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Monorepo for Tangled
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Rust
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const DEFAULT_DNS_PROXY_ADDR: &str = "127.0.0.1:53";const SHUTTLE_DNS_PROXY_ADDR_ENV: &str = "SHUTTLE_DNS_PROXY_ADDR";
const MAX_DNS_MESSAGE_BYTES: usize = u16::MAX as usize;const DNS_IO_TIMEOUT: Duration = Duration::from_secs(10);const DNS_TCP_IDLE_TIMEOUT: Duration = Duration::from_secs(120);
// implements a proxy that sends dns requests to the spindle and// lets the spindle resolve any queries, and streams the response back.//// we use this because the way spindle isolates QEMU VMs is unreliable// to rely on. if we unblock the blackholed-routes for private nameservers// like slirp one, we risk leaking internal DNS zones, even if the guest// can't connect to them. there is also potentially DNS rebinding issues.// and other slirp4netns quirks...//// this way we also get to filter the DNS queries very easily, so we can// make sure we remove everything that would leak a host information.pub struct DnsProxy { handles: Vec<JoinHandle<()>>,}
#[derive(Clone)]struct HostDnsClient { host_cid: u32, host_port: u32,}
impl DnsProxy { pub async fn start(host_cid: u32, host_port: u32) -> Result<Option<Self>> { if host_port == 0 { return Ok(None); }
let addr = std::env::var(SHUTTLE_DNS_PROXY_ADDR_ENV) .unwrap_or_else(|_| DEFAULT_DNS_PROXY_ADDR.to_owned());
let udp = Arc::new( UdpSocket::bind(&addr) .await .with_context(|| format!("bind dns udp listener {addr}"))?, );
let tcp = TcpListener::bind(&addr) .await .with_context(|| format!("bind dns tcp listener {addr}"))?;
let host = HostDnsClient { host_cid, host_port, };
let handles = vec![ tokio::spawn(udp_loop(udp, host.clone())), tokio::spawn(tcp_loop(tcp, host)), ];
info!(%addr, host_cid, host_port, "dns proxy ready"); Ok(Some(Self { handles })) }}
impl Drop for DnsProxy { fn drop(&mut self) { for handle in self.handles.drain(..) { handle.abort(); } }}
impl HostDnsClient { async fn query(&self, query: Vec<u8>) -> Result<Vec<u8>> { match self.query_once(&query).await { Ok(response) => Ok(response), Err(first_error) => self.query_once(&query).await.with_context(|| { format!("dns host query failed after retry; first error: {first_error:#}") }), } }
async fn query_once(&self, query: &[u8]) -> Result<Vec<u8>> { let addr = VsockAddr::new(self.host_cid, self.host_port);
let mut host = tokio::time::timeout(DNS_IO_TIMEOUT, VsockStream::connect(addr)) .await .context("dns host connect timed out")? .with_context(|| { format!( "dial host dns proxy cid={} port={}", self.host_cid, self.host_port ) })?;
tokio::time::timeout(DNS_IO_TIMEOUT, async { write_dns_packet(&mut host, query) .await .context("write dns query to host")?;
read_dns_packet(&mut host) .await .context("read dns response from host")? .context("host dns proxy closed without response") }) .await .context("dns host query timed out")? }}
async fn udp_loop(socket: Arc<UdpSocket>, host: HostDnsClient) { let mut buf = vec![0; MAX_DNS_MESSAGE_BYTES]; let mut tasks = JoinSet::new();
loop { tokio::select! { received = socket.recv_from(&mut buf) => match received { Ok((len, peer)) => { let query = buf[..len].to_vec(); let socket = socket.clone(); let host = host.clone();
tasks.spawn(async move { if let Err(error) = handle_udp_query(socket, peer, query, host).await { warn!(%peer, %error, "dns udp query failed"); } }); } Err(error) => warn!(%error, "dns udp recv failed"), },
Some(result) = tasks.join_next(), if !tasks.is_empty() => { log_dns_task_result(result); } } }}
async fn handle_udp_query( socket: Arc<UdpSocket>, peer: SocketAddr, query: Vec<u8>, host: HostDnsClient,) -> Result<()> { let response = host.query(query).await?;
socket .send_to(&response, peer) .await .context("send dns udp response")?;
Ok(())}
async fn tcp_loop(listener: TcpListener, host: HostDnsClient) { let mut tasks = JoinSet::new();
loop { tokio::select! { accepted = listener.accept() => match accepted { Ok((conn, peer)) => { let host = host.clone();
tasks.spawn(async move { if let Err(error) = handle_tcp_conn(conn, host).await { warn!(%peer, %error, "dns tcp connection failed"); } }); } Err(error) => warn!(%error, "dns tcp accept failed"), },
Some(result) = tasks.join_next(), if !tasks.is_empty() => { log_dns_task_result(result); } } }}
async fn handle_tcp_conn(mut tcp: TcpStream, host: HostDnsClient) -> Result<()> { loop { let query = tokio::time::timeout(DNS_TCP_IDLE_TIMEOUT, read_dns_packet(&mut tcp)) .await .context("dns tcp idle timeout")? .context("read dns tcp query")?;
let Some(query) = query else { return Ok(()); };
let response = host.query(query).await?;
write_dns_packet(&mut tcp, &response) .await .context("write dns tcp response")?; }}
async fn read_dns_packet<R>(reader: &mut R) -> io::Result<Option<Vec<u8>>>where R: AsyncRead + Unpin,{ let mut len_buf = [0; 2];
match reader.read_exact(&mut len_buf).await { Ok(_) => {} Err(error) if error.kind() == io::ErrorKind::UnexpectedEof => return Ok(None), Err(error) => return Err(error), }
let len = u16::from_be_bytes(len_buf) as usize; if len == 0 { return Err(io::Error::new( io::ErrorKind::InvalidData, "empty dns packet", )); }
let mut packet = vec![0; len]; reader.read_exact(&mut packet).await?; Ok(Some(packet))}
async fn write_dns_packet<W>(writer: &mut W, packet: &[u8]) -> io::Result<()>where W: AsyncWrite + Unpin,{ if packet.is_empty() || packet.len() > MAX_DNS_MESSAGE_BYTES { return Err(io::Error::new( io::ErrorKind::InvalidData, format!("invalid dns packet size {}", packet.len()), )); }
writer .write_all(&(packet.len() as u16).to_be_bytes()) .await?; writer.write_all(packet).await?; writer.flush().await}
fn log_dns_task_result(result: Result<(), JoinError>) { if let Err(error) = result { warn!(%error, "dns proxy task failed"); }}