = inw(dev->iobase + STATUS_REG);
 	if ((status & INTR_BIT) == 0)
 		return IRQ_NONE;
-- 
2.53.0