rtnetlink: Update inet6_dump_ifinfo for strict data checking

Update inet6_dump_ifinfo for strict data checking. If the flag is
set, the dump request is expected to have an ifinfomsg 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/addrconf.c

@@ -5644,6 +5644,31 @@ static int inet6_fill_ifinfo(struct sk_buff *skb, struct inet6_dev *idev,
 	return -EMSGSIZE;
 }
 
+static int inet6_valid_dump_ifinfo(const struct nlmsghdr *nlh,
+				   struct netlink_ext_ack *extack)
+{
+	struct ifinfomsg *ifm;
+
+	if (nlh->nlmsg_len < nlmsg_msg_size(sizeof(*ifm))) {
+		NL_SET_ERR_MSG_MOD(extack, "Invalid header for link dump request");
+		return -EINVAL;
+	}
+
+	if (nlmsg_attrlen(nlh, sizeof(*ifm))) {
+		NL_SET_ERR_MSG_MOD(extack, "Invalid data after header");
+		return -EINVAL;
+	}
+
+	ifm = nlmsg_data(nlh);
+	if (ifm->__ifi_pad || ifm->ifi_type || ifm->ifi_flags ||
+	    ifm->ifi_change || ifm->ifi_index) {
+		NL_SET_ERR_MSG_MOD(extack, "Invalid values in header for dump request");
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
 static int inet6_dump_ifinfo(struct sk_buff *skb, struct netlink_callback *cb)
 {
 	struct net *net = sock_net(skb->sk);
@@ -5653,6 +5678,16 @@ static int inet6_dump_ifinfo(struct sk_buff *skb, struct netlink_callback *cb)
 	struct inet6_dev *idev;
 	struct hlist_head *head;
 
+	/* only requests using strict checking can pass data to
+	 * influence the dump
+	 */
+	if (cb->strict_check) {
+		int err = inet6_valid_dump_ifinfo(cb->nlh, cb->extack);
+
+		if (err < 0)
+			return err;
+	}
+
 	s_h = cb->args[0];
 	s_idx = cb->args[1];