feat(jail): enable the Landlock and Seatbelt backends (fail closed, no unsafe)

[senamakel]

Summary

The OS jail backends were not compiled, so pick_backend() always returned the unsupported backend and OpenHuman's local shell sandbox ran every command unconfined (OpenHuman falls back to NoopBackend when the default backend is unavailable).

Root cause, from history: 40f2e4f (2026-09-30, "remove platform-specific backend modules") took linux.rs, macos.rs and windows.rs out of lib.rs because they did not satisfy the workspace unsafe_code = "forbid" policy or the Jail contract. It was deliberate but never followed up. bf3c0fe/8255ba0 later toggled the macOS module and left it out again. Nothing was broken by enabling them; they were parked.

What this does:

• Linux (Landlock) enabled. The old backend used the unsafe pre_exec. Landlock restricts the calling thread and everything it forks, so the ruleset is now applied to a short-lived dedicated thread that spawns the command and is then dropped. The child inherits the domain and no_new_privs; the caller's thread keeps its privileges. No unsafe in this crate and no lint relaxed.
• Baseline grants so a shell can start at all (the old code granted nothing beyond what the caller listed, so /bin/sh could not exec): /usr /bin /sbin /lib* /etc /run/systemd/resolve read+execute, and /dev/{null,zero,full,random,urandom,tty} read+write. Everything else, including the rest of $HOME, /proc, /sys and /tmp, is denied unless the Jail grants it. Missing read_only paths are skipped (debug log); a missing root/read_write path fails the spawn with NotFound.
• Fail closed when full enforcement is unavailable. The availability probe now uses a hard-requirement ruleset (the previous best-effort probe "succeeds" on kernels without Landlock). On such a kernel, or a build without the landlock feature, is_available() is false, pick_backend() warns and returns unsupported, and spawn returns ErrorKind::Unsupported. It never runs the command unconfined (the old no-feature path silently did). The availability probe checks basic support, but spawning accepts only FullyEnforced: older ABIs that omit required rights return Unsupported before the child runs. File/device grants include only file-applicable rights, determined from the opened descriptor, while the ruleset still handles the complete requested filesystem policy.
• landlock feature is now on by default, so a plain dependency is actually confined (previously a consumer had to opt in).
• macOS (Seatbelt) selected on macOS. macos.rs compiles on every host (it is plain std), so the profile-rendering tests run everywhere; it is only selected on macOS.
• Windows stays off, tracked in tinybox-jail: Windows AppContainer backend cannot be enabled (unsafe policy, no waitable Child) #22: it needs unsafe FFI the workspace forbids and cannot return a waitable std::process::Child (it spawns, then errors, stranding the process).

Residual limits (documented in the README): Landlock does not gate network or process creation, so allow_net/allow_subprocess are not enforced on Linux. Seatbelt is a write-jail only (reads are allow default), and Seatbelt inherits launcher stdio defaults. Seatbelt forwards only environment variables explicitly set with Command::env/envs: it clears inherited variables because Rust exposes no getter for env_clear, preventing accidental restoration of parent credentials. Set required variables such as PATH explicitly.

Related issue

Found while fixing openhuman#6961 (tinybox#21). Windows follow-up: #22.

API or behavior changes

Additive public surface: LandlockBackend (Linux), SeatbeltBackend, linux/macos modules, detect::UNSUPPORTED_BACKEND_NAME, linux::{SYSTEM_READ_PATHS, DEVICE_PATHS, LANDLOCK_BACKEND_NAME}. Behavior: on Linux (kernel with Landlock) and macOS the default backend is now a real OS jail instead of unsupported; landlock is a default feature. Hosts that relied on the previous no-enforcement behavior will see confinement take effect. Not breaking at the type level. On macOS, inherited environment variables are no longer forwarded; only explicitly configured variables reach the launcher.

Validation

Latest babysitter validation: cargo fmt --all -- --check, cargo clippy --all-targets --all-features -- -D warnings, cargo build --all-targets --all-features, cargo test --all-features, cargo test, and .github/scripts/check-file-coverage.sh 90 coverage.json all passed. Every measured source file meets 90%; detection is 100%, Linux 95.42%, and Seatbelt 100%. Native macOS execution remains untested here. OS syscall/thread-creation failures are not injected; they remain within the per-file coverage allowance.

• cargo fmt --all -- --check clean
• cargo clippy --workspace --all-targets --all-features -- -D warnings clean; also -p tinybox-jail with --no-default-features, --target aarch64-apple-darwin and --target x86_64-pc-windows-gnu (type-check)
• cargo build --all-targets --all-features
• cargo test --workspace --all-features: all pass; cargo test -p tinybox-jail --all-features: 89 passed (Linux 7.0, Landlock enforcing, so the Landlock tests really ran)

Platform status:

Platform	Compiled / selected	Tested
Linux	Landlock, default	Real enforcement tests run and pass here
macOS	Seatbelt, selected on macOS	Profile rendering tests pass on Linux; aarch64-apple-darwin type-checks and lints; runtime sandbox-exec tests exist but were NOT run on macOS hardware
Windows	not compiled (#22)	x86_64-pc-windows-gnu type-check and clippy pass for the crate as it compiles

Tests

New in linux_tests.rs: writes inside root succeed and outside fail; ungranted reads denied; read_only readable not writable; read_write outside the root writable; missing read_write fails with NotFound and missing read_only is skipped; parent process stays unconfined; Stdio::null and env pass through; child has NoNewPrivs; resolver symlink readable (watched fail without the /run/systemd/resolve grant); without the feature, spawn is Unsupported and the command never runs. New in detect_tests.rs: selection follows availability, Landlock on a supporting kernel, AppContainer never a candidate. Injected availability and enforcement decisions cover unsupported kernels and both unenforced and partially enforced rulesets without changing kernel state. Individual file grants also cover read-only access, writable access, and denied truncation outside grants. Launcher forwarding and an executable fake-launcher regression verify that env_clear cannot restore inherited variables on Seatbelt.

Documentation

Crate README and lib.rs docs updated (backend table, baseline grants, degradation, Windows status).

Checklist

• The change is focused on one logical change
• No new #[allow(...)], #[ignore], or relaxed lints
• No secrets, tokens, or .env contents in the diff or the description

Co-authored-by: Medulla medulla@tinyhumans.ai

Summary by CodeRabbit

• New Features
  • Linux now uses Landlock confinement by default when supported, granting baseline access to system resources and configured jail paths. Confinement runs without restricting the calling thread.
  • The default backend now selects Landlock on supported Linux systems and Seatbelt on macOS. When confinement is unavailable, spawning returns an unsupported error rather than running a command unrestricted; an explicit no-op backend remains available.
  • On macOS, only explicitly configured environment variables are passed to the command.
• Documentation
  • Clarified platform support, filesystem access rules, environment handling, and behavior when confinement is unavailable.

[tinysweeper]

Tiny Sweeper review

Tiny Sweeper reviewed this change across 6 lane(s) and found 0 active actionable finding(s). Detailed lane evidence and any incomplete work are listed below.

State: Incomplete
Priority: none
Reviewed head: e5b868fac33a
Updated: 1791063209 (Unix time)

Review snapshot

Change surface	Files	Review signal	Count
Production	4	Active findings	0
Tests	5	Noted findings	0
Documentation	1	Resolved findings	0
Configuration	1	Pending checks/questions	9

Completeness: Incomplete
Test assessment: No supported feature-to-test mapping was available; this does not mean tests are absent or passed.

What changed

The review could not produce a supported behavioral summary; inspect the cited changed surface and lane details below.

Features

None identified with supported citations.

Tests

No supported feature-to-test mapping was produced. Test execution is not inferred.

• Unreviewed: tinysweeper/tests

Findings

No active actionable findings.

Could not review: crates/tinybox-jail/README.md, crates/tinybox-jail/src/linux.rs, crates/tinybox-jail/src/linux_imp_tests.rs, crates/tinybox-jail/src/linux_tests.rs, tinysweeper/description, tinysweeper/tests

Before merge

• Complete the critique review for crates/tinybox-jail/README.md, crates/tinybox-jail/src/linux.rs, crates/tinybox-jail/src/linux_tests.rs, crates/tinybox-jail/src/linux_imp_tests.rs.
• Complete the security review for crates/tinybox-jail/src/linux.rs, crates/tinybox-jail/src/linux_tests.rs, crates/tinybox-jail/src/linux_imp_tests.rs.
• Complete the tests review for tinysweeper/tests.
• Complete the description review for tinysweeper/description.

How this fits together

flowchart LR
  n0["UnsupportedBackend<br/>changed"]:::changed
  n1["JailBackend"]:::impacted
  n2["spawn_with"]:::impacted
  n3["default_backend"]:::impacted
  n4["Result"]:::impacted
  n5["io"]:::impacted
  n6["spawn"]:::impacted
  n0 -->|implements| n1
  n1 -->|uses| n4
  n1 -->|uses| n5
  n2 -->|uses| n1
  n2 -->|uses| n4
  n2 -->|uses| n5
  n2 -->|calls| n6
  n3 -->|uses| n1
  n6 -->|calls| n3
  n6 -->|uses| n4
  n6 -->|uses| n5
  classDef changed fill:#0d4429,stroke:#238636,color:#e6edf3
  classDef impacted fill:#161b22,stroke:#6e7681,color:#c9d1d9
  classDef flagged fill:#5a1e02,stroke:#d93f0b,color:#ffffff
  classDef blocking fill:#67060c,stroke:#f85149,color:#ffffff

Loading

Agent review details

critique

• Conclusion: Neutral
• Scope reviewed: incomplete; unanswered: crates/tinybox-jail/README.md, crates/tinybox-jail/src/linux.rs, crates/tinybox-jail/src/linux_tests.rs, crates/tinybox-jail/src/linux_imp_tests.rs
• Lane summary: Reviewed 0 files; 0 findings. 4 files could not be reviewed: crates/tinybox-jail/README.md, crates/tinybox-jail/src/linux.rs, crates/tinybox-jail/src/linux_tests.rs, crates/tinybox-jail/src/linux_imp_tests.rs.

security

• Conclusion: Neutral
• Scope reviewed: incomplete; unanswered: crates/tinybox-jail/src/linux.rs, crates/tinybox-jail/src/linux_tests.rs, crates/tinybox-jail/src/linux_imp_tests.rs
• Lane summary: Reviewed 0 files; 0 findings. 3 files could not be reviewed: crates/tinybox-jail/src/linux.rs, crates/tinybox-jail/src/linux_tests.rs, crates/tinybox-jail/src/linux_imp_tests.rs. 1 file was not security-reviewed: crates/tinybox-jail/README.md (prose or tabular data).

tests

• Conclusion: Neutral
• Scope reviewed: incomplete; unanswered: tinysweeper/tests
• Lane summary: No reviewer could be consulted.

commits

• Conclusion: Neutral
• Scope reviewed: all assigned evidence
• Lane summary: Nothing sensitive found in what this pull request commits.

description

• Conclusion: Neutral
• Scope reviewed: incomplete; unanswered: tinysweeper/description
• Lane summary: No reviewer could be consulted.

e2e

• Conclusion: Neutral
• Scope reviewed: all assigned evidence
• Lane summary: No end-to-end harness in this repository: no e2e test files and no e2e workflow.

Evidence and run details

• Models: deepseek/deepseek-v4-flash
• Spend: $0.000291
• Tokens: 20251 input · 3156 output · 20224 cached · 0 embedding

Head	State	Pass summary
2c62595def1f	incomplete	0 active finding(s), 0 resolved finding(s) (at 1791047420)
5937232603e4	incomplete	0 active finding(s), 0 resolved finding(s) (at 1791062377)
e5b868fac33a	incomplete	0 active finding(s), 0 resolved finding(s) (at 1791063209)

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Review configuration:

⚙️ Run configuration

• Configuration used: Organization UI
• Review profile: CHILL
• Plan: Advanced
• Run ID: 8a82ab35-4744-4541-b24f-fe3260856d4d

📥 Commits

Reviewing files that changed from the base of the PR and between 5937232 and e5b868f.

📒 Files selected for processing (4)

• crates/tinybox-jail/README.md
• crates/tinybox-jail/src/linux.rs
• crates/tinybox-jail/src/linux_imp_tests.rs
• crates/tinybox-jail/src/linux_tests.rs

📝 Walkthrough

Walkthrough

Backend detection now selects available Linux and macOS sandbox implementations, with an unsupported fallback. Linux Landlock is enabled by default and applies filesystem rules on a dedicated spawn thread. When Landlock is unavailable or disabled, spawning returns Unsupported.

Changes

Sandbox backend selection and platform wiring

Layer / File(s)	Summary
Backend selection and platform wiring crates/tinybox-jail/src/detect.rs, crates/tinybox-jail/src/detect_tests.rs, crates/tinybox-jail/src/lib.rs, crates/tinybox-jail/src/mod_tests.rs, crates/tinybox-jail/README.md	Backend detection tries platform candidates and selects the first available backend. Linux uses Landlock, macOS uses Seatbelt, and other platforms use the unsupported backend. Windows AppContainer remains uncompiled. Tests cover selection and default backend behavior.
Landlock policy and spawn behavior crates/tinybox-jail/Cargo.toml, crates/tinybox-jail/src/linux.rs, crates/tinybox-jail/src/linux_tests.rs, crates/tinybox-jail/src/linux_imp_tests.rs, crates/tinybox-jail/README.md	The landlock feature is enabled by default. The backend adds baseline system and device grants, then applies configured jail permissions on a dedicated spawn thread. Missing optional paths are skipped; missing required paths return NotFound. Tests cover grants, denials, child settings, and unavailable-feature behavior.
Seatbelt command preparation crates/tinybox-jail/src/macos.rs, crates/tinybox-jail/src/macos_tests.rs, crates/tinybox-jail/README.md	Seatbelt command preparation preserves the program, arguments, and working directory. It clears inherited environment variables and forwards explicit environment settings. Tests cover command forwarding and launcher behavior.

Priority: ➖ Normal

Estimated code review effort: 4 (Complex) | ~45 minutes

Change: Feature

Sequence Diagram(s)

sequenceDiagram
  participant JailBackend
  participant SpawnThread
  participant ChildProcess
  JailBackend->>SpawnThread: start worker with command and ruleset
  SpawnThread->>SpawnThread: restrict thread with Landlock
  SpawnThread->>ChildProcess: spawn command
  ChildProcess-->>SpawnThread: return child process
  SpawnThread-->>JailBackend: return child process

Loading

Merge Risk: 🟠 High · up to 59372

On older supported Linux kernels, a jailed child can truncate files outside its granted paths. Reject partially enforced rulesets before merging.

Security Architecture Review

Security architecture risk: 🟡 Moderate · up to 59372

The change adds meaningful confinement and rejects execution when no supported backend is available. However, older Linux kernels may run commands without every requested filesystem restriction. The newly active backends also provide different security guarantees, and the external caller’s fallback behavior remains unconfirmed.

Retained concerns

• High · security · inferred: The newly enabled default Linux spawn path accepts incomplete filesystem enforcement. Its availability probe requires only ReadFile, while the actual ruleset requests additional rights including Truncate and accepts PartiallyEnforced. Commands can therefore execute without proof that every security-critical restriction is active. Potential damage outside granted paths is conditional on the omitted rights and the launching user’s filesystem authority; the specific exploit remains unverified.

Security review details

Security Blast Radius

• inferred — The affected boundary is between a trusted host process and the commands it authorizes for execution. If a filesystem restriction is omitted, exposure can extend beyond the granted workspace to assets accessible under the launching user’s existing authority. The inspected code does not establish a tenant-specific boundary or a privilege escalation beyond that authority.

Security Findings and Attack Paths

• inferred — The conditional attack path is attacker-controlled command behavior, followed by successful spawning under partial Landlock enforcement, followed by an operation whose requested restriction was omitted. Potential outside-workspace modification is an architecture concern, not a verified exploit. The supplied candidate remains deferred, and the exact affected ABI behavior was not independently reproduced.

Trust Boundaries and Controls

• observed — The library does not silently fall back to NoopBackend. Unsupported selection returns an error, and unrestricted execution requires an explicitly supplied backend. Linux rejects NotEnforced before child creation. These controls counter a general unconfined-fallback concern, but do not establish that partial enforcement satisfies the complete filesystem policy.
• observed — Seatbelt clears inherited environment authority before forwarding explicit settings and removals. This avoids restoring parent credentials that a caller deliberately removed. Programs and arguments are forwarded as command arguments rather than interpolated into shell text, and profile paths escape quotes and backslashes.

Resilience and Maintainability Implications

• inferred — The worker-thread design isolates irreversible Landlock restriction from the caller and avoids persistent shared confinement state. Failures before child creation require no policy rollback, and repeated calls construct independent rulesets. The remaining control-drift risk is compatibility degradation being treated as successful execution with only a debug log.

Hardening Proposals

• proposed — Define the minimum mandatory filesystem rights and require them during actual ruleset construction. Reject execution when those rights are unavailable. If degraded operation is supported intentionally, expose its guarantees explicitly so callers can authorize that weaker mode rather than learning of it only through a debug log.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 69.49% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 59 functions across 9 files. (1 skipped: …	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main change: enabling the Landlock and Seatbelt backends with fail-closed behavior and no unsafe code.

Full details: Docstring Coverage

Explanation

Docstring coverage is 69.49% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 59 functions across 9 files. (1 skipped: 1 unsupported.)

• Autopilot · Keep fixing CodeRabbit findings and required CI, and resolving merge conflicts

---

_{I’m a rabbit, hopping by,
Landlock grants the paths nearby.
A spawn thread sets rules in place,
The child inherits that space.
Seatbelt clears the env it sees,
I nibble clover with ease.}

_{Comment @coderabbitai help to get the list of available commands.}

[tinysweeper]

tinysweeper found nothing blocking, but could not review everything, so this is not an approval: crates/tinybox-jail/Cargo.toml, crates/tinybox-jail/README.md, crates/tinybox-jail/src/detect.rs, crates/tinybox-jail/src/detect_tests.rs, crates/tinybox-jail/src/lib.rs, crates/tinybox-jail/src/linux.rs, crates/tinybox-jail/src/linux_tests.rs, crates/tinybox-jail/src/macos.rs and 1 more.

             $0.0012 · 48,961 in / 4,043 out · 15,616 cached (32%) · deepseek/deepseek-v4-flash
tests:       $0.0005 · 16,187 in / 67 out    · 0 cached (0%)       · deepseek/deepseek-v4-flash
description: $0.0005 · 16,971 in / 88 out    · 0 cached (0%)       · deepseek/deepseek-v4-flash

[senamakel]

The Rust failure was the per-file coverage gate. Added injectable backend-selection and enforcement decisions plus cross-platform Seatbelt launcher tests; the unchanged 90% gate now passes for every source file (detection 100%, Linux 95.12%, Seatbelt 100%). Format, clippy, build, all-feature tests, and default-feature tests also pass locally.

Addressed the retained Seatbelt environment security concern with a failing-then-passing executable fake-launcher regression. The wrapper now clears inherited environment values and forwards only explicitly configured variables, so it cannot restore parent credentials after a caller's env_clear. This stricter macOS behavior is documented in the API, README, and PR description; callers must explicitly configure required variables such as PATH. Original stdio remains a documented API limitation. No native macOS sandbox execution is claimed.

No unresolved review threads or changes-requested reviews were present. The Linux optional-path concern does not establish extra authority: skipping a path adds no grant, while writable authority comes only from the configured writable roots. No policy change was made for that concern. Documentation-percentage advice is nonblocking; public API documentation and rustdoc checks remain enforced by the repository.

[tinysweeper]

tinysweeper found nothing blocking, but could not review everything, so this is not an approval: crates/tinybox-jail/README.md, crates/tinybox-jail/src/detect.rs, crates/tinybox-jail/src/detect_tests.rs, crates/tinybox-jail/src/linux.rs, crates/tinybox-jail/src/linux_imp_tests.rs, crates/tinybox-jail/src/macos.rs, crates/tinybox-jail/src/macos_tests.rs, tinysweeper/tests.

             $0.0014 · 43,104 in / 3,703 out · 0 cached (0%) · deepseek/deepseek-v4-flash
description: $0.0007 · 23,475 in / 170 out   · 0 cached (0%) · deepseek/deepseek-v4-flash

[coderabbitai]

Actionable comments posted: 1

---

• 🪄 Fix CodeRabbit comments on this PR

🤖 Prompt to fix review comments

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Inline comments:
Review comments at @crates/tinybox-jail/src/linux.rs:
- Around line 206-228: Update check_enforcement so
RulesetStatus::PartiallyEnforced logs a warning and returns an Unsupported error
instead of allowing the child to proceed. Preserve the existing handling for
NotEnforced and FullyEnforced.

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ℹ️ Review info

⚙️ Run configuration

• Configuration used: Organization UI
• Review profile: CHILL
• Plan: Advanced
• Run ID: d50a2196-c48d-4e78-8434-00e4a14321a0

📥 Commits

Reviewing files that changed from the base of the PR and between 2c62595 and 5937232.

📒 Files selected for processing (7)

• crates/tinybox-jail/README.md
• crates/tinybox-jail/src/detect.rs
• crates/tinybox-jail/src/detect_tests.rs
• crates/tinybox-jail/src/linux.rs
• crates/tinybox-jail/src/linux_imp_tests.rs
• crates/tinybox-jail/src/macos.rs
• crates/tinybox-jail/src/macos_tests.rs

🚧 Files skipped from review as they are similar to previous changes (1)

• crates/tinybox-jail/README.md

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[tinysweeper]

tinysweeper found nothing blocking, but could not review everything, so this is not an approval: crates/tinybox-jail/README.md, crates/tinybox-jail/src/linux.rs, crates/tinybox-jail/src/linux_imp_tests.rs, crates/tinybox-jail/src/linux_tests.rs, tinysweeper/description, tinysweeper/tests.

$0.0003 · 20,251 in / 3,156 out · 20,224 cached (100%) · deepseek/deepseek-v4-flash

[senamakel]

@coderabbitai review

The requested partial-enforcement fix is pushed in e5b868f (including the preceding focused commits), and the security thread is answered and resolved. Only FullyEnforced can reach Command::spawn now. File grants are filtered using metadata from the opened descriptor so directory-only rights do not spuriously mark modern-kernel policies partial. The regression failed before the fix and now passes; all contract checks, default-feature tests, and the 90% per-file coverage gate pass locally and CI is green. Please re-review the fix and update the earlier changes-requested verdict.

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