HID: uhid: fix leak for 64/32 UHID_CREATE

UHID allows short writes so user-space can omit unused fields. We
automatically set them to 0 in the kernel. However, the 64/32 bit
compat-handler didn't do that in the UHID_CREATE fallback. This will
reveal random kernel heap data (of random size, even) to user-space.

Fixes: befde022 ('HID: uhid: make creating devices work on 64/32 systems')
Reported-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/uhid.c

@@ -287,7 +287,7 @@ static int uhid_event_from_user(const char __user *buffer, size_t len,
 			 */
 			struct uhid_create_req_compat *compat;
 
-			compat = kmalloc(sizeof(*compat), GFP_KERNEL);
+			compat = kzalloc(sizeof(*compat), GFP_KERNEL);
 			if (!compat)
 				return -ENOMEM;