gotatun 0.4.1

// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at https://mozilla.org/MPL/2.0/.
//
// This file incorporates work covered by the following copyright and
// permission notice:
//
//   Copyright (c) Mullvad VPN AB. All rights reserved.
//   Copyright (c) 2019 Cloudflare, Inc. All rights reserved.
//
// SPDX-License-Identifier: MPL-2.0

use super::errors::WireGuardError;
use crate::noise::Tunn;
use crate::packet::WgKind;

use std::mem;
use std::ops::{Index, IndexMut};
use std::time::Duration;

use bytes::BytesMut;
#[cfg(feature = "mock_instant")]
use mock_instant::thread_local::Instant;

#[cfg(not(feature = "mock_instant"))]
use crate::sleepyinstant::Instant;

// Some constants, represent time in seconds
// https://www.wireguard.com/papers/wireguard.pdf#page=14
pub(crate) const REKEY_AFTER_TIME: Duration = Duration::from_secs(120);
const REJECT_AFTER_TIME: Duration = Duration::from_secs(180);
const REKEY_ATTEMPT_TIME: Duration = Duration::from_secs(90);
pub(crate) const REKEY_TIMEOUT: Duration = Duration::from_secs(5);
const KEEPALIVE_TIMEOUT: Duration = Duration::from_secs(10);
const COOKIE_EXPIRATION_TIME: Duration = Duration::from_secs(120);

#[derive(Debug)]
pub enum TimerName {
    /// Current time, updated each call to `update_timers`
    TimeCurrent,
    /// Time when last handshake was completed
    TimeSessionEstablished,
    /// Time the last attempt for a new handshake began
    TimeLastHandshakeStarted,
    /// Time we last received and authenticated a packet
    TimeLastPacketReceived,
    /// Time we last send a packet
    TimeLastPacketSent,
    /// Time we last received and authenticated a DATA packet
    TimeLastDataPacketReceived,
    /// Time we last send a DATA packet
    TimeLastDataPacketSent,
    /// Time we last received a cookie
    TimeCookieReceived,
    /// Time we last sent persistent keepalive
    TimePersistentKeepalive,
    Top,
}

use self::TimerName::*;

#[derive(Debug)]
pub struct Timers {
    /// Is the owner of the timer the initiator or the responder for the last handshake?
    is_initiator: bool,
    /// Start time of the tunnel
    time_started: Instant,
    timers: [Duration; TimerName::Top as usize],
    pub(super) session_timers: [Duration; super::N_SESSIONS],
    /// Did we receive data without sending anything back?
    want_keepalive: bool,
    /// First data packet sent without hearing back
    want_handshake: Option<Duration>,
    persistent_keepalive: usize,
}

impl Timers {
    pub(super) fn new(persistent_keepalive: Option<u16>) -> Timers {
        Timers {
            is_initiator: false,
            time_started: Instant::now(),
            timers: Default::default(),
            session_timers: Default::default(),
            want_keepalive: Default::default(),
            want_handshake: Default::default(),
            persistent_keepalive: usize::from(persistent_keepalive.unwrap_or(0)),
        }
    }

    fn is_initiator(&self) -> bool {
        self.is_initiator
    }

    // We don't really clear the timers, but we set them to the current time to
    // so the reference time frame is the same
    pub(super) fn clear(&mut self) {
        let now = self.now();
        for t in &mut self.timers[..] {
            *t = now;
        }
        self.want_handshake = None;
        self.want_keepalive = false;
    }

    /// Compute the time elapsed since [`Self::time_started`] based on [`Instant::now`].
    /// This is guaranteed to be monotonic and no less than `self[TimeCurrent]`.
    /// It never panics.
    fn now(&self) -> Duration {
        Instant::now()
            .checked_duration_since(self.time_started)
            .unwrap_or(Duration::ZERO)
            .max(self[TimeCurrent])
    }
}

impl Index<TimerName> for Timers {
    type Output = Duration;
    fn index(&self, index: TimerName) -> &Duration {
        &self.timers[index as usize]
    }
}

impl IndexMut<TimerName> for Timers {
    fn index_mut(&mut self, index: TimerName) -> &mut Duration {
        &mut self.timers[index as usize]
    }
}

impl Tunn {
    pub(super) fn timer_tick(&mut self, timer_name: TimerName) {
        let time = self.timers[TimeCurrent];

        match timer_name {
            TimeLastPacketReceived => {
                self.timers.want_keepalive = true;
                self.timers.want_handshake = None;
            }
            TimeLastPacketSent => {
                self.timers.want_keepalive = false;
            }
            TimeLastDataPacketSent => {
                self.timers.want_handshake.get_or_insert(time);
            }
            _ => {}
        }

        self.timers[timer_name] = time;
    }

    pub(super) fn timer_tick_session_established(
        &mut self,
        is_initiator: bool,
        session_idx: usize,
    ) {
        self.timer_tick(TimeSessionEstablished);
        self.timers.session_timers[session_idx % crate::noise::N_SESSIONS] =
            self.timers[TimeCurrent];
        self.timers.is_initiator = is_initiator;
    }

    // We don't really clear the timers, but we set them to the current time to
    // so the reference time frame is the same
    fn clear_all(&mut self) {
        for session in &mut self.sessions {
            *session = None;
        }

        self.packet_queue.clear();

        self.timers.clear();
    }

    fn update_session_timers(&mut self, time_now: Duration) {
        let timers = &mut self.timers;

        for (i, t) in timers.session_timers.iter_mut().enumerate() {
            if time_now - *t > REJECT_AFTER_TIME {
                // Forget about expired sesssions
                if let Some(session) = self.sessions[i].take() {
                    log::trace!(
                        "SESSION_EXPIRED(REJECT_AFTER_TIME): {}",
                        session.receiving_index
                    );
                }
                *t = time_now;
            }
        }
    }

    /// Update the tunnel timers
    ///
    /// This returns `Ok(None)` if no action is needed, `Ok(Some(packet))` if a packet
    /// (keepalive or handshake) should be sent, or an error if something went wrong.
    pub fn update_timers(&mut self) -> Result<Option<WgKind>, WireGuardError> {
        let mut handshake_initiation_required = false;
        let mut keepalive_required = false;

        self.rate_limiter.try_reset_count();

        // All the times are counted from tunnel initiation, for efficiency our timers are rounded
        // to a second, as there is no real benefit to having highly accurate timers.
        let now = self.timers.now();
        self.timers[TimeCurrent] = now;

        self.update_session_timers(now);

        // Load timers only once:
        let session_established = self.timers[TimeSessionEstablished];
        let handshake_started = self.timers[TimeLastHandshakeStarted];
        let aut_packet_sent = self.timers[TimeLastPacketSent];
        let data_packet_received = self.timers[TimeLastDataPacketReceived];
        let data_packet_sent = self.timers[TimeLastDataPacketSent];
        let persistent_keepalive = self.timers.persistent_keepalive;

        {
            if self.handshake.is_expired() {
                return Err(WireGuardError::ConnectionExpired);
            }

            // Clear cookie after COOKIE_EXPIRATION_TIME
            if self.handshake.has_cookie()
                && now - self.timers[TimeCookieReceived] >= COOKIE_EXPIRATION_TIME
            {
                self.handshake.clear_cookie();
            }

            // All ephemeral private keys and symmetric session keys are zeroed out after
            // (REJECT_AFTER_TIME * 3) ms if no new keys have been exchanged.
            if now - session_established >= REJECT_AFTER_TIME * 3 {
                log::trace!("CONNECTION_EXPIRED(REJECT_AFTER_TIME * 3)");
                self.handshake.set_expired();
                self.clear_all();
                return Err(WireGuardError::ConnectionExpired);
            }

            if let Some(time_init_sent) = self.handshake.timer() {
                // Handshake Initiation Retransmission
                if now - handshake_started >= REKEY_ATTEMPT_TIME {
                    // After REKEY_ATTEMPT_TIME ms of trying to initiate a new handshake,
                    // the retries give up and cease, and clear all existing packets queued
                    // up to be sent. If a packet is explicitly queued up to be sent, then
                    // this timer is reset.
                    log::debug!("CONNECTION_EXPIRED(REKEY_ATTEMPT_TIME)");
                    self.handshake.set_expired();
                    self.clear_all();
                    return Err(WireGuardError::ConnectionExpired);
                }

                if time_init_sent.elapsed() >= REKEY_TIMEOUT {
                    // We avoid using `time` here, because it can be earlier than `time_init_sent`.
                    // Once `checked_duration_since` is stable we can use that.
                    // A handshake initiation is retried after REKEY_TIMEOUT + jitter ms,
                    // if a response has not been received, where jitter is some random
                    // value between 0 and 333 ms.
                    log::debug!("HANDSHAKE(REKEY_TIMEOUT)");
                    handshake_initiation_required = true;
                }
            } else {
                if self.timers.is_initiator() {
                    // After sending a packet, if the sender was the original initiator
                    // of the handshake and if the current session key is REKEY_AFTER_TIME
                    // ms old, we initiate a new handshake. If the sender was the original
                    // responder of the handshake, it does not re-initiate a new handshake
                    // after REKEY_AFTER_TIME ms like the original initiator does.
                    if session_established < data_packet_sent
                        && now - session_established >= REKEY_AFTER_TIME
                    {
                        log::trace!("HANDSHAKE(REKEY_AFTER_TIME (on send))");
                        handshake_initiation_required = true;
                    }

                    // After receiving a packet, if the receiver was the original initiator
                    // of the handshake and if the current session key is REJECT_AFTER_TIME
                    // - KEEPALIVE_TIMEOUT - REKEY_TIMEOUT ms old, we initiate a new
                    // handshake.
                    if session_established < data_packet_received
                        && now - session_established
                            >= REJECT_AFTER_TIME - KEEPALIVE_TIMEOUT - REKEY_TIMEOUT
                    {
                        log::trace!(
                            "HANDSHAKE(REJECT_AFTER_TIME - KEEPALIVE_TIMEOUT - \
                        REKEY_TIMEOUT \
                        (on receive))"
                        );
                        handshake_initiation_required = true;
                    }
                }

                // If we have sent a data packet to a given peer but have not received a
                // packet after from that peer for `(KEEPALIVE + REKEY_TIMEOUT)`,
                // we initiate a new handshake.
                if let Some(since) = self.timers.want_handshake
                    && now.saturating_sub(since) >= KEEPALIVE_TIMEOUT + REKEY_TIMEOUT
                {
                    log::trace!("HANDSHAKE(KEEPALIVE + REKEY_TIMEOUT)");
                    handshake_initiation_required = true;
                    self.timers.want_handshake = None;
                }

                if !handshake_initiation_required {
                    // If a packet has been received from a given peer, but we have not sent one
                    // back to the given peer in KEEPALIVE ms, we send an empty packet.
                    if data_packet_received > aut_packet_sent
                        && now - aut_packet_sent >= KEEPALIVE_TIMEOUT
                        && mem::replace(&mut self.timers.want_keepalive, false)
                    {
                        log::trace!("KEEPALIVE(KEEPALIVE_TIMEOUT)");
                        keepalive_required = true;
                    }

                    // Persistent KEEPALIVE
                    if persistent_keepalive > 0
                        && (now - self.timers[TimePersistentKeepalive]
                            >= Duration::from_secs(persistent_keepalive as _))
                    {
                        log::trace!("KEEPALIVE(PERSISTENT_KEEPALIVE)");
                        self.timer_tick(TimePersistentKeepalive);
                        keepalive_required = true;
                    }
                }
            }
        }

        if handshake_initiation_required {
            return Ok(self.format_handshake_initiation(true).map(Into::into));
        }

        if keepalive_required {
            return Ok(self
                .handle_outgoing_packet(crate::packet::Packet::from_bytes(BytesMut::new()), None));
        }

        Ok(None)
    }

    /// Get the time elapsed since the last successful handshake.
    ///
    /// Returns `None` if no session has been established.
    pub fn time_since_last_handshake(&self) -> Option<Duration> {
        let current_session = self.current;
        if self.sessions[current_session % super::N_SESSIONS].is_some() {
            let duration_since_tun_start = self.timers.now();
            let duration_since_session_established = self.timers[TimeSessionEstablished];

            Some(duration_since_tun_start.saturating_sub(duration_since_session_established))
        } else {
            None
        }
    }

    /// Get the persistent keepalive interval in seconds.
    ///
    /// Returns `None` if persistent keepalive is disabled (set to 0).
    pub fn persistent_keepalive(&self) -> Option<u16> {
        let keepalive = self.timers.persistent_keepalive;

        if keepalive > 0 {
            Some(keepalive as u16)
        } else {
            None
        }
    }

    /// Set the persistent keepalive interval in seconds.
    ///
    /// Pass `None` or `Some(0)` to disable persistent keepalive.
    pub fn set_persistent_keepalive(&mut self, seconds: Option<u16>) {
        self.timers.persistent_keepalive = usize::from(seconds.unwrap_or(0));

        // Reset timer if we disable persistent keepalive
        if self.timers.persistent_keepalive == 0 {
            self.timers[TimePersistentKeepalive] = Duration::ZERO;
        }
    }
}