GCP - Federation Abuse

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OIDC - Github Actions Abuse

GCP

GithubリポジトリからGCP サービスアカウントへのGithub Actionsのアクセスを許可するためには、以下の手順が必要です：

• 必要な権限を持つサービスアカウントを作成して、github actionsからアクセスできるようにします：

projectId=FIXME
gcloud config set project $projectId

# Create the Service Account
gcloud iam service-accounts create "github-demo-sa"
saId="github-demo-sa@${projectId}.iam.gserviceaccount.com"

# Enable the IAM Credentials API
gcloud services enable iamcredentials.googleapis.com

# Give permissions to SA

gcloud projects add-iam-policy-binding $projectId \
--member="serviceAccount:$saId" \
--role="roles/iam.securityReviewer"

• 新しいワークロードアイデンティティプールを生成します:

# Create a Workload Identity Pool
poolName=wi-pool

gcloud iam workload-identity-pools create $poolName \
--location global \
--display-name $poolName

poolId=$(gcloud iam workload-identity-pools describe $poolName \
--location global \
--format='get(name)')

• 新しい ワークロードアイデンティティプール OIDC プロバイダー を生成し、信頼する github actions（このシナリオでは org/repo 名による）:

attributeMappingScope=repository # could be sub (GitHub repository and branch) or repository_owner (GitHub organization)

gcloud iam workload-identity-pools providers create-oidc $poolName \
--location global \
--workload-identity-pool $poolName \
--display-name $poolName \
--attribute-mapping "google.subject=assertion.${attributeMappingScope},attribute.actor=assertion.actor,attribute.aud=assertion.aud,attribute.repository=assertion.repository" \
--issuer-uri "https://token.actions.githubusercontent.com"

providerId=$(gcloud iam workload-identity-pools providers describe $poolName \
--location global \
--workload-identity-pool $poolName \
--format='get(name)')

• 最後に、プロバイダーからのプリンシパルがサービスプリンシパルを使用できるようにします：

gitHubRepoName="repo-org/repo-name"
gcloud iam service-accounts add-iam-policy-binding $saId \
--role "roles/iam.workloadIdentityUser" \
--member "principalSet://iam.googleapis.com/${poolId}/attribute.${attributeMappingScope}/${gitHubRepoName}"

# Workload Identity Poolを作成
poolName=wi-pool2

gcloud iam workload-identity-pools create $poolName \
--location global \
--display-name $poolName

poolId=$(gcloud iam workload-identity-pools describe $poolName \
--location global \
--format='get(name)')

gcloud iam workload-identity-pools providers create-oidc $poolName \
--project="${projectId}" \
--location="global" \
--workload-identity-pool="$poolName" \
--display-name="Demo provider" \
--attribute-mapping="google.subject=assertion.sub,attribute.actor=assertion.actor,attribute.aud=assertion.aud" \
--issuer-uri="https://token.actions.githubusercontent.com"

providerId=$(gcloud iam workload-identity-pools providers describe $poolName \
--location global \
--workload-identity-pool $poolName \
--format='get(name)')

# ワイルドカードを確認
gcloud iam service-accounts add-iam-policy-binding "${saId}" \
--project="${projectId}" \
--role="roles/iam.workloadIdentityUser" \
  --member="principalSet://iam.googleapis.com/${poolId}/*"

Github

**${providerId}と${saId}**をそれぞれの値に変更することを忘れないでください：

name: Check GCP action
on:
workflow_dispatch:
pull_request:
branches:
- main

permissions:
id-token: write

jobs:
Get_OIDC_ID_token:
runs-on: ubuntu-latest
steps:
- id: "auth"
name: "Authenticate to GCP"
uses: "google-github-actions/auth@v2.1.3"
with:
create_credentials_file: "true"
workload_identity_provider: "${providerId}" # In the providerId, the numerical project ID (12 digit number) should be used
service_account: "${saId}" # instead of the alphanumeric project ID. ex:
activate_credentials_file: true # projects/123123123123/locations/global/workloadIdentityPools/iam-lab-7-gh-pool/providers/iam-lab-7-gh-pool-oidc-provider'
- id: "gcloud"
name: "gcloud"
run: |-
gcloud config set project <project-id>
gcloud config set account '${saId}'
gcloud auth login --brief --cred-file="${{ steps.auth.outputs.credentials_file_path }}"
gcloud auth list
gcloud projects list
gcloud secrets list