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Understanding and managing pod security admission

Pod security admission and security context constraints

Pod security admission standards and security context constraints are reconciled and enforced by two independent controllers. The two controllers work independently using the following processes to enforce security policies:

  1. The security context constraint controller may mutate some security context fields per the pod’s assigned SCC. For example, if the seccomp profile is empty or not set and if the pod’s assigned SCC enforces seccompProfiles field to be runtime/default, the controller sets the default type to RuntimeDefault.

  2. The security context constraint controller validates the pod’s security context against the matching SCC.

  3. The pod security admission controller validates the pod’s security context against the pod security standard assigned to the namespace.

Security context constraint synchronization with pod security standards

OKD includes Kubernetes pod security admission. Globally, the privileged profile is enforced, and the restricted profile is used for warnings and audits.

In addition to the global pod security admission control configuration, a controller exists that applies pod security admission control warn and audit labels to namespaces according to the SCC permissions of the service accounts that are in a given namespace.

Namespaces that are defined as part of the cluster payload have pod security admission synchronization disabled permanently. You can enable pod security admission synchronization on other namespaces as necessary. If an Operator is installed in a user-created openshift-* namespace, synchronization is turned on by default after a cluster service version (CSV) is created in the namespace.

The controller examines ServiceAccount object permissions to use security context constraints in each namespace. Security context constraints (SCCs) are mapped to pod security profiles based on their field values; the controller uses these translated profiles. Pod security admission warn and audit labels are set to the most privileged pod security profile found in the namespace to prevent warnings and audit logging as pods are created.

Namespace labeling is based on consideration of namespace-local service account privileges.

Applying pods directly might use the SCC privileges of the user who runs the pod. However, user privileges are not considered during automatic labeling.

Controlling pod security admission synchronization

You can enable or disable automatic pod security admission synchronization for most namespaces.

Namespaces that are defined as part of the cluster payload have pod security admission synchronization disabled permanently. These namespaces include:

  • default

  • kube-node-lease

  • kube-system

  • kube-public

  • openshift

  • All system-created namespaces that are prefixed with openshift-, except for openshift-operators

By default, all namespaces that have an openshift- prefix are not synchronized. You can enable synchronization for any user-created openshift-* namespaces. You cannot enable synchronization for any system-created openshift-* namespaces, except for openshift-operators.

If an Operator is installed in a user-created openshift-* namespace, synchronization is turned on by default after a cluster service version (CSV) is created in the namespace. The synchronized label inherits the permissions of the service accounts in the namespace.
Procedure

  • For each namespace that you want to configure, set a value for the security.openshift.io/scc.podSecurityLabelSync label:

    • To disable pod security admission label synchronization in a namespace, set the value of the security.openshift.io/scc.podSecurityLabelSync label to false.

      Run the following command:

      $ oc label namespace <namespace> security.openshift.io/scc.podSecurityLabelSync=false

    • To enable pod security admission label synchronization in a namespace, set the value of the security.openshift.io/scc.podSecurityLabelSync label to true.

      Run the following command:

      $ oc label namespace <namespace> security.openshift.io/scc.podSecurityLabelSync=true

    Use the --overwrite flag to overwrite the value if this label is already set on the namespace.

About pod security admission alerts

A PodSecurityViolation alert is triggered when the Kubernetes API server reports that there is a pod denial on the audit level of the pod security admission controller. This alert persists for one day.

View the Kubernetes API server audit logs to investigate alerts that were triggered. As an example, a workload is likely to fail admission if global enforcement is set to the restricted pod security level.

For assistance in identifying pod security admission violation audit events, see Audit annotations in the Kubernetes documentation.

Identifying pod security violations

The PodSecurityViolation alert does not provide details on which workloads are causing pod security violations. You can identify the affected workloads by reviewing the Kubernetes API server audit logs. This procedure uses the must-gather tool to gather the audit logs and then searches for the pod-security.kubernetes.io/audit-violations annotation.

Prerequisites

  • You have installed jq.

  • You have access to the cluster as a user with the cluster-admin role.

Procedure

  1. To gather the audit logs, enter the following command:

    $ oc adm must-gather -- /usr/bin/gather_audit_logs

  2. To output the affected workload details, enter the following command:

    $ zgrep -h pod-security.kubernetes.io/audit-violations must-gather.local.<archive_id>/<image_digest_id>/audit_logs/kube-apiserver/*log.gz \
  | jq -r 'select((.annotations["pod-security.kubernetes.io/audit-violations"] != null) and (.objectRef.resource=="pods")) | .objectRef.namespace + " " + .objectRef.name' \
  | sort | uniq -c

    Replace <archive_id> and <image_digest_id> with the actual path names.

    Example output
    1 test-namespace my-pod

Additional resources