feat: use Landlock for sandboxing on Linux in TypeScript CLI (#763)

Building on top of https://github.com/openai/codex/pull/757, this PR
updates Codex to use the Landlock executor binary for sandboxing in the
Node.js CLI. Note that Codex has to be invoked with either `--full-auto`
or `--auto-edit` to activate sandboxing. (Using `--suggest` or
`--dangerously-auto-approve-everything` ensures the sandboxing codepath
will not be exercised.)

When I tested this on a Linux host (specifically, `Ubuntu 24.04.1 LTS`),
things worked as expected: I ran Codex CLI with `--full-auto` and then
asked it to do `echo 'hello mbolin' into hello_world.txt` and it
succeeded without prompting me.

However, in my testing, I discovered that the sandboxing did *not* work
when using `--full-auto` in a Linux Docker container from a macOS host.
I updated the code to throw a detailed error message when this happens:


![image](https://github.com/user-attachments/assets/e5b99def-f00e-4ade-a0c5-2394d30df52e)

codex-cli/src/utils/agent/exec.ts

@@ -4,6 +4,7 @@ import type { ParseEntry } from "shell-quote";
 
 import { process_patch } from "./apply-patch.js";
 import { SandboxType } from "./sandbox/interface.js";
+import { execWithLandlock } from "./sandbox/landlock.js";
 import { execWithSeatbelt } from "./sandbox/macos-seatbelt.js";
 import { exec as rawExec } from "./sandbox/raw-exec.js";
 import { formatCommandForDisplay } from "../../format-command.js";
@@ -42,26 +43,30 @@ export function exec(
   sandbox: SandboxType,
   abortSignal?: AbortSignal,
 ): Promise<ExecResult> {
-  // This is a temporary measure to understand what are the common base commands
-  // until we start persisting and uploading rollouts
-
   const opts: SpawnOptions = {
     timeout: timeoutInMillis || DEFAULT_TIMEOUT_MS,
     ...(requiresShell(cmd) ? { shell: true } : {}),
     ...(workdir ? { cwd: workdir } : {}),
   };
-  // Merge default writable roots with any user-specified ones.
-  const writableRoots = [
-    process.cwd(),
-    os.tmpdir(),
-    ...additionalWritableRoots,
-  ];
-  if (sandbox === SandboxType.MACOS_SEATBELT) {
-    return execWithSeatbelt(cmd, opts, writableRoots, abortSignal);
-  }
 
-  // SandboxType.NONE (or any other) falls back to the raw exec implementation
-  return rawExec(cmd, opts, abortSignal);
+  switch (sandbox) {
+    case SandboxType.NONE: {
+      // SandboxType.NONE uses the raw exec implementation.
+      return rawExec(cmd, opts, abortSignal);
+    }
+    case SandboxType.MACOS_SEATBELT: {
+      // Merge default writable roots with any user-specified ones.
+      const writableRoots = [
+        process.cwd(),
+        os.tmpdir(),
+        ...additionalWritableRoots,
+      ];
+      return execWithSeatbelt(cmd, opts, writableRoots, abortSignal);
+    }
+    case SandboxType.LINUX_LANDLOCK: {
+      return execWithLandlock(cmd, opts, additionalWritableRoots, abortSignal);
+    }
+  }
 }
 
 export function execApplyPatch(

codex-cli/src/utils/agent/handle-exec-command.ts

@@ -303,6 +303,11 @@ async function getSandbox(runInSandbox: boolean): Promise<SandboxType> {
           "Sandbox was mandated, but 'sandbox-exec' was not found in PATH!",
         );
       }
+    } else if (process.platform === "linux") {
+      // TODO: Need to verify that the Landlock sandbox is working. For example,
+      // using Landlock in a Linux Docker container from a macOS host may not
+      // work.
+      return SandboxType.LINUX_LANDLOCK;
     } else if (CODEX_UNSAFE_ALLOW_NO_SANDBOX) {
       // Allow running without a sandbox if the user has explicitly marked the
       // environment as already being sufficiently locked-down.

codex-cli/src/utils/agent/sandbox/landlock.ts

@@ -0,0 +1,173 @@
+import type { ExecResult } from "./interface.js";
+import type { SpawnOptions } from "child_process";
+
+import { exec } from "./raw-exec.js";
+import { execFile } from "child_process";
+import fs from "fs";
+import path from "path";
+import { log } from "src/utils/logger/log.js";
+import { fileURLToPath } from "url";
+
+/**
+ * Runs Landlock with the following permissions:
+ * - can read any file on disk
+ * - can write to process.cwd()
+ * - can write to the platform user temp folder
+ * - can write to any user-provided writable root
+ */
+export async function execWithLandlock(
+  cmd: Array<string>,
+  opts: SpawnOptions,
+  userProvidedWritableRoots: ReadonlyArray<string>,
+  abortSignal?: AbortSignal,
+): Promise<ExecResult> {
+  const sandboxExecutable = await getSandboxExecutable();
+
+  const extraSandboxPermissions = userProvidedWritableRoots.flatMap(
+    (root: string) => ["--sandbox-permission", `disk-write-folder=${root}`],
+  );
+
+  const fullCommand = [
+    sandboxExecutable,
+    "--sandbox-permission",
+    "disk-full-read-access",
+
+    "--sandbox-permission",
+    "disk-write-cwd",
+
+    "--sandbox-permission",
+    "disk-write-platform-user-temp-folder",
+
+    ...extraSandboxPermissions,
+
+    "--",
+    ...cmd,
+  ];
+
+  return exec(fullCommand, opts, abortSignal);
+}
+
+/**
+ * Lazily initialized promise that resolves to the absolute path of the
+ * architecture-specific Landlock helper binary.
+ */
+let sandboxExecutablePromise: Promise<string> | null = null;
+
+async function detectSandboxExecutable(): Promise<string> {
+  // Find the executable relative to the package.json file.
+  const __filename = fileURLToPath(import.meta.url);
+  let dir: string = path.dirname(__filename);
+
+  // Ascend until package.json is found or we reach the filesystem root.
+  // eslint-disable-next-line no-constant-condition
+  while (true) {
+    try {
+      // eslint-disable-next-line no-await-in-loop
+      await fs.promises.access(
+        path.join(dir, "package.json"),
+        fs.constants.F_OK,
+      );
+      break; // Found the package.json ⇒ dir is our project root.
+    } catch {
+      // keep searching
+    }
+
+    const parent = path.dirname(dir);
+    if (parent === dir) {
+      throw new Error("Unable to locate package.json");
+    }
+    dir = parent;
+  }
+
+  const sandboxExecutable = getLinuxSandboxExecutableForCurrentArchitecture();
+  const candidate = path.join(dir, "bin", sandboxExecutable);
+  try {
+    await fs.promises.access(candidate, fs.constants.X_OK);
+  } catch {
+    throw new Error(`${candidate} not found or not executable`);
+  }
+
+  // Will throw if the executable is not working in this environment.
+  await verifySandboxExecutable(candidate);
+  return candidate;
+}
+
+const ERROR_WHEN_LANDLOCK_NOT_SUPPORTED = `\
+The combination of seccomp/landlock that Codex uses for sandboxing is not
+supported in this environment.
+
+If you are running in a Docker container, you may want to try adding
+restrictions to your Docker container such that it provides your desired
+sandboxing guarantees and then run Codex with the
+--dangerously-auto-approve-everything option inside the container.
+
+If you are running on an older Linux kernel that does not support newer
+features of seccomp/landlock, you will have to update your kernel to a newer
+version.
+`;
+
+/**
+ * Now that we have the path to the executable, make sure that it works in
+ * this environment. For example, when running a Linux Docker container from
+ * macOS like so:
+ *
+ * docker run -it alpine:latest /bin/sh
+ *
+ * Running `codex-linux-sandbox-x64 -- true` in the container fails with:
+ *
+ * ```
+ * Error: sandbox error: seccomp setup error
+ *
+ * Caused by:
+ *     0: seccomp setup error
+ *     1: Error calling `seccomp`: Invalid argument (os error 22)
+ *     2: Invalid argument (os error 22)
+ * ```
+ */
+function verifySandboxExecutable(sandboxExecutable: string): Promise<void> {
+  // Note we are running `true` rather than `bash -lc true` because we want to
+  // ensure we run an executable, not a shell built-in. Note that `true` should
+  // always be available in a POSIX environment.
+  return new Promise((resolve, reject) => {
+    const args = ["--", "true"];
+    execFile(sandboxExecutable, args, (error, stdout, stderr) => {
+      if (error) {
+        log(
+          `Sandbox check failed for ${sandboxExecutable} ${args.join(" ")}: ${error}`,
+        );
+        log(`stdout: ${stdout}`);
+        log(`stderr: ${stderr}`);
+        reject(new Error(ERROR_WHEN_LANDLOCK_NOT_SUPPORTED));
+      } else {
+        resolve();
+      }
+    });
+  });
+}
+
+/**
+ * Returns the absolute path to the architecture-specific Landlock helper
+ * binary. (Could be a rejected promise if not found.)
+ */
+function getSandboxExecutable(): Promise<string> {
+  if (!sandboxExecutablePromise) {
+    sandboxExecutablePromise = detectSandboxExecutable();
+  }
+
+  return sandboxExecutablePromise;
+}
+
+/** @return name of the native executable to use for Linux sandboxing. */
+function getLinuxSandboxExecutableForCurrentArchitecture(): string {
+  switch (process.arch) {
+    case "arm64":
+      return "codex-linux-sandbox-arm64";
+    case "x64":
+      return "codex-linux-sandbox-x64";
+    // Fall back to the x86_64 build for anything else – it will obviously
+    // fail on incompatible systems but gives a sane error message rather
+    // than crashing earlier.
+    default:
+      return "codex-linux-sandbox-x64";
+  }
+}