rstrict

A lightweight, secure sandbox for running Linux processes using the Linux kernel's Landlock LSM, implemented in Rust with the excellent landlock-rs crate.

rstrict leverages the Linux Landlock security module to sandbox processes, allowing you to run commands with restricted access to the filesystem and network, reducing the potential impact of vulnerabilities or unintended actions.

For detailed information about the underlying Landlock security module, see the official Linux kernel documentation.

Quote:

The goal of Landlock is to enable restriction of ambient rights (e.g. global filesystem or network access) for a set of processes. Because Landlock is a stackable LSM, it makes it possible to create safe security sandboxes as new security layers in addition to the existing system-wide access-controls. This kind of sandbox is expected to help mitigate the security impact of bugs or unexpected/malicious behaviors in user space applications. Landlock empowers any process, including unprivileged ones, to securely restrict themselves.

The two existing types of rules are:

Filesystem rules For these rules, the object is a file hierarchy, and the related filesystem actions are defined with filesystem access rights.

Network rules (since ABI v4) For these rules, the object is a TCP port, and the related actions are defined with network access rights. -- Landlock

Quick Start Examples

The basic command structure is:

rstrict [OPTIONS] -- <COMMAND> [COMMAND_ARGS...]

Example Sandboxing

# allow `ls` and its linked libraries to run, allow access to read /tmp
rstrict --log-level debug --ro /tmp --ldd --add-exec -- ls -l /tmp 


# Curl sandbox example
# --add-exec Allow executing curl binary (optional helper)
# --ldd Allow executing curl's libraries (optional helper)
# --ro Read DNS configuration
# --ro Read Name service configuration
# --ro Read Hosts file
# --ro Read SSL certificates
# --connect-tcp <port> Allow connections to HTTPS Port
rstrict --log-level info \
        --add-exec \
        --ldd \
        --ro /etc/resolv.conf \
        --ro /etc/nsswitch.conf \
        --ro /etc/hosts \
        --ro /etc/ssl/certs \
        --connect-tcp 443 \
        -- \
        curl https://example.com

** --ldd and --add-exec are optional convenience flags, including the executables path and any dependencies with --rox will have the same effect.

Security Model

rstrict follows the fundamental security principle of "deny by default, allow explicitly." When a process is sandboxed with rstrict:

1. Default Denial: All handled Landlock operations are denied unless explicitly allowed by rules
2. Inheritance: Restrictions automatically apply to child processes
3. Accumulation: New rules can only add restrictions, never remove them
4. Least Privilege: Target only required resources with minimal permissions

Features and Landlock Mapping

rstrict provides user-friendly flags that directly map to Landlock's underlying access control mechanisms:

Filesystem Access Controls

rstrict's filesystem flags provide intuitive access control that maps to Landlock's more granular permissions:

• --ro <PATH>: Allow read-only access to the specified path

  • If PATH is a directory: Permissions apply recursively to all files/directories beneath it
  • If PATH is a file: Permissions apply only to that specific file
  • Maps to LANDLOCK_ACCESS_FS_READ_FILE and LANDLOCK_ACCESS_FS_READ_DIR
  • Example use: Configuration files, static assets

• --rw <PATH>: Allow read-write access to the specified path

  • If PATH is a directory: Read-write permissions apply recursively to all files/directories beneath it
  • If PATH is a file: Read-write permissions apply only to that specific file
  • Includes all --ro rights plus write operations like:
    • LANDLOCK_ACCESS_FS_WRITE_FILE
    • LANDLOCK_ACCESS_FS_TRUNCATE (ABI v3+)
    • LANDLOCK_ACCESS_FS_REMOVE_FILE/LANDLOCK_ACCESS_FS_REMOVE_DIR
    • LANDLOCK_ACCESS_FS_MAKE_REG/LANDLOCK_ACCESS_FS_MAKE_DIR, etc.
  • Example use: Log directories, temp folders

• --rox <PATH>: Allow read and execute access to the specified path

  • If PATH is a directory: Read-execute permissions apply recursively to all files/directories beneath it
  • If PATH is a file: Read-execute permissions apply only to that specific file
  • Includes --ro rights plus LANDLOCK_ACCESS_FS_EXECUTE
  • Example use: System libraries, binaries, scripts

• --rwx <PATH>: Allow read, write, and execute access to the specified path

  • If PATH is a directory: Read-write-execute permissions apply recursively to all files/directories beneath it
  • If PATH is a file: Read-write-execute permissions apply only to that specific file
  • Combines --rw and --rox permissions
  • Example use: Application working directories needing full access

Network Access Controls

rstrict's network flags directly correspond to Landlock's TCP socket controls (available since ABI v4):

• --bind-tcp <PORT>: Allow binding to the specified TCP port

  • Maps to LANDLOCK_ACCESS_NET_BIND_TCP
  • Example use: Web servers, database services

• --connect-tcp <PORT>: Allow outgoing TCP connections to the specified port

  • Maps to LANDLOCK_ACCESS_NET_CONNECT_TCP
  • Example use: API clients, web scrapers

Important Note: Landlock network rules currently only restrict TCP bind/connect operations. UDP, ICMP, and other protocols are NOT restricted by these rules.

Helper Flags

rstrict provides convenience flags to simplify common sandboxing tasks:

• --add-exec: Automatically find <COMMAND> in $PATH and add it to the --rox list

  • Saves you from having to manually locate and specify the executable path

• --ldd: Run ldd on <COMMAND> to find and add shared library dependencies

  • Automatically discovers and adds libraries with appropriate execute permissions
  • Adds common system library directories (like /lib, /usr/lib) to the --rox list

• --env <VAR>: Manage environment variables for the sandboxed process

  • --env KEY=VALUE: Sets an environment variable
  • --env KEY: Inherits a value from the current environment

Requirements

• Linux Kernel:
  • 5.13+ for basic Landlock filesystem sandboxing (ABI v1).
  • 5.15+ for LANDLOCK_ACCESS_FS_REFER support (ABI v2).
  • 5.16+ for truncate operations via LANDLOCK_ACCESS_FS_TRUNCATE (ABI v3).
  • 5.19+ for network sandboxing via LANDLOCK_ACCESS_NET_* (ABI v4).
  • 6.2+ for device ioctl control via LANDLOCK_ACCESS_FS_IOCTL_DEV (ABI v5).
  • 6.5+ for IPC scoping controls (ABI v6).
• Rust Toolchain: (Latest stable recommended for building from source).
• ldd command: Required only if using the --ldd helper flag.

Installation

From Crates.io (Recommended)

cargo install rstrict

From Source

1. Clone the repository:

   git clone https://github.com/creslinux/rstrict.git
   cd rstrict
   

2. Build the release binary:

   cargo build --release
   

3. The binary will be located at target/release/rstrict. You can copy it to a location in your $PATH:

   sudo cp target/release/rstrict /usr/local/bin/
   

Usage

The basic command structure is:

rstrict [OPTIONS] -- <COMMAND> [COMMAND_ARGS...]

The basic command structure is:

rstrict [OPTIONS] -- <COMMAND> [COMMAND_ARGS...]

• [OPTIONS]: Flags to configure the sandbox rules (see table above).
• --: Required: Separates rstrict options from the command you want to run.
• <COMMAND>: The command to execute inside the sandbox.
• [COMMAND_ARGS...]: Arguments for the command being executed.

Options

Filesystem Access:

• --ro <PATH>: Allow read-only access to the specified path. If PATH is a directory, permissions apply recursively to everything beneath it. If PATH is a file, permissions apply only to that specific file. Can be used multiple times.
• --rw <PATH>: Allow read-write access to the specified path. If PATH is a directory, permissions apply recursively to everything beneath it. If PATH is a file, permissions apply only to that specific file. Can be used multiple times.
• --rox <PATH>: Allow read + execute access to the specified path. If PATH is a directory, permissions apply recursively to everything beneath it. If PATH is a file, permissions apply only to that specific file. Can be used multiple times.
• --rwx <PATH>: Allow read-write + execute access to the specified path. If PATH is a directory, permissions apply recursively to everything beneath it. If PATH is a file, permissions apply only to that specific file. Can be used multiple times.

Network Access (TCP Only):

• --bind-tcp <PORT>: Allow binding to the specified TCP port. Can be used multiple times.
• --connect-tcp <PORT>: Allow outgoing TCP connections to the specified port. Can be used multiple times.

Helper Flags:

• --add-exec: Automatically find <COMMAND> in $PATH and add it to the --rox list.
• --ldd: Run ldd on <COMMAND> to find shared library dependencies and add them to --rox.
• --env <VAR>: Specify environment variables for the sandboxed process.
  • --env KEY=VALUE: Sets the variable KEY to VALUE.
  • --env KEY: Inherits the value of KEY from the current environment.

Unrestricted Access:

• --unrestricted-filesystem: Disable Landlock filesystem rules.
• --unrestricted-network: Disable Landlock network (TCP) rules.

Logging & Meta:

• --log-level <LEVEL>: Set logging verbosity. Options: error (default), warn, info, debug, trace.
• --help: Show help message and exit.
• --version: Show version information and exit.

How It Works

1. Command Parsing: rstrict processes command-line flags to build a sandboxing configuration
2. Path Resolution: Paths specified in flags are resolved to their absolute locations
3. Library Discovery: If --ldd is used, shared libraries are automatically discovered
4. Ruleset Creation: rstrict creates a Landlock ruleset with the specified access rights
5. Rule Addition: Each path/port rule is added to the ruleset with appropriate permissions
6. Self-Restriction: rstrict applies the ruleset to itself using Landlock's restrict_self()
7. Command Execution: rstrict uses execvpe to replace itself with the target command
8. Inherited Restrictions: The target command runs with the Landlock restrictions already in place

This approach ensures the security boundary is established before the target program begins execution.

Examples

1. Running ls with minimal read access:

# Basic filesystem sandbox
rstrict --log-level info \
        --ro /home \
        --add-exec \
        --ldd \
        -- \
        ls -l /home

Output should show details for /bin/bash. Trying ls -l /tmp would fail with a permission error.

2. Running curl to fetch a webpage (HTTPS):

rstrict --log-level info \
        --add-exec \
        --ldd \
        --ro /etc/resolv.conf \
        --ro /etc/nsswitch.conf \
        --ro /etc/hosts \
        --ro /etc/ssl/certs \
        --connect-tcp 443 \
        -- \
        curl https://example.com

• --add-exec, --ldd: Allow curl and its libraries to run
• --ro /etc/resolv.conf, etc.: Allow DNS resolver configuration access
• --ro /etc/ssl/certs: Allow TLS certificate verification
• --connect-tcp 443: Allow HTTPS connections

3. Allowing write access to a specific directory:

# Create a temporary directory first
mkdir ./my_temp_data

# Run touch with write access to only that directory
rstrict --log-level info \
        --rw ./my_temp_data \
        --add-exec \
        --ldd \
        -- \
        touch ./my_temp_data/test_file.txt

4. Running a web server on port 8080 can connect to MySQL on 3306:

rstrict --log-level info \
        --ro /app/static \
        --rw /app/logs \
        --bind-tcp 8080 \
        --connect-tcp 3306 \
        --add-exec \
        --ldd \
        -- \
        /app/myserver --port 8080

Landlock ABI Version Compatibility

rstrict adapts to the available Landlock features on your kernel at runtime. It will use the highest supported ABI version and adjust its behavior accordingly:

Limitations

• Linux Only: Landlock is a Linux-specific kernel feature.
• Kernel Version: Features depend on kernel support for specific Landlock ABIs.
• Network Restrictions (TCP Only): UDP, ICMP, etc. are not restricted.
• No UID/GID Changes: rstrict does not change user or group IDs.
• Maximum Ruleset Layers: Limited to 16 stacked rulesets per process.

Contributing

Contributions (bug reports, feature requests, pull requests) are welcome! Please open an issue on the GitHub repository to discuss changes.

License

This project is licensed under the MIT License.