HID: hiddev: potential info leak in hiddev_ioctl()

Smatch has a new check for Rosenberg type information leaks where
structs are copied to the user with uninitialized stack data in them.

In this case, the hiddev_devinfo struct has a two byte hole.

struct hiddev_devinfo {
        __u32                      bustype;              /*     0     4 */
        __u32                      busnum;               /*     4     4 */
        __u32                      devnum;               /*     8     4 */
        __u32                      ifnum;                /*    12     4 */
        __s16                      vendor;               /*    16     2 */
        __s16                      product;              /*    18     2 */
        __s16                      version;              /*    20     2 */

        /* XXX 2 bytes hole, try to pack */

        __u32                      num_applications;     /*    24     4 */
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/usbhid/hiddev.c

@@ -641,6 +641,8 @@ static long hiddev_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 			struct usb_device *dev = hid_to_usb_dev(hid);
 			struct usbhid_device *usbhid = hid->driver_data;
 
+			memset(&dinfo, 0, sizeof(dinfo));
+
 			dinfo.bustype = BUS_USB;
 			dinfo.busnum = dev->bus->busnum;
 			dinfo.devnum = dev->devnum;