gpio: Fix kernel stack leak to userspace

The GPIO event descriptor was leaking kernel stack to
userspace because we don't zero the variable before
use. Ooops. Fix this.

Cc: stable@vger.kernel.org
Reported-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Bartosz Golaszewski <brgl@bgdev.pl>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpiolib.c

@@ -744,6 +744,9 @@ static irqreturn_t lineevent_irq_thread(int irq, void *p)
 	struct gpioevent_data ge;
 	int ret, level;
 
+	/* Do not leak kernel stack to userspace */
+	memset(&ge, 0, sizeof(ge));
+
 	ge.timestamp = ktime_get_real_ns();
 	level = gpiod_get_value_cansleep(le->desc);