krata/network/src/proxynat/icmp.rs

use std::{net::IpAddr, time::Duration};

use anyhow::{anyhow, Result};
use async_trait::async_trait;
use etherparse::{
    Icmpv4Header, Icmpv4Type, Icmpv6Header, Icmpv6Type, IpNumber, NetSlice, PacketBuilder,
    SlicedPacket,
};
use log::{debug, warn};
use smoltcp::wire::IpAddress;
use tokio::{
    select,
    sync::mpsc::{Receiver, Sender},
};

use crate::{
    icmp::{IcmpClient, IcmpProtocol, IcmpReply},
    nat::{NatHandler, NatKey},
};

const ICMP_PING_TIMEOUT_SECS: u64 = 20;
const ICMP_TIMEOUT_SECS: u64 = 30;

pub struct ProxyIcmpHandler {
    key: NatKey,
    rx_sender: Sender<Vec<u8>>,
}

#[async_trait]
impl NatHandler for ProxyIcmpHandler {
    async fn receive(&self, data: &[u8]) -> Result<()> {
        self.rx_sender.try_send(data.to_vec())?;
        Ok(())
    }
}

enum ProxyIcmpSelect {
    Internal(Vec<u8>),
    Close,
}

impl ProxyIcmpHandler {
    pub fn new(key: NatKey, rx_sender: Sender<Vec<u8>>) -> Self {
        ProxyIcmpHandler { key, rx_sender }
    }

    pub async fn spawn(
        &mut self,
        rx_receiver: Receiver<Vec<u8>>,
        tx_sender: Sender<Vec<u8>>,
        reclaim_sender: Sender<NatKey>,
    ) -> Result<()> {
        let client = IcmpClient::new(IcmpProtocol::Icmp4)?;
        let key = self.key;
        tokio::spawn(async move {
            if let Err(error) =
                ProxyIcmpHandler::process(client, key, rx_receiver, tx_sender, reclaim_sender).await
            {
                warn!("processing of icmp proxy failed: {}", error);
            }
        });
        Ok(())
    }

    async fn process(
        client: IcmpClient,
        key: NatKey,
        mut rx_receiver: Receiver<Vec<u8>>,
        tx_sender: Sender<Vec<u8>>,
        reclaim_sender: Sender<NatKey>,
    ) -> Result<()> {
        loop {
            let deadline = tokio::time::sleep(Duration::from_secs(ICMP_TIMEOUT_SECS));
            let selection = select! {
                x = rx_receiver.recv() => if let Some(data) = x {
                    ProxyIcmpSelect::Internal(data)
                } else {
                    ProxyIcmpSelect::Close
                },
                _ =  deadline => ProxyIcmpSelect::Close,
            };

            match selection {
                ProxyIcmpSelect::Internal(data) => {
                    let packet = SlicedPacket::from_ethernet(&data)?;
                    let Some(ref net) = packet.net else {
                        continue;
                    };

                    match net {
                        NetSlice::Ipv4(ipv4) => {
                            if ipv4.header().protocol() != IpNumber::ICMP {
                                continue;
                            }

                            let (header, payload) =
                                Icmpv4Header::from_slice(ipv4.payload().payload)?;
                            if let Icmpv4Type::EchoRequest(echo) = header.icmp_type {
                                let IpAddr::V4(external_ipv4) = key.external_ip.addr.into() else {
                                    continue;
                                };

                                let Some(IcmpReply::Icmp4 {
                                    header: _,
                                    echo,
                                    payload,
                                }) = client
                                    .ping4(
                                        external_ipv4,
                                        echo.id,
                                        echo.seq,
                                        payload,
                                        Duration::from_secs(ICMP_PING_TIMEOUT_SECS),
                                    )
                                    .await?
                                else {
                                    continue;
                                };

                                let packet =
                                    PacketBuilder::ethernet2(key.local_mac.0, key.client_mac.0);
                                let packet = match (key.external_ip.addr, key.client_ip.addr) {
                                    (
                                        IpAddress::Ipv4(external_addr),
                                        IpAddress::Ipv4(client_addr),
                                    ) => packet.ipv4(external_addr.0, client_addr.0, 20),
                                    _ => {
                                        return Err(anyhow!("IP endpoint mismatch"));
                                    }
                                };
                                let packet = packet.icmpv4_echo_reply(echo.id, echo.seq);
                                let mut buffer: Vec<u8> = Vec::new();
                                packet.write(&mut buffer, &payload)?;
                                if let Err(error) = tx_sender.try_send(buffer) {
                                    debug!("failed to transmit icmp packet: {}", error);
                                }
                            }
                        }

                        NetSlice::Ipv6(ipv6) => {
                            if ipv6.header().next_header() != IpNumber::ICMP {
                                continue;
                            }

                            let (header, payload) =
                                Icmpv6Header::from_slice(ipv6.payload().payload)?;
                            if let Icmpv6Type::EchoRequest(echo) = header.icmp_type {
                                let IpAddr::V6(external_ipv6) = key.external_ip.addr.into() else {
                                    continue;
                                };

                                let Some(IcmpReply::Icmp6 {
                                    header: _,
                                    echo,
                                    payload,
                                }) = client
                                    .ping6(
                                        external_ipv6,
                                        echo.id,
                                        echo.seq,
                                        payload,
                                        Duration::from_secs(ICMP_PING_TIMEOUT_SECS),
                                    )
                                    .await?
                                else {
                                    continue;
                                };

                                let packet =
                                    PacketBuilder::ethernet2(key.local_mac.0, key.client_mac.0);
                                let packet = match (key.external_ip.addr, key.client_ip.addr) {
                                    (
                                        IpAddress::Ipv6(external_addr),
                                        IpAddress::Ipv6(client_addr),
                                    ) => packet.ipv6(external_addr.0, client_addr.0, 20),
                                    _ => {
                                        return Err(anyhow!("IP endpoint mismatch"));
                                    }
                                };
                                let packet = packet.icmpv6_echo_reply(echo.id, echo.seq);
                                let mut buffer: Vec<u8> = Vec::new();
                                packet.write(&mut buffer, &payload)?;
                                if let Err(error) = tx_sender.try_send(buffer) {
                                    debug!("failed to transmit icmp packet: {}", error);
                                }
                            }
                        }
                    }
                }

                ProxyIcmpSelect::Close => {
                    reclaim_sender.send(key).await?;
                    break;
                }
            }
        }

        Ok(())
    }
}