Landlock LSM¶

Landlock is a Linux security module (LSM) that provides kernel-level filesystem access control. Missy's LandlockPolicy module uses Landlock via ctypes syscalls to enforce filesystem restrictions at the kernel level, complementing the userspace FilesystemPolicyEngine.

How It Works¶

On supported Linux kernels (5.13+), Landlock restricts filesystem access for the current process. Once applied, restrictions cannot be relaxed — only tightened.

graph LR
    A[Tool Request] --> B[FilesystemPolicyEngine]
    B -->|userspace check| C{Allowed?}
    C -->|yes| D[Landlock LSM]
    D -->|kernel check| E{Allowed?}
    E -->|yes| F[File Access]
    C -->|no| G[PolicyViolationError]
    E -->|no| H[PermissionError]

Two-Layer Defense¶

Even if a bug in the Python process bypasses the userspace policy engine, Landlock prevents unauthorized filesystem access at the kernel level.

Configuration¶

Landlock uses the same paths configured in filesystem.allowed_read_paths and filesystem.allowed_write_paths. No additional configuration is needed — it activates automatically on supported kernels.

Requirements¶

• Linux kernel 5.13+ with Landlock enabled
• No additional Python dependencies (uses ctypes)

Limitations¶

• Not available on macOS or Windows
• Once applied to a process, restrictions cannot be removed
• Some filesystem operations (e.g., device files) may require additional Landlock access rights