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fzymgc-house Cluster Docs

Grant NAS sandbox dataset access via DEFAULT idmap plus per-dataset ACLs

Date: 2026-06-27 Status: Accepted Decision: hl-3ek7 Deciders: sean

Context

Section titled “Context”

The NAS sandbox needs read-write access to specific data datasets for space curation. Spike testing proved TrueNAS 26 container.* LXC has no privileged/no-shift mode: idmap.type accepts only DEFAULT or ISOLATED, and omitting it defaults to DEFAULT. Under DEFAULT, container-root maps to host UID 2147000001, which cannot write 0:0-owned dataset trees (/mnt/main, /mnt/apps roots) without an explicit grant.

Decision

Section titled “Decision”

Run the sandbox with idmap: {type: DEFAULT} (unprivileged, UID-shifted) and grant read-write to specific curation datasets via per-dataset ACLs for the mapped UID 2147000001 — “specific access to the data shares”, not root-to-everything. The grant is acltype-aware: setfacl for POSIX1E datasets, midclt filesystem.setacl (USER ACE, FULL_CONTROL, INHERIT) for NFSv4 datasets.

Rationale

Section titled “Rationale”
  • A privileged container is not available through container.* — forced by the API, then embraced as the secure default.
  • ACL-scoped access matches the original intent (“specific access to the data shares”) and minimizes blast radius.
  • A dataset survey found ~87 POSIX1E / 15 NFSv4; the high-value curation targets (multimedia, software, time-machine) are NFSv4, so both grant mechanisms are required. Both were proven end-to-end by spike.

Alternatives Considered

Section titled “Alternatives Considered”
  • DEFAULT idmap + per-dataset ACLs (chosen): secure, supported, proven; bounded write reach.
  • Privileged / idmap=None container (rejected — impossible): no such mode exists in container.*.
  • chown of existing trees to the mapped UID (rejected): rewrites real data ownership; ACLs are non-destructive.
  • Host-level / root Docker-app curation (deferred): more capable for unrestricted writes, but defeats the interactive-sandbox goal; revisit only if ACL scoping proves insufficient.

Consequences

Section titled “Consequences”
  • Positive: secure-by-default; no privileged container; non-destructive grants; works for both ACL types.
  • Negative: curation is bounded to ACL-prepared datasets (not “anything”); the ACL-granting task must branch on acltype.
  • Neutral: the mapped UID 2147000001 is the DEFAULT-namespace base — assumed stable across recreation; the plan re-confirms it from /proc/<pid>/uid_map after creating the real container.