template.yaml

# Copyright 2021 Open Policy Agent
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

# https://raw.githubusercontent.com/open-policy-agent/gatekeeper-library/master/library/pod-security-policy/flexvolume-drivers/template.yaml
apiVersion: templates.gatekeeper.sh/v1beta1
kind: ConstraintTemplate
metadata:
  name: pspflexvolumes
  annotations:
    description: Controls the allowlist of Flexvolume drivers.
spec:
  crd:
    spec:
      names:
        kind: PSPFlexVolumes
      validation:
        # Schema for the `parameters` field
        openAPIV3Schema:
          type: object
          properties:
            allowedFlexVolumes:
              type: array
              items:
                type: object
                properties:
                  driver:
                    type: string
  targets:
    - target: admission.k8s.gatekeeper.sh
      rego: |
        package pspflexvolumes

        violation[{"msg": msg, "details": {}}] {
          volume := input_flexvolumes[_]
          not input_flexvolumes_allowed(volume)
          msg := sprintf("FlexVolume %v is not allowed, pod: %v. Allowed drivers: %v", [volume, input.review.object.metadata.name, input.parameters.allowedFlexVolumes])
        }

        input_flexvolumes_allowed(volume) {
          input.parameters.allowedFlexVolumes[_].driver == volume.flexVolume.driver
        }

        input_flexvolumes[v] {
          v := input.review.object.spec.volumes[_]
          has_field(v, "flexVolume")
        }

        # has_field returns whether an object has a field
        has_field(object, field) = true {
          object[field]
        }