What is Linux Landlock and how does it differ from seccomp-bpf and AppArmor/SELinux?

Landlock is a Linux Security Module (LSM) introduced in Linux 5.13 that enables unprivileged processes (no root or CAP_SYS_ADMIN required) to restrict their own ambient rights to the file system and network. Unlike traditional LSMs like SELinux or AppArmor which require root to configure global system-wide policies, Landlock is designed for application self-confinement. Unlike seccomp-bpf, which inspects raw syscall numbers and register arguments (and cannot safely dereference user-space pointer arguments due to Time-of-Check to Time-of-Use / TOCTOU vulnerabilities), Landlock operates at the kernel VFS and network socket layers, enforcing path and port permissions directly on resolved kernel objects.

Why is prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) mandatory before applying Landlock rulesets?

Before calling landlock_restrict_self(), a process must set the NO_NEW_PRIVS bit via prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0). This kernel flag ensures that neither the process nor any of its future child processes can ever gain privileges (such as executing setuid/setgid binaries like su or sudo). Without NO_NEW_PRIVS, an unprivileged attacker could construct a Landlock ruleset, execute a setuid binary, and deny critical files (like /etc/shadow or security configs) to trick the privileged binary into insecure fallback branches. NO_NEW_PRIVS neutralizes this privilege escalation vector.

How does Landlock ruleset stacking and inheritance work across fork and execve?

Landlock rulesets are strictly additive and irrevocable. When a process applies a ruleset via landlock_restrict_self(), the ruleset binds to the process credentials. Upon fork() or execve(), child processes inherit the exact same security domain. If an application later creates and applies a second ruleset, Landlock creates a stack: a syscall is allowed only if it satisfies the intersection of ALL rulesets on the stack. An application can progressively narrow its attack surface (e.g. initial setup -> drop write access -> drop network access) without any possibility of relaxing previously applied restrictions.

What new security capabilities were introduced across Landlock ABI v1 through v5?

ABI v1 (Linux 5.13) provided core filesystem access rights (EXECUTE, READ_FILE, WRITE_FILE, READ_DIR, REMOVE_DIR, REMOVE_FILE, MAKE_REG, MAKE_DIR, MAKE_SYM, etc.). ABI v2 (Linux 5.19) introduced LANDLOCK_ACCESS_FS_REFER, enabling fine-grained control over linking and renaming files across parent directories. ABI v3 (Linux 6.2) added LANDLOCK_ACCESS_FS_TRUNCATE. ABI v4 (Linux 6.7) expanded Landlock beyond filesystems into the network domain with LANDLOCK_ACCESS_NET_BIND_TCP and LANDLOCK_ACCESS_NET_CONNECT_TCP. ABI v5 (Linux 6.10+) introduced LANDLOCK_ACCESS_FS_IOCTL_DEV and scoped IPC restrictions, controlling ioctl commands on character/block devices and isolating abstract UNIX sockets and signals across sandbox domains.

Linux Landlock LSM & Unprivileged Sandboxing Studio: Rulesets, ABI v1-v5 & FS/Net Isolation

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Linux Landlock LSM & Unprivileged Sandboxing Studio

Configure unprivileged self-restriction security rulesets: model filesystem masks, TCP network confinement, kernel ABI feature detection, and test syscall verdicts.

ABI v5 Supported NO_NEW_PRIVS Enforced

15 Flags

Filesystem Access Mask Coverage

443 / 8080

Allowed Network Socket Access

4 Paths

Configured Path Rules

< 150 ns

LSM Hook Evaluation Overhead

1. Landlock Ruleset & ABI Target Configuration

Target Kernel ABI Version In production, use landlock_create_ruleset flags to query runtime host ABI and gracefully downgrade bitmasks.

Execution Profile Template

Handled Filesystem Access Rights (Bitmask)

Handled Network Access Rights (ABI v4+)

2. Whitelisted Paths & Ports (Exception Hierarchy)

Path Allow-List (VFS Inodes)

TCP Port Allow-List (Sockets)

3. Syscall Sandbox Interceptor & Policy Verifier

Test arbitrary system call attempts against the active Landlock ruleset to verify allow/denied enforcement and kernel error code emissions.

Click "Execute Syscall" to evaluate kernel permission check.

4. Generated Production Sandbox Implementation

// Generated Landlock ruleset code

Linux Landlock LSM & Unprivileged Sandboxing Studio

1. Landlock Ruleset & ABI Target Configuration

Handled Filesystem Access Rights (Bitmask)

Handled Network Access Rights (ABI v4+)

2. Whitelisted Paths & Ports (Exception Hierarchy)

Path Allow-List (VFS Inodes)

TCP Port Allow-List (Sockets)

3. Syscall Sandbox Interceptor & Policy Verifier

4. Generated Production Sandbox Implementation

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