175 lines
8.1 KiB
Markdown
175 lines
8.1 KiB
Markdown
# Kubernetes Role-Based Access Control (RBAC)
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## Role-Based Access Control (RBAC)
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Kubernetes has an **authorization module named Role-Based Access Control** ([**RBAC**](https://kubernetes.io/docs/reference/access-authn-authz/rbac/)) that helps to set utilization permissions to the API server.\
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The RBAC table is constructed from “**Roles**” and “**ClusterRoles**.” The difference between them is just where the role will be applied – a “**Role**” will grant access to only **one** **specific** **namespace**, while a “**ClusterRole**” can be used in **all namespaces** in the cluster. Moreover, ClusterRoles can also grant access to:
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* cluster-scoped resources (like nodes).
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* non-resource endpoints (like /healthz).
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* namespaced resources (like Pods), across all namespaces.
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In the template of a role or a cluster role you will need to indicate the **name of the role**, the **namespace** (in roles) and then the **apiGroups**, **resources** and **verbs** of the role:
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* The **apiGroups** is an array that contains the different **API namespaces** that this rule applies to. For example, a Pod definition uses apiVersion: v1. _It can has values such as rbac.authorization.k8s.io or \[\*]_.
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* The **resources** is an array that defines **which resources this rule applies to**. You can find all the resources with: `kubectl api-resources --namespaced=true`
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* The **verbs** is an array that contains the **allowed verbs**. The verb in Kubernetes defines the **type of action** you need to apply to the resource. For example, the list verb is used against collections while "get" is used against a single resource.
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### Rules Verbs
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(_This info was taken from_ [_**here**_](https://kubernetes.io/docs/reference/access-authn-authz/authorization/#determine-the-request-verb))
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| HTTP verb | request verb |
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| --------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------- |
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| POST | create |
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| GET, HEAD | get (for individual resources), list (for collections, including full object content), watch (for watching an individual resource or collection of resources) |
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| PUT | update |
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| PATCH | patch |
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| DELETE | delete (for individual resources), deletecollection (for collections) |
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Kubernetes sometimes checks authorization for additional permissions using specialized verbs. For example:
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* [PodSecurityPolicy](https://kubernetes.io/docs/concepts/policy/pod-security-policy/)
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* `use` verb on `podsecuritypolicies` resources in the `policy` API group.
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* [RBAC](https://kubernetes.io/docs/reference/access-authn-authz/rbac/#privilege-escalation-prevention-and-bootstrapping)
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* `bind` and `escalate` verbs on `roles` and `clusterroles` resources in the `rbac.authorization.k8s.io` API group.
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* [Authentication](https://kubernetes.io/docs/reference/access-authn-authz/authentication/)
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* `impersonate` verb on `users`, `groups`, and `serviceaccounts` in the core API group, and the `userextras` in the `authentication.k8s.io` API group.
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### Examples
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Example of **Role** **configuration**:
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```yaml
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apiVersion: rbac.authorization.k8s.io/v1
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kind: Role
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metadata:
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namespace: defaultGreen
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name: pod-and-pod-logs-reader
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rules:
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- apiGroups: [""]
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resources: ["pods", "pods/log"]
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verbs: ["get", "list", "watch"]
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```
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Example of **ClusterRole** configuration:
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```yaml
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apiVersion: rbac.authorization.k8s.io/v1
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kind: ClusterRole
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metadata:
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# "namespace" omitted since ClusterRoles are not namespaced
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name: secret-reader
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rules:
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- apiGroups: [""]
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resources: ["secrets"]
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verbs: ["get", "watch", "list"]
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```
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For example you can use a **ClusterRole** to allow a particular user to run:
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```
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kubectl get pods --all-namespaces
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```
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**Role and ClusterRole Binding concept**
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A **role binding** **grants the permissions defined in a role to a user or set of users**. It holds a list of subjects (users, groups, or service accounts), and a reference to the role being granted. A **RoleBinding** grants permissions within a specific **namespace** whereas a **ClusterRoleBinding** grants that access **cluster-wide**.
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**RoleBinding** example:
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```yaml
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apiVersion: rbac.authorization.k8s.io/v1
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# This role binding allows "jane" to read pods in the "default" namespace.
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# You need to already have a Role named "pod-reader" in that namespace.
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kind: RoleBinding
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metadata:
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name: read-pods
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namespace: default
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subjects:
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# You can specify more than one "subject"
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- kind: User
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name: jane # "name" is case sensitive
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apiGroup: rbac.authorization.k8s.io
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roleRef:
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# "roleRef" specifies the binding to a Role / ClusterRole
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kind: Role #this must be Role or ClusterRole
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name: pod-reader # this must match the name of the Role or ClusterRole you wish to bind to
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apiGroup: rbac.authorization.k8s.io
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```
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**ClusterRoleBinding** example:
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```yaml
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apiVersion: rbac.authorization.k8s.io/v1
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# This cluster role binding allows anyone in the "manager" group to read secrets in any namespace.
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kind: ClusterRoleBinding
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metadata:
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name: read-secrets-global
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subjects:
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- kind: Group
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name: manager # Name is case sensitive
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apiGroup: rbac.authorization.k8s.io
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roleRef:
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kind: ClusterRole
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name: secret-reader
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apiGroup: rbac.authorization.k8s.io
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```
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**Permissions are additive** so if you have a clusterRole with “list” and “delete” secrets you can add it with a Role with “get”. So be aware and test always your roles and permissions and **specify what is ALLOWED, because everything is DENIED by default.**
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### **Enumerating RBAC**
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```bash
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# Get current privileges
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kubectl auth can-i --list
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## use `--as=system:serviceaccount:<namespace>:<sa_name>` to impersonate a service account
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# List Cluster Roles
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kubectl get clusterroles
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kubectl describe clusterroles
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# List Cluster Roles Bindings
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kubectl get clusterrolebindings
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kubectl describe clusterrolebindings
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# List Roles
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kubectl get roles
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kubectl describe roles
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# List Roles Bindings
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kubectl get rolebindings
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kubectl describe rolebindings
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```
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### RBAC Structure
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RBAC’s permission is built from three individual parts:
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1. **Role\ClusterRole –** The actual permission. It contains _**rules**_ that represent a set of permissions. Each rule contains [resources](https://kubernetes.io/docs/reference/kubectl/overview/#resource-types) and [verbs](https://kubernetes.io/docs/reference/access-authn-authz/authorization/#determine-the-request-verb). The verb is the action that will apply on the resource.
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2. **Subject (User, Group or ServiceAccount) –** The object that will receive the permissions.
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3. **RoleBinding\ClusterRoleBinding –** The connection between Role\ClusterRole and the subject.
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This is what it will look like in a real cluster:
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“**Fine-grained** role bindings **provide greater security**, but **require more effort to administrate**."
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From **Kubernetes** 1.6 onwards, **RBAC** policies are **enabled by default**. **** But to enable RBAC you can use something like:
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```
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kube-apiserver --authorization-mode=Example,RBAC --other-options --more-options
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```
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This is enabled by default. RBAC functions:
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* Restrict the access to the resources to users or ServiceAccounts.
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* An RBAC Role or ClusterRole contains rules that represent a set of permissions.
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* Permissions are purely additive (there are no “deny” rules).
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* RBAC works with Roles and Bindings
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{% hint style="info" %}
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When configuring roles and permissions it's highly important to always follow the principle of Least Privileges
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{% endhint %}
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