# Based on https://kyverno.io/policies/pod-security/baseline/disallow-host-namespaces/disallow-host-namespaces/
apiVersion: kyverno.io/v1
kind: ClusterPolicy
metadata:
  name: disallow-host-namespaces
  annotations:
    policies.kyverno.io/category: Pod Security Standards (Baseline)
    policies.kyverno.io/severity: medium
    policies.kyverno.io/subject: Pod
    policies.kyverno.io/description: >-
      Host namespaces (Process ID namespace, Inter-Process Communication namespace, and
      network namespace) allow access to shared information and can be used to elevate
      privileges. Pods should not be allowed access to host namespaces.      
spec:
  validationFailureAction: audit
  background: true
  rules:
    - name: host-namespaces
      match:
        resources:
          kinds:
            - Pod
      # allow host namespaces on kube-system and calico-system
      exclude:
        resources:
          namespaces:
            - calico-system
            - tigera-operator
            - monitoring
      validate:
        message: >-
          Sharing the host namespaces is disallowed. The fields spec.hostNetwork,
          spec.hostIPC, and spec.hostPID must not be set to true.          
        pattern:
          spec:
            =(hostPID): "false"
            =(hostIPC): "false"
            =(hostNetwork): "false"