Fission: Cross-namespace Environment reference via unvalidated EnvironmentRef in Function admission webhook

Summary

The Fission Function admission webhook (pkg/webhook/function.go) validated that spec.secrets[].namespace and spec.configmaps[].namespace equalled the function's own namespace but performed no equivalent check on spec.environment.namespace.

Details

An attacker with permission to create Functions in their own namespace could set spec.environment.namespace to any other tenant's namespace. poolmgr and newdeploy would then look up and use the victim's Environment CRD when scheduling function pods, so the attacker's function executed inside the victim's container image.

This is useful both for code and credential theft — the victim's runtime image may contain hardcoded secrets — and for confused-deputy attacks where the victim's runtime image is a privileged sidecar.

Impact

A tenant with functions.fission.io/create could run their own function code inside another tenant's container image, breaking the namespace trust boundary that the Function specification implies.

Fix

Fixed in #3389 and released in v1.24.0.

• Admission webhook (pkg/webhook/function.go::Validate) rejects Function.spec.environment.namespace != metadata.namespace. An empty namespace remains accepted (the CLI defaults it to the function's namespace).
• Controller belt-and-braces: the same check runs before the cross-namespace Environments(...).Get in poolmgr getFunctionEnv and newdeploy fnCreate / RefreshFuncPods, covering webhook-bypass clusters (failurePolicy=Ignore) and stale Function objects from upgrade-before-restart windows.

Behavioural change

Functions that explicitly set spec.environment.namespace to a different namespace are now rejected at admission. Empty-string remains accepted.