policy-library/policies/templates/gcp_compute_allowed_networks.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.
#
# Checks network interfaces on a compute instance against a provided allowlist of networks

apiVersion: templates.gatekeeper.sh/v1alpha1
kind: ConstraintTemplate
metadata:
  name: gcp-compute-allowed-networks-v2
spec:
  crd:
    spec:
      names:
        kind: GCPComputeAllowedNetworksConstraintV2
      validation:
        openAPIV3Schema:
          properties:
            allowed:
              description: "A list of full object URIs of the networks allowed, for
                example: ['https://www.googleapis.com/compute/v1/projects/vpc-sc-pub-sub-billing-alerts/global/networks/default1']"
              type: array
              items:
                type: string
  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.GCPComputeAllowedNetworksConstraintV2

        import data.validator.gcp.lib as lib

        deny[{
        	"msg": message,
        	"details": metadata,
        }] {
        	constraint := input.constraint
        	asset := input.asset
        	asset.asset_type == "compute.googleapis.com/Instance"

        	lib.get_constraint_params(input.constraint, params)

        	instance := asset.resource.data

        	interfaces := lib.get_default(instance, "networkInterfaces", [])
        	interface := interfaces[_]
        	full_network_uri := interface.network

        	allowlist := lib.get_default(params, "allowed", [])
        	allowed_networks := {n | n = allowlist[_]}

        	access_configs := lib.get_default(interface, "accessConfigs", [])

        	is_external_network := count(access_configs) > 0
        	is_network_allowed := count({full_network_uri} - allowed_networks) == 0

        	is_external_network == true
        	is_network_allowed == false

        	message := sprintf("Compute instance %v has interface %v with invalid access configuration.", [asset.name, interface.name])
        	metadata := {"resource": asset.name}
        }
        #ENDINLINE