istio.io/content/en/docs/tasks/security/auth-sds/index.md

title	description	weight	keywords
Provisioning Identity through SDS	Shows how to enable SDS (secret discovery service) for Istio identity provisioning.	70	security auth-sds

This task shows how to enable SDS (secret discovery service) for Istio identity provisioning.

Prior to Istio 1.1, the keys and certificates of Istio workloads were generated by Citadel and distributed to sidecars through secret-volume mounted files, this approach has the following minor drawbacks:

• Performance regression during certificate rotation: When certificate rotation happens, Envoy is hot restarted to pick up the new key and certificate, causing performance regression.

• Potential security vulnerability: The workload private keys are distributed through Kubernetes secrets, with known risks.

These issues are addressed in Istio 1.1 through the SDS identity provision flow. The workflow can be described as follows.

1. The workload sidecar Envoy requests the key and certificates from the Citadel agent: The Citadel agent is a SDS server, which runs as per-node DaemonSet. In the request, Envoy passes a Kubernetes service account JWT to the agent.

2. The Citadel agent generates a key pair and sends the CSR request to Citadel: Citadel verifies the JWT and issues the certificate to the Citadel agent.

3. The Citadel agent sends the key and certificate back to the workload sidecar.

This approach has the following benefits:

• The private key never leaves the node: It is only in the Citadel agent and Envoy sidecar's memory.

• The secret volume mount is no longer needed: The reliance on the Kubernetes secrets is eliminated.

• The sidecar Envoy is able to dynamically renew the key and certificate through the SDS API: Certificate rotations no longer require Envoy to restart.

Before you begin

• Set up Istio by following the instructions using Helm with SDS setup and global mutual TLS enabled.

Service-to-service mutual TLS using key/certificate provisioned through SDS

Follow the authentication policy task to setup test services.

{{< text bash >}} $ kubectl create ns foo $ kubectl apply -f <(istioctl kube-inject -f @samples/httpbin/httpbin.yaml@) -n foo $ kubectl apply -f <(istioctl kube-inject -f @samples/sleep/sleep.yaml@) -n foo $ kubectl create ns bar $ kubectl apply -f <(istioctl kube-inject -f @samples/httpbin/httpbin.yaml@) -n bar $ kubectl apply -f <(istioctl kube-inject -f @samples/sleep/sleep.yaml@) -n bar {{< /text >}}

Verify all mutual TLS requests succeed:

{{< text bash >}} for from in "foo" "bar"; do for to in "foo" "bar"; do kubectl exec(kubectl get pod -l app=sleep -n {from} -o jsonpath={.items..metadata.name}) -c sleep -n {from} -- curl "http://httpbin.{to}:8000/ip" -s -o /dev/null -w "sleep.{from} to httpbin.${to}: %{http_code}\n"; done; done sleep.foo to httpbin.foo: 200 sleep.foo to httpbin.bar: 200 sleep.bar to httpbin.foo: 200 sleep.bar to httpbin.bar: 200 {{< /text >}}

Verifying no secret-volume mounted file is generated

To verify that no secret-volume mounted file is generated, access the deployed workload sidecar container:

{{< text bash >}} kubectl exec -it(kubectl get pod -l app=sleep -n foo -o jsonpath={.items..metadata.name}) -c istio-proxy -n foo -- /bin/bash {{< /text >}}

As you can see there is no secret file mounted at /etc/certs folder.

Securing SDS with pod security policies

The Istio Secret Discovery Service (SDS) uses the Citadel agent to distribute the certificate to the Envoy sidecar via a Unix domain socket. All pods running in the same Kubernetes node share the Citadel agent and Unix domain socket.

To prevent unexpected modifications to the Unix domain socket, enable the pod security policy to restrict the pod's permission on the Unix domain socket. Otherwise, a malicious user who has the permission to modify the deployment could hijack the Unix domain socket to break the SDS service or steal the identity credentials from other pods running on the same Kubernetes node.

To enable the pod security policy, perform the following steps:

1. The Citadel agent fails to start unless it can create the required Unix domain socket. Apply the following pod security policy to only allow the Citadel agent to modify the Unix domain socket:

   {{< text bash >}} $ cat <<EOF | kubectl apply -f - apiVersion: policy/v1beta1 kind: PodSecurityPolicy metadata: name: istio-nodeagent spec: allowedHostPaths:

   • pathPrefix: "/var/run/sds" seLinux: rule: RunAsAny supplementalGroups: rule: RunAsAny runAsUser: rule: RunAsAny fsGroup: rule: RunAsAny volumes:
   • '*'

   ---

   kind: Role apiVersion: rbac.authorization.k8s.io/v1 metadata: name: istio-nodeagent namespace: istio-system rules:

   • apiGroups:
     • extensions resources:
     • podsecuritypolicies resourceNames:
     • istio-nodeagent verbs:
     • use

   ---

   apiVersion: rbac.authorization.k8s.io/v1 kind: RoleBinding metadata: name: istio-nodeagent namespace: istio-system roleRef: apiGroup: rbac.authorization.k8s.io kind: Role name: istio-nodeagent subjects:

   • kind: ServiceAccount name: istio-nodeagent-service-account namespace: istio-system EOF {{< /text >}}

2. To stop other pods from modifying the Unix domain socket, change the allowedHostPaths configuration for the the path the Citadel agent uses for the Unix domain socket to readOnly: true.

   {{< warning >}} The following pod security policy assumes no other pod security policy was applied before. If you already applied another pod security policy, add the following configuration values to the existing policies instead of applying the configuration directly. {{< /warning >}}

   {{< text bash >}} $ cat <<EOF | kubectl apply -f - apiVersion: policy/v1beta1 kind: PodSecurityPolicy metadata: name: istio-sds-uds spec:

   Protect the unix domain socket from unauthorized modification

   allowedHostPaths:

   • pathPrefix: "/var/run/sds" readOnly: true

   Allow the istio sidecar injector to work

   allowedCapabilities:

   • NET_ADMIN seLinux: rule: RunAsAny supplementalGroups: rule: RunAsAny runAsUser: rule: RunAsAny fsGroup: rule: RunAsAny volumes:
   • '*'

   ---

   kind: ClusterRole apiVersion: rbac.authorization.k8s.io/v1 metadata: name: istio-sds-uds rules:

   • apiGroups:
     • extensions resources:
     • podsecuritypolicies resourceNames:
     • istio-sds-uds verbs:
     • use

   ---

   apiVersion: rbac.authorization.k8s.io/v1 kind: ClusterRoleBinding metadata: name: istio-sds-uds roleRef: apiGroup: rbac.authorization.k8s.io kind: ClusterRole name: istio-sds-uds subjects:

   • apiGroup: rbac.authorization.k8s.io kind: Group name: system:serviceaccounts EOF {{< /text >}}

3. Enable pod security policies for your platform. Each supported platform enables pod security policies differently. Please refer to the pertinent documentation for your platform. If you are using the Google Kubernetes Engine (GKE), you must enable the pod security policy controller.

   {{< warning >}} Grant all needed permissions in the pod security policy before enabling it. Once the policy is enabled, pods won't start if they require any permissions not granted. {{< /warning >}}

4. Run the following command to restart the Citadel agents:

   {{< text bash >}} $ kubectl delete pod -l 'app=nodeagent' -n istio-system pod "istio-nodeagent-dplx2" deleted pod "istio-nodeagent-jrbmx" deleted pod "istio-nodeagent-rz878" deleted {{< /text >}}

5. To verify that the Citadel agents work with the enabled pod security policy, wait a few seconds and run the following command to confirm the agents started successfully:

   {{< text bash >}} $ kubectl get pod -l 'app=nodeagent' -n istio-system NAME READY STATUS RESTARTS AGE istio-nodeagent-p4p7g 1/1 Running 0 4s istio-nodeagent-qdwj6 1/1 Running 0 5s istio-nodeagent-zsk2b 1/1 Running 0 14s {{< /text >}}

6. Run the following command to start a normal pod.

   {{< text bash >}} $ cat <<EOF | kubectl apply -f - apiVersion: apps/v1 kind: Deployment metadata: name: normal spec: replicas: 1 selector: matchLabels: app: normal template: metadata: labels: app: normal spec: containers: - name: normal image: pstauffer/curl command: ["/bin/sleep", "3650d"] imagePullPolicy: IfNotPresent EOF {{< /text >}}

7. To verify that the normal pod works with the pod security policy enabled, wait a few seconds and run the following command to confirm the normal pod started successfully.

   {{< text bash >}} $ kubectl get pod -l 'app=normal' NAME READY STATUS RESTARTS AGE normal-64c6956774-ptpfh 2/2 Running 0 8s {{< /text >}}

8. Start a malicious pod that tries to mount the Unix domain socket using a write permission.

   {{< text bash >}} $ cat <<EOF | kubectl apply -f - apiVersion: apps/v1 kind: Deployment metadata: name: malicious spec: replicas: 1 selector: matchLabels: app: malicious template: metadata: labels: app: malicious spec: containers: - name: malicious image: pstauffer/curl command: ["/bin/sleep", "3650d"] imagePullPolicy: IfNotPresent volumeMounts: - name: sds-uds mountPath: /var/run/sds volumes: - name: sds-uds hostPath: path: /var/run/sds type: "" EOF {{< /text >}}

9. To verify that the Unix domain socket is protected, run the following command to confirm the malicious pod failed to start due to the pod security policy:

   {{< text bash >}} $ kubectl describe rs -l 'app=malicious' | grep Failed Pods Status: 0 Running / 0 Waiting / 0 Succeeded / 0 Failed ReplicaFailure True FailedCreate Warning FailedCreate 4s (x13 over 24s) replicaset-controller Error creating: pods "malicious-7dcfb8d648-" is forbidden: unable to validate against any pod security policy: [spec.containers[0].volumeMounts[0].readOnly: Invalid value: false: must be read-only] {{< /text >}}

Cleanup

1. Clean up the test services and the Istio control plane:

   {{< text bash >}} $ kubectl delete ns foo $ kubectl delete ns bar $ kubectl delete -f istio-auth-sds.yaml {{< /text >}}

2. Disable the pod security policy in the cluster using the documentation of your platform. If you are using GKE, disable the pod security policy controller.

3. Delete the pod security policy and the test deployments:

   {{< text bash >}} $ kubectl delete psp istio-sds-uds istio-nodeagent $ kubectl delete role istio-nodeagent -n istio-system $ kubectl delete rolebinding istio-nodeagent -n istio-system $ kubectl delete clusterrole istio-sds-uds $ kubectl delete clusterrolebinding istio-sds-uds $ kubectl delete deploy malicious $ kubectl delete deploy normal {{< /text >}}

Caveats

Currently, the SDS identity provision flow has the following caveats:

• SDS support is currently in Alpha.

• Smoothly migrating a cluster from using secret volume mount to using SDS is a work in progress.