gpio: GPIOHANDLE_GET_LINE_VALUES_IOCTL: Fix information leak

commit 3eded5d8 upstream.

The GPIOHANDLE_GET_LINE_VALUES_IOCTL handler allocates a gpiohandle_data
struct on the stack and then passes it to copy_to_user(). But depending on
the number of requested line handles the struct is only partially
initialized.

This exposes the previous, potentially sensitive, stack content to the
issuing userspace application. To avoid this make sure that the struct is
fully initialized.

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

@@ -342,6 +342,8 @@ static long linehandle_ioctl(struct file *filep, unsigned int cmd,
 	if (cmd == GPIOHANDLE_GET_LINE_VALUES_IOCTL) {
 		int val;
 
+		memset(&ghd, 0, sizeof(ghd));
+
 		/* TODO: check if descriptors are really input */
 		for (i = 0; i < lh->numdescs; i++) {
 			val = gpiod_get_value_cansleep(lh->descs[i]);