[rfc] Separate Chains controller system and userspace identities.

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Evaluación

Dificultad
5/5
Tiempo estimado
Más de una semana
Aptitud para principiantes
25/100
Tipo de issue
Nueva funcionalidad
Claridad
Necesita aclaración
Estado de actividad
Estancado
Stack tecnológico
go
Área
security

Línea de trabajo

Empieza leyendo la sección sobre keyless signing de docs/sigstore.md y la discusión sobre el límite de confianza de la propuesta. No se nombran archivos de implementación ni pruebas; el issue es un RFC, por lo que avanzar requiere decidir si se acepta el diseño del controlador con dos cuentas de servicio y definir el alcance de su despliegue y configuración.

Escrito por el modelo de indexación a partir del texto del issue.

Descripción

Writing down some thoughts that have been rattling in my head for a bit. Please leave any feedback + comments!

/cc @lcarva @chitrangpatel for explicit feedback, but feedback welcome from everyone.

tl;dr: I think we should separate Chains into 2 separate service account identities: trusted build provenance attestations and untrusted userspace signing.

Background

Chains today will sign 2 types of things:

  • Build (i.e. Run) Provenance that it generates itself
  • OCI images specified in Run output by user pipelines.

Today, we run Chains in a single reconciler with a single service account and single config - this means that the same key/identity that is used to sign build provenance is also used to sign OCI refs that users output from their pipelines.

This can make it hard to reason about the trust boundary of things Chains signs - especially if clients choose to do unexpected things like have Chains sign an "OCI image" that is actually another provenance document, or something that wasn't actually output by the Pipeline.

Proposal

Split the trust boundary into 2 parts separated by service account:

  • tekton-chains (existing service account): service account that outputs trusted system-generated provenance.
  • tekton-chains-userspace: service account that outputs "untrusted" (really depends on how much you trust the underlying pipelines) userspace derived signatures.

By separating by service account, we can guarantee distinct identities even with use of keyless signing. The consequence of this means that the controller will need to be split into 2 deployments/configs/etc. (one for each service account), though this also opens up a bunch of possibilities for different Chains deployments such as having a cluster-wide build provenance config (tekton-chains) and configurable namespace/tenant configs (tekton-chains-userspace).

Alternatives
  • Remove OCI signing from chains and recommend everyone to sign in their Runs - I think there's value in having the auto-sign behavior, even if it doesn't give you as much metadata as signing within the build itself. I'd like to avoid this.
  • Keep things as they are - This is going to be a problem for deployments where the Chains operators don't trust the user pipelines (this came up in a recent Slack thread). I think we need some answer.
  • Same controller/service account, different configs / keys - This won't work for keyless signing, since they'd have the same identity.
Lenguaje dominante
Go
Estrellas
279
Forks
171
Merge medio
2 d 4 h
PR fusionados (30 d)
70

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