Cron: malformed tenant annotation can stop scheduled actions of other tenants #275

The OpenServerless 0.9.0 Cron scheduler processes scheduled actions from all namespaces in one batch. An authenticated tenant can persist a malformed cron annotation on an action in its own namespace. The scheduler passes that value to the cron parser without checking its type; an uncaught exception can stop the batch before later tenants' actions are processed. The annotation persists, so subsequent scheduled runs can be affected as well.

Impact: cross-tenant availability of scheduled actions when the Cron component is enabled. This requires a normal tenant credential. We found no anonymous entry point, cross-tenant invocation, or credential disclosure in this path.

Proposed change in openserverless-operator for branch 0.9.0: reject non-string, empty, and excessively long cron expressions before parsing; isolate errors while processing each action so one malformed action cannot stop the remaining batch; add a regression test covering two tenants and valid recurring/one-shot actions.

Validation: the regression reproduced the failure before the fix in a local harness and passed afterward with the pinned croniter 1.4.1. In an isolated K3s lab, Alpha and Beta each produced two fresh scheduled heartbeats while a malformed Alpha action existed. A scheduler job logged the malformed Alpha annotation before successfully dispatching Beta's heartbeat action. The malformed action was removed after the test, and the baseline CronJob image was restored.

Proposed fix: apache/openserverless-operator#144 (target branch 0.9.0).