fix(webhook): prevent unlabeled ConfigMaps from bypassing validation

[infernus01]

Changes

Fixes a bug where unlabeled ConfigMaps could bypass webhook validation and get loaded by the controller without validation.

Problem

The webhook's objectSelector requires these labels:

 app.kubernetes.io/part-of: tekton-pruner
 pruner.tekton.dev/config-type: namespace

If a user creates a ConfigMap with the correct name (tekton-pruner-namespace-spec) but without labels, Kubernetes API server filters it out and never calls the webhook. The controller informer only checked cm.Name == "tekton-pruner-namespace-spec", so it would reconcile the unlabeled ConfigMap and load it via LoadNamespaceConfig() which had no label validation.

Solution

Implemented defense-in-depth with three validation layers:

Layer 1: Controller Informer Filter (pkg/reconciler/namespaceprunerconfig/controller.go)

• Checks both ConfigMap name AND required labels
• Logs warnings for unlabeled ConfigMaps
• Prevents them from entering reconciliation queue

Layer 2: Config Loading Validation (pkg/config/config.go)

• LoadGlobalConfig() validates labels before parsing
• LoadNamespaceConfig() validates labels before parsing

Layer 3: Webhook (unchanged)

• Validates labeled ConfigMaps against global limits
• objectSelector ensures only labeled ConfigMaps reach webhook code

Submitter Checklist

As the author of this PR, please check off the items in this checklist:

• Has Docs if any changes are user facing, including updates to minimum requirements e.g. Kubernetes version bumps
• Has Tests included if any functionality added or changed
• pre-commit Passed
• Follows the commit message standard
• Meets the Tekton contributor standards (including functionality, content, code)
• Has a kind label. You can add one by adding a comment on this PR that contains /kind <type>. Valid types are bug, cleanup, design, documentation, feature, flake, misc, question, tep
• Release notes block below has been updated with any user facing changes (API changes, bug fixes, changes requiring upgrade notices or deprecation warnings). See some examples of good release notes.
• Release notes contains the string "action required" if the change requires additional action from users switching to the new release

Release Notes

Controller now validates required labels before loading ConfigMaps, preventing unauthorized configuration overrides.

[tekton-robot]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 58.64%. Comparing base (570867a) to head (f65b3f2).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #453      +/-   ##
==========================================
+ Coverage   55.67%   58.64%   +2.97%     
==========================================
  Files          19       19              
  Lines        1886     1966      +80     
==========================================
+ Hits         1050     1153     +103     
+ Misses        836      813      -23     

Flag	Coverage Δ
unit-tests	58.64% <ø> (+2.97%)	⬆️

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[infernus01]

/kind bug