ducoterra
03ab9c0cb1
A single bash script that runs a coding harness (pi by default) inside a rootless Ubuntu 24.04 container with only the current directory mounted at /project, an explicit egress allowlist and an explicit environment: nothing is passed in that was not named on the command line or in a config file. Network enforcement here is empirical rather than assumed (tests/spike_network.sh, docs/networking.md). The original design -- a sidecar proxy on an internal network -- does not work rootless on this host, so allow mode runs pasta with --map-host-loopback, installs an inet aisb ruleset inside the container that drops every egress path except the gate's, and relays through a squid gate bound to the host's loopback that resolves names itself and refuses anything unlisted. The entrypoint checks that the default-drop rule really exists before setpriv drops to uid 1000 with an empty capability set, and exits 77/78 rather than run unenforced. The Containerfile, the entrypoint, the squid config generator and the ruleset renderer all live in bin/ai-sandbox, and the image is tagged by content hash, so a policy change can never silently reuse a stale image. Tests are pure bash: 161 assertions start no container and touch no network, 256 run real ones, including proof that a raw socket, a stripped proxy env and DNS all stay blocked while an allowlisted host works over both http and CONNECT. LLM-Generated: true
84 lines
5.2 KiB
Markdown
84 lines
5.2 KiB
Markdown
# PLAN
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Execution plan for `ai-sandbox`, with the state each phase leaves behind.
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Every phase ends with a gate that must pass before the next one starts.
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Status as of this writing: **phases 1-7 complete**, follow-ups listed at the end.
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| # | Phase | Gate | Status |
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|---|-------|------|--------|
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| 0 | Measure the host before designing | `tests/spike_network.sh` results recorded in `docs/networking.md` | ✅ done — killed the sidecar-on-internal-network design, found `pasta --map-host-loopback` + in-container nftables |
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| 1 | Skeleton: CLI, config, preview modes | `make test` (args, config, precedence) | ✅ done |
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| 2 | Image build | build, cache, content-hash tag, contents asserted | ✅ done (`tests/e2e/10_image.sh`) |
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| 3 | Enforcement in the container | generated ruleset shape + real-container capability checks | ✅ done (`tests/unit/06_entrypoint.sh`, `tests/e2e/11_net.sh`) |
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| 4 | Egress gate | allowlisted host reachable, everything else refused, gate lifecycle | ✅ done (`tests/e2e/11_net.sh`) |
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| 5 | Environment passing | deny-by-default, `0600` delivery, redaction, fail-closed on unset | ✅ done (`tests/unit/04_env.sh`, `tests/e2e/12_sandbox.sh`) |
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| 6 | Limits, lifecycle, observability | exit codes, cleanup, caps, session log, `--keep` | ✅ done (`tests/e2e/12_sandbox.sh`) |
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| 7 | Harness defaults, docs, portability sweep | alias UX, README/threat model, shellcheck clean, no personal paths | ✅ done |
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## Phase detail
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### 0 — Measure first (this is why the design looks unusual)
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Ran `tests/spike_network.sh`. Three results decided the architecture:
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containers on one user-defined network cannot talk to each other rootless here
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(so no sidecar proxy on an internal network); `--network=host` works rootless and
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has internet (so a host-loopback gate is possible); `pasta:--map-host-loopback,<addr>`
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makes a container's connection to `<addr>` land on the host's loopback; and
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`--cap-add=NET_ADMIN` lets root *inside* the container install nftables that
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genuinely gate the pasta path. Also learned bind mounts need `:z` under SELinux.
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### 1 — Skeleton
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`parse_args` with the alias-friendly rule (sandbox flags until the first
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positional/unknown flag; those become arguments to the harness; `--` replaces the
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command), config files at two levels, `AISB_*` overrides, `--dry-run` /
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`--print-policy` / `--print-entrypoint` / `--print-containerfile`.
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Precedence is built-in < config file < env < flag, and the built-in defaults live
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only in `resolve_opts()` — materialising them at the top of the script silently
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made the environment beat config files, which is a bug worth remembering.
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### 2 — Image
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Generated Containerfile, tag = content hash of base image + versions + install
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list + entrypoint + Containerfile itself, so a policy change never reuses a stale
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image and variants coexist. Node tarballs are checksum-verified against
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nodejs.org. `pi` is baked in so the `pi` alias works after one build.
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### 3 — Enforcement
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`entrypoint_script()`: read policy → render `inet aisb` with `policy drop` →
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`nft -f` → verify the default-drop rule exists → `setpriv` drop to uid 1000 with
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`--inh-caps=-all --bounding-set=-all --no-new-privs`. Refuses to start (77/78)
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rather than run unenforced.
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### 4 — Gate
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Per-session squid container on `--network=host`, bound to `127.0.0.1:<free port>`,
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config generated and bind-mounted read-only, `http_access deny all` last.
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Sandbox gets proxy env + a ruleset that allows nothing else out. Torn down with
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the session unless `gate up` created a named one.
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### 5-7 — Environment, lifecycle, polish
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`0600` env file delivery and redaction everywhere; limits and caps asserted from
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inside; `--keep` leaves the container *and* the session dir for forensics;
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`clean` reaps (`--all` for running ones, `--volumes[=GLOB]` for unused home caches,
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never a volume a container still references); `doctor` verifies the host including a
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real bind/uid round-trip; docs; shellcheck-clean in a container.
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`/home/sandbox` is a named volume so npm and tool caches survive between runs. It
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outlives the image, which is the one kind of staleness this design cannot hash away:
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change the image's home layout and existing volumes keep the old files, so
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`ensure_home_volume()` creates it labelled and `clean --volumes` is the documented way
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to drop it.
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## Follow-ups (not yet done)
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* **`--net unix` mode**: `--network=none` plus a unix-socket proxy and an in-container
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TCP→socket forwarder. Structurally stronger (no IP stack at all); needs a story
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for tools that resolve names themselves.
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* **Re-resolve `--no-gate` domains** on a timer, or resolve through the gate and pin
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the returned answers, so long-running sessions do not go stale against CDNs.
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* **Idle gate reaping** beyond `clean`: a `--gate-ttl` label check on start.
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* **`--allow-from-lockfile`**: derive a first-cut allowlist from
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`package.json`/`requirements.txt` registries so the first run is not a blank page.
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* **Quarantine mode for untrusted repos**: `--net none` + read-only mount +
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`--ephemeral-home` as a single flag, plus a warning if `.git` hooks exist.
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* **`--record`**: optional pcap/CONNECT-log capture of a session for review.
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* **`--mount` for agent skills/plugins**: first-class flag instead of a generic mount.
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* Packaging: a `quadlet`/systemd unit for a long-lived named gate.
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