463 lines
17 KiB
Rust
463 lines
17 KiB
Rust
use crate::{Error, Result};
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use crate::wire::{EthernetAddress, IpProtocol, IpAddress,
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Ipv4Cidr, Ipv4Address, Ipv4Repr,
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UdpRepr, UDP_HEADER_LEN,
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DhcpPacket, DhcpRepr, DhcpMessageType, DHCP_CLIENT_PORT, DHCP_SERVER_PORT, DHCP_MAX_DNS_SERVER_COUNT};
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use crate::wire::dhcpv4::{field as dhcpv4_field};
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use crate::socket::SocketMeta;
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use crate::time::{Instant, Duration};
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use super::{PollAt, Socket};
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const DISCOVER_TIMEOUT: Duration = Duration::from_secs(10);
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// timeout doubles every 2 tries.
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// total time 5 + 5 + 10 + 10 + 20 = 50s
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const REQUEST_TIMEOUT: Duration = Duration::from_secs(5);
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const REQUEST_RETRIES: u16 = 5;
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const MIN_RENEW_TIMEOUT: Duration = Duration::from_secs(60);
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const DEFAULT_LEASE_DURATION: u32 = 120;
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const PARAMETER_REQUEST_LIST: &[u8] = &[
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dhcpv4_field::OPT_SUBNET_MASK,
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dhcpv4_field::OPT_ROUTER,
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dhcpv4_field::OPT_DOMAIN_NAME_SERVER,
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];
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/// IPv4 configuration data provided by the DHCP server.
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#[derive(Debug, Eq, PartialEq)]
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#[cfg_attr(feature = "defmt", derive(defmt::Format))]
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pub struct Config {
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/// IP address
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pub address: Ipv4Cidr,
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/// Router address, also known as default gateway. Does not necessarily
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/// match the DHCP server's address.
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pub router: Option<Ipv4Address>,
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/// DNS servers
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pub dns_servers: [Option<Ipv4Address>; DHCP_MAX_DNS_SERVER_COUNT],
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}
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/// Information on how to reach a DHCP server.
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#[derive(Debug, Clone, Copy)]
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#[cfg_attr(feature = "defmt", derive(defmt::Format))]
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struct ServerInfo {
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/// IP address to use as destination in outgoing packets
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address: Ipv4Address,
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/// Server identifier to use in outgoing packets. Usually equal to server_address,
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/// but may differ in some situations (eg DHCP relays)
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identifier: Ipv4Address,
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}
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#[derive(Debug)]
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#[cfg_attr(feature = "defmt", derive(defmt::Format))]
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struct DiscoverState {
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/// When to send next request
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retry_at: Instant,
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}
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#[derive(Debug)]
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#[cfg_attr(feature = "defmt", derive(defmt::Format))]
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struct RequestState {
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/// When to send next request
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retry_at: Instant,
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/// How many retries have been done
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retry: u16,
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/// Server we're trying to request from
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server: ServerInfo,
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/// IP address that we're trying to request.
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requested_ip: Ipv4Address,
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}
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#[derive(Debug)]
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#[cfg_attr(feature = "defmt", derive(defmt::Format))]
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struct RenewState {
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/// Server that gave us the lease
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server: ServerInfo,
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/// Active networkc config
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config: Config,
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/// Renew timer. When reached, we will start attempting
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/// to renew this lease with the DHCP server.
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/// Must be less or equal than `expires_at`.
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renew_at: Instant,
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/// Expiration timer. When reached, this lease is no longer valid, so it must be
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/// thrown away and the ethernet interface deconfigured.
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expires_at: Instant,
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}
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#[derive(Debug)]
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#[cfg_attr(feature = "defmt", derive(defmt::Format))]
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enum ClientState {
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/// Discovering the DHCP server
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Discovering(DiscoverState),
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/// Requesting an address
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Requesting(RequestState),
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/// Having an address, refresh it periodically.
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Renewing(RenewState),
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}
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/// Return value for the `Dhcpv4Socket::poll` function
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pub enum Event<'a> {
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/// No change has occured to the configuration.
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NoChange,
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/// Configuration has been lost (for example, the lease has expired)
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Deconfigured,
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/// Configuration has been newly acquired, or modified.
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Configured(&'a Config),
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}
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#[derive(Debug)]
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pub struct Dhcpv4Socket {
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pub(crate) meta: SocketMeta,
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/// State of the DHCP client.
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state: ClientState,
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/// Set to true on config/state change, cleared back to false by the `config` function.
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config_changed: bool,
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/// xid of the last sent message.
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transaction_id: u32,
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/// Max lease duration. If set, it sets a maximum cap to the server-provided lease duration.
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/// Useful to react faster to IP configuration changes and to test whether renews work correctly.
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max_lease_duration: Option<Duration>,
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}
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/// DHCP client socket.
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///
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/// The socket acquires an IP address configuration through DHCP autonomously.
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/// You must query the configuration with `.poll()` after every call to `Interface::poll()`,
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/// and apply the configuration to the `Interface`.
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impl Dhcpv4Socket {
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/// Create a DHCPv4 socket
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#[allow(clippy::new_without_default)]
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pub fn new() -> Self {
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Dhcpv4Socket {
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meta: SocketMeta::default(),
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state: ClientState::Discovering(DiscoverState{
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retry_at: Instant::from_millis(0),
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}),
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config_changed: true,
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transaction_id: 1,
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max_lease_duration: None,
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}
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}
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pub fn max_lease_duration(&self) -> Option<Duration> {
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self.max_lease_duration
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}
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pub fn set_max_lease_duration(&mut self, max_lease_duration: Option<Duration>) {
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self.max_lease_duration = max_lease_duration;
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}
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pub(crate) fn poll_at(&self) -> PollAt {
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let t = match &self.state {
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ClientState::Discovering(state) => state.retry_at,
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ClientState::Requesting(state) => state.retry_at,
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ClientState::Renewing(state) => state.renew_at.min(state.expires_at),
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};
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PollAt::Time(t)
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}
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pub(crate) fn process(&mut self, now: Instant, ethernet_addr: EthernetAddress, ip_repr: &Ipv4Repr, repr: &UdpRepr, payload: &[u8]) -> Result<()> {
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let src_ip = ip_repr.src_addr;
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if repr.src_port != DHCP_SERVER_PORT || repr.dst_port != DHCP_CLIENT_PORT {
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return Ok(())
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}
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let dhcp_packet = match DhcpPacket::new_checked(payload) {
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Ok(dhcp_packet) => dhcp_packet,
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Err(e) => {
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net_debug!("DHCP invalid pkt from {}: {:?}", src_ip, e);
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return Ok(());
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}
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};
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let dhcp_repr = match DhcpRepr::parse(&dhcp_packet) {
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Ok(dhcp_repr) => dhcp_repr,
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Err(e) => {
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net_debug!("DHCP error parsing pkt from {}: {:?}", src_ip, e);
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return Ok(());
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}
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};
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if dhcp_repr.client_hardware_address != ethernet_addr { return Ok(()) }
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if dhcp_repr.transaction_id != self.transaction_id { return Ok(()) }
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let server_identifier = match dhcp_repr.server_identifier {
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Some(server_identifier) => server_identifier,
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None => {
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net_debug!("DHCP ignoring {:?} because missing server_identifier", dhcp_repr.message_type);
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return Ok(());
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}
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};
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net_debug!("DHCP recv {:?} from {} ({})", dhcp_repr.message_type, src_ip, server_identifier);
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match (&mut self.state, dhcp_repr.message_type){
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(ClientState::Discovering(_state), DhcpMessageType::Offer) => {
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if !dhcp_repr.your_ip.is_unicast() {
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net_debug!("DHCP ignoring OFFER because your_ip is not unicast");
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return Ok(())
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}
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self.state = ClientState::Requesting(RequestState {
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retry_at: now,
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retry: 0,
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server: ServerInfo {
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address: src_ip,
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identifier: server_identifier,
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},
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requested_ip: dhcp_repr.your_ip // use the offered ip
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});
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}
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(ClientState::Requesting(state), DhcpMessageType::Ack) => {
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if let Some((config, renew_at, expires_at)) = Self::parse_ack(now, ip_repr, &dhcp_repr, self.max_lease_duration) {
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self.config_changed = true;
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self.state = ClientState::Renewing(RenewState{
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server: state.server,
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config,
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renew_at,
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expires_at,
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});
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}
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}
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(ClientState::Requesting(_), DhcpMessageType::Nak) => {
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self.reset();
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}
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(ClientState::Renewing(state), DhcpMessageType::Ack) => {
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if let Some((config, renew_at, expires_at)) = Self::parse_ack(now, ip_repr, &dhcp_repr, self.max_lease_duration) {
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state.renew_at = renew_at;
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state.expires_at = expires_at;
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if state.config != config {
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self.config_changed = true;
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state.config = config;
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}
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}
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}
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(ClientState::Renewing(_), DhcpMessageType::Nak) => {
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self.reset();
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}
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_ => {
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net_debug!("DHCP ignoring {:?}: unexpected in current state", dhcp_repr.message_type);
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}
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}
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Ok(())
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}
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fn parse_ack(now: Instant, _ip_repr: &Ipv4Repr, dhcp_repr: &DhcpRepr, max_lease_duration: Option<Duration>) -> Option<(Config, Instant, Instant)> {
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let subnet_mask = match dhcp_repr.subnet_mask {
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Some(subnet_mask) => subnet_mask,
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None => {
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net_debug!("DHCP ignoring ACK because missing subnet_mask");
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return None
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}
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};
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let prefix_len = match IpAddress::Ipv4(subnet_mask).to_prefix_len() {
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Some(prefix_len) => prefix_len,
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None => {
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net_debug!("DHCP ignoring ACK because subnet_mask is not a valid mask");
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return None
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}
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};
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if !dhcp_repr.your_ip.is_unicast() {
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net_debug!("DHCP ignoring ACK because your_ip is not unicast");
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return None
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}
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let lease_duration = dhcp_repr.lease_duration.unwrap_or(DEFAULT_LEASE_DURATION);
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let mut lease_duration = Duration::from_secs(lease_duration as _);
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if let Some(max_lease_duration) = max_lease_duration {
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lease_duration = lease_duration.min(max_lease_duration);
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}
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// Cleanup the DNS servers list, keeping only unicasts/
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// TP-Link TD-W8970 sends 0.0.0.0 as second DNS server if there's only one configured :(
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let mut dns_servers = [None; DHCP_MAX_DNS_SERVER_COUNT];
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if let Some(received) = dhcp_repr.dns_servers {
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let mut i = 0;
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for addr in received.iter() {
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if let Some(addr) = addr{
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if addr.is_unicast() {
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// This can never be out-of-bounds since both arrays have length DHCP_MAX_DNS_SERVER_COUNT
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dns_servers[i] = Some(*addr);
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i += 1;
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}
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}
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}
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}
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let config = Config{
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address: Ipv4Cidr::new(dhcp_repr.your_ip, prefix_len),
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router: dhcp_repr.router,
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dns_servers: dns_servers
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};
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// RFC 2131 indicates clients should renew a lease halfway through its expiration.
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let renew_at = now + lease_duration / 2;
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let expires_at = now + lease_duration;
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Some((config, renew_at, expires_at))
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}
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pub(crate) fn dispatch<F>(&mut self, now: Instant, ethernet_addr: EthernetAddress, ip_mtu: usize, emit: F) -> Result<()>
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where F: FnOnce((Ipv4Repr, UdpRepr, DhcpRepr)) -> Result<()> {
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// Worst case biggest IPv4 header length.
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// 0x0f * 4 = 60 bytes.
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const MAX_IPV4_HEADER_LEN: usize = 60;
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// We don't directly increment transaction_id because sending the packet
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// may fail. We only want to update state after succesfully sending.
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let next_transaction_id = self.transaction_id + 1;
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let mut dhcp_repr = DhcpRepr {
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message_type: DhcpMessageType::Discover,
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transaction_id: next_transaction_id,
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client_hardware_address: ethernet_addr,
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client_ip: Ipv4Address::UNSPECIFIED,
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your_ip: Ipv4Address::UNSPECIFIED,
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server_ip: Ipv4Address::UNSPECIFIED,
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router: None,
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subnet_mask: None,
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relay_agent_ip: Ipv4Address::UNSPECIFIED,
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broadcast: true,
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requested_ip: None,
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client_identifier: Some(ethernet_addr),
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server_identifier: None,
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parameter_request_list: Some(PARAMETER_REQUEST_LIST),
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max_size: Some((ip_mtu - MAX_IPV4_HEADER_LEN - UDP_HEADER_LEN) as u16),
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lease_duration: None,
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dns_servers: None,
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};
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let udp_repr = UdpRepr {
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src_port: DHCP_CLIENT_PORT,
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dst_port: DHCP_SERVER_PORT,
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};
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let mut ipv4_repr = Ipv4Repr {
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src_addr: Ipv4Address::UNSPECIFIED,
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dst_addr: Ipv4Address::BROADCAST,
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protocol: IpProtocol::Udp,
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payload_len: 0, // filled right before emit
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hop_limit: 64,
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};
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match &mut self.state {
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ClientState::Discovering(state) => {
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if now < state.retry_at {
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return Err(Error::Exhausted)
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}
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// send packet
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net_debug!("DHCP send DISCOVER to {}: {:?}", ipv4_repr.dst_addr, dhcp_repr);
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ipv4_repr.payload_len = udp_repr.header_len() + dhcp_repr.buffer_len();
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emit((ipv4_repr, udp_repr, dhcp_repr))?;
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// Update state AFTER the packet has been successfully sent.
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state.retry_at = now + DISCOVER_TIMEOUT;
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self.transaction_id = next_transaction_id;
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Ok(())
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}
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ClientState::Requesting(state) => {
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if now < state.retry_at {
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return Err(Error::Exhausted)
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}
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if state.retry >= REQUEST_RETRIES {
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net_debug!("DHCP request retries exceeded, restarting discovery");
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self.reset();
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// return Ok so we get polled again
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return Ok(())
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}
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dhcp_repr.message_type = DhcpMessageType::Request;
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dhcp_repr.broadcast = false;
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dhcp_repr.requested_ip = Some(state.requested_ip);
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dhcp_repr.server_identifier = Some(state.server.identifier);
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net_debug!("DHCP send request to {}: {:?}", ipv4_repr.dst_addr, dhcp_repr);
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ipv4_repr.payload_len = udp_repr.header_len() + dhcp_repr.buffer_len();
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emit((ipv4_repr, udp_repr, dhcp_repr))?;
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// Exponential backoff: Double every 2 retries.
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state.retry_at = now + (REQUEST_TIMEOUT << (state.retry as u32 / 2));
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state.retry += 1;
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self.transaction_id = next_transaction_id;
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Ok(())
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}
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ClientState::Renewing(state) => {
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if state.expires_at <= now {
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net_debug!("DHCP lease expired");
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self.reset();
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// return Ok so we get polled again
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return Ok(())
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}
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if now < state.renew_at {
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return Err(Error::Exhausted)
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}
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ipv4_repr.src_addr = state.config.address.address();
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ipv4_repr.dst_addr = state.server.address;
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dhcp_repr.message_type = DhcpMessageType::Request;
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dhcp_repr.client_ip = state.config.address.address();
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dhcp_repr.broadcast = false;
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net_debug!("DHCP send renew to {}: {:?}", ipv4_repr.dst_addr, dhcp_repr);
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ipv4_repr.payload_len = udp_repr.header_len() + dhcp_repr.buffer_len();
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emit((ipv4_repr, udp_repr, dhcp_repr))?;
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// In both RENEWING and REBINDING states, if the client receives no
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// response to its DHCPREQUEST message, the client SHOULD wait one-half
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// of the remaining time until T2 (in RENEWING state) and one-half of
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// the remaining lease time (in REBINDING state), down to a minimum of
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// 60 seconds, before retransmitting the DHCPREQUEST message.
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state.renew_at = now + MIN_RENEW_TIMEOUT.max((state.expires_at - now) / 2);
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self.transaction_id = next_transaction_id;
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Ok(())
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}
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}
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}
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/// Reset state and restart discovery phase.
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///
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/// Use this to speed up acquisition of an address in a new
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/// network if a link was down and it is now back up.
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pub fn reset(&mut self) {
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net_trace!("DHCP reset");
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if let ClientState::Renewing(_) = &self.state {
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self.config_changed = true;
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}
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self.state = ClientState::Discovering(DiscoverState{
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retry_at: Instant::from_millis(0),
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});
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}
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/// Query the socket for configuration changes.
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///
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/// The socket has an internal "configuration changed" flag. If
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/// set, this function returns the configuration and resets the flag.
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pub fn poll(&mut self) -> Event<'_> {
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if !self.config_changed {
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Event::NoChange
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} else if let ClientState::Renewing(state) = &self.state {
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self.config_changed = false;
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Event::Configured(&state.config)
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} else {
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self.config_changed = false;
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Event::Deconfigured
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}
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}
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}
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impl<'a> Into<Socket<'a>> for Dhcpv4Socket {
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fn into(self) -> Socket<'a> {
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Socket::Dhcpv4(self)
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}
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}
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