Provides all features of the restricted
SCC, but allows users to run with any UID and any GID.
Similar to the way that RBAC resources control user access, administrators can use security context constraints (SCCs) to control permissions for pods. These permissions include actions that a pod can perform and what resources it can access. You can use SCCs to define a set of conditions that a pod must run with to be accepted into the system.
Security context constraints allow an administrator to control:
Whether a pod can run privileged containers with the allowPrivilegedContainer
flag.
Whether a pod is constrained with the allowPrivilegeEscalation
flag.
The capabilities that a container can request
The use of host directories as volumes
The SELinux context of the container
The container user ID
The use of host namespaces and networking
The allocation of an FSGroup
that owns the pod volumes
The configuration of allowable supplemental groups
Whether a container requires write access to its root file system
The usage of volume types
The configuration of allowable seccomp
profiles
Do not set the |
The cluster contains several default security context constraints (SCCs) as described in the table below. Additional SCCs might be installed when you install Operators or other components to OKD.
Do not modify the default SCCs. Customizing the default SCCs can lead to issues when some of the platform pods deploy or OKD is upgraded. During upgrades between some versions of OKD, the values of the default SCCs are reset to the default values, which discards all customizations to those SCCs. Instead, create new SCCs as needed. |
Security context constraint | Description | ||||
---|---|---|---|---|---|
|
Provides all features of the |
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|
Allows access to all host namespaces but still requires pods to be run with a UID and SELinux context that are allocated to the namespace.
|
||||
|
Provides all the features of the
|
||||
|
Allows using host networking and host ports but still requires pods to be run with a UID and SELinux context that are allocated to the namespace.
|
||||
|
Like the
|
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|
Used for the Prometheus node exporter.
|
||||
|
Provides all features of the |
||||
|
Like the
|
||||
|
Allows access to all privileged and host features and the ability to run as any user, any group, any FSGroup, and with any SELinux context.
The
|
||||
|
Denies access to all host features and requires pods to be run with a UID, and SELinux context that are allocated to the namespace. The
In clusters that were upgraded from OKD 4.10 or earlier, this SCC is available for use by any authenticated user. The |
||||
|
Like the
This is the most restrictive SCC provided by a new installation and will be used by default for authenticated users.
|
Security context constraints (SCCs) are composed of settings and strategies that control the security features a pod has access to. These settings fall into three categories:
Category | Description |
---|---|
Controlled by a boolean |
Fields of this type default to the most restrictive value. For example,
|
Controlled by an allowable set |
Fields of this type are checked against the set to ensure their value is allowed. |
Controlled by a strategy |
Items that have a strategy to generate a value provide:
|
CRI-O has the following default list of capabilities that are allowed for each container of a pod:
CHOWN
DAC_OVERRIDE
FSETID
FOWNER
SETGID
SETUID
SETPCAP
NET_BIND_SERVICE
KILL
The containers use the capabilities from this default list, but pod manifest authors can alter the list by requesting additional capabilities or removing some of the default behaviors. Use the allowedCapabilities
, defaultAddCapabilities
, and requiredDropCapabilities
parameters to control such requests from the pods. With these parameters you can specify which capabilities can be requested, which ones must be added to each container, and which ones must be forbidden, or dropped, from each container.
You can drop all capabilites from containers by setting the |
MustRunAs
- Requires a runAsuser
to be configured. Uses the configured
runAsuser
as the default. Validates against the configured runAsuser
.
MustRunAs
snippet...
runAsuser:
type: MustRunAs
uid: <id>
...
MustRunAsRange
- Requires minimum and maximum values to be defined if not
using pre-allocated values. Uses the minimum as the default. Validates against
the entire allowable range.
MustRunAsRange
snippet...
runAsuser:
type: MustRunAsRange
uidRangeMax: <maxvalue>
uidRangeMin: <minvalue>
...
MustRunAsNonRoot
- Requires that the pod be submitted with a non-zero
runAsuser
or have the user
directive defined in the image. No default
provided.
MustRunAsNonRoot
snippet...
runAsuser:
type: MustRunAsNonRoot
...
RunAsAny
- No default provided. Allows any runAsuser
to be specified.
RunAsAny
snippet...
runAsuser:
type: RunAsAny
...
MustRunAs
- Requires seLinuxOptions
to be configured if not using
pre-allocated values. Uses seLinuxOptions
as the default. Validates against
seLinuxOptions
.
RunAsAny
- No default provided. Allows any seLinuxOptions
to be
specified.
MustRunAs
- Requires at least one range to be specified if not using
pre-allocated values. Uses the minimum value of the first range as the default.
Validates against all ranges.
RunAsAny
- No default provided. Allows any supplementalGroups
to be
specified.
MustRunAs
- Requires at least one range to be specified if not using
pre-allocated values. Uses the minimum value of the first range as the default.
Validates against the first ID in the first range.
RunAsAny
- No default provided. Allows any fsGroup
ID to be specified.
The usage of specific volume types can be controlled by setting the volumes
field of the SCC. The allowable values of this field correspond to the volume
sources that are defined when creating a volume:
photonPersistentDisk
* (A special value to allow the use of all volume types.)
none
(A special value to disallow the use of all volumes types. Exists only for backwards compatibility.)
The recommended minimum set of allowed volumes for new SCCs are configMap
,
downwardAPI
, emptyDir
, persistentVolumeClaim
, secret
, and projected
.
This list of allowable volume types is not exhaustive because new types are added with each release of OKD. |
For backwards compatibility, the usage of |
Admission control with SCCs allows for control over the creation of resources based on the capabilities granted to a user.
In terms of the SCCs, this means that an admission controller can inspect the user information made available in the context to retrieve an appropriate set of SCCs. Doing so ensures the pod is authorized to make requests about its operating environment or to generate a set of constraints to apply to the pod.
The set of SCCs that admission uses to authorize a pod are determined by the user identity and groups that the user belongs to. Additionally, if the pod specifies a service account, the set of allowable SCCs includes any constraints accessible to the service account.
When you create a workload resource, such as deployment, only the service account is used to find the SCCs and admit the pods when they are created. |
Admission uses the following approach to create the final security context for the pod:
Retrieve all SCCs available for use.
Generate field values for security context settings that were not specified on the request.
Validate the final settings against the available constraints.
If a matching set of constraints is found, then the pod is accepted. If the request cannot be matched to an SCC, the pod is rejected.
A pod must validate every field against the SCC. The following are examples for just two of the fields that must be validated:
These examples are in the context of a strategy using the pre-allocated values. |
An FSGroup SCC strategy of MustRunAs
If the pod defines a fsGroup
ID, then that ID must equal the default
fsGroup
ID. Otherwise, the pod is not validated by that SCC and the next SCC
is evaluated.
If the SecurityContextConstraints.fsGroup
field has value RunAsAny
and the pod specification omits the Pod.spec.securityContext.fsGroup
,
then this field is considered valid. Note that it is possible that during
validation, other SCC settings will reject other pod fields and thus cause the
pod to fail.
A SupplementalGroups
SCC strategy of MustRunAs
If the pod specification defines one or more supplementalGroups
IDs, then
the pod’s IDs must equal one of the IDs in the namespace’s
openshift.io/sa.scc.supplemental-groups
annotation. Otherwise, the pod is not
validated by that SCC and the next SCC is evaluated.
If the SecurityContextConstraints.supplementalGroups
field has value RunAsAny
and the pod specification omits the Pod.spec.securityContext.supplementalGroups
,
then this field is considered valid. Note that it is possible that during
validation, other SCC settings will reject other pod fields and thus cause the
pod to fail.
Security context constraints (SCCs) have a priority field that affects the ordering when attempting to validate a request by the admission controller.
A priority value of 0
is the lowest possible priority. A nil priority is considered a 0
, or lowest, priority. Higher priority SCCs are moved to the front of the set when sorting.
When the complete set of available SCCs is determined, the SCCs are ordered in the following manner:
The highest priority SCCs are ordered first.
If the priorities are equal, the SCCs are sorted from most restrictive to least restrictive.
If both the priorities and restrictions are equal, the SCCs are sorted by name.
By default, the anyuid
SCC granted to cluster administrators is given priority
in their SCC set. This allows cluster administrators to run pods as any
user by specifying RunAsuser
in the pod’s SecurityContext
.
The admission controller is aware of certain conditions in the security context constraints (SCCs) that trigger it to look up pre-allocated values from a namespace and populate the SCC before processing the pod. Each SCC strategy is evaluated independently of other strategies, with the pre-allocated values, where allowed, for each policy aggregated with pod specification values to make the final values for the various IDs defined in the running pod.
The following SCCs cause the admission controller to look for pre-allocated values when no ranges are defined in the pod specification:
A RunAsuser
strategy of MustRunAsRange
with no minimum or maximum set.
Admission looks for the openshift.io/sa.scc.uid-range
annotation to populate
range fields.
An SELinuxContext
strategy of MustRunAs
with no level set. Admission
looks for the openshift.io/sa.scc.mcs
annotation to populate the level.
A FSGroup
strategy of MustRunAs
. Admission looks for the
openshift.io/sa.scc.supplemental-groups
annotation.
A SupplementalGroups
strategy of MustRunAs
. Admission looks for the
openshift.io/sa.scc.supplemental-groups
annotation.
During the generation phase, the security context provider uses default values for any parameter values that are not specifically set in the pod. Default values are based on the selected strategy:
RunAsAny
and MustRunAsNonRoot
strategies do not provide default
values. If the pod needs a parameter value, such as a group ID, you
must define the value in the pod specification.
MustRunAs
(single value) strategies provide a default value that is
always used. For example, for group IDs, even if the pod specification defines
its own ID value, the namespace’s default parameter value also appears in the pod’s
groups.
MustRunAsRange
and MustRunAs
(range-based) strategies provide the
minimum value of the range. As with a single value MustRunAs
strategy, the
namespace’s default parameter value appears in the running pod. If a range-based
strategy is configurable with multiple ranges, it provides the minimum value
of the first configured range.
|
By default, the annotation-based |
The |
The following examples show the security context constraints (SCC) format and annotations:
privileged
SCCallowHostDirVolumePlugin: true
allowHostIPC: true
allowHostNetwork: true
allowHostPID: true
allowHostPorts: true
allowPrivilegedContainer: true
allowedCapabilities: (1)
- '*'
apiVersion: security.openshift.io/v1
defaultAddCapabilities: [] (2)
fsGroup: (3)
type: RunAsAny
groups: (4)
- system:cluster-admins
- system:nodes
kind: SecurityContextConstraints
metadata:
annotations:
kubernetes.io/description: 'privileged allows access to all privileged and host
features and the ability to run as any user, any group, any fsGroup, and with
any SELinux context. WARNING: this is the most relaxed SCC and should be used
only for cluster administration. Grant with caution.'
creationTimestamp: null
name: privileged
priority: null
readOnlyRootFilesystem: false
requiredDropCapabilities: (5)
- KILL
- MKNOD
- SETUID
- SETGID
runAsuser: (6)
type: RunAsAny
seLinuxContext: (7)
type: RunAsAny
seccompProfiles:
- '*'
supplementalGroups: (8)
type: RunAsAny
users: (9)
- system:serviceaccount:default:registry
- system:serviceaccount:default:router
- system:serviceaccount:openshift-infra:build-controller
volumes:
- '*'
1 | A list of capabilities that a pod can request. An empty list means
that none of capabilities can be requested while the special symbol *
allows any capabilities. |
2 | A list of additional capabilities that are added to any pod. |
3 | The FSGroup strategy, which dictates the allowable values for the
security context. |
4 | The groups that can access this SCC. |
5 | A list of capabilities to drop from a pod. Or, specify ALL to drop all
capabilities. |
6 | The runAsuser strategy type, which dictates the allowable values for the
Security Context. |
7 | The seLinuxContext strategy type, which dictates the allowable values for
the Security Context. |
8 | The supplementalGroups strategy, which dictates the allowable supplemental
groups for the Security Context. |
9 | The users who can access this SCC. |
The users
and groups
fields on the SCC control which users can access the
SCC.
By default, cluster administrators, nodes, and the build controller are granted
access to the privileged SCC. All authenticated users are granted access to the
restricted-v2
SCC.
runAsuser
settingapiVersion: 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
1 | When a container or pod does not request a user ID under which it should be run,
the effective UID depends on the SCC that emits this pod. Because the restricted-v2 SCC
is granted to all authenticated users by default, it will be available to all
users and service accounts and used in most cases. The restricted-v2 SCC uses
MustRunAsRange strategy for constraining and defaulting the possible values of
the securityContext.runAsuser field. The admission plugin will look for the
openshift.io/sa.scc.uid-range annotation on the current project to populate
range fields, as it does not provide this range. In the end, a container will
have runAsuser equal to the first value of the range that is
hard to predict because every project has different ranges. |
runAsuser
settingapiVersion: 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
1 | A container or pod that requests a specific user ID will be accepted by OKD only when a service account or a user is granted access to a SCC that allows such a user ID. The SCC can allow arbitrary IDs, an ID that falls into a range, or the exact user ID specific to the request. |
This configuration is valid for SELinux, fsGroup, and Supplemental Groups.
You can create security context constraints (SCCs) by using the OpenShift CLI (oc
).
Install the OpenShift CLI (oc
).
Log in to the cluster as a user with the cluster-admin
role.
Define the SCC in a YAML file named scc_admin.yaml
:
SecurityContextConstraints
object definitionkind: SecurityContextConstraints
apiVersion: security.openshift.io/v1
metadata:
name: scc-admin
allowPrivilegedContainer: true
runAsuser:
type: RunAsAny
seLinuxContext:
type: RunAsAny
fsGroup:
type: RunAsAny
supplementalGroups:
type: RunAsAny
users:
- my-admin-user
groups:
- my-admin-group
Optionally, you can drop specific capabilities for an SCC by setting the
requiredDropCapabilities
field with the desired values. Any specified
capabilities are dropped from the container. To drop all capabilities, specify ALL
. For example, to create an SCC
that drops the KILL
, MKNOD
, and SYS_CHROOT
capabilities, add
the following to the SCC object:
requiredDropCapabilities:
- KILL
- MKNOD
- SYS_CHROOT
You cannot list a capability in both |
CRI-O supports the same list of capability values that are found in the Docker documentation.
Create the SCC by passing in the file:
$ oc create -f scc_admin.yaml
securitycontextconstraints "scc-admin" created
Verify that the SCC was created:
$ oc get scc scc-admin
NAME PRIV CAPS SELINUX RUNASuser FSGROUP SUPGROUP PRIORITY READONLYROOTFS VOLUMES
scc-admin true [] RunAsAny RunAsAny RunAsAny RunAsAny <none> false [awsElasticBlockStore azureDisk azureFile cephFS cinder configMap downwardAPI emptyDir fc flexVolume flocker gcePersistentDisk gitRepo glusterfs iscsi nfs persistentVolumeClaim photonPersistentDisk quobyte rbd secret vsphere]
You can specify SCCs as resources that are handled by RBAC. This allows you to scope access to your SCCs to a certain project or to the entire cluster. Assigning users, groups, or service accounts directly to an SCC retains cluster-wide scope.
You cannot assign a SCC to pods created in one of the default namespaces: |
To include access to SCCs for your role, specify the scc
resource
when creating a role.
$ oc create role <role-name> --verb=use --resource=scc --resource-name=<scc-name> -n <namespace>
This results in the following role definition:
apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
...
name: role-name (1)
namespace: namespace (2)
...
rules:
- apiGroups:
- security.openshift.io (3)
resourceNames:
- scc-name (4)
resources:
- securitycontextconstraints (5)
verbs: (6)
- use
1 | The role’s name. |
2 | Namespace of the defined role. Defaults to default if not specified. |
3 | The API group that includes the SecurityContextConstraints resource.
Automatically defined when scc is specified as a resource. |
4 | An example name for an SCC you want to have access. |
5 | Name of the resource group that allows users to specify SCC names in
the resourceNames field. |
6 | A list of verbs to apply to the role. |
A local or cluster role with such a rule allows the subjects that are
bound to it with a role binding or a cluster role binding to use the
user-defined SCC called scc-name
.
Because RBAC is designed to prevent escalation, even project administrators
are unable to grant access to an SCC. By default, they are not
allowed to use the verb |
You can manage security context constraints (SCCs) in your instance as normal API objects using the OpenShift CLI (oc
).
You must have |
To get a current list of SCCs:
$ oc get scc
NAME PRIV CAPS SELINUX RUNASuser FSGROUP SUPGROUP PRIORITY READONLYROOTFS VOLUMES
anyuid false <no value> MustRunAs RunAsAny RunAsAny RunAsAny 10 false ["configMap","downwardAPI","emptyDir","persistentVolumeClaim","projected","secret"]
hostaccess false <no value> MustRunAs MustRunAsRange MustRunAs RunAsAny <no value> false ["configMap","downwardAPI","emptyDir","hostPath","persistentVolumeClaim","projected","secret"]
hostmount-anyuid false <no value> MustRunAs RunAsAny RunAsAny RunAsAny <no value> false ["configMap","downwardAPI","emptyDir","hostPath","nfs","persistentVolumeClaim","projected","secret"]
hostnetwork false <no value> MustRunAs MustRunAsRange MustRunAs MustRunAs <no value> false ["configMap","downwardAPI","emptyDir","persistentVolumeClaim","projected","secret"]
hostnetwork-v2 false ["NET_BIND_SERVICE"] MustRunAs MustRunAsRange MustRunAs MustRunAs <no value> false ["configMap","downwardAPI","emptyDir","persistentVolumeClaim","projected","secret"]
node-exporter true <no value> RunAsAny RunAsAny RunAsAny RunAsAny <no value> false ["*"]
nonroot false <no value> MustRunAs MustRunAsNonRoot RunAsAny RunAsAny <no value> false ["configMap","downwardAPI","emptyDir","persistentVolumeClaim","projected","secret"]
nonroot-v2 false ["NET_BIND_SERVICE"] MustRunAs MustRunAsNonRoot RunAsAny RunAsAny <no value> false ["configMap","downwardAPI","emptyDir","persistentVolumeClaim","projected","secret"]
privileged true ["*"] RunAsAny RunAsAny RunAsAny RunAsAny <no value> false ["*"]
restricted false <no value> MustRunAs MustRunAsRange MustRunAs RunAsAny <no value> false ["configMap","downwardAPI","emptyDir","persistentVolumeClaim","projected","secret"]
restricted-v2 false ["NET_BIND_SERVICE"] MustRunAs MustRunAsRange MustRunAs RunAsAny <no value> false ["configMap","downwardAPI","emptyDir","persistentVolumeClaim","projected","secret"]
You can view information about a particular SCC, including which users, service accounts, and groups the SCC is applied to.
For example, to examine the restricted
SCC:
$ oc describe scc restricted
Name: restricted
Priority: <none>
Access:
users: <none> (1)
Groups: <none> (2)
Settings:
Allow Privileged: false
Allow Privilege Escalation: true
Default Add Capabilities: <none>
Required Drop Capabilities: KILL,MKNOD,SETUID,SETGID
Allowed Capabilities: <none>
Allowed Seccomp Profiles: <none>
Allowed Volume Types: configMap,downwardAPI,emptyDir,persistentVolumeClaim,projected,secret
Allowed Flexvolumes: <all>
Allowed Unsafe Sysctls: <none>
Forbidden Sysctls: <none>
Allow Host Network: false
Allow Host Ports: false
Allow Host PID: false
Allow Host IPC: false
Read Only Root Filesystem: false
Run As user Strategy: MustRunAsRange
UID: <none>
UID Range Min: <none>
UID Range Max: <none>
SELinux Context Strategy: MustRunAs
user: <none>
Role: <none>
Type: <none>
Level: <none>
FSGroup Strategy: MustRunAs
Ranges: <none>
Supplemental Groups Strategy: RunAsAny
Ranges: <none>
1 | Lists which users and service accounts the SCC is applied to. |
2 | Lists which groups the SCC is applied to. |
To preserve customized SCCs during upgrades, do not edit settings on the default SCCs. |