[PATCH] comedi: pcl812: Fix bit shift out of bounds

[Ian Abbott]

When checking for a supported IRQ number, the following test is used:

	if ((1 << it->options[1]) & board->irq_bits) {

However, `it->options[i]` is an unchecked `int` value from userspace, so
the shift amount could be negative or out of bounds.  Fix the test by
requiring `it->options[1]` to be within bounds before proceeding with
the original test.  Valid `it->options[1]` values that select the IRQ
will be in the range [1,15]. The value 0 explicitly disables the use of
interrupts.

Reported-by: syzbot+32de323b0addb9e114ff@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=32de323b0addb9e114ff
Fixes: fcdb427bc7cf ("Staging: comedi: add pcl821 driver")
Cc: <stable@xxxxxxxxxxxxxxx> # 5.13+
Signed-off-by: Ian Abbott <abbotti@xxxxxxxxx>
---
Patch does not apply cleanly to longterm kernels 5.4.x and 5.10.x.
---
 drivers/comedi/drivers/pcl812.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/comedi/drivers/pcl812.c b/drivers/comedi/drivers/pcl812.c
index 0df639c6a595..abca61a72cf7 100644
--- a/drivers/comedi/drivers/pcl812.c
+++ b/drivers/comedi/drivers/pcl812.c
@@ -1149,7 +1149,8 @@ static int pcl812_attach(struct comedi_device *dev, struct comedi_devconfig *it)
 		if (IS_ERR(dev->pacer))
 			return PTR_ERR(dev->pacer);
 
-		if ((1 << it->options[1]) & board->irq_bits) {
+		if (it->options[1] > 0 && it->options[1] < 16 &&
+		    (1 << it->options[1]) & board->irq_bits) {
 			ret = request_irq(it->options[1], pcl812_interrupt, 0,
 					  dev->board_name, dev);
 			if (ret == 0)
-- 
2.47.2