gpio: fix line flag validation in linehandle_create

linehandle_create should not allow both GPIOHANDLE_REQUEST_INPUT
and GPIOHANDLE_REQUEST_OUTPUT to be set.

Fixes: d7c51b47 ("gpio: userspace ABI for reading/writing GPIO lines")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Kent Gibson <warthog618@gmail.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>

drivers/gpio/gpiolib.c

@@ -535,6 +535,14 @@ static int linehandle_create(struct gpio_device *gdev, void __user *ip)
 	if (lflags & ~GPIOHANDLE_REQUEST_VALID_FLAGS)
 		return -EINVAL;
 
+	/*
+	 * Do not allow both INPUT & OUTPUT flags to be set as they are
+	 * contradictory.
+	 */
+	if ((lflags & GPIOHANDLE_REQUEST_INPUT) &&
+	    (lflags & GPIOHANDLE_REQUEST_OUTPUT))
+		return -EINVAL;
+
 	/*
 	 * Do not allow OPEN_SOURCE & OPEN_DRAIN flags in a single request. If
 	 * the hardware actually supports enabling both at the same time the