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|
// -*- coding: utf-8 -*-
//
// Copyright (C) 2024 Michael Büsch <m@bues.ch>
//
// Licensed under the Apache License version 2.0
// or the MIT license, at your option.
// SPDX-License-Identifier: Apache-2.0 OR MIT
use crate::{
firewall_client::{FirewallClient, PortType},
server::ConnectionOps,
};
use anyhow::{self as ah, format_err as err};
use letmein_conf::{Config, Resource};
use letmein_proto::{Message, Operation, ResourceId, UserId};
use std::{net::SocketAddr, path::Path};
use tokio::time::timeout;
pub struct Protocol<'a, C> {
conn: C,
conf: &'a Config,
rundir: &'a Path,
user_id: Option<UserId>,
resource_id: Option<ResourceId>,
}
impl<'a, C: ConnectionOps> Protocol<'a, C> {
pub fn new(conn: C, conf: &'a Config, rundir: &'a Path) -> Self {
Self {
conn,
conf,
rundir,
user_id: None,
resource_id: None,
}
}
pub fn addr(&self) -> SocketAddr {
self.conn.addr()
}
async fn recv_msg(&mut self, expect_operation: Operation) -> ah::Result<Message> {
if let Some(msg) = timeout(self.conf.control_timeout(), self.conn.recv_msg())
.await
.map_err(|_| err!("RX communication with peer timed out"))??
{
if msg.operation() != expect_operation {
let _ = self.send_go_away().await;
return Err(err!(
"Invalid reply message operation. Expected {:?}, got {:?}",
expect_operation,
msg.operation()
));
}
if let Some(user_id) = self.user_id {
if msg.user() != user_id {
let _ = self.send_go_away().await;
return Err(err!("Received message user mismatch"));
}
}
if let Some(resource_id) = self.resource_id {
if msg.resource() != resource_id {
let _ = self.send_go_away().await;
return Err(err!("Received message resource mismatch"));
}
}
Ok(msg)
} else {
Err(err!("Disconnected."))
}
}
async fn send_msg(&mut self, msg: &Message) -> ah::Result<()> {
timeout(self.conf.control_timeout(), self.conn.send_msg(msg))
.await
.map_err(|_| err!("TX communication with peer timed out"))?
}
async fn send_go_away(&mut self) -> ah::Result<()> {
self.send_msg(&Message::new(
Operation::GoAway,
self.user_id.unwrap_or(u32::MAX.into()),
self.resource_id.unwrap_or(u32::MAX.into()),
))
.await
}
pub async fn run(&mut self) -> ah::Result<()> {
let knock = self.recv_msg(Operation::Knock).await?;
let user_id = knock.user();
self.user_id = Some(user_id);
let resource_id = knock.resource();
self.resource_id = Some(resource_id);
// Get the shared key.
let Some(key) = self.conf.key(user_id) else {
let _ = self.send_go_away().await;
return Err(err!("Unknown user: {user_id}"));
};
// Authenticate the received message.
// This check is not replay-safe. But that's fine.
if !knock.check_auth_ok_no_challenge(key) {
let _ = self.send_go_away().await;
return Err(err!("Knock: Authentication failed"));
}
// Get the requested resource from the configuration.
let Some(resource) = self.conf.resource(resource_id) else {
let _ = self.send_go_away().await;
return Err(err!("Unknown resource: {resource_id}"));
};
// Check if the authenticating user is allowed to access this resource.
match resource {
Resource::Port {
port,
tcp: _,
udp: _,
users: _,
} => {
// Check the mapped user on the resource.
if !resource.contains_user(user_id) {
let _ = self.send_go_away().await;
return Err(err!(
"Resource {resource_id} not allowed for user {user_id}"
));
}
// The control port is never allowed.
let control_port = self.conf.port();
if *port == control_port {
let _ = self.send_go_away().await;
return Err(err!(
"Incorrect configuration: The resource {resource_id} uses the \
letmein control port {control_port}. That is not allowed."
));
}
}
}
// Generate and send a challenge.
let mut challenge = Message::new(Operation::Challenge, user_id, resource_id);
challenge.generate_challenge();
self.send_msg(&challenge).await?;
// Receive the response.
let response = self.recv_msg(Operation::Response).await?;
// Authenticate the challenge-response.
if !response.check_auth_ok(key, challenge) {
let _ = self.send_go_away().await;
return Err(err!("Response: Authentication failed"));
}
// Reconfigure the firewall.
match resource {
Resource::Port {
port,
tcp,
udp,
users: _,
} => {
// Port type to open.
let port_type = match (tcp, udp) {
(true, false) => PortType::Tcp,
(false, true) => PortType::Udp,
(true, true) => PortType::TcpUdp,
(false, false) => unreachable!(),
};
// Connect to letmeinfwd unix socket.
let mut fw = match FirewallClient::new(self.rundir).await {
Err(e) => {
let _ = self.send_go_away().await;
return Err(err!("Failed to connect to letmeinfwd: {e}"));
}
Ok(fw) => fw,
};
// Send an open-port request to letmeinfwd.
if let Err(e) = fw.open_port(self.addr().ip(), port_type, *port).await {
let _ = self.send_go_away().await;
return Err(err!("letmeinfwd firewall open: {e}"));
}
}
}
// Send a come-in message.
let comein = Message::new(Operation::ComeIn, user_id, resource_id);
self.send_msg(&comein).await?;
Ok(())
}
}
// vim: ts=4 sw=4 expandtab
|
