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//! Implement a simple DNS resolver that relay request over Tor.
//!
//! A resolver is launched with [`run_dns_resolver()`], which listens for new
//! connections and then runs
use futures::stream::StreamExt;
use futures::task::SpawnExt;
use std::net::{IpAddr, Ipv4Addr, Ipv6Addr, SocketAddr};
use std::sync::Arc;
use tracing::{error, info, warn};
use trust_dns_proto::op::{
header::MessageType, op_code::OpCode, response_code::ResponseCode, Message,
};
use trust_dns_proto::rr::{DNSClass, Name, RData, Record, RecordType};
use trust_dns_proto::serialize::binary::{BinDecodable, BinEncodable};
use arti_client::{StreamPrefs, TorClient};
use tor_rtcompat::{Runtime, UdpSocket};
use anyhow::{anyhow, Result};
/// Maximum length for receiving a single datagram
const MAX_DATAGRAM_SIZE: usize = 1536;
/// Send an error DNS response with code NotImplemented
async fn not_implemented<U: UdpSocket>(id: u16, addr: &SocketAddr, socket: &U) -> Result<()> {
let response = Message::error_msg(id, OpCode::Query, ResponseCode::NotImp);
socket.send(&response.to_bytes()?, addr).await?;
Ok(())
}
/// A Key used to isolate dns requests.
///
/// Composed of an usize (representing which listener socket accepted
/// the connection and the source IpAddr of the client)
#[derive(Debug, Clone, PartialEq, Eq)]
struct DnsIsolationKey(usize, IpAddr);
impl arti_client::isolation::IsolationHelper for DnsIsolationKey {
fn compatible_same_type(&self, other: &Self) -> bool {
self == other
}
fn join_same_type(&self, other: &Self) -> Option<Self> {
if self == other {
Some(self.clone())
} else {
None
}
}
}
/// Given a datagram containing a DNS query, resolve the query over
/// the Tor network and send the response back.
async fn handle_dns_req<R, U>(
tor_client: TorClient<R>,
socket_id: usize,
packet: &[u8],
addr: SocketAddr,
socket: Arc<U>,
) -> Result<()>
where
R: Runtime,
U: UdpSocket,
{
let mut query = Message::from_bytes(packet)?;
let id = query.id();
let mut answers = Vec::new();
let mut prefs = StreamPrefs::new();
prefs.set_isolation(DnsIsolationKey(socket_id, addr.ip()));
for query in query.queries() {
let mut a = Vec::new();
let mut ptr = Vec::new();
// TODO maybe support ANY?
match query.query_class() {
DNSClass::IN => {
match query.query_type() {
typ @ RecordType::A | typ @ RecordType::AAAA => {
let mut name = query.name().clone();
// name would be "torproject.org." without this
name.set_fqdn(false);
let res = tor_client
.resolve_with_prefs(&name.to_utf8(), &prefs)
.await?;
for ip in res {
a.push((query.name().clone(), ip, typ));
}
}
RecordType::PTR => {
let addr = query.name().parse_arpa_name()?.addr();
let res = tor_client.resolve_ptr_with_prefs(addr, &prefs).await?;
for domain in res {
let domain = Name::from_utf8(domain)?;
ptr.push((query.name().clone(), domain));
}
}
_ => {
return not_implemented(id, &addr, &*socket).await;
}
}
}
_ => {
return not_implemented(id, &addr, &*socket).await;
}
}
for (name, ip, typ) in a {
match (ip, typ) {
(IpAddr::V4(v4), RecordType::A) => {
answers.push(Record::from_rdata(name, 3600, RData::A(v4)));
}
(IpAddr::V6(v6), RecordType::AAAA) => {
answers.push(Record::from_rdata(name, 3600, RData::AAAA(v6)));
}
_ => (),
}
}
for (ptr, name) in ptr {
answers.push(Record::from_rdata(ptr, 3600, RData::PTR(name)));
}
}
let mut response = Message::new();
response
.set_id(id)
.set_message_type(MessageType::Response)
.set_op_code(OpCode::Query)
.set_recursion_desired(query.recursion_desired())
.set_recursion_available(true)
.add_queries(query.take_queries())
.add_answers(answers);
// TODO maybe add some edns?
socket.send(&response.to_bytes()?, &addr).await?;
Ok(())
}
/// Launch a DNS resolver to listen on a given local port, and run indefinitely.
pub async fn run_dns_resolver<R: Runtime>(
runtime: R,
tor_client: TorClient<R>,
dns_port: u16,
) -> Result<()> {
let mut listeners = Vec::new();
// We actually listen on two ports: one for ipv4 and one for ipv6.
let localhosts: [IpAddr; 2] = [Ipv4Addr::LOCALHOST.into(), Ipv6Addr::LOCALHOST.into()];
// Try to bind to the DNS ports.
for localhost in &localhosts {
let addr: SocketAddr = (*localhost, dns_port).into();
match runtime.bind(&addr).await {
Ok(listener) => {
info!("Listening on {:?}.", addr);
listeners.push(listener);
}
Err(e) => warn!("Can't listen on {:?}: {}", addr, e),
}
}
// We weren't able to bind any ports: There's nothing to do.
if listeners.is_empty() {
error!("Couldn't open any DNS listeners.");
return Err(anyhow!("Couldn't open any DNS listeners"));
}
let mut incoming = futures::stream::select_all(
listeners
.into_iter()
.map(|socket| {
futures::stream::unfold(Arc::new(socket), |socket| async {
let mut packet = [0; MAX_DATAGRAM_SIZE];
let packet = socket
.recv(&mut packet)
.await
.map(|(size, remote)| (packet, size, remote, socket.clone()));
Some((packet, socket))
})
})
.enumerate()
.map(|(listener_id, incoming_packet)| {
Box::pin(incoming_packet.map(move |packet| (packet, listener_id)))
}),
);
while let Some((packet, id)) = incoming.next().await {
let (packet, size, addr, socket) = match packet {
Ok(packet) => packet,
Err(err) => {
// TODO move crate::socks::accept_err_is_fatal somewhere else and use it here?
warn!("Incoming datagram failed: {}", err);
continue;
}
};
let client_ref = tor_client.clone();
runtime.spawn(async move {
let res = handle_dns_req(client_ref, id, &packet[..size], addr, socket).await;
if let Err(e) = res {
warn!("connection exited with error: {}", e);
}
})?;
}
Ok(())
}
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