Merge pull request #41837 from liggitt/storageclass-param-validation

Automatic merge from submit-queue

Reserve kubernetes.io and k8s.io namespace for flex volume options

Split from https://github.com/kubernetes/kubernetes/pull/39488.

Flex volume already stuffs system information into the options map, and assumes it is free to do so:
```
	optionFSType    = "kubernetes.io/fsType"
	optionReadWrite = "kubernetes.io/readwrite"
	optionKeySecret = "kubernetes.io/secret"
```

this formalizes that by reserving the `kubernetes.io` and `k8s.io` namespaces so that user-specified options are never stomped by the system, and flex plugins can know that options with those namespaces came from the system, not user-options.

```release-note
Parameter keys in a StorageClass `parameters` map may not use the `kubernetes.io` or `k8s.io` namespaces.
```

pkg/api/validation/validation.go

@@ -920,6 +920,19 @@ func validateFlexVolumeSource(fv *api.FlexVolumeSource, fldPath *field.Path) fie
 	if len(fv.Driver) == 0 {
 		allErrs = append(allErrs, field.Required(fldPath.Child("driver"), ""))
 	}
+
+	// Make sure user-specified options don't use kubernetes namespaces
+	for k := range fv.Options {
+		namespace := k
+		if parts := strings.SplitN(k, "/", 2); len(parts) == 2 {
+			namespace = parts[0]
+		}
+		normalized := "." + strings.ToLower(namespace)
+		if strings.HasSuffix(normalized, ".kubernetes.io") || strings.HasSuffix(normalized, ".k8s.io") {
+			allErrs = append(allErrs, field.Invalid(fldPath.Child("options").Key(k), k, "kubernetes.io and k8s.io namespaces are reserved"))
+		}
+	}
+
 	return allErrs
 }