xfrm_user: fix info leak in build_expire()

The memory reserved to dump the expired xfrm state includes padding
bytes in struct xfrm_user_expire added by the compiler for alignment. To
prevent the heap info leak, memset(0) the remainder of the struct.
Initializing the whole structure isn't needed as copy_to_user_state()
already takes care of clearing the padding bytes within the 'state'
member.
Signed-off-by: Mathias Krause <minipli@googlemail.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/xfrm/xfrm_user.c

@@ -2578,6 +2578,8 @@ static int build_expire(struct sk_buff *skb, struct xfrm_state *x, const struct
 	ue = nlmsg_data(nlh);
 	copy_to_user_state(x, &ue->state);
 	ue->hard = (c->data.hard != 0) ? 1 : 0;
+	/* clear the padding bytes */
+	memset(&ue->hard + 1, 0, sizeof(*ue) - offsetofend(typeof(*ue), hard));
 
 	err = xfrm_mark_put(skb, &x->mark);
 	if (err)