policy-library/policies/templates/gcp_gke_cluster_version_v1.yaml

# Copyright 2021 Google LLC
#
# 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
#
#     https://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.

apiVersion: templates.gatekeeper.sh/v1alpha1
kind: ConstraintTemplate
metadata:
  name: gcp-gke-cluster-version-v1
spec:
  crd:
    spec:
      names:
        kind: GKEClusterVersionConstraintV1
      validation:
        openAPIV3Schema:
          properties:
            mode:
              type: string
              enum: [denylist, allowlist]
              description: "String identifying the operational mode, allowlist or
                denylist. In allowlist mode, GKE clusters are only allowed to have
                a master/node version specified in the 'version_type' parameter. In
                denylist mode, resources are allowed any master/node versions except
                those listed in the 'version_type' parameter. Default is allowlist."
            version_type:
              type: string
              enum: [master, node]
              description: "String identifying the GKE cluster version type to look
                for, master or node. master refers to the Kubernetes version for GKE
                cluster masters. node refers to the Kubernetes version for GKE cluster
                nodes. Default is master."
            exemptions:
              type: array
              items:
                type: string
              description: "Array of GKE clusters in the form of glob expressions
                to exempt from version restriction. Delimiter is '/'. E.g. `//container.googleapis.com/projects/project-abc/zones/*/clusters/*`
                will exempt any clusters whose asset name has the format '//container.googleapis.com/projects/project-abc/zones/{ANY
                ZONE}/clusters/{ANY NAME}'. such as: '//container.googleapis.com/projects/project-abc/zones/us-central1-c/clusters/my-cluster'
                but NOT '//container.googleapis.com/projects/wrong-project/zones/us-central1-c/clusters/wrong-cluster'"
            versions:
              type: array
              items:
                type: string
              description: "Array of versions that GKE clusters are allowed to have,
                e.g. 1.12.10-gke.17 for master version_type or 1.4.4 for node version_type."
  targets:
    validation.gcp.forsetisecurity.org:
      rego: |
        #
        # Copyright 2021 Google LLC
        #
        # 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
        #
        #     https://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.
        #

        package templates.gcp.GKEClusterVersionConstraintV1

        import data.validator.gcp.lib as lib

        deny[{
        	"msg": message,
        	"details": metadata,
        }] {
        	constraint := input.constraint
        	lib.get_constraint_params(constraint, params)
        	asset := input.asset
        	asset.asset_type == "container.googleapis.com/Cluster"

        	mode := lib.get_default(params, "mode", "allowlist")

        	# Check if resource is in exempt list
        	exempt_list := lib.get_default(params, "exemptions", [])
        	not is_exempt(exempt_list, asset.name)

        	# Get the version value in the asset
        	params_version_type := lib.get_default(params, "version_type", "master")
        	target_version_type := get_version_type(params_version_type)
        	target_version := get_target_value(asset.resource.data, target_version_type)

        	# Check that version is in allowlist/denylist
        	asset_version := params.versions
        	version_matches := {target_version} & cast_set(asset_version)
        	desired_count := target_version_match_count(params.mode)
        	count(version_matches) == desired_count

        	message := sprintf("Cluster %v has a disallowed %v field", [asset.name, target_version_type])
        	metadata := {"resource": asset.name}
        }

        ###########################
        # Rule Utilities
        ###########################

        get_version_type(version_type) = target_version {
        	version_type == "master"
        	target_version := "currentMasterVersion"
        }

        get_version_type(version_type) = target_version {
        	version_type == "node"
        	target_version := "currentNodeVersion"
        }

        is_exempt(exempt_list, asset_name) {
        	exempt_list != []
        	glob.match(exempt_list[_], ["/"], asset_name)
        }

        get_target_value(data_resource, field_name) = output {
        	output := lib.get_default(data_resource, field_name, "")
        }

        # Determine the overlap between versions under test and constraint
        # By default (allowlist), we violate if there isn't overlap.
        target_version_match_count(mode) = 0 {
        	mode != "denylist"
        }

        target_version_match_count(mode) = 1 {
        	mode == "denylist"
        }
        #ENDINLINE