Validate atelet RPC inputs that become host filesystem paths

[fkautz]

Summary

atelet builds host filesystem paths from several Run/Restore/Checkpoint request fields without validating them. Since atelet listens on an insecure hostPort (bypassing the API server), any reachable caller can smuggle a path separator or .. through these fields and make atelet read / RemoveAll / write outside the intended actor tree, or collide bundles.

Unvalidated fields

1. target_ateom_uid → /run/netns/ateom:<uid> and .../ateoms/<uid>/ateom.sock. Separators or .. redirect the netns/socket paths.

   • internal/ateompath/ateompath.go:45,56 (AteomSocketPath, AteomNetNSPath)

2. spec.containers[].name → OCIBundlePath(ns, tmpl, id, name), where atelet runs os.RemoveAll / os.MkdirAll / writes config.json. / or .. escapes the bundle dir.

   • pkg/api/v1alpha1/actortemplate_types.go:43 (no constraint on Container.Name)
   • internal/ateompath/ateompath.go:96 (OCIBundlePath)

3. Reserved / duplicate container names — prepareOCIBundles builds the pause bundle and app bundles (keyed by name) concurrently. An app container named pause writes the same path as the sandbox-infra container (nondeterministic race / corruption); two app containers with the same name clobber each other.

   • cmd/atelet/main.go (prepareOCIBundles), cmd/ateom-gvisor/main.go:459 (hard-coded pause)

Suggested fix

Validate all path-constructing inputs at the three RPC boundaries before any path is built:

• target_ateom_uid and each container name as DNS-1123 labels (UUIDs and normal names qualify; separators/.. rejected).
• Reject the reserved name pause and duplicate container names.
• Optional defense-in-depth: +kubebuilder:validation:Pattern on Container.Name.

Note: PR #184 already validates namespace/template/actor-id this way; this extends the same mechanism to the remaining path-constructing fields.