Verifying Kublr docker images

Overview

Kublr starting from version 1.25.1 signs its Docker images. Before downloading Kublr Docker image, you can make sure you deal with the official, signed image.

Checking Kublr Docker image signatures

To check Kublr Docker images signatures, use the verify script presented below.

Script prerequisites:

• list.txt - the list of Kublr Docker images. Note that only the cr.kublr.com images are controlled and signed by Kublr.

  To get the list file, in the Release Notes for your Kublr version, search for kublr-agent-images.

• cosign.pub - public key, against which the validity of Kublr signatures is checked.

  Public key file can be downloaded here.

• Cosign - open-source tool used by Kublr for signing container images. You will require it for verifying and image copying as well. If you do not have the tool, install it as described here.

Script:

#!/bin/bash
if [[ $# -eq 0 ]] ; then
    echo 'You need to provide list of files and path to the public key'
    echo "Example: $0 list.txt cosign.pub"
    exit 1
fi
 
if ! command -v cosign #&> /dev/null
then
  echo "COSIGN could not be found, you need to install it first"
  exit 1
fi
 
# maybe add check 'sha256sum $(command -v cosign)'
 
while read p; do
  echo "Get $p"
  p=${p/docker.beta.kublr.com/cr.kublr.com}
  echo "Verify $p"
  cosign verify --key $2 $p
done <$1

This script:

• Checks whether Cosign utility is installed.
• Transforms Kublr internal addresses into external ones:
  • docker.beta.kublr.com → cr.kublr.com
• Against each row of list.txt, checks Kublr signature using the provided public key.
• Returns information on whether the listed images are signed by Kublr.

Copying Kublr Docker images

If you deploy Kublr in an air-gapped environment, to copy Kublr Docker images to it, use the copy script presented below.

#!/bin/bash
if [[ $# -eq 0 ]] ;
  then
    echo 'You need to provide list of files, directory for images and path to your registry'
    echo "Example: $0 list.txt images quay.io/username/kublr"
    exit 1
fi
 
if ! command -v cosign #&> /dev/null
  then
    echo "COSIGN could not be found, you need to install it first"
    exit 1
fi
 
# maybe add check 'sha256sum $(command -v cosign)'
 
while read p; do
  #docker.beta.kublr.com -> cr.kublr.com
  p=${p/docker.beta.kublr.com/cr.kublr.com}
  if [[ $p == *"sha256"* ]];
    then
      tag=$(echo $p|sed 's:.*/::'|grep -oP '.*?(?=@sha256:)')
    else
      tag=$(echo $p|sed 's:.*/::')
  fi
  cosign save $p --dir $2
  cosign load --dir $2 $3/$tag
done <$1

This script uses Cosign utility to copy images along with signatures into your isolated environment.

Verifying Kublr image signatures in Kubernetes

In Kubernetes, you can verify Kublr image signatures using Kyverno policy management utility. This is done using the Verify Image policy that checks the signature of an image repo to ensure it has been signed by verifying its signature against the provided public key.

For details, see the Verify Images article in the Kyverno documentation.

Below is the example that checks new pods in namespaces that begins on k (k*) and have images like quay.io/imname* against the provided public key.

apiVersion: kyverno.io/v1
kind: ClusterPolicy
metadata:
  name: check-image
spec:
  validationFailureAction: enforce
  background: false
  rules:
    - name: check-image
      match:
        resources:
          kinds:
            - Pod
          namespaces:
            - "k*"
      verifyImages:
      - image: "quay.io/imname*"
        key: |-
          -----BEGIN PUBLIC KEY-----
          ************************==
          -----END PUBLIC KEY-----