Skip to content
All posts
2 min readtebakopackagingtutorial

Advanced payloads: Jails and profiles: decide what it may touch (2 of 5)

The advanced payloads series: jails and profiles: decide what it may touch.

The Tebako team

github.com/tamatebako
Note

Post 2 of 5 in the series Advanced payloads.

○ ● ○ ○ ○

  1. Advanced payloads: Trace: see what your payload touches

  2. Advanced payloads: Jails and profiles: decide what it may touch (this post)

  3. Advanced payloads: The image toolbox

  4. Advanced payloads: Runtimes and native code

  5. Advanced payloads: packed-mn: one download, any document
Note

Reference guide: Set a jail policy.

The observe half of the boundary was the last post. This post is the constrain half: profiles and jails — how the policy drafted in the previous post becomes the policy that runs, and what is enforced where.

Jails and profiles one payload, three profiles profile: strict deny, nothing granted profile: standard deny + declared needs profile: open legacy escape hatch one jail grammar the run binds TEBAKO_JAIL=deny · --jail deny:arg · jail.yaml env, flag, or baked manifest — precedence is fixed record mode drafts the grants: TEBAKO_JAIL=record tebako run ./myapp -- build tfs needs --from-journal ~/.tebako/journal.log

Figure 1 — Profiles select a policy, the run binds it from env, flag, or manifest, and record mode drafts the grants from a real run.

The grammar

A jail policy has one setting and a list of grants:

jail:
  default: deny        # or open
  mounts:
    - path: $HOME/.fontist
      access: rw
      when: [macos]
      why: "fontist caches and resolves fonts here"

Everything not granted is invisible to the process. The why is mandatory: a declaration that cannot explain itself does not parse.

Binding, three ways

The same policy binds from an environment variable, a command flag, or the manifest itself — TEBAKO_JAIL=deny, --jail deny:arg, or a baked jail.yaml — with a fixed precedence. Per-invocation flags win, so an operator can tighten any payload for one run without modifying the payload:

$ tebako run ./myapp --jail deny -- --help
$ tebako run ./myapp --mount "$HOME/sources:/work:ro" -- build /work

Draft, don’t guess

Record mode — the bridge from the previous post — turns a real run into the draft policy:

$ TEBAKO_JAIL=record tebako run ./myapp -- build
$ tfs needs --from-journal ~/.tebako/journal.log

One declaration, every platform

The declaration is identical everywhere. On Linux and macOS the choke point sits in the filesystem layer; on Windows, enforcement moves to the spawn tier — executables materialize into a cache and start under the same policy computed from the same declarations.

What you can do now

This post has decided, precisely and reviewably, what a payload may touch — on every platform tebako ships. The next post opens the images themselves.

Note

Continue with part 3 of 5: The image toolbox.