gpio: GPIO_GET_LINEHANDLE_IOCTL: Validate line offset

commit e405f9fc upstream.

The line offset that is used as an index into the descs array is provided
by userspace and might go beyond the bounds of the array. If that happens
undefined behavior will occur.

Make sure that the offset is within the bounds of the desc array and reject
any requests that specify a value outside of it.

Fixes: d7c51b47 ("gpio: userspace ABI for reading/writing GPIO lines")
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/gpio/gpiolib.c

@@ -442,6 +442,11 @@ static int linehandle_create(struct gpio_device *gdev, void __user *ip)
 		u32 lflags = handlereq.flags;
 		struct gpio_desc *desc;
 
+		if (offset >= gdev->ngpio) {
+			ret = -EINVAL;
+			goto out_free_descs;
+		}
+
 		desc = &gdev->descs[offset];
 		ret = gpiod_request(desc, lh->label);
 		if (ret)