docs: the restricted tier — README, design doc, plan doc with measured results (#74)
The plan doc records what was measured and why each decision fell where it did: the private bridge is worse than unhardened (a live NAT bridge with IPv6 on), incus-user blocks snapshots, no daemon-level template exists (read in incus-user's source), widening survives re-sync (same source, then measured live). box-design gains the access-tiers section — including why narrowing to boxnet-only is the load-bearing decision and why the nft bridge drop is the layer a restricted user cannot strip. RUNS.md logs MU-1..3. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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28
CHANGELOG.md
28
CHANGELOG.md
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@ -7,6 +7,28 @@ which records not just what changed but what each drill run proved.
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### Added
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- **The restricted tier: multi-user hosts** (#74, redesigning #72) — an admin
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runs `box grant <user>` and that user gets their own boxes on the same
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hardened `boxnet`, seeing nobody else's; `box revoke <user>` takes it back
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(`--purge` deletes their world, and asserts the absence). The tier rides
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incus-user, whose defaults miss box's contract three measured ways (Debian
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13 / Incus 6.0.4): a private *unhardened* NAT bridge per user, snapshots
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blocked, the `box-net` profile invisible — so grant is an idempotent
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convergence: project narrowed to `boxnet` **and only boxnet** (listing the
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private bridge too, the obvious fix, would keep an unhardened network one
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`--network` flag away), snapshots allowed, the shipped profile installed
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into their project. `box_tier()` (live credentials, argless `id -nG`)
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drives the tier-aware surface: `expose` refuses honestly before any daemon
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call, `setup-host` and `doctor` answer at the caller's tier. Rehearsed
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end-to-end by `drill/multiuser.sh` (criteria a–l: confinement, lifecycle,
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cross-user visibility, name collisions, the in-box isolation contract,
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escape hatches, re-sync survival, revoke) — 41/41 on the design host, in
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both container and VM mode.
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- **CI runs the multi-user rehearsal on a real Incus** — a second `rehearsal`
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job stands up the full stack on the runner (setup-host, doctor, then
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`multiuser.sh --container`), so every PR proves the tier's semantics
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against a live daemon, not a mock. The VM trust boundary itself remains a
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real-hardware ritual, like the full drill.
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- **Global / root install** (#71) — run as root, box installs *once* to
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`/opt/box` (world-readable) with the `box` symlink on `/usr/local/bin`, so
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every operator on a shared host runs the same tree. Per-user installs are
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@ -24,6 +46,12 @@ which records not just what changed but what each drill run proved.
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### Fixed
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- **`box restore` never worked against Incus 6** — the command table
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dispatched `incus restore`, a subcommand that does not exist (Incus 6
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spells it `incus snapshot restore`), so every restore died on "unknown
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command". Found by #74's rehearsal exercising the full lifecycle as a
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restricted user; fixed for every tier, and the rehearsal + a grep-guard in
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`test/cli.sh` now hold it.
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- **`box tmux` works on every template** (#65) — `box tmux` runs
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`tmux new-session` *inside* the box, but the templates did not install tmux, so
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it failed with `tmux: command not found`. `tmux` is now in each template's
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43
README.md
43
README.md
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@ -106,6 +106,49 @@ re-homes each legacy box onto `boxnet` (authed state preserved), and
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`box migrate-host --retire-legacy` removes the old bridge and profile once no
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legacy box remains.
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## Multi-user hosts: the restricted tier
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One host, several people, and not everyone should hold the daemon. Incus's
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socket is all-or-nothing — `incus-admin` group members own every instance on
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the machine — so box layers a second tier on
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[incus-user](https://linuxcontainers.org/incus/docs/main/projects/):
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| tier | who | what they hold |
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|---|---|---|
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| **admin** | root, or the `incus-admin` group | everything: all boxes, the stack, `setup-host`, `expose`, `grant` |
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| **restricted** | the `incus` group | their **own** boxes only, on the same hardened network |
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| none | everyone else | no socket, nothing |
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An admin hands the tier out per user, and takes it back:
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```sh
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box grant dev1 # dev1 can now: box new / list / shell / snapshot / rm — their boxes only
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box revoke dev1 # locked out; their boxes survive (grant again restores)
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box revoke dev1 --purge # ...or delete everything they had
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```
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`grant` is an idempotent convergence, not a flag flip, because incus-user's
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defaults miss box's contract three ways (measured on Debian 13 / Incus 6.0.4,
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see [the plan doc](docs/plans/2026-07-18-restricted-tier.md)): it pins each
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user to a private *unhardened* NAT bridge, it blocks snapshots, and it cannot
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see the `box-net` profile. Granting rewires all three: the user's project is
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restricted to `boxnet` **and only boxnet** — the hardened network is not their
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default placement but the only one their certificate can express — snapshots
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are allowed, and the shipped profile is installed into their project. Re-run
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`box grant <user>` after upgrading box to refresh the profile, like
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`setup-host` for the stack.
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What a restricted user gets is the full contract: same ACL, same DNS
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isolation, same pinned resolver, same port isolation, same box↔box drop —
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and their boxes cannot reach another user's box, which is the same
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box↔box drop doing its one job. What they can't do stays honest: `box
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expose` (daemon-global state) says to ask an admin, `box setup-host` and
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`box doctor` answer at their tier instead of failing at it.
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`drill/multiuser.sh` rehearses all of it live — two users, real grants, real
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boxes, probes from inside — and CI runs it on every PR (container mode; the
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VM boundary itself is proven on real hardware, like the rest of the drill).
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## Quick start
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```sh
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@ -127,7 +127,58 @@ The rule that keeps this honest: **isolation claims are tested, never reasoned
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about.** The box→box hole existed because a plausible code reading said it could
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not. See `drill/RUNS.md`.
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## Multi-user hosts: access tiers
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The daemon socket is binary — `incus-admin` holds everything on the machine —
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so a shared host needs a second tier, and Incus ships one: **incus-user**
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confines an `incus`-group member to an auto-created project `user-<uid>`,
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behind a restricted certificate that cannot name any other project. The tier
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is decided once, from the process's live credentials (`box_tier()`: UID 0 or
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`incus-admin` → admin; `incus` alone → restricted; neither → none), and every
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tier-aware verb reads that one function.
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What incus-user does *not* do is honor box's contract — measured on Debian 13
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/ Incus 6.0.4 (#74), after the design that assumed it (#72) was vetoed by its
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own Task-0 rehearsal:
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- it pins each user's project to a private auto-created bridge
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(`incusbr-<uid>`) — a stock NAT bridge with **none** of the hardening: no
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ACL, no `dns.mode=none`, no resolver pin, IPv6 on;
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- it blocks snapshots — box's entire reuse workflow;
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- the `box-net` profile lives in the default project, invisible to theirs.
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So the tier is an **admin-run convergence** (`box grant <user>`), not a
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group membership: put them in `incus`, touch incus-user once as them (the
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project is created lazily; nothing exists to converge until it does), then
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rewire the project — network access narrowed to `boxnet` **and only
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`boxnet`**, snapshots allowed, the shipped profile installed. Narrowing is
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the load-bearing decision: granting `boxnet,incusbr-<uid>` (the obvious fix)
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would leave an unhardened NAT bridge one `--network` flag away from any box
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they mint. With the private bridge unreferenced (its `eth0` is removed from
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their default profile) and outside `restricted.networks.access`, the hardened
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network is not their default placement — it is the only placement their
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certificate can express. The grant survives incus-user restarts by that
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tool's own design (it configures a project only at creation), and a restricted
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certificate cannot widen its own project — both measured, not read.
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Cross-USER isolation is the same mechanism as cross-box isolation, on
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purpose: their instances share `boxnet` with everyone's, and the bridge-family
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drop + port isolation + `dns.mode=none` already make any two boxes strangers.
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A restricted user CAN strip `security.port_isolation` from the profile copy
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in their own project — which is why the nft bridge drop, which they cannot
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touch, exists as the second, host-owned layer. Defense in depth, both layers
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measured (`drill/multiuser.sh`, criteria a–l).
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`box revoke` is two strengths: bare, it removes the group — the socket
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closes, their boxes keep *running* (revoking a person does not kill their
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workloads) and `grant` restores everything; `--purge` deletes their world
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(boxes, images, project, private bridge, trust-store certificate) and asserts
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the absence afterwards.
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## Non-goals
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- No unattended/CI bring-up — the flow is interactive.
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- Interactive-first: install and setup prompt by default (`BOX_YES=1` and the
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CI rehearsal job are the sanctioned unattended paths).
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- No credential storage or injection by the tool.
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- No per-user resource quotas on the restricted tier (Incus's
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`limits.*`/`restricted.*` project keys exist when someone needs them).
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@ -1,27 +1,128 @@
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# Restricted incus tier — implementation plan (issue #74)
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# Restricted incus tier — design and measured results (#74)
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> **Status: placeholder.** This PR is a work in progress; the design below is being
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> validated by a live multi-user rehearsal before the implementation lands. Do not
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> review yet — the PR stays in draft until the rehearsal passes.
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**Status: implemented and rehearsed.** 41/41 rehearsal criteria green on the
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design host (Debian 13 trixie, Incus 6.0.4, nested KVM), in container mode
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and VM mode. This doc records the design, what was measured, and why each
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decision fell where it did. It supersedes the vetoed #72 design
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(`docs/plans/2026-07-17-multiuser-hosts.md` on `feat/restricted-tier-wip`).
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## Scope
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## What #74 asked
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Deliver the restricted (`incus`-group) tier described in #74:
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A restricted (`incus`-group) user can `box new/list/shell/snapshot/rm` their
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own boxes, on a network carrying box's **full** isolation contract, seeing no
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one else's; the convergence is a documented, idempotent path; the rehearsal
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passes criteria (a)–(f); the admin tier is unchanged.
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- A restricted user can `box new/list/shell/snapshot/rm` **their own** boxes.
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- Their boxes ride a network carrying box's full isolation contract
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(ACL, `dns.mode=none`, resolver pin, `security.port_isolation`, nft box↔box drop).
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- No cross-user visibility. Admin tier unchanged.
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- The admin-side convergence is a documented, idempotent command — not manual
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per-user `incus project set`.
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## The three facts that shaped the design
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## Planned shape (subject to rehearsal)
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Task-0 (#72) measured one: incus-user confines users to `user-<uid>` projects
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(sound), but pins them to a private auto-created bridge `incusbr-<uid>` and
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`restricted.networks.access: incusbr-<uid>` — they cannot even see `boxnet`.
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- `box grant <user>` / `box revoke <user>` — admin convergence hook per #74
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option 1: widen `restricted.networks.access` to include `boxnet` and install
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the `box-net` profile into the user's `user-<uid>` project.
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- CLI awareness of running inside a restricted project.
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- `drill/multiuser.sh` rehearsal criteria (a)–(f) green on a real multi-user host.
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- Test suite expansion + CI wiring.
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This round measured two more:
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Tracking issue: heavy-duty/box#74.
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1. **The private bridge is worse than unhardened.** `incusbr-<uid>` is a
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fully functional NAT bridge — `ipv4.nat=true`, **`ipv6.nat=true`** — with
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no ACL, no `dns.mode=none`, no resolver pin, no port isolation, and IPv6
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egress box's contract explicitly forbids. Any instance placed on it holds
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a door to the host's LAN.
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2. **incus-user projects block snapshots** (`Project "user-<uid>" doesn't
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allow for snapshot creation`) — box's entire reuse workflow.
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And two open questions from #74, answered from incus-user's own source
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(`cmd/incus-user/server.go`, stable-6.0) and then confirmed live:
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- **Daemon-level project template?** None exists — the project config is
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hardcoded in `serverSetupUser()`. A per-user admin hook is the only path.
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- **Does widening survive a re-sync?** Yes. Setup runs only when the project
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does not exist (and early-outs when the user's certificate is already
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trusted); incus-user never rewrites an existing project. Confirmed live:
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`systemctl restart incus-user.socket` leaves the convergence intact.
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## The decision: option 1, tightened
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#74 offered (1) converge users onto the shared `boxnet` or (2) harden each
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private bridge. Option 2 multiplies every mechanism per user (ACL, resolver
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pin, dnsmasq, nft rules, firewall coexistence) and turns the shipped static
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profile into N generated ones. Option 1 keeps one hardened network and one
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shipped profile — and the existing box↔box mechanisms already make
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cross-user isolation free: the nft bridge-family drop and `dns.mode=none`
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are host/network-owned, so they bind every instance on `boxnet` no matter
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whose project it lives in.
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One tightening beyond the issue's sketch: the issue proposed
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`restricted.networks.access boxnet,incusbr-<uid>` ("must list both" — true
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as long as the default profile still references the private bridge). Listing
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both leaves fact 1's unhardened bridge one `--network` flag away, forever.
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Instead, `box grant`:
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- removes `eth0` from the project's default profile (nothing references the
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private bridge anymore, so the narrowing validates), and
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- sets `restricted.networks.access boxnet` — **only**.
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After which the hardened network is not the user's default placement but the
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only placement their certificate can express. Measured: `incus launch
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--network incusbr-<uid>` as the user → `Network not found`; the user cannot
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widen their own project (`Error: Certificate is restricted`); they cannot
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touch `boxnet`'s config or the ACL (`no permission for project "default"`).
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A restricted user CAN edit the `box-net` profile copy in their own project
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(they own project profiles — `features.profiles=true`), including stripping
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`security.port_isolation`. That is why the host-owned nft bridge drop is the
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second layer: `meta ibrname boxnet obrname boxnet drop` fires on every
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port-to-port frame regardless of per-NIC flags. Cross-user sibling probes are
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dropped either way — measured from inside the boxes.
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## What `box grant <user>` converges (idempotent, re-run to refresh)
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1. `usermod -aG incus` (not `incus-admin` — that is the tier)
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2. first-touch incus-user as the user (`runuser`/`sudo -u`, stdin pinned) —
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the project is created lazily and cannot be pre-created by an admin
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3. remove the default profile's private-bridge `eth0`
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4. `restricted.networks.access boxnet`
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5. `restricted.snapshots allow`
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6. install/refresh the shipped `box-net` profile into the project
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7. verify from the user's side of the socket
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`box revoke <user>` is the inverse, two strengths: bare = group removal (the
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socket closes; boxes keep running; re-grant restores), `--purge` = boxes,
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images, project, private bridge, trust-store certificate, incus-user state —
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then asserts the absence (the wipe.sh discipline).
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## The tier in the CLI
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`box_tier()` — UID 0 / `incus-admin` → admin, `incus` alone → restricted,
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neither → none — decided from live process credentials (argless `id -nG`),
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byte-identical in `bin/box` and `host/setup-host.sh` (diffed by a test).
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Tier-aware surface: `new` pre-flights the profile and names the right fix per
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tier; `expose` refuses before any daemon call (its plumbing is daemon-global;
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without the guard the failure is a lie — a restricted user cannot read
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boxnet's redacted config, so box_net_ip would claim their running box has no
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address); `setup-host` exits 0 with the honest note; `doctor` runs a
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restricted check-set (is the tier granted, does their box resolve/route)
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instead of judging host state they cannot see.
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Found along the way, fixed for every tier: `box restore` dispatched
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`incus restore`, which does not exist in Incus 6 (`incus snapshot restore`).
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It had never worked.
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## Rehearsal and CI
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`drill/multiuser.sh` (root, opt-in via `BOX_MULTIUSER_REHEARSAL=1`) proves
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criteria (a)–(f) from #74 plus the measured extensions (g)–(l): the in-box
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isolation contract (egress, DNS, box→host, RFC1918, cross-user sibling drop,
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name enumeration, IPv6-off), the closed escape hatches, re-sync survival, and
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scoped revoke. Two real users, real grants, real mints, probes from inside;
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`--container` for CI, VM mode on real hardware; cleanup deletes everything it
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made.
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CI gains a `rehearsal` job (ubuntu-latest): install incus, stage the checkout
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at `/opt/box` (the #71 layout), `setup-host`, `doctor`, then the rehearsal in
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container mode. The tier's semantics are proven on every PR against a live
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daemon; the VM trust boundary stays a real-hardware ritual, like the drill.
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## Environment
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Debian 13 (trixie), Incus 6.0.4, `incus-user.socket` shipped in the incus
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package (Debian 13 and Ubuntu 24.04 both), `/dev/kvm` present (VM-mode run),
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btrfs pool. Companion work: rig#24 (`box` role), rig#12/#25 (host-class).
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|
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@ -91,3 +91,27 @@ installed and runnable; authenticating is yours.
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If the host has no `/dev/kvm`, box falls back to container mode. The drill
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still runs, but it says loudly that **the VM trust boundary was not validated**
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rather than passing quietly on a weaker one.
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## The multi-user rehearsal (`multiuser.sh`)
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The restricted tier (#74) has its own rehearsal — the drill proves one
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operator's host; this proves a *shared* one:
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```sh
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sudo BOX_MULTIUSER_REHEARSAL=1 bash drill/multiuser.sh --yes
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```
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Root only, opt-in twice (it creates system users and edits the group
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database). It creates two throwaway users, grants them the tier through the
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real `box grant`, mints real boxes as them, and measures — from inside those
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boxes — that each user is confined to their own project (a), the full
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lifecycle works (b), no cross-user visibility (c), names don't collide (d),
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`expose`/`setup-host`/`doctor` answer honestly at the tier (e/f), the boxes
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ride `boxnet` under the full isolation contract including the cross-user
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sibling drop (g), the private-bridge escape hatches are closed (h), the grant
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survives an incus-user restart (k), and `revoke --purge` erases one user
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without touching the other (l). Everything it makes, it deletes.
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`--container` skips VM mints (CI runs it this way on every PR — the tier's
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semantics are instance-type-independent); on real hardware run it bare so the
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boxes are VMs. `--keep` leaves the users and boxes up for inspection.
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|
|
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|
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@ -195,6 +195,9 @@ No listener is needed, and none should be started: see trap 3.
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|
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| Run | Result | What it cost |
|
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| --- | --- | --- |
|
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| **MU-3** | **41/0 (containers) + 41/0 (VMs) — the tier holds** | `multiuser.sh` (#74) from zero on Debian 13 / Incus 6.0.4: grant, confinement, lifecycle, the in-box contract with the cross-user sibling drop, closed escape hatches, re-sync survival, scoped revoke. The VM pass needed right-sized boxes (1GiB): two 2GiB nested VMs on a 7.7GiB host measured swap, not isolation |
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| MU-2 | 40/41 (VMs) | the egress probe cried broken over a TLS handshake that outlived its 8s budget under nested-KVM memory pressure — every isolation probe (which PASSES on silence) was immune. Probe budgets raised, reachable-probes retry once, and the mint keeps its log for the post-mortem |
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| MU-1 | 39/41 (containers) | both FAILs were the instrument: a `box new` rc swallowed with its narration (the drill's oldest sin, relearned), and the enumeration probe resolving the box's OWN name — /etc/hosts answered, not the gateway. Probe a SIBLING's name or you measure cloud-init's hostname hygiene. Found for real along the way: `box restore` dispatched `incus restore`, which does not exist in Incus 6 — broken for every tier since the rename |
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| 1 | hung at C7; ~9 false FAILs | traps 1, 2, 4 — pipefail, the exec-pty hang, the DHCP race |
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| 2 | 42/49 | trap 5 — an interrupted run 1 left boxes behind, cascading 5 FAILs. Found the `claude`-on-PATH bug. Phase D delivered B1 (`@internal` rejected) and a B3 reading of *broken* |
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| 3 | 48/49 | trap 4 — `eth0_ip` never matched, so A3 again unprobed. B3 now read *intact*, contradicting run 2 |
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Reference in a new issue