net/ipv6: Update ip6addrlbl_dump for strict data checking

Update ip6addrlbl_dump for strict data checking. If the flag is set,
the dump request is expected to have an ifaddrlblmsg struct as the
header. All elements of the struct are expected to be 0 and no
attributes can be appended.
Signed-off-by: David Ahern <dsahern@gmail.com>
Acked-by: Christian Brauner <christian@brauner.io>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/addrlabel.c

@@ -458,20 +458,52 @@ static int ip6addrlbl_fill(struct sk_buff *skb,
 	return 0;
 }
 
+static int ip6addrlbl_valid_dump_req(const struct nlmsghdr *nlh,
+				     struct netlink_ext_ack *extack)
+{
+	struct ifaddrlblmsg *ifal;
+
+	if (nlh->nlmsg_len < nlmsg_msg_size(sizeof(*ifal))) {
+		NL_SET_ERR_MSG_MOD(extack, "Invalid header for address label dump request");
+		return -EINVAL;
+	}
+
+	ifal = nlmsg_data(nlh);
+	if (ifal->__ifal_reserved || ifal->ifal_prefixlen ||
+	    ifal->ifal_flags || ifal->ifal_index || ifal->ifal_seq) {
+		NL_SET_ERR_MSG_MOD(extack, "Invalid values in header for address label dump request");
+		return -EINVAL;
+	}
+
+	if (nlmsg_attrlen(nlh, sizeof(*ifal))) {
+		NL_SET_ERR_MSG_MOD(extack, "Invalid data after header for address label dump requewst");
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
 static int ip6addrlbl_dump(struct sk_buff *skb, struct netlink_callback *cb)
 {
+	const struct nlmsghdr *nlh = cb->nlh;
 	struct net *net = sock_net(skb->sk);
 	struct ip6addrlbl_entry *p;
 	int idx = 0, s_idx = cb->args[0];
 	int err;
 
+	if (cb->strict_check) {
+		err = ip6addrlbl_valid_dump_req(nlh, cb->extack);
+		if (err < 0)
+			return err;
+	}
+
 	rcu_read_lock();
 	hlist_for_each_entry_rcu(p, &net->ipv6.ip6addrlbl_table.head, list) {
 		if (idx >= s_idx) {
 			err = ip6addrlbl_fill(skb, p,
 					      net->ipv6.ip6addrlbl_table.seq,
 					      NETLINK_CB(cb->skb).portid,
-					      cb->nlh->nlmsg_seq,
+					      nlh->nlmsg_seq,
 					      RTM_NEWADDRLABEL,
 					      NLM_F_MULTI);
 			if (err < 0)