Image Digests

Description

Requires container images to contain a digest. https://kubernetes.io/docs/concepts/containers/images/

Template

apiVersion: templates.gatekeeper.sh/v1
kind: ConstraintTemplate
metadata:
  name: k8simagedigests
  annotations:
    metadata.gatekeeper.sh/title: "Image Digests"
    metadata.gatekeeper.sh/version: 1.0.1
    description: >-
      Requires container images to contain a digest.

      https://kubernetes.io/docs/concepts/containers/images/
spec:
  crd:
    spec:
      names:
        kind: K8sImageDigests
      validation:
        openAPIV3Schema:
          type: object
          description: >-
            Requires container images to contain a digest.

            https://kubernetes.io/docs/concepts/containers/images/
          properties:
            exemptImages:
              description: >-
                Any container that uses an image that matches an entry in this list will be excluded
                from enforcement. Prefix-matching can be signified with `*`. For example: `my-image-*`.

                It is recommended that users use the fully-qualified Docker image name (e.g. start with a domain name)
                in order to avoid unexpectedly exempting images from an untrusted repository.
              type: array
              items:
                type: string
  targets:
    - target: admission.k8s.gatekeeper.sh
      rego: |
        package k8simagedigests

        import data.lib.exempt_container.is_exempt

        violation[{"msg": msg}] {
          container := input.review.object.spec.containers[_]
          not is_exempt(container)
          not regex.match("@[a-z0-9]+([+._-][a-z0-9]+)*:[a-zA-Z0-9=_-]+", container.image)
          msg := sprintf("container <%v> uses an image without a digest <%v>", [container.name, container.image])
        }

        violation[{"msg": msg}] {
          container := input.review.object.spec.initContainers[_]
          not is_exempt(container)
          not regex.match("@[a-z0-9]+([+._-][a-z0-9]+)*:[a-zA-Z0-9=_-]+", container.image)
          msg := sprintf("initContainer <%v> uses an image without a digest <%v>", [container.name, container.image])
        }

        violation[{"msg": msg}] {
          container := input.review.object.spec.ephemeralContainers[_]
          not is_exempt(container)
          not regex.match("@[a-z0-9]+([+._-][a-z0-9]+)*:[a-zA-Z0-9=_-]+", container.image)
          msg := sprintf("ephemeralContainer <%v> uses an image without a digest <%v>", [container.name, container.image])
        }
      libs:
        - |
          package lib.exempt_container

          is_exempt(container) {
              exempt_images := object.get(object.get(input, "parameters", {}), "exemptImages", [])
              img := container.image
              exemption := exempt_images[_]
              _matches_exemption(img, exemption)
          }

          _matches_exemption(img, exemption) {
              not endswith(exemption, "*")
              exemption == img
          }

          _matches_exemption(img, exemption) {
              endswith(exemption, "*")
              prefix := trim_suffix(exemption, "*")
              startswith(img, prefix)
          }

Usage

kubectl apply -f https://raw.githubusercontent.com/open-policy-agent/gatekeeper-library/master/library/general/imagedigests/template.yaml

Examples

container-image-must-have-digest

constraint

apiVersion: constraints.gatekeeper.sh/v1beta1
kind: K8sImageDigests
metadata:
  name: container-image-must-have-digest
spec:
  match:
    kinds:
      - apiGroups: [""]
        kinds: ["Pod"]
    namespaces:
      - "default"

Usage

kubectl apply -f https://raw.githubusercontent.com/open-policy-agent/gatekeeper-library/master/library/general/imagedigests/samples/container-image-must-have-digest/constraint.yaml

example-allowed

apiVersion: v1
kind: Pod
metadata:
  name: opa-allowed
spec:
  containers:
    - name: opa
      image: openpolicyagent/opa:0.9.2@sha256:04ff8fce2afd1a3bc26260348e5b290e8d945b1fad4b4c16d22834c2f3a1814a
      args:
        - "run"
        - "--server"
        - "--addr=localhost:8080"

Usage

kubectl apply -f https://raw.githubusercontent.com/open-policy-agent/gatekeeper-library/master/library/general/imagedigests/samples/container-image-must-have-digest/example_allowed.yaml

example-disallowed

apiVersion: v1
kind: Pod
metadata:
  name: opa-disallowed
spec:
  initContainers:
    - name: opainit
      image: openpolicyagent/opa:0.9.2
      args:
        - "run"
        - "--server"
        - "--addr=localhost:8080"
  containers:
    - name: opa
      image: openpolicyagent/opa:0.9.2
      args:
        - "run"
        - "--server"
        - "--addr=localhost:8080"

Usage

kubectl apply -f https://raw.githubusercontent.com/open-policy-agent/gatekeeper-library/master/library/general/imagedigests/samples/container-image-must-have-digest/example_disallowed.yaml

disallowed-all

apiVersion: v1
kind: Pod
metadata:
  name: opa-disallowed
spec:
  initContainers:
    - name: opainit
      image: openpolicyagent/opa:0.9.2
      args:
        - "run"
        - "--server"
        - "--addr=localhost:8080"
  containers:
    - name: opa
      image: openpolicyagent/opa:0.9.2
      args:
        - "run"
        - "--server"
        - "--addr=localhost:8080"
  ephemeralContainers:
    - name: opa
      image: openpolicyagent/opa:0.9.2
      args:
        - "run"
        - "--server"
        - "--addr=localhost:8080"

Usage

kubectl apply -f https://raw.githubusercontent.com/open-policy-agent/gatekeeper-library/master/library/general/imagedigests/samples/container-image-must-have-digest/disallowed_all.yaml