built-in-references/Kubernetes/container-allowed-capabilities/template.yaml

apiVersion: templates.gatekeeper.sh/v1beta1
kind: ConstraintTemplate
metadata:
  name: k8sazureallowedcapabilities
spec:
  crd:
    spec:
      names:
        kind: K8sAzureAllowedCapabilities
      validation:
        # Schema for the `parameters` field
        openAPIV3Schema:
          properties:
            allowedCapabilities:
              type: array
              items:
                type: string
            requiredDropCapabilities:
              type: array
              items:
                type: string
  targets:
    - target: admission.k8s.gatekeeper.sh
      rego: |
        package k8sazureallowedcapabilities

        violation[{"msg": msg}] {
          container := input_containers[_]
          has_disallowed_capabilities(container)
          msg := sprintf("container <%v> has a disallowed capability. Allowed capabilities are %v", [container.name, get_default(input.parameters, "allowedCapabilities", "NONE")])
        }

        violation[{"msg": msg}] {
          container := input_containers[_]
          missing_drop_capabilities(container)
          msg := sprintf("container <%v> is not dropping all required capabilities. Container must drop all of %v", [container.name, input.parameters.requiredDropCapabilities])
        }

        has_disallowed_capabilities(container) {
          allowed := {c | c := input.parameters.allowedCapabilities[_]}
          not allowed["*"]
          capabilities := {c | c := container.securityContext.capabilities.add[_]}
          count(capabilities - allowed) > 0
        }

        missing_drop_capabilities(container) {
          must_drop := {c | c := input.parameters.requiredDropCapabilities[_]}
          dropped := {c | c := container.securityContext.capabilities.drop[_]}
          count(must_drop - dropped) > 0
        }

        get_default(obj, param, _default) = out {
          out = obj[param]
        }

        get_default(obj, param, _default) = out {
          not obj[param]
          not obj[param] == false
          out = _default
        }
        input_containers[c] {
            c := input.review.object.spec.containers[_]
        }
        input_containers[c] {
            c := input.review.object.spec.initContainers[_]
        }