gpio: Fix kernel stack leak to userspace

commit 24bd3efc9d upstream.

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

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/gpio/gpiolib.c

@@ -723,6 +723,9 @@ 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);