Enable policy enforcement in a supply chain with Scan 2.0

This topic tells you how to enable policy enforcement in a supply chain with Supply Chain Security Tools (SCST) - Scan 2.0.

Policy enforcement is not built into SCST - Scan 2.0 and is not in any of the Out of the Box supply chains. You must author a custom supply chain to enable policy enforcement.

To enforce a policy in a supply chain you need a ClusterImageTemplate that uses a Tekton TaskRun to evaluate the vulnerabilities and enforce the set policy. This topic provides a sample TaskRun and a sample ClusterImageTemplate for you to edit.

Prepare for the TaskRun

The TaskRun queries the Metadata Store to get the list of vulnerabilities for the image. Authenticate with the Metadata Store API by obtaining an access token and a certificate:

Generate an image that has the curl and jq commands. You can build your own image (recommended) or use a base Ubuntu image that gets you started faster but is only for testing purposes.
Build your own image
Build an image that contains curl and jq for the Tekton Task to use.
VMware recommends that you use this option because the image has stable versions and dependencies that are deterministic. The image does not need to download curl and jq each time the script runs.

To build your image:
1. Create a Dockerfile with the following in a blank directory:
  
  FROM ubuntu:latest RUN apt-get update RUN apt-get install -y jq curl
2. Build and push the image to a registry that the Build cluster can access by running:
  
  docker build . -t REGISTRY-URL-LOCATION/IMAGE-NAME:IMAGE-TAG docker push REGISTRY-URL-LOCATION/IMAGE-NAME:IMAGE-TAG
  
  Where:
  
  REGISTRY-URL-LOCATION is the registry URL. For example, registry.hub.docker.com/project.
  
  IMAGE-NAME is the name of the image. For example, curl-jq-bash.
  
  IMAGE-TAG is the tag of the image. For example, latest.
3. If you are pushing to a private registry, on the Build cluster run:
  
  tanzu secret registry add registry-credentials --server REGISTRY-SERVER --username \ REGISTRY-USERNAME --password REGISTRY-PASSWORD --export-to-all-namespaces --yes \ --namespace tap-install
  
  Where:
  
  REGISTRY-SERVER is the registry URL. For example, registry.hub.docker.com.
  
  REGISTRY-USERNAME the user name that is allowed to read the pushed curl jq image.
  
  REGISTRY-PASSWORD the password that is allowed to read the pushed curl jq image.
Use a base Ubuntu image
To get started quicker you can embed the downloading of curl and jq in the Task script and use a base Ubuntu image.
Caution
Do not use this option in production environments. VMware recommends that you build your own image that contains curl and jq so that it has predetermined dependencies and versions.

Here is example Task YAML:
```
---
apiVersion: tekton.dev/v1
kind: Task
metadata:
  name: tekton-policy-enforcement
  namespace: DEVELOPER-NAMESPACE
spec:
  params:
    - name: image
      type: string
  steps:
    - name: enforce-policy
      image: ubuntu:latest # <-- ubuntu base image
      ...
      script: |
        apt-get update # <-- update download links
        apt-get install -y jq curl # <-- install jq and curl

        if [ ${GATE} = "none" ]; then
            exit 0
        fi
      ...
```

In the View cluster, get the access token and the Certificate Authority (CA) certificate from the Metadata Store by running these commands:

ACCESS_TOKEN=$(kubectl get secrets -n metadata-store  metadata-store-read-write-client -o json \
| jq -r ".data.token" | base64 -d)

METADATA_STORE_CA_CERT=$(kubectl get secret -n metadata-store ingress-cert -o json | jq -r ".data.\"ca.crt\"" \
| base64 -d)

Verify that both variables are populated by running:
```
echo $ACCESS_TOKEN
echo $METADATA_STORE_CA_CERT
```

In the Build cluster, create metadata-store-access-token and metadata-store-cert secrets by running:

DEVELOPER_NAMESPACE=DEVELOPER-NAMESPACE

kubectl create secret generic metadata-store-access-token \
  --from-literal=accessToken="${ACCESS_TOKEN}" -n ${DEVELOPER_NAMESPACE}

kubectl create secret generic metadata-store-cert \
  --from-literal=caCrt="${METADATA_STORE_CA_CERT}" -n ${DEVELOPER_NAMESPACE}

Where DEVELOPER-NAMESPACE is the developer namespace.

Edit the Task sample to enforce the policy

The following sample Task waits until the vulnerability data is available for the image in the Metadata Store. When the data is available, the vulnerabilities are aggregated by severity. The policy that GATE sets determines whether TaskRun succeeds or fails.

Create a file named task-policy-enforcement.yaml by editing this template for your needs:

---
apiVersion: tekton.dev/v1
kind: Task
metadata:
  name: tekton-policy-enforcement
  namespace: DEVELOPER-NAMESPACE
spec:
  params:
    - name: image
      type: string
  steps:
    - name: enforce-policy
      image: TASK-RUN-IMAGE-WITH-CURL-AND-JQ
      env:
      - name: GATE
        value: THRESHOLD
      - name: METADATA_STORE_URL
        value: METADATA-STORE-URL
      - name: ACCESS_TOKEN
        valueFrom:
          secretKeyRef:
            name: metadata-store-access-token
            key: accessToken
      script: |
        if [ ${GATE} = "none" ]; then
            exit 0
        fi

        IMAGE_DIGEST=$(echo $(params.image) | cut -d "@" -f 2)
        while true; do
          response_code=$(curl https://${METADATA_STORE_URL}/api/v1/images/${IMAGE_DIGEST} -H "Authorization: Bearer ${ACCESS_TOKEN}" -H 'accept: application/json' --cacert /var/cert/caCrt -o vulnerabilities.json -w "%{http_code}")
          if [ $response_code -eq 200 ]; then
            echo "Vulnerabilities data is available in AMR"
            break
          else
            echo "Vulnerabilities data is not available in AMR, waiting..."
            sleep 10
          fi
        done

        critical=$(cat vulnerabilities.json | jq '[.Packages[].Vulnerabilities[] | select(.Ratings[].Severity | contains("Critical"))] | unique | length')
        high=$(cat vulnerabilities.json | jq '[.Packages[].Vulnerabilities[] | select(.Ratings[].Severity | contains("High"))] | unique | length')
        medium=$(cat vulnerabilities.json | jq '[.Packages[].Vulnerabilities[] | select(.Ratings[].Severity | contains("Medium"))] | unique | length')
        low=$(cat vulnerabilities.json | jq '[.Packages[].Vulnerabilities[] | select(.Ratings[].Severity | contains("Low"))] | unique | length')
        vulnerabilitiesCount=0
        case $GATE in
          low)
            vulnerabilitiesCount=$(($low+$medium+$high+$critical))
            ;;
          medium)
            vulnerabilitiesCount=$(($medium+$high+$critical))
            ;;

          high)
            vulnerabilitiesCount=$(($high+$critical))
            ;;

          critical)
            vulnerabilitiesCount=$(($critical))
            ;;
        esac
        echo "Vulnerabilities: ${vulnerabilitiesCount}"
        if [ ${vulnerabilitiesCount} -gt 0 ];then
          exit 1
        fi
      volumeMounts:
      - name: cert
        mountPath: /var/cert
  volumes:
    - name: cert
      secret:
        secretName: metadata-store-cert

Where:

THRESHOLD sets the threshold for severity in the policy. The accepted values are low, medium, high, and critical. For example, if the THRESHOLD is set to high, the TaskRun fails if it finds high or critical vulnerabilities for the image. If the THRESHOLD is set to none, no policy is enforced and TaskRun succeeds.
METADATA-STORE-URL-VALUE is the URL for reaching the Metadata Store. The format is metadata-store. followed by the View cluster ingress domain. For example, metadata-store.VIEW-CLUSTER-INGRESS-DOMAIN. Alternatively, you can get the URL from the View cluster by running:
```
kubectl get httpproxy metadata-store-ingress -n metadata-store -o jsonpath='{.spec.virtualhost.fqdn}'
```
TASK-RUN-IMAGE-WITH-CURL-AND-JQ is any image that contains the bash, curl, and jq commands. If you did not build an image in the first step, you can use the ubuntu:latest image and install jq and curl at the beginning of the script section.

Caution
Do not use this option in production environments. VMware recommends that you build your own image that contains curl and jq so that it has predetermined dependencies and versions.

For example:
```
image: ubuntu:latest
...
...
script: |
apt-get update
apt-get install -y jq curl

if [ ${GATE} = "none" ]; then
   exit 0
fi
...
...
```

Apply the Task to the DEVELOPER-NAMESPACE by running:
```
kubectl apply -f task-policy-enforcement.yaml -n DEVELOPER-NAMESPACE
```
Where DEVELOPER-NAMESPACE is the developer namespace.
Apply the Task to every other developer namespace that uses the policy enforcement.

Include the policy ClusterImageTemplate in the newly authored supply chain

To include the policy ClusterImageTemplate in the newly authored supply chain:

Create a file named policy-cluster-image-and-runnable-template.yaml with this content:

apiVersion: carto.run/v1alpha1
kind: ClusterImageTemplate
metadata:
  name: policy-enforcement-template
spec:
  healthRule:
    singleConditionType: Ready
  imagePath: .status.outputs.imagePath
  lifecycle: mutable
  ytt: |-
    #@ load("@ytt:data", "data")

    #@ def merge_labels(fixed_values):
    #@   labels = {}
    #@   if hasattr(data.values.workload.metadata, "labels"):
    #@     exclusions = ["kapp.k14s.io/app", "kapp.k14s.io/association"]
    #@     for k,v in dict(data.values.workload.metadata.labels).items():
    #@       if k not in exclusions:
    #@         labels[k] = v
    #@       end
    #@     end
    #@   end
    #@   labels.update(fixed_values)
    #@   return labels
    #@ end

    #@ def merged_tekton_params():
    #@   params = []
    #@   params.append({ "name": "image", "value": data.values.image })
    #@   return params
    #@ end
    ---
    apiVersion: carto.run/v1alpha1
    kind: Runnable
    metadata:
      name: #@ data.values.workload.metadata.name + "-policy"
      labels: #@ merge_labels({ "app.kubernetes.io/component": "test" })
    spec:
      retentionPolicy:
        maxFailedRuns: 1
        maxSuccessfulRuns: 1

      #@ if/end hasattr(data.values.workload.spec, "serviceAccountName"):
      serviceAccountName: #@ data.values.workload.spec.serviceAccountName

      runTemplateRef:
        name: tekton-policy-enforcement-taskrun
        kind: ClusterRunTemplate

      resource:
        apiVersion: tekton.dev/v1
        kind: TaskRun

      inputs:
        tekton-params: #@ merged_tekton_params()

---
apiVersion: carto.run/v1alpha1
kind: ClusterRunTemplate
metadata:
  name: tekton-policy-enforcement-taskrun
spec:
  outputs:
    imagePath: spec.params[?(@.name=="image")].value
  template:
    apiVersion: tekton.dev/v1
    kind: TaskRun
    metadata:
      generateName: $(runnable.metadata.name)$-
      labels: $(runnable.metadata.labels)$
    spec:
      params: $(runnable.spec.inputs.tekton-params)$
      serviceAccountName: default
      taskRef:
        name: tekton-policy-enforcement

Create a new supply chain named custom-supply-chain.yaml by following the steps in Author your supply chains.

The scan step generates the vulnerability data that the policy step queries the Metadata Store for. Therefore the policy step must be after the scan step and must take the image produced by the scan step as an input image. You can place any step that requires an image as input after the policy step. For example:

---
apiVersion: carto.run/v1alpha1
kind: ClusterSupplyChain
metadata:
  name: CUSTOM-SUPPLY-CHAIN-NAME
spec:
  resources:
  .... # previous steps

  - name: image-scanner
    templateRef:
      kind: ClusterImageTemplate
      name: image-vulnerability-scan-trivy
    params:
      - name: registry
        default:
          server: tanzu.packages.broadcom.com
          repository: tanzu-image-signing/test-policy
    images:
      - resource: image-provider
        name: image

  - name: policy
    templateRef:
      kind: ClusterImageTemplate
      name: policy-enforcement-template
    images:
    - name: image
      resource: image-scanner

  - name: config-provider
    params:
    - default: default
      name: serviceAccount
    templateRef:
      kind: ClusterConfigTemplate
      name: convention-template
    images:
    - name: image
      resource: policy

  .... # supply chain continues

Where CUSTOM-SUPPLY-CHAIN-NAME is the name of the custom supply chain.

Apply the template, supply chain, and workload

To apply the template, supply chain, and workload:

Apply the generated ClusterImageTemplate and ClusterSupplyChain by running:

kubectl apply -f policy-cluster-image-and-runnable-template.yaml
kubectl apply -f custom-supply-chain.yaml

Create a workload in the developer namespace that can trigger the supply chain. For more information about selectors and how to use them with a custom supply chain, see Providing your own supply chain.

Troubleshoot the policy

If the policy is still waiting to find the vulnerabilities data for the image in the Metadata Store, troubleshoot the policy:

Verify that the observer is healthy and running.
Verify that the observer registered the controller to monitor the ImageVulnerabilityScan kind. For more information about troubleshooting the observer, see Troubleshooting Artifact Metadata Repository.