r_lanlib/scanners/

syn_scanner.rs

//! Provides Scanner implementation for SYN scanning

use derive_builder::Builder;
use pnet::packet::{Packet, ethernet, ip, ipv4, tcp};
use std::{
    collections::HashMap,
    net::Ipv4Addr,
    sync::{self, Arc, LazyLock, Mutex, mpsc},
    thread::{self, JoinHandle},
    time::Duration,
};

use crate::{
    error::{RLanLibError, Result},
    network::NetworkInterface,
    packet::{
        self, Reader, Sender, rst_packet::RstPacketBuilder,
        syn_packet::SynPacketBuilder,
    },
    scanners::{PortSet, Scanning, heartbeat::HeartBeat},
    targets::ports::PortTargets,
};

use super::{Device, Port, ScanMessage, Scanner};

static SERVICES: LazyLock<HashMap<u16, &str>> = LazyLock::new(|| {
    HashMap::from([
        (20, "ftp-data"),
        (21, "ftp"),
        (22, "ssh"),
        (23, "telnet"),
        (25, "smtp"),
        (53, "dns"),
        (80, "http"),
        (110, "pop3"),
        (143, "imap"),
        (443, "https"),
        (445, "microsoft-ds"),
        (587, "submission"),
        (993, "imaps"),
        (995, "pop3s"),
        (1433, "mssql"),
        (3306, "mysql"),
        (3389, "rdp"),
        (5432, "postgresql"),
        (5900, "vnc"),
        (6379, "redis"),
        (8080, "http-alt"),
        (8443, "https-alt"),
        (27017, "mongodb"),
    ])
});

/// Data structure representing a SYN scanner
#[derive(Clone, Builder)]
#[builder(setter(into))]
pub struct SYNScanner {
    /// Network interface to use for scanning
    interface: Arc<NetworkInterface>,
    /// Packet reader for receiving SYN-ACK responses
    packet_reader: Arc<Mutex<dyn Reader>>,
    /// Packet sender for transmitting SYN packets
    packet_sender: Arc<Mutex<dyn Sender>>,
    /// Devices to scan for open ports
    targets: Vec<Device>,
    /// Port targets to scan on each device
    ports: Arc<PortTargets>,
    /// Source port for packet listener and incoming packet identification
    source_port: u16,
    /// Duration to wait for responses after scanning completes
    idle_timeout: Duration,
    /// Channel for sending scan results and status messages
    notifier: mpsc::Sender<ScanMessage>,
}

impl SYNScanner {
    /// Returns a builder for SYNScanner
    pub fn builder() -> SYNScannerBuilder {
        SYNScannerBuilder::default()
    }

    fn process_port(&self, port: u16) -> Result<()> {
        for device in self.targets.iter() {
            // throttle packet sending to prevent packet loss
            thread::sleep(packet::DEFAULT_PACKET_SEND_TIMING);

            log::debug!("scanning SYN target: {}:{}", device.ip, port);

            let dest_ipv4 = device.ip;
            let dest_mac = device.mac;

            let syn_packet = SynPacketBuilder::default()
                .source_ip(self.interface.ipv4)
                .source_mac(self.interface.mac)
                .source_port(self.source_port)
                .dest_ip(dest_ipv4)
                .dest_mac(dest_mac)
                .dest_port(port)
                .build()?;

            let pkt_buf = syn_packet.to_raw();

            // send info message to consumer
            self.notifier
                .send(ScanMessage::Info(Scanning {
                    ip: device.ip,
                    port: Some(port),
                }))
                .map_err(RLanLibError::from_channel_send_error)?;

            let mut sender = self.packet_sender.lock()?;

            // scan device @ port
            sender.send(&pkt_buf).map_err(|e| RLanLibError::Scan {
                ip: Some(device.ip.to_string()),
                port: Some(port.to_string()),
                error: e.to_string(),
            })?;
        }

        Ok(())
    }

    fn process_incoming_packet(
        &self,
        pkt: &[u8],
        device_map: &HashMap<Ipv4Addr, Device>,
    ) -> Result<()> {
        let Some(eth) = ethernet::EthernetPacket::new(pkt) else {
            return Ok(());
        };

        let Some(header) = ipv4::Ipv4Packet::new(eth.payload()) else {
            return Ok(());
        };

        let device_ip = header.get_source();
        let protocol = header.get_next_level_protocol();
        let payload = header.payload();

        if protocol != ip::IpNextHeaderProtocols::Tcp {
            return Ok(());
        }

        let Some(tcp_packet) = tcp::TcpPacket::new(payload) else {
            return Ok(());
        };

        let destination_port = tcp_packet.get_destination();
        let matches_destination = destination_port == self.source_port;
        let flags: u8 = tcp_packet.get_flags();
        let sequence = tcp_packet.get_sequence();
        let is_syn_ack = flags == tcp::TcpFlags::SYN + tcp::TcpFlags::ACK;

        if !matches_destination || !is_syn_ack {
            return Ok(());
        }

        let Some(device) = device_map.get(&device_ip) else {
            return Ok(());
        };

        let port = tcp_packet.get_source();

        // send rst packet to prevent SYN Flooding
        // https://en.wikipedia.org/wiki/SYN_flood
        // https://security.stackexchange.com/questions/128196/whats-the-advantage-of-sending-an-rst-packet-after-getting-a-response-in-a-syn
        let dest_ipv4 = device.ip;
        let dest_mac = device.mac;

        let rst_packet = RstPacketBuilder::default()
            .source_ip(self.interface.ipv4)
            .source_mac(self.interface.mac)
            .source_port(self.source_port)
            .dest_ip(dest_ipv4)
            .dest_mac(dest_mac)
            .dest_port(port)
            .sequence_number(sequence + 1)
            .build()?;

        let rst_packet = rst_packet.to_raw();

        let mut rst_sender = self.packet_sender.lock()?;

        log::debug!("sending RST packet to {}:{}", device.ip, port);

        rst_sender.send(&rst_packet)?;

        let service = SERVICES
            .get(&port)
            .map(|s| s.to_string())
            .unwrap_or_default();

        let mut ports = PortSet::new();
        ports.0.insert(Port { id: port, service });

        self.notifier
            .send(ScanMessage::SYNScanDevice(Device {
                open_ports: ports,
                ..device.clone()
            }))
            .map_err(RLanLibError::from_channel_send_error)?;

        Ok(())
    }

    // Implements packet reading in a separate thread so we can send and
    // receive packets simultaneously
    fn read_packets(
        &self,
        done_rx: mpsc::Receiver<()>,
    ) -> Result<JoinHandle<Result<()>>> {
        let self_clone = self.clone();
        let (heartbeat_tx, heartbeat_rx) = sync::mpsc::channel::<()>();

        let heartbeat = HeartBeat::builder()
            .source_mac(self.interface.mac)
            .source_ipv4(self.interface.ipv4)
            .source_port(self.source_port)
            .packet_sender(Arc::clone(&self.packet_sender))
            .build()?;

        let heart_handle = heartbeat.start_in_thread(heartbeat_rx)?;

        Ok(thread::spawn(move || -> Result<()> {
            let mut reader = self_clone.packet_reader.lock()?;

            // Build a HashMap for O(1) device lookups instead of O(n) linear search
            let device_map: HashMap<Ipv4Addr, Device> = self_clone
                .targets
                .iter()
                .map(|d| (d.ip, d.clone()))
                .collect();

            loop {
                if done_rx.try_recv().is_ok() {
                    log::debug!("exiting syn packet reader");
                    if let Err(e) = heartbeat_tx.send(()) {
                        log::error!("failed to stop heartbeat: {}", e);
                    }

                    break;
                }

                let pkt = reader.next_packet()?;
                self_clone.process_incoming_packet(pkt, &device_map)?;
            }

            heart_handle.join()??;

            Ok(())
        }))
    }
}

// Implements the Scanner trait for SYNScanner
impl Scanner for SYNScanner {
    fn scan(&self) -> Result<JoinHandle<Result<()>>> {
        log::debug!("performing SYN scan on targets: {:?}", self.targets);

        let self_clone = self.clone();
        let (done_tx, done_rx) = mpsc::channel::<()>();

        log::debug!("starting syn packet reader");

        let read_handle = self.read_packets(done_rx)?;

        // prevent blocking thread so messages can be freely sent to consumer
        let handle = thread::spawn(move || -> Result<()> {
            let mut scan_error: Option<RLanLibError> = None;

            if let Err(err) =
                self_clone.ports.lazy_loop(|p| self_clone.process_port(p))
            {
                scan_error = Some(err);
            }

            thread::sleep(self_clone.idle_timeout);

            self_clone
                .notifier
                .send(ScanMessage::Done)
                .map_err(RLanLibError::from_channel_send_error)?;

            // ignore errors here as the thread may already be dead due to error
            // we'll catch any errors from that thread below and report
            let _ = done_tx.send(());

            let read_result = read_handle.join()?;

            if let Some(err) = scan_error {
                return Err(err);
            }

            read_result
        });

        Ok(handle)
    }
}

#[cfg(test)]
#[path = "./syn_scanner_tests.rs"]
mod tests;