[PATCH 4/6] comedi: dmm32at: validate the IRQ supplied by userspace

[Yogesh Gaur <yogeshgaur.83@gmail.com>]

comedi boards are configured through the COMEDI_DEVCONFIG ioctl, so
it->options[1] is a number chosen by userspace. dmm32at passes it to
request_irq() without checking it first, which lets an interrupt owned by
another irqdomain -- a PCI device's IO-APIC GSI, for instance -- be
claimed for this board. When the owner of that interrupt is later
released the descriptor is freed while this driver's handler is still
installed on it.

Every interrupt this board can assert is a legacy ISA one, so the ISA
range is the right bound; it is also sufficient, because
mp_chip_data->isa_irq is set only by alloc_isa_irq_from_domain() and
mp_unmap_irq() returns early when it is set.

Bound the value before requesting it, as das16m1.c already does. An
out-of-range value is ignored rather than rejected, so the board still
attaches without interrupt support, exactly as it does today when
request_irq() fails.

Fixes: 3c501880ac44 ("Staging: comedi: add dmm32at driver")
Assisted-by: LLM
Signed-off-by: Yogesh Gaur <yogeshgaur.83@gmail.com>
---
 drivers/comedi/drivers/dmm32at.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/comedi/drivers/dmm32at.c b/drivers/comedi/drivers/dmm32at.c
index d1d9f75e168f..c6a6ba2899e6 100644
--- a/drivers/comedi/drivers/dmm32at.c
+++ b/drivers/comedi/drivers/dmm32at.c
@@ -600,7 +600,8 @@ static int dmm32at_attach(struct comedi_device *dev,
 		return ret;
 	}
 
-	if (it->options[1]) {
+	/* only ISA interrupts are valid on this board */
+	if (it->options[1] >= 1 && it->options[1] <= 15) {
 		ret = request_irq(it->options[1], dmm32at_isr, 0,
 				  dev->board_name, dev);
 		if (ret == 0)
-- 
2.55.0.windows.5