Implement remote execution

src/exec.rs

@@ -0,0 +1,259 @@
+//! PowerShell remote-exec worker.
+//!
+//! Subscribes to `librustdesk::hbbs_http::sync::exec_signal_receiver()` — a
+//! broadcast channel that the vendored sync loop populates whenever the
+//! server returns an `exec` field in a heartbeat reply (see
+//! rustdesk-server/docs/AGENT-API-AUTH.md). For each `ExecRequest` we:
+//!
+//!   1. Spawn `powershell.exe -NoProfile -NonInteractive -ExecutionPolicy
+//!      Bypass -Command -` and write the script to stdin.
+//!   2. Concurrently drain stdout and stderr into 1 MiB-capped buffers.
+//!   3. Apply a wall-clock timeout (default 5 min); kill on expiry.
+//!   4. POST the result to `/api/agent/exec-result` with the same Ed25519
+//!      signature the heartbeat / sysinfo posts use.
+//!
+//! The whole thing only makes sense on Windows (the agent's target OS),
+//! so the module body is `#[cfg(windows)]` and other platforms get a
+//! no-op `start()` to keep the call site in `service.rs` portable.
+
+#[cfg(windows)]
+mod windows_impl {
+    use anyhow::{anyhow, Result};
+    use hbb_common::config::Config;
+    use librustdesk::hbbs_http::sync::ExecRequest;
+    use std::process::Stdio;
+    use std::sync::{Arc, Mutex};
+    use std::time::Duration;
+    use tokio::io::{AsyncReadExt, AsyncWriteExt};
+
+    pub fn start() {
+        std::thread::spawn(|| {
+            let rt = match tokio::runtime::Builder::new_current_thread()
+                .enable_all()
+                .build()
+            {
+                Ok(rt) => rt,
+                Err(e) => {
+                    log::warn!("exec worker: build runtime: {e}");
+                    return;
+                }
+            };
+            rt.block_on(run_loop());
+        });
+    }
+
+    async fn run_loop() {
+        // The vendored sync layer creates the broadcast channel lazily on
+        // first `subscribe()`. Calling here also primes it for the parser.
+        let mut rx = librustdesk::hbbs_http::sync::exec_signal_receiver();
+        log::info!("exec worker: subscribed to heartbeat exec channel");
+        loop {
+            match rx.recv().await {
+                Ok(req) => {
+                    log::info!(
+                        "exec worker: received cmd_id={} script_len={} max_secs={} max_bytes={}",
+                        req.cmd_id,
+                        req.script.len(),
+                        req.max_secs,
+                        req.max_bytes
+                    );
+                    let outcome = run_one(&req).await;
+                    if let Err(e) = report(&req, &outcome).await {
+                        log::warn!(
+                            "exec worker: report failed for cmd_id={}: {e:#}",
+                            req.cmd_id
+                        );
+                    }
+                }
+                Err(tokio::sync::broadcast::error::RecvError::Lagged(n)) => {
+                    log::warn!("exec worker: lagged, dropped {n} exec requests");
+                }
+                Err(tokio::sync::broadcast::error::RecvError::Closed) => {
+                    log::warn!("exec worker: channel closed, exiting");
+                    return;
+                }
+            }
+        }
+    }
+
+    struct Outcome {
+        exit_code: i64,
+        stdout: String,
+        stderr: String,
+        timed_out: bool,
+        truncated: bool,
+    }
+
+    async fn run_one(req: &ExecRequest) -> Outcome {
+        // Defensive lower bound — a misconfigured server shouldn't be able to
+        // send max_secs=0 and have us skip the wait.
+        let timeout = Duration::from_secs(req.max_secs.max(1));
+        let max_bytes = req.max_bytes.max(1024) as usize;
+
+        // `-Command -` makes PowerShell read the script body from stdin,
+        // which avoids quoting / length issues that plague `-Command "…"`
+        // for multi-line scripts. `-NoProfile` skips both the
+        // machine-wide and user-wide profile loads — those would change
+        // behaviour depending on which AD-managed PowerShell profile the
+        // service account inherited. `-NonInteractive` makes prompts fail
+        // instead of hanging the run.
+        let mut child = match tokio::process::Command::new("powershell.exe")
+            .args([
+                "-NoProfile",
+                "-NonInteractive",
+                "-ExecutionPolicy",
+                "Bypass",
+                "-Command",
+                "-",
+            ])
+            .stdin(Stdio::piped())
+            .stdout(Stdio::piped())
+            .stderr(Stdio::piped())
+            .spawn()
+        {
+            Ok(c) => c,
+            Err(e) => {
+                return Outcome {
+                    exit_code: -1,
+                    stdout: String::new(),
+                    stderr: format!("spawn failed: {e}"),
+                    timed_out: false,
+                    truncated: false,
+                };
+            }
+        };
+
+        if let Some(mut stdin) = child.stdin.take() {
+            let _ = stdin.write_all(req.script.as_bytes()).await;
+            let _ = stdin.shutdown().await;
+        }
+
+        let stdout = child.stdout.take().expect("piped stdout was requested");
+        let stderr = child.stderr.take().expect("piped stderr was requested");
+
+        // Concurrent capped readers. Each task accumulates up to
+        // `max_bytes` bytes, then drains and discards the rest so the
+        // pipe doesn't block the child writer.
+        let stdout_buf: Arc<Mutex<(Vec<u8>, bool)>> = Arc::new(Mutex::new((Vec::new(), false)));
+        let stderr_buf: Arc<Mutex<(Vec<u8>, bool)>> = Arc::new(Mutex::new((Vec::new(), false)));
+        let so = tokio::spawn(read_capped(stdout, stdout_buf.clone(), max_bytes));
+        let se = tokio::spawn(read_capped(stderr, stderr_buf.clone(), max_bytes));
+
+        let wait_result = tokio::time::timeout(timeout, child.wait()).await;
+        let (exit_code, timed_out) = match wait_result {
+            Ok(Ok(s)) => (s.code().unwrap_or(-1) as i64, false),
+            Ok(Err(_)) => (-1, false),
+            Err(_) => {
+                // Timed out: kill, then wait the killed child so it
+                // reaps cleanly (and so the read tasks finish via EOF).
+                let _ = child.kill().await;
+                let _ = child.wait().await;
+                (-1, true)
+            }
+        };
+        let _ = so.await;
+        let _ = se.await;
+
+        let (out_bytes, out_trunc) = {
+            let g = stdout_buf.lock().unwrap();
+            (g.0.clone(), g.1)
+        };
+        let (err_bytes, err_trunc) = {
+            let g = stderr_buf.lock().unwrap();
+            (g.0.clone(), g.1)
+        };
+        Outcome {
+            exit_code,
+            // PowerShell on a current Windows defaults to UTF-8 when
+            // OutputEncoding is set, but the agent service inherits the
+            // legacy code page on older boxes. `from_utf8_lossy`
+            // guarantees we always have a UTF-8 string to ship; the
+            // operator sees a U+FFFD when raw bytes weren't UTF-8.
+            stdout: String::from_utf8_lossy(&out_bytes).into_owned(),
+            stderr: String::from_utf8_lossy(&err_bytes).into_owned(),
+            timed_out,
+            truncated: out_trunc || err_trunc,
+        }
+    }
+
+    async fn read_capped<R: AsyncReadExt + Unpin>(
+        mut reader: R,
+        buf: Arc<Mutex<(Vec<u8>, bool)>>,
+        cap: usize,
+    ) {
+        let mut chunk = [0u8; 8192];
+        loop {
+            match reader.read(&mut chunk).await {
+                Ok(0) => return,
+                Ok(n) => {
+                    let mut g = buf.lock().unwrap();
+                    if g.0.len() < cap {
+                        let room = cap - g.0.len();
+                        if n <= room {
+                            g.0.extend_from_slice(&chunk[..n]);
+                        } else {
+                            g.0.extend_from_slice(&chunk[..room]);
+                            g.1 = true; // truncated; keep draining
+                        }
+                    }
+                    // else: already truncated, drop this chunk on the floor.
+                }
+                Err(_) => return,
+            }
+        }
+    }
+
+    async fn report(req: &ExecRequest, out: &Outcome) -> Result<()> {
+        let api = librustdesk::common::get_api_server(
+            Config::get_option("api-server"),
+            Config::get_option("custom-rendezvous-server"),
+        );
+        if api.is_empty() {
+            return Err(anyhow!("no api-server configured"));
+        }
+        let url = format!("{api}/api/agent/exec-result");
+        let id = Config::get_id();
+        let uuid = librustdesk::common::encode64(hbb_common::get_uuid());
+        let body = hbb_common::serde_json::json!({
+            "id": id,
+            "uuid": uuid,
+            "cmd_id": req.cmd_id,
+            "exit_code": out.exit_code,
+            "stdout": out.stdout,
+            "stderr": out.stderr,
+            "timed_out": out.timed_out,
+            "truncated": out.truncated,
+        })
+        .to_string();
+
+        let headers = librustdesk::hbbs_http::sign::build_signed_headers(
+            "POST",
+            "/api/agent/exec-result",
+            body.as_bytes(),
+        )
+        .unwrap_or_default();
+        if headers.is_empty() {
+            // Server rejects unsigned exec-result posts unconditionally
+            // (see api/agent_exec.rs); bail loudly so the operator can
+            // see the agent isn't ready to sign yet.
+            return Err(anyhow!("no signing keypair available"));
+        }
+
+        let resp = librustdesk::common::post_request(url, body, &headers)
+            .await
+            .map_err(|e| anyhow!("post: {e}"))?;
+        if resp.trim() == "OK" {
+            Ok(())
+        } else {
+            Err(anyhow!("unexpected response: {}", resp.trim()))
+        }
+    }
+}
+
+#[cfg(windows)]
+pub use windows_impl::start;
+
+#[cfg(not(windows))]
+pub fn start() {
+    log::info!("exec worker: skipped (non-Windows build)");
+}

src/main.rs

@@ -28,6 +28,8 @@ mod inventory;
 #[cfg(target_os = "windows")]
 mod cm_popup;
 #[cfg(target_os = "windows")]
+mod exec;
+#[cfg(target_os = "windows")]
 mod service;
 #[cfg(target_os = "windows")]
 mod unattended_password;
@@ -278,6 +280,15 @@ fn run_server() {
         }
     });
 
+    // Start the PowerShell remote-exec worker. Subscribes to the
+    // broadcast channel in the vendored sync layer; the channel is
+    // shared in-process so the worker MUST run in this --server process
+    // (where sync.rs lives), not the --service supervisor. The worker
+    // is idle until an admin dispatches an exec from the dashboard.
+    // Gated server-side on peer.managed=1 + strategy.enable-remote-exec.
+    #[cfg(target_os = "windows")]
+    exec::start();
+
     // `start_server` is `#[tokio::main]` and runs forever. (is_server=true,
     // no_server=false). It boots the default IPC server, input service,
     // rendezvous mediator, and heartbeat sync.