yippee

src/main.rs

@@ -33,7 +33,7 @@ async fn main() -> anyhow::Result<()> {
     let config = Config::from_args().with_context(|| "Failed to read config")?;
     let port_pool = Arc::new(PortPool::new());
 
-    let wg = WireGuardTunnel::new(&config)
+    let wg = WireGuardTunnel::new(&config, port_pool.clone())
         .await
         .with_context(|| "Failed to initialize WireGuard tunnel")?;
     let wg = Arc::new(wg);

src/port_pool.rs

@@ -7,23 +7,37 @@ const MAX_PORT: u16 = 60999;
 const PORT_RANGE: Range<u16> = MIN_PORT..MAX_PORT;
 
 pub struct PortPool {
+    /// Remaining ports
     inner: lockfree::queue::Queue<u16>,
+    /// Ports in use
+    taken: lockfree::set::Set<u16>,
 }
 
 impl PortPool {
     pub fn new() -> Self {
         let inner = lockfree::queue::Queue::default();
         PORT_RANGE.for_each(|p| inner.push(p) as ());
-        Self { inner }
+        Self {
+            inner,
+            taken: lockfree::set::Set::new(),
+        }
     }
 
     pub fn next(&self) -> anyhow::Result<u16> {
-        self.inner
+        let port = self
+            .inner
             .pop()
-            .with_context(|| "Virtual port pool is exhausted")
+            .with_context(|| "Virtual port pool is exhausted")?;
+        self.taken.insert(port);
+        Ok(port)
     }
 
     pub fn release(&self, port: u16) {
         self.inner.push(port);
+        self.taken.remove(&port);
+    }
+
+    pub fn is_in_use(&self, port: u16) -> bool {
+        self.taken.contains(&port)
     }
 }

src/wg.rs

@@ -1,18 +1,26 @@
-use std::net::SocketAddr;
+use std::net::{IpAddr, Ipv4Addr, Ipv6Addr, SocketAddr};
+use std::sync::Arc;
 use std::time::Duration;
 
 use anyhow::Context;
 use boringtun::noise::{Tunn, TunnResult};
 use log::Level;
+use smoltcp::phy::ChecksumCapabilities;
+use smoltcp::wire::{
+    IpAddress, IpProtocol, IpRepr, IpVersion, Ipv4Address, Ipv4Packet, Ipv4Repr, Ipv6Address,
+    Ipv6Packet, Ipv6Repr, TcpControl, TcpPacket, TcpRepr, TcpSeqNumber,
+};
 use tokio::net::UdpSocket;
 
 use crate::config::Config;
+use crate::port_pool::PortPool;
 use crate::MAX_PACKET;
 
 /// The capacity of the broadcast channel for received IP packets.
 const BROADCAST_CAPACITY: usize = 1_000_000;
 
 pub struct WireGuardTunnel {
+    source_peer_ip: IpAddr,
     /// `boringtun` peer/tunnel implementation, used for crypto & WG protocol.
     peer: Box<Tunn>,
     /// The UDP socket for the public WireGuard endpoint to connect to.
@@ -21,12 +29,16 @@ pub struct WireGuardTunnel {
     endpoint: SocketAddr,
     /// Broadcast sender for received IP packets.
     ip_broadcast_tx: tokio::sync::broadcast::Sender<Vec<u8>>,
+    /// Placeholder so that the broadcaster doesn't close.
     ip_broadcast_rx: tokio::sync::broadcast::Receiver<Vec<u8>>,
+    /// Port pool.
+    port_pool: Arc<PortPool>,
 }
 
 impl WireGuardTunnel {
     /// Initialize a new WireGuard tunnel.
-    pub async fn new(config: &Config) -> anyhow::Result<Self> {
+    pub async fn new(config: &Config, port_pool: Arc<PortPool>) -> anyhow::Result<Self> {
+        let source_peer_ip = config.source_peer_ip;
         let peer = Self::create_tunnel(&config)?;
         let udp = UdpSocket::bind("0.0.0.0:0")
             .await
@@ -36,11 +48,13 @@ impl WireGuardTunnel {
             tokio::sync::broadcast::channel(BROADCAST_CAPACITY);
 
         Ok(Self {
+            source_peer_ip,
             peer,
             udp,
             endpoint,
             ip_broadcast_tx,
             ip_broadcast_rx,
+            port_pool,
         })
     }
 
@@ -175,10 +189,16 @@ impl WireGuardTunnel {
                     // For debugging purposes: parse packet
                     trace_ip_packet("Received IP packet", packet);
 
+                    match self.route(packet) {
+                        RouteResult::Broadcast => {
                             // Broadcast IP packet
+                            if self.ip_broadcast_tx.receiver_count() > 1 {
                                 match self.ip_broadcast_tx.send(packet.to_vec()) {
                                     Ok(n) => {
-                            trace!("Broadcasted received IP packet to {} recipients", n);
+                                        trace!(
+                                            "Broadcasted received IP packet to {} virtual interfaces",
+                                            n - 1
+                                        );
                                     }
                                     Err(e) => {
                                         error!(
@@ -188,6 +208,18 @@ impl WireGuardTunnel {
                                     }
                                 }
                             }
+                        }
+                        RouteResult::TcpReset(packet) => {
+                            trace!("Resetting dead TCP connection after packet from WireGuard endpoint");
+                            self.send_ip_packet(&packet)
+                                .await
+                                .unwrap_or_else(|e| error!("Failed to sent TCP reset: {:?}", e));
+                        }
+                        RouteResult::Drop => {
+                            trace!("Dropped incoming IP packet from WireGuard endpoint");
+                        }
+                    }
+                }
                 _ => {}
             }
         }
@@ -205,6 +237,126 @@ impl WireGuardTunnel {
         .map_err(|s| anyhow::anyhow!("{}", s))
         .with_context(|| "Failed to initialize boringtun Tunn")
     }
+
+    fn route(&self, packet: &[u8]) -> RouteResult {
+        match IpVersion::of_packet(&packet) {
+            Ok(IpVersion::Ipv4) => Ipv4Packet::new_checked(&packet)
+                .ok()
+                // Only care if the packet is destined for this tunnel
+                .filter(|packet| Ipv4Addr::from(packet.dst_addr()) == self.source_peer_ip)
+                .map(|packet| match packet.protocol() {
+                    IpProtocol::Tcp => TcpPacket::new_checked(packet.payload()).ok().map(|tcp| {
+                        if self.port_pool.is_in_use(tcp.dst_port()) {
+                            RouteResult::Broadcast
+                        } else if tcp.rst() {
+                            RouteResult::Drop
+                        } else {
+                            // Port is not in use, but it's a TCP packet so we'll craft a RST.
+                            RouteResult::TcpReset(craft_tcp_rst_reply(
+                                IpVersion::Ipv4,
+                                packet.src_addr().into(),
+                                tcp.src_port(),
+                                packet.dst_addr().into(),
+                                tcp.dst_port(),
+                                tcp.ack_number(),
+                            ))
+                        }
+                    }),
+                    // Unrecognized protocol, so we'll allow it.
+                    _ => Some(RouteResult::Broadcast),
+                })
+                .flatten()
+                .unwrap_or(RouteResult::Drop),
+            // TODO: IPv6
+            _ => RouteResult::Drop,
+        }
+    }
+}
+
+fn craft_tcp_rst_reply(
+    ip_version: IpVersion,
+    source_addr: IpAddress,
+    source_port: u16,
+    dest_addr: IpAddress,
+    dest_port: u16,
+    ack_number: TcpSeqNumber,
+) -> Vec<u8> {
+    let tcp_repr = TcpRepr {
+        src_port: dest_port,
+        dst_port: source_port,
+        control: TcpControl::Rst,
+        seq_number: ack_number,
+        ack_number: None,
+        window_len: 0,
+        window_scale: None,
+        max_seg_size: None,
+        sack_permitted: false,
+        sack_ranges: [None, None, None],
+        payload: &[],
+    };
+
+    let mut tcp_buffer = vec![0u8; 20];
+    let mut tcp_packet = &mut TcpPacket::new_unchecked(&mut tcp_buffer);
+    tcp_repr.emit(
+        &mut tcp_packet,
+        &dest_addr,
+        &source_addr,
+        &ChecksumCapabilities::default(),
+    );
+
+    let mut ip_buffer = vec![0u8; MAX_PACKET];
+
+    let (header_len, total_len) = match ip_version {
+        IpVersion::Ipv4 => {
+            let dest_addr = match dest_addr {
+                IpAddress::Ipv4(dest_addr) => dest_addr,
+                _ => panic!(),
+            };
+            let source_addr = match source_addr {
+                IpAddress::Ipv4(source_addr) => source_addr,
+                _ => panic!(),
+            };
+
+            let mut ip_packet = &mut Ipv4Packet::new_unchecked(&mut ip_buffer);
+            let ip_repr = Ipv4Repr {
+                src_addr: dest_addr,
+                dst_addr: source_addr,
+                protocol: IpProtocol::Tcp,
+                payload_len: tcp_buffer.len(),
+                hop_limit: 64,
+            };
+            ip_repr.emit(&mut ip_packet, &ChecksumCapabilities::default());
+            (
+                ip_packet.header_len() as usize,
+                ip_packet.total_len() as usize,
+            )
+        }
+        IpVersion::Ipv6 => {
+            let dest_addr = match dest_addr {
+                IpAddress::Ipv6(dest_addr) => dest_addr,
+                _ => panic!(),
+            };
+            let source_addr = match source_addr {
+                IpAddress::Ipv6(source_addr) => source_addr,
+                _ => panic!(),
+            };
+            let mut ip_packet = &mut Ipv6Packet::new_unchecked(&mut ip_buffer);
+            let ip_repr = Ipv6Repr {
+                src_addr: dest_addr,
+                dst_addr: source_addr,
+                next_header: IpProtocol::Tcp,
+                payload_len: tcp_buffer.len(),
+                hop_limit: 64,
+            };
+            ip_repr.emit(&mut ip_packet);
+            (ip_packet.header_len(), ip_packet.total_len())
+        }
+        _ => panic!(),
+    };
+
+    ip_buffer[header_len..total_len].copy_from_slice(&tcp_buffer);
+    let packet: &[u8] = &ip_buffer[..total_len];
+    packet.to_vec()
 }
 
 fn trace_ip_packet(message: &str, packet: &[u8]) {
@@ -226,3 +378,12 @@ fn trace_ip_packet(message: &str, packet: &[u8]) {
         }
     }
 }
+
+enum RouteResult {
+    /// The packet can be broadcasted to the virtual interfaces
+    Broadcast,
+    /// The packet is not routable so it may be reset.
+    TcpReset(Vec<u8>),
+    /// The packet can be safely ignored.
+    Drop,
+}