[PATCH] comedi: das6402: Fix bit shift out of bounds

[Ian Abbott]

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

	/* IRQs 2,3,5,6,7, 10,11,15 are valid for "enhanced" mode */
	if ((1 << it->options[1]) & 0x8cec) {

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.

Fixes: 79e5e6addbb1 ("staging: comedi: das6402: rewrite broken 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/das6402.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/comedi/drivers/das6402.c b/drivers/comedi/drivers/das6402.c
index 68f95330de45..7660487e563c 100644
--- a/drivers/comedi/drivers/das6402.c
+++ b/drivers/comedi/drivers/das6402.c
@@ -567,7 +567,8 @@ static int das6402_attach(struct comedi_device *dev,
 	das6402_reset(dev);
 
 	/* IRQs 2,3,5,6,7, 10,11,15 are valid for "enhanced" mode */
-	if ((1 << it->options[1]) & 0x8cec) {
+	if (it->options[1] > 0 && it->options[1] < 16 &&
+	    (1 << it->options[1]) & 0x8cec) {
 		ret = request_irq(it->options[1], das6402_interrupt, 0,
 				  dev->board_name, dev);
 		if (ret == 0) {
-- 
2.47.2