Chapter 15. Managing Security Context Constraints

apiVersion: v1
kind: Pod
metadata:
  name: security-context-demo
spec:
  securityContext: 1
  containers:
  - name: sec-ctx-demo
    image: gcr.io/google-samples/node-hello:1.0

apiVersion: v1
kind: Pod
metadata:
  name: security-context-demo
spec:
  securityContext:
    runAsUser: 1000 1
  containers:
    - name: sec-ctx-demo
      image: gcr.io/google-samples/node-hello:1.0

This works with SELinux, fsGroup, and Supplemental Groups. See Volume Security for more information.

In some cases, an administrator might want to allow users or groups outside the administrator group access to create more privileged pods. To do so, you can:

First, create a service account. For example, to create service account mysvcacct in project myproject:

$ oc create serviceaccount mysvcacct -n myproject

Then, add the service account to the privileged SCC.

$ oc adm policy add-scc-to-user privileged system:serviceaccount:myproject:mysvcacct

Then, ensure that the resource is being created on behalf of the service account. To do so, set the spec.serviceAccountName field to a service account name. Leaving the service account name blank will result in the default service account being used.

Then, ensure that at least one of the pod’s containers is requesting a privileged mode in the security context.

To relax the security in your cluster so that images are not forced to run as a pre-allocated UID, without granting everyone access to the privileged SCC:

Some container images (examples: postgres and redis) require root access and have certain expectations about how volumes are owned. For these images, add the service account to the anyuid SCC.

$ oc adm policy add-scc-to-user anyuid system:serviceaccount:myproject:mysvcacct

It is recommended that persistent storage using PersistentVolume and PersistentVolumeClaim objects be used for registry deployments. If you are testing and would like to instead use the oc adm registry command with the --mount-host option, you must first create a new service account for the registry and add it to the privileged SCC. See the Administrator Guide for full instructions.

In some cases, an image may require capabilities that Docker does not provide out of the box. You can provide the ability to request additional capabilities in the pod specification which will be validated against an SCC.

When used in conjunction with a non-root user, you must also ensure that the file that requires the additional capability is granted the capabilities using the setcap command. For example, in the Dockerfile of the image:

setcap cap_net_raw,cap_net_admin+p /usr/bin/ping

Further, if a capability is provided by default in Docker, you do not need to modify the pod specification to request it. For example, NET_RAW is provided by default and capabilities should already be set on ping, therefore no special steps should be required to run ping.

To provide additional capabilities:

When you grant access to the anyuid SCC for everyone, your cluster:

 $ oc adm policy add-scc-to-group anyuid system:authenticated

To modify your cluster so that it does not pre-allocate UIDs and does not allow containers to run as root, grant access to the nonroot SCC for everyone:

 $ oc adm policy add-scc-to-group nonroot system:authenticated

To relax the security in your cluster so that pods are allowed to use the hostPath volume plug-in without granting everyone access to more privileged SCCs such as privileged, hostaccess, or hostmount-anyuid, perform the following actions:

Now, all the pods that request hostPath volumes are admitted by the hostpath SCC.

You may control the sort ordering of SCCs in admission by setting the Priority field of the SCCs. See the SCC Prioritization section for more information on sorting.

Before adding an SCC to a user or group, you can first use the scc-review option to check if the user or group can create a pod. See the Authorization topic for more information.

SCCs are not granted directly to a project. Instead, you add a service account to an SCC and either specify the service account name on your pod or, when unspecified, run as the default service account.

To add an SCC to a user:

$ oc adm policy add-scc-to-user <scc_name> <user_name>

To add an SCC to a service account:

$ oc adm policy add-scc-to-user <scc_name> \
    system:serviceaccount:<serviceaccount_namespace>:<serviceaccount_name>

If you are currently in the project to which the service account belongs, you can use the -z flag and just specify the <serviceaccount_name>.

$ oc adm policy add-scc-to-user <scc_name> -z <serviceaccount_name>

To add an SCC to a group:

$ oc adm policy add-scc-to-group <scc_name> <group_name>

To add an SCC to all service accounts in a namespace:

$ oc adm policy add-scc-to-group <scc_name> \
    system:serviceaccounts:<serviceaccount_namespace>