policy-library/policies/templates/gcp_compute_ip_forward.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-compute-ip-forward-v2
spec:
  crd:
    spec:
      names:
        kind: GCPComputeIpForwardConstraintV2
      validation:
        openAPIV3Schema:
          properties:
            mode:
              type: string
              enum: [denylist, allowlist]
              description: "If allowlist, IP forwarding will only be allowed on specified
                instances. If denylist, IP forwarding will be allowed except on specified
                instances."
            match_mode:
              type: string
              enum: [exact, regex]
              description: "Whether to use exact string matching or regular expressions
                against instance names"
            instances:
              type: array
              items:
                type: string
              description: "The list of instances in your allowlist or denylist"
  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.GCPComputeIpForwardConstraintV2

        import data.validator.gcp.lib as lib

        ###########################
        # Find allowlist/denylist Violations
        ###########################
        deny[{
        	"msg": message,
        	"details": metadata,
        }] {
        	constraint := input.constraint
        	lib.get_constraint_params(constraint, params)
        	asset := input.asset
        	asset.asset_type == "compute.googleapis.com/Instance"

        	instance := asset.resource.data
        	lib.get_default(instance, "canIpForward", false) == true

        	# Check if instance is in denylist/allowlist
        	match_mode := lib.get_default(params, "match_mode", "exact")
        	mode := lib.get_default(params, "mode", "allowlist")
        	target_instances := lib.get_default(params, "instances", [])
        	trace(sprintf("asset name:%v, target_instances: %v, mode: %v, match_mode: %v", [asset.name, target_instances, mode, match_mode]))
        	instance_name_targeted(asset.name, target_instances, mode, match_mode)
        	message := sprintf("%v is not allowed to have IP forwarding enabled.", [asset.name])
        	metadata := {"resource": asset.name}
        }

        ###########################
        # Rule Utilities
        ###########################
        instance_name_targeted(asset_name, instance_filters, mode, match_mode) {
        	mode == "allowlist"
        	match_mode == "exact"
        	matches := {asset_name} & cast_set(instance_filters)
        	count(matches) == 0
        }

        instance_name_targeted(asset_name, instance_filters, mode, match_mode) {
        	mode == "denylist"
        	match_mode == "exact"
        	matches := {asset_name} & cast_set(instance_filters)
        	count(matches) > 0
        }

        instance_name_targeted(asset_name, instance_filters, mode, match_mode) {
        	mode == "allowlist"
        	match_mode == "regex"
        	not re_match_name(asset_name, instance_filters)
        }

        instance_name_targeted(asset_name, instance_filters, mode, match_mode) {
        	mode == "denylist"
        	match_mode == "regex"
        	re_match_name(asset_name, instance_filters)
        }

        re_match_name(name, filters) {
        	re_match(filters[_], name)
        }
        #ENDINLINE