# 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.
#

# This template is for policies restricting the locations
# of compute (VM instance / persistent disk) resources to
# specific zones in GCP. It supports allowlist or denylist
# modes, as well as exempting selected assets from the list.

apiVersion: templates.gatekeeper.sh/v1alpha1
kind: ConstraintTemplate
metadata:
  name: gcp-compute-zone-v1
spec:
  crd:
    spec:
      names:
        kind: GCPComputeZoneConstraintV1
      validation:
        openAPIV3Schema:
          properties:
            mode:
              type: string
              enum: [denylist, allowlist]
              description: "String identifying the operational mode, allowlist or
                denylist. In allowlist mode, resources are only allowed in the zones
                specified in the 'zones' parameter. In denylist mode, resources are
                allowed in all zones except those listed in the 'zones' parameter."
            exemptions:
              type: array
              items:
                type: string
              description: "Array of compute assets to exempt from zonal restriction.
                String values in the array should correspond to the full name values
                of exempted devices."
            zones:
              type: array
              items:
                type: string
              description: "Array of zone names to be allowed or denied. Should be
                the simple form of the zone name, e.g. asia-east1-b."
  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.GCPComputeZoneConstraintV1

        import data.validator.gcp.lib as lib

        #####################################
        # Find Compute Asset Zone Violations
        #####################################
        deny[{
        	"msg": message,
        	"details": metadata,
        }] {
        	constraint := input.constraint
        	lib.get_constraint_params(constraint, params)

        	# Verify that resource is Instance or Disk
        	asset := input.asset
        	{asset.asset_type} == {asset.asset_type} & {"compute.googleapis.com/Instance", "compute.googleapis.com/Disk"}

        	# Check if resource is in exempt list
        	exempt_list := params.exemptions
        	matches := {asset.name} & cast_set(exempt_list)
        	count(matches) == 0

        	# Check that zone is in allowlist/denylist
        	target_zones := params.zones
        	asset_zone_tokens := split(asset.resource.data.zone, "/")
        	asset_zone := asset_zone_tokens[minus(count(asset_zone_tokens), 1)]
        	zone_matches := {asset_zone} & cast_set(target_zones)
        	target_zone_match_count(params.mode, desired_count)
        	count(zone_matches) == desired_count

        	message := sprintf("%v is in a disallowed zone.", [asset.name])
        	metadata := {"zone": asset_zone}
        }

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

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

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