Description:

Apply Security Context to Your Pods and Containers

Rationale:

A security context defines the operating system security settings (uid, gid, capabilities, SELinux role, etc..) applied to a container. When designing your containers and pods, make sure that you configure the security context for your pods, containers, and volumes. A security context is a property defined in the deployment yaml. It controls the security parameters that will be assigned to the pod/container/volume. There are two levels of security context: pod level security context, and container level security context.

If you incorrectly apply security contexts, you may have trouble running the pods.

As a best practice we recommend that you scope the binding for privileged pods to service accounts within a particular namespace, e.g. kube-system, and limiting access to that namespace. For all other serviceaccounts/namespaces, we recommend implementing a more restrictive policy such as this:

apiVersion: policy/v1beta1
kind: PodSecurityPolicy
metadata:
name: restricted
annotations:
seccomp.security.alpha.kubernetes.io/allowedProfileNames: 'docker/default,runtime/default'
apparmor.security.beta.kubernetes.io/allowedProfileNames: 'runtime/default'
seccomp.security.alpha.kubernetes.io/defaultProfileName: 'runtime/default'
apparmor.security.beta.kubernetes.io/defaultProfileName: 'runtime/default'
spec:
privileged: false

Required to prevent escalations to root.

allowPrivilegeEscalation: false

This is redundant with non-root + disallow privilege escalation,

but we can provide it for defense in depth.

requiredDropCapabilities:

• ALL

Allow core volume types.

volumes:

• 'configMap'
• 'emptyDir'
• 'projected'
• 'secret'
• 'downwardAPI'

Assume that persistentVolumes set up by the cluster admin are safe to use.

• 'persistentVolumeClaim'
  hostNetwork: false
  hostIPC: false
  hostPID: false
  runAsUser:

Require the container to run without root privileges.

rule: 'MustRunAsNonRoot'
seLinux:

This policy assumes the nodes are using AppArmor rather than SELinux.

rule: 'RunAsAny'
supplementalGroups:
rule: 'MustRunAs'
ranges:

Forbid adding the root group.

• min: 1
  max: 65535
  fsGroup:
  rule: 'MustRunAs'
  ranges:

Forbid adding the root group.

• min: 1
  max: 65535
  readOnlyRootFilesystem: false

This policy prevents pods from running as privileged or escalating privileges. It also restricts the types of volumes that can be mounted and the root supplemental groups that can be added.

Another, albeit similar, approach is to start with policy that locks everything down and incrementally add exceptions for applications that need looser restrictions such as logging agents which need the ability to mount a host path.