tipc: fix info leak from kernel tipc_event

We initialize a struct tipc_event allocated on the kernel stack to
zero to avert info leak to user space.

Reported-by: syzbot+057458894bc8cada4dee@syzkaller.appspotmail.com
Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tipc/group.c

@@ -666,6 +666,7 @@ static void tipc_group_create_event(struct tipc_group *grp,
 	struct sk_buff *skb;
 	struct tipc_msg *hdr;
 
+	memset(&evt, 0, sizeof(evt));
 	evt.event = event;
 	evt.found_lower = m->instance;
 	evt.found_upper = m->instance;