Add native doctor auth diagnostics

src/bin/dosh-client.rs

@@ -16,9 +16,10 @@ use dosh::native::{
 };
 use dosh::protocol::{
     self, AttachOk, AttachReject, BootstrapAttachRequest, CLIENT_TO_SERVER, Frame, Input,
-    NativeAuthOkBody, NativeClientHelloBody, NativeServerHelloBody, NativeUserAuthBody, PacketKind,
-    Resize, ResumeRequest, SERVER_TO_CLIENT, StreamClose, StreamData, StreamOpen, StreamOpenOk,
-    StreamOpenReject, TicketAttachBody, TicketAttachEnvelope, TicketAttachOkEnvelope,
+    NativeAuthCheckOkBody, NativeAuthOkBody, NativeClientHelloBody, NativeServerHelloBody,
+    NativeUserAuthBody, PacketKind, Resize, ResumeRequest, SERVER_TO_CLIENT, StreamClose,
+    StreamData, StreamOpen, StreamOpenOk, StreamOpenReject, TicketAttachBody, TicketAttachEnvelope,
+    TicketAttachOkEnvelope,
 };
 use dosh::ssh_agent;
 use serde::{Deserialize, Serialize};
@@ -162,6 +163,9 @@ async fn main() -> Result<()> {
     if args.server.as_deref() == Some("trust") {
         return run_trust_command(&config, &args);
     }
+    if args.server.as_deref() == Some("doctor") {
+        return run_doctor_command(&config, &args).await;
+    }
     let requested_server = args.server.clone().unwrap_or_else(|| config.server.clone());
     let hosts = load_hosts_config(None).unwrap_or_default();
     let host = hosts
@@ -492,6 +496,119 @@ fn run_trust_command(config: &dosh::config::ClientConfig, args: &Args) -> Result
     Ok(())
 }
 
+async fn run_doctor_command(config: &dosh::config::ClientConfig, args: &Args) -> Result<()> {
+    let requested = args
+        .command
+        .first()
+        .cloned()
+        .ok_or_else(|| anyhow!("usage: dosh doctor <host>"))?;
+    let hosts = load_hosts_config(None).unwrap_or_default();
+    let host_config = hosts.hosts.get(&requested).cloned().unwrap_or_default();
+    let server = host_config.ssh.clone().unwrap_or_else(|| requested.clone());
+    let ssh_port = args.ssh_port.or(host_config.ssh_port).or(config.ssh_port);
+    let dosh_port = args
+        .dosh_port
+        .or(host_config.port)
+        .unwrap_or(config.dosh_port);
+    println!("Dosh doctor for {requested}");
+
+    match ssh_config(&server, ssh_port) {
+        Ok(parsed) => {
+            let hostname = parsed
+                .hostname
+                .clone()
+                .unwrap_or_else(|| ssh_destination_host(&server));
+            println!(
+                "[ok] ssh config: host={} user={} port={}",
+                hostname,
+                parsed.user.as_deref().unwrap_or("<default>"),
+                parsed.port.unwrap_or(ssh_port.unwrap_or(22))
+            );
+        }
+        Err(err) => println!("[fail] ssh config: {err:#}"),
+    }
+
+    match ssh_fallback_probe(
+        &server,
+        ssh_port,
+        args.ssh_key.as_deref(),
+        args.ssh_known_hosts.as_deref(),
+    ) {
+        Ok(()) => println!("[ok] ssh fallback: reachable"),
+        Err(err) => println!("[warn] ssh fallback: {err:#}"),
+    }
+
+    let udp_host = args
+        .dosh_host
+        .clone()
+        .or_else(|| host_config.dosh_host.clone())
+        .or_else(|| config.dosh_host.clone())
+        .unwrap_or_else(|| {
+            ssh_config_hostname(&server, ssh_port).unwrap_or_else(|_| ssh_destination_host(&server))
+        });
+    println!("[info] native endpoint: {udp_host}:{dosh_port}");
+    let socket = UdpSocket::bind("0.0.0.0:0").await?;
+    match try_native_auth_check(
+        &socket,
+        config,
+        &requested,
+        &server,
+        ssh_port,
+        &udp_host,
+        dosh_port,
+        args.ssh_key.as_deref(),
+    )
+    .await
+    {
+        Ok(check) => {
+            println!("[ok] native udp: reachable");
+            println!("[ok] known host: trusted");
+            println!("[ok] native auth: authorized as {}", check.requested_user);
+            println!(
+                "[ok] forwarding policy: tcp={} remote={} agent={}",
+                check.allow_tcp_forwarding,
+                check.allow_remote_forwarding,
+                check.allow_agent_forwarding
+            );
+            Ok(())
+        }
+        Err(err) => {
+            println!("[fail] native/auth check: {err:#}");
+            Err(err.context("dosh doctor failed"))
+        }
+    }
+}
+
+fn ssh_fallback_probe(
+    server: &str,
+    ssh_port: Option<u16>,
+    ssh_key: Option<&Path>,
+    ssh_known_hosts: Option<&Path>,
+) -> Result<()> {
+    let mut command = Command::new("ssh");
+    command.arg("-o").arg("BatchMode=yes");
+    command.arg("-o").arg("ConnectTimeout=5");
+    command.arg("-T");
+    if let Some(ssh_port) = ssh_port {
+        command.arg("-p").arg(ssh_port.to_string());
+    }
+    if let Some(key) = ssh_key {
+        command.arg("-i").arg(key);
+    }
+    if let Some(known_hosts) = ssh_known_hosts {
+        command
+            .arg("-o")
+            .arg(format!("UserKnownHostsFile={}", known_hosts.display()));
+    }
+    let output = command.arg(server).arg("true").output()?;
+    anyhow::ensure!(
+        output.status.success(),
+        "{}",
+        String::from_utf8_lossy(&output.stderr)
+    );
+    Ok(())
+}
+
 fn fetch_host_key_over_ssh(
     server: &str,
     ssh_port: Option<u16>,
@@ -1241,6 +1358,132 @@ async fn try_native_auth(
     Ok((frame, cred))
 }
 
+async fn try_native_auth_check(
+    socket: &UdpSocket,
+    config: &dosh::config::ClientConfig,
+    requested_server: &str,
+    server: &str,
+    ssh_port: Option<u16>,
+    udp_host: &str,
+    udp_port: u16,
+    cli_identity: Option<&Path>,
+) -> Result<NativeAuthCheckOkBody> {
+    let addr = resolve_addr(udp_host, udp_port)?;
+    let ssh_config = ssh_config(server, ssh_port).unwrap_or_default();
+    let requested_user = ssh_username(server)
+        .or(ssh_config.user.clone())
+        .unwrap_or_else(|| std::env::var("USER").unwrap_or_else(|_| "unknown".to_string()));
+    let (client_secret, client_public) = generate_native_ephemeral();
+    let hello = dosh::native::NativeClientHello {
+        protocol_version: dosh::native::NATIVE_PROTOCOL_VERSION,
+        client_random: crypto::random_32(),
+        client_ephemeral_public: client_public,
+        requested_host: requested_server.to_string(),
+        requested_user,
+        requested_session: "doctor".to_string(),
+        requested_mode: "doctor".to_string(),
+        terminal_size: (80, 24),
+        supported_aead: vec!["chacha20poly1305".to_string()],
+        supported_user_key_algorithms: vec!["ssh-ed25519".to_string()],
+        cached_host_key_fingerprint: None,
+        attach_ticket_envelope: None,
+    };
+    let packet = protocol::encode_plain(
+        PacketKind::NativeClientHello,
+        [0u8; 16],
+        1,
+        0,
+        &protocol::to_body(&NativeClientHelloBody {
+            hello: hello.clone(),
+        })?,
+    )?;
+    socket.send_to(&packet, addr).await?;
+
+    let mut buf = vec![0u8; 65535];
+    let (n, _) = tokio::time::timeout(
+        Duration::from_millis(config.native_auth_timeout_ms.max(1)),
+        socket.recv_from(&mut buf),
+    )
+    .await??;
+    let packet = protocol::decode(&buf[..n])?;
+    if packet.header.kind != PacketKind::NativeServerHello {
+        if packet.header.kind == PacketKind::AttachReject {
+            let reject: AttachReject = protocol::from_body(&packet.body)?;
+            return Err(anyhow!("native doctor rejected: {}", reject.reason));
+        }
+        return Err(anyhow!("native doctor received unexpected server response"));
+    }
+    let server_hello: NativeServerHelloBody = protocol::from_body(&packet.body)?;
+    verify_server_hello(&hello, &server_hello.hello)?;
+
+    let known_hosts = expand_tilde(&config.known_hosts);
+    match verify_known_host(&known_hosts, requested_server, &server_hello.hello.host_key)? {
+        KnownHostStatus::Trusted => {}
+        KnownHostStatus::Unknown if config.trust_on_first_use => {
+            trust_host(
+                &known_hosts,
+                requested_server,
+                &server_hello.hello.host_key,
+                "tofu",
+                false,
+            )?;
+        }
+        KnownHostStatus::Unknown => {
+            return Err(anyhow!(
+                "Dosh host key for {requested_server} is not trusted; run `dosh trust {requested_server}` first"
+            ));
+        }
+        KnownHostStatus::Mismatch { expected, actual } => {
+            return Err(anyhow!(
+                "Dosh host key mismatch for {requested_server}: expected {expected}, got {actual}"
+            ));
+        }
+    }
+
+    let session_key = derive_native_session_key(
+        &client_secret,
+        server_hello.hello.server_ephemeral_public,
+        &hello,
+        &server_hello.hello,
+    )?;
+    let auth = sign_native_user_auth(
+        config,
+        cli_identity,
+        &ssh_config,
+        &hello,
+        &server_hello.hello,
+        Vec::new(),
+    )?;
+    let mut pending_id = [0u8; 16];
+    pending_id.copy_from_slice(&server_hello.hello.auth_challenge[..16]);
+    let packet = protocol::encode_encrypted(
+        PacketKind::NativeUserAuth,
+        pending_id,
+        2,
+        1,
+        &session_key,
+        CLIENT_TO_SERVER,
+        &protocol::to_body(&NativeUserAuthBody { auth })?,
+    )?;
+    socket.send_to(&packet, addr).await?;
+
+    let (n, _) = tokio::time::timeout(
+        Duration::from_millis(config.native_auth_timeout_ms.max(1)),
+        socket.recv_from(&mut buf),
+    )
+    .await??;
+    let packet = protocol::decode(&buf[..n])?;
+    if packet.header.kind != PacketKind::NativeAuthCheckOk {
+        if packet.header.kind == PacketKind::AttachReject {
+            let reject: AttachReject = protocol::from_body(&packet.body)?;
+            return Err(anyhow!("native doctor rejected: {}", reject.reason));
+        }
+        return Err(anyhow!("native doctor received unexpected auth response"));
+    }
+    let plain = protocol::decrypt_body(&packet, &session_key, SERVER_TO_CLIENT)?;
+    protocol::from_body(&plain)
+}
+
 fn sign_native_user_auth(
     config: &dosh::config::ClientConfig,
     cli_identity: Option<&Path>,

src/bin/dosh-server.rs

@@ -13,9 +13,10 @@ use dosh::native::{
 };
 use dosh::protocol::{
     self, AttachOk, AttachReject, BootstrapAttachRequest, CLIENT_TO_SERVER, Frame, Input,
-    NativeAuthOkBody, NativeClientHelloBody, NativeServerHelloBody, NativeUserAuthBody, PacketKind,
-    ReplayWindow, Resize, ResumeRequest, SERVER_TO_CLIENT, StreamClose, StreamData, StreamOpen,
-    StreamOpenOk, StreamOpenReject, TicketAttachBody, TicketAttachEnvelope, TicketAttachOkEnvelope,
+    NativeAuthCheckOkBody, NativeAuthOkBody, NativeClientHelloBody, NativeServerHelloBody,
+    NativeUserAuthBody, PacketKind, ReplayWindow, Resize, ResumeRequest, SERVER_TO_CLIENT,
+    StreamClose, StreamData, StreamOpen, StreamOpenOk, StreamOpenReject, TicketAttachBody,
+    TicketAttachEnvelope, TicketAttachOkEnvelope,
 };
 use dosh::pty::{PtyHandle, PtyOutput, spawn_pty_session};
 use std::collections::{HashMap, VecDeque};
@@ -402,6 +403,38 @@ async fn handle_native_user_auth(
     }
     let body = protocol::decrypt_body(packet, &pending.session_key, CLIENT_TO_SERVER)?;
     let req: NativeUserAuthBody = protocol::from_body(&body)?;
+    if pending.client.requested_mode == "doctor" {
+        let check = {
+            let locked = state.lock().expect("server state poisoned");
+            verify_native_user_auth_from_config(
+                &locked.config,
+                &pending.client,
+                &pending.server,
+                &req.auth,
+            )
+            .context("verify native user auth")?;
+            NativeAuthCheckOkBody {
+                requested_user: pending.client.requested_user.clone(),
+                native_auth_enabled: locked.config.native_auth,
+                allow_tcp_forwarding: locked.config.allow_tcp_forwarding,
+                allow_remote_forwarding: locked.config.allow_remote_forwarding,
+                allow_agent_forwarding: locked.config.allow_agent_forwarding,
+                policy_flags: Vec::new(),
+            }
+        };
+        let body = protocol::to_body(&check)?;
+        let out = protocol::encode_encrypted(
+            PacketKind::NativeAuthCheckOk,
+            packet.header.conn_id,
+            1,
+            packet.header.seq,
+            &pending.session_key,
+            SERVER_TO_CLIENT,
+            &body,
+        )?;
+        socket.send_to(&out, peer).await?;
+        return Ok(());
+    }
 
     let attached: Result<(
         [u8; 16],