Kubernetes/Security and RBAC

API Server and Role Base Access Control

Once the API server has determined who you are (whether a pod or a user), the authorization is handled by RBAC.

To prevent unauthorized users from modifying the cluster state, RBAC is used by defining roles and role bindings for a user. A service account resource is created for a pod to determine what control has over the cluster state. For example, the default service account will not allow you to list the services in a namespace.

The Kubernetes API server provides CRUD actions (Create, Read, Update, Delete) interface for interacting with cluster state over a RESTful API. API calls can come only from 2 sources:

• kubectl
• POD

There is 4 stage process

1. Authentication
2. Authorization
3. Admission
4. Writing the configuration state CRUD actions to persistent store etcd database

Example plugins:

• serviceaccount plugin applies default serviceaccount to pods that don't explicitly specify

RBAC is managed by 4 resources, divided over 2 groups

RBAC resources

Group-1 namespace resources	Group-2 cluster level resources	resources type
roles	cluster roles	defines what can be done
role bindings	cluster role bindings	defines who can do it

When deploying a pod a default serviceaccount is assigned if not specified in the pod manifest. The serviceaccount represents an identity of an app running on a pod. Token file holds authentication token. Let's create a namespace and create a test pod to try to list available services.

kubectl create ns rbac
kubectl run apitest --image=nginx -n rbac #create test container, to run API call test from

Each pod has serviceaccount, the API authentication token is on a pod. When a pod makes API call uses the token, this allows to assumes the serviceaccount, so it gets identity. You can preview the token on the pod.

kubectl -n rbac1 exec -it apitest-<UID> -- /bin/sh  #connect to the container shell

#display token and namespace that allows to connect to API server from this pod
root$ cat /var/run/secrets/kubernetes.io/serviceaccount/{token,namespace} 

#call API server to list K8s services in 'rbac' namespace
root$ curl localhost:8001/api/v1/namespaces/rbac/services

List all serviceaccounts. Serviceaccounts can only be used within the same namespace.

kubectl get serviceaccounts -n rbac
kubectl get secrets
NAME                  TYPE                                  DATA   AGE
default-token-qqzc7   kubernetes.io/service-account-token   3      39h
kubectl get secrets default-token-qqzc7 -o yaml #display secrets

ServiceAccount

The API server is first evaluating if the request is coming from a service account or a normal user /or normal user account meeting, a private key, a user store or even a file with a list of user names and passwords. Kubernetes doesn't have objects that represent normal user accounts, and normal users cannot be added to the cluster through.

kubectl get    serviceaccounts #or 'sa' in short
kubectl create serviceaccount  jenkins

kubectl get    serviceaccounts jenkins -o yaml
apiVersion: v1
kind: ServiceAccount
metadata:
  creationTimestamp: "2019-08-05T07:10:40Z"
  name: jenkins
  namespace: default
  resourceVersion: "678"
  selfLink: /api/v1/namespaces/default/serviceaccounts/jenkins
  uid: 21cba4bb-b750-11e9-86b3-0800274143a9
secrets:
- name: jenkins-token-cspjm

kubectl get secret [secret_name]

Assign ServiceAccoubt to a pod

apiVersion: v1
kind: Pod
metadata:
  name: busybox
  namespace: default
spec:
  serviceAccountName: jenkins #<-- ServiceAccount
  containers:
  - image: busybox:1.28.4
    command:
      - sleep
      - "3600"
    imagePullPolicy: IfNotPresent
    name: busybox
  restartPolicy: Always

#Verify
kubectl.exe get pods -o yaml | sls serviceAccount

        {"apiVersion":"v1","kind":"Pod","metadata":{"annotations":{},"name":"busybox","namespace":"default"},"spec":{"c
ontainers":[{"command":["sleep","3600"],"image":"busybox:1.28.4","imagePullPolicy":"IfNotPresent","name":"busybox"}],"r
estartPolicy":"Always","serviceAccountName":"jenkins"}}
      - mountPath: /var/run/secrets/kubernetes.io/serviceaccount
    serviceAccount: jenkins
    serviceAccountName: jenkins

Create Administrative account

This is a process of setting up a new remote administrator.

kubectl.exe config set-credentials piotr --username=piotr --password=password

#new section in ~/.kube/config has been added:
users:
- name: user1
...
- name: piotr
  user:
    password: password
    username: piotr

#create clusterrolebinding, this is for authonomus users not-recommended
kubectl create clusterrolebinding cluster-system-anonymous --clusterrole=cluster-admin --user=system:anonymous
clusterrolebinding.rbac.authorization.k8s.io/cluster-system-anonymous created

#copy server ca.crt
laptop$ scp ubuntu@k8s-cluster.acme.com:/etc/kubernetes/pki/ca.crt .

#set kubeconfig 
kubectl config set-cluster kubernetes --server=https://k8s-cluster.acme.com:6443 --certificate-authority=ca.crt --embed-certs=true

#Create context
kubectl config set-context kubernetes --cluster=kubernetes --user=piotr --namespace=default

#Use contect to current
kubectl config use-context kubernetes

Create a role (namespaced permissions)

The role describes what actions can be performed. This role allows to list services from a web namespace.

apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  namespace: web #this need to be created beforehand
  name: service-reader
rules:
- apiGroups: [""]
  verbs: ["get", "list"]
  resources: ["services"]

The role does not specify who can do it. Thus we create a roleBinding with a user, serviceAccount or group. The roleBinding can only reference a single role, but can bind to multi: users, serviceAccounts or groups

kubectl create rolebinding roleBinding-test --role=service-reader --serviceaccount=web:default -n web

# Verify access has been granted
curl localhost:8001/api/v1/namespaces/web/services

Create a clusterrole (cluster-wide permissions)

In this example we create ClusterRole that can access persitenvolumes APIs, then we will create ClusterRolebinding (pv-test) with a default ServiceAccount (name: default) in 'web' namespace. The SA is a account that pod assumes/uses by default when getting Authenticated by API-server. When we then attach to the container and try to list cluster-wide resource - persitenvolumes , this will be allowed because of ClusterRole, that the pod has assumed.

# Create a ClusterRole to access PersistentVolumes:
kubectl create clusterrole pv-reader --verb=get,list --resource=persistentvolumes

# Create a ClusterRoleBinding for the cluster role:
kubectl create clusterrolebinding pv-test --clusterrole=pv-reader --serviceaccount=web:default

The YAML for a pod that includes a curl and proxy container:

apiVersion: v1
kind: Pod
metadata:
  name: curlpod
  namespace: web
spec:
  containers:
  - image: tutum/curl
    command: ["sleep", "9999999"]
    name: main
  - image: linuxacademycontent/kubectl-proxy
    name: proxy
  restartPolicy: Always

Create the pod that will allow you to curl directly from the container:

kubectl apply -f curlpod.yaml
kubectl get pods -n web               # Get the pods in the web namespace
kubectl exec -it curlpod -n web -- sh # Open a shell to the container:

#Verify you can access PersistentVolumes (cluster-level) from the pod
/ # curl localhost:8001/api/v1/persistentvolumes
{
  "kind": "PersistentVolumeList",
  "apiVersion": "v1",
  "metadata": {
    "selfLink": "/api/v1/persistentvolumes",
    "resourceVersion": "7173"
  },
  "items": []
}/ #

List all API resources

PS C:> kubectl.exe proxy
Starting to serve on 127.0.0.1:8001

List all API resources

Text

Web browser

PS C:> curl http://localhost:8001 StatusCode  : 200 StatusDescription : OK Content  : { "paths": [ "/api", "/api/v1", "/apis", "/apis/", "/apis/admissionregistration.k8s.io", "/apis/admissionregistration.k8s.io/v1beta1", "/apis/apiextensions.k8s.io", "... RawContent  : HTTP/1.1 200 OK Content-Length: 2738 Content-Type: application/json Date: Wed, 14 Aug 2019 07:21:12 GMT { "paths": [ "/api", "/api/v1", "/apis", "/apis/", "/apis/admissionr... Forms  : {} Headers  : {[Content-Length, 2738], [Content-Type, application/json], [Date, Wed, 14 Aug 2019 07:21:12 GMT]} Images  : {} InputFields  : {} Links  : {} ParsedHtml  : System.__ComObject RawContentLength  : 2738

:

Network policies

Network policies allow you to specify which pods can talk to other pods. The example Calico's plugin allows for securing communication by:

• applying network policy based on:
  • pod label-selector
  • namespace label-selector
  • CIDR block range
• securing communication (who can access pods) by setting up:
  • ingress rules
  • egress rules

POSTing any NetworkPolicy manifest to the API server will have no effect unless your chosen networking solution supports network policy. Network Policy is just an API resource that defines a set of rules for Pod access. However, to enable a network policy, we need a network plugin that supports it. We have a few options:

• Calico, Cilium, Kube-router, Romana, Weave Net

Install Calico canal network policies plugin:

wget -O canal.yaml https://docs.projectcalico.org/v3.5/getting-started/kubernetes/installation/hosted/canal/canal.yaml
kubectl apply -f canal.yaml

Minikube local cluster with NetworkPolicy. Cilium DaemonSet will place one Pod per node. Each Pod then will enforce network policies on the traffic using Berkeley Packet Filter (BPF).

minikube start --network-plugin=cni --memory=4096 --kubernetes-version=1.13
kubectl create -f https://raw.githubusercontent.com/cilium/cilium/1.4.0/examples/kubernetes/1.13/cilium-minikube.yaml

Create a 'default' isolation policy for a namespace by creating a NetworkPolicy that selects all pods but does not allow any ingress traffic to those pods

Default policies

Default deny all ingress traffic	Default allow all ingress traffic
apiVersion: networking.k8s.io/v1 kind: NetworkPolicy metadata: name: deny-all spec: podSelector: {} # blank,all pods in NS policyTypes: # inherit this policy - Ingress	apiVersion: networking.k8s.io/v1 kind: NetworkPolicy metadata: name: allow-all spec: podSelector: {} ingress: - {} policyTypes: - Ingress

Apply and show

$ kubectl.exe apply -f policy-denyall.yaml
networkpolicy.networking.k8s.io/deny-all created
ubuntu@quasimodo:/mnt/c/Users/Sylwia/k8s-manifests$ kubectl.exe get networkPolicy -A
NAMESPACE   NAME       POD-SELECTOR   AGE
default     deny-all   <none>         6s

Run test pod

kubectl run nginx --image=nginx --replicas=3
kubectl expose deployment nginx --port=80

# try to access a nginx service from another pod
kubectl run busybox --rm -it --image=busybox /bin/sh
#wget --spider --timeout=1 nginx #this should timeout
                                 #--spider dont download just browse

Create NetworkPolicy that allows ingress port 5432 from pods with 'web' label

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: db-netpolicy
spec:
  podSelector:
    matchLabels:
      app: db
  ingress:
  - from:
    - podSelector:
        matchLabels:
          app: web
    ports:
    - port: 5432

Label a pod to get the NetworkPolicy:

kubectl label pods [pod_name] app=db
kubectl run busybox --rm -it --image=busybox /bin/sh
#wget --spider --timeout=1 nginx #this should timeout

NetowrkPolicy examples

namespace NetworkPolicy	IP block NetworkPolicy	egress NetworkPolicy
apiVersion: networking.k8s.io/v1 kind: NetworkPolicy metadata: name: ns-netpolicy spec: podSelector: matchLabels: app: db ingress: - from: - namespaceSelector: matchLabels: tenant: web ports: - port: 5432	apiVersion: networking.k8s.io/v1 kind: NetworkPolicy metadata: name: ipblock-netpolicy spec: podSelector: matchLabels: app: db ingress: - from: - ipBlock: cidr: 192.168.1.0/24	apiVersion: networking.k8s.io/v1 kind: NetworkPolicy metadata: name: egress-netpol spec: podSelector: matchLabels: app: web egress: - to: - podSelector: matchLabels: app: db ports: - port: 5432

Resources

• Controlling access to API server K8s docs
• Authentication