landstrip

landstrip runs a tool in an OS-level sandbox using Landlock LSM on Linux, Seatbelt on macOS, and LPAC AppContainer on Windows. It accepts the Anthropic Sandbox Runtime JSON subset as the policy, in JSON or YAML syntax.

Installation

npm

npm install --save-dev @landstrip/landstrip

npx landstrip -p policy.json cargo test

The npm package installs a small Node.js wrapper and a platform-specific native binary package.

Platforms

Windows AppContainer

Win32 API provides AppContainer for application level sandboxing. The platform creates a per-run LPAC AppContainer profile, grants its SID access to the lowered read and write roots, and removes those grants after the sandboxed process tree exits. Windows policies must use explicit read allowlists.

Landstrip assigns the sandboxed process to a Job Object with KILL_ON_JOB_CLOSE, so child processes are kept in the sandbox process tree and are terminated when the launcher exits.

allowNetwork grants the internet and private-network AppContainer capabilities, while the default container holds none and denies all network access.

AppContainer capabilities are coarse: fine-grained TCP policies by host or port require Windows Filtering Platform rules keyed by the AppContainer SID. I.e., this would require elevated privileges, which is not sustainable for a agent sandbox runtime, which should rely on unprivileged tools and techniques.

Policy Format

JSON is the default policy format. Use --format yaml for YAML policy files or YAML read from standard input.

landstrip --format yaml -p policy.yaml cargo test

YAML path fields can use normal lists or one statement per line:

filesystem:
  allowWrite: |
    .
    ~/.cargo
  denyRead: |
    ~/.ssh
  allowRead: |
    ~/.ssh/config
network:
  allowNetwork: true

Windows-only hardening options live under windows. They are optional because some tools, shells, JITs, and GUI helpers may rely on the blocked behaviors:

{
  "windows": {
    "disableWin32k": true,
    "disableExtensionPoints": true,
    "strictHandleChecks": true,
    "imageLoadNoRemote": true,
    "imageLoadNoLowLabel": true,
    "imageLoadPreferSystem32": true
  }
}

Network Policy

Sandbox mode denies direct network access by default. Proxy ports, local binding, and Unix sockets can be allowed with the Anthropic Sandbox Runtime network fields.

For a filesystem-only sandbox with unrestricted direct network access, set:

{
  "network": {
    "allowNetwork": true
  }
}

allowNetwork disables landstrip network enforcement while leaving filesystem policy enforcement in place. On Windows this grants the AppContainer its network capabilities; without it the container denies all network access.

Denial Traps

Sandbox denials are reported as JSON objects, one per line, each with a fixed kind discriminant and a stable code. Consumers route on kind for coarse grouping and on code for the policy denial class. Traps go to standard error by default; --trap-fd FD writes them to an already-open descriptor instead.

landstrip --trap-fd 3 -p policy.json cargo test 3>landstrip-traps.txt

The two trap kinds are:

• filesystem (code FILESYSTEM_DENIED): operation is read or write, path is the resolved path, requested_path is the tool's original path when available, and syscall, errno, flags, reason, suggested_grant, and process carry routing context.
• network (code NETWORK_DENIED): operation is connect or bind and target is address:port, with syscall, errno, and process context.

reason is a platform-independent classification of the decision, derived from the policy and the requested path:

• allow_miss: the path matched no allow root and was denied by default.
• deny_match: the path matched an explicit deny root that overrides an allow.

mechanism records the kernel layer that detected the denial. Per-denial traps are always seccomp, the only layer with a per-denial callback; Landlock enforces in-kernel without one.

{
  "kind": "filesystem",
  "code": "FILESYSTEM_DENIED",
  "operation": "write",
  "path": "/repo/out",
  "requested_path": "out",
  "syscall": "openat",
  "errno": "EACCES",
  "flags": ["O_WRONLY", "O_CREAT", "O_TRUNC"],
  "reason": "allow_miss",
  "suggested_grant": { "allowWrite": "/repo/out" },
  "mechanism": "seccomp",
  "process": { "pid": 1234, "exe": "/usr/bin/sh", "cwd": "/repo" }
}
{
  "kind": "network",
  "code": "NETWORK_DENIED",
  "operation": "connect",
  "target": "127.0.0.1:9999",
  "syscall": "connect",
  "errno": "EACCES",
  "mechanism": "seccomp",
  "process": { "pid": 1234, "exe": "/usr/bin/nc", "cwd": "/repo" }
}

Traps are informational; the configured policy always applies. landstrip is otherwise quiet on success — standard error belongs to landstrip, standard output to the sandboxed tool. Usage, policy, launch, and platform errors are printed as plain text; usage errors exit with status 2. Writing to --trap-fd is best-effort: it needs an already-open descriptor (3 or greater; 0-2 are reserved), and if the write fails the denial is dropped while the policy stays in effect.

Development

Commit messages

• <subsystem>: <message>
• Long description for non-trivial changes.
• Kernel style commit messages.
• Signed-off-by

Documenting errors

The following snippet demonstrates the recommended pattern for documenting the return values on error:

/// # Errors
///
/// Returns [`<variant's unqualified name>`](<variant's unqualified name>)
/// Returns ...

Licensing

The JavaScript npm wrapper is licensed under Apache-2.0. The Rust source and native binaries are licensed under LGPL-2.1-or-later. Corresponding source for each published native binary is available from the GitHub repository tag that matches the package version.