Use custom organization policies for allow policies

This page shows you how to use Organization Policy Service custom constraints to restrict specific operations on the following Google Cloud resources:

• iam.googleapis.com/AllowPolicy

To learn more about Organization Policy, see Custom organization policies.

About organization policies and constraints

The Google Cloud Organization Policy Service gives you centralized, programmatic control over your organization's resources. As the organization policy administrator, you can define an organization policy, which is a set of restrictions called constraints that apply to Google Cloud resources and descendants of those resources in the Google Cloud resource hierarchy. You can enforce organization policies at the organization, folder, or project level.

Organization Policy provides predefined constraints for various Google Cloud services. However, if you want more granular, customizable control over the specific fields that are restricted in your organization policies, you can also create custom constraints and use those custom constraints in an organization policy.

Policy inheritance

By default, organization policies are inherited by the descendants of the resources on which you enforce the policy. For example, if you enforce a policy on a folder, Google Cloud enforces the policy on all projects in the folder. To learn more about this behavior and how to change it, refer to Hierarchy evaluation rules.

Benefits

You can use custom organization policies that reference IAM attributes to control how your allow policies can be modified. Specifically, you can control the following:

• Who can be granted roles
• Who can have their roles revoked
• Which roles can be granted
• Which roles can be revoked

For example, you can prevent roles that contain the word admin from being granted to principals whose email addresses end in @gmail.com.

Limitations

• Custom organization policies in dry-run mode that reference IAM attributes have some limitations. Namely, audit logs for violations that involve the setIamPolicy method might be missing the following fields:

  • resourceName
  • serviceName
  • methodName

• Audit logs aren't generated for all IAM-related custom organization policy violations. Namely, if a custom organization policy causes a setIamPolicy operation on the organization resource to fail, then Google Cloud doesn't generate an audit log for that event.

• Custom organization policies that reference IAM attributes don't affect the following:

  • Default grants by Cloud Storage ACLs.
  • Automatic role grants for Cloud Storage convenience values and BigQuery default dataset access.
  • Roles granted by default allow policies—for example, a project creator automatically being granted the Owner role (roles/owner) on the project.

• Users can be sent invitations to become owners, even if you have a custom organization policy that prevents the Owner role (roles/owner) from being granted. However, while the custom organization policy doesn't prevent an invitation from being sent, it does prevent invited users from being granted the Owner role. If invited users try to accept the invitation, they'll encounter an error and won't be granted the Owner role.

• Some actions in Google Cloud, such as creating resources or enabling APIs, involve automatically granting a role to a service agent or default service account. If an action involves automatically granting a role and an organization policy prevents that role from being granted, then the entire operation might fail.

  If you encounter this issue, you can use tags to temporarily disable the constraint that prevents the role grant. Then, perform the action. After the action finishes, re-enable the constraint.

Before you begin

• If you want to test out custom organization policies that reference IAM resources, create a new project. Testing these organization policies in an existing project could disrupt security workflows.

  1. In the Google Cloud console, go to the project selector page.

     Go to project selector

  2. Select or create a Google Cloud project.

Required roles

To get the permissions that you need to manage organization policies, ask your administrator to grant you the following IAM roles:

• Organization Policy Administrator (roles/orgpolicy.policyAdmin) on the organization
• Test the organization policies described on this page: Project IAM Admin (roles/resourcemanager.projectIamAdmin) on the project

For more information about granting roles, see Manage access to projects, folders, and organizations.

These predefined roles contain the permissions required to manage organization policies. To see the exact permissions that are required, expand the Required permissions section:

You might also be able to get these permissions with custom roles or other predefined roles.

Create a custom constraint

A custom constraint is defined in a YAML file by the resources, methods, conditions, and actions that are supported by the service on which you are enforcing the organization policy. Conditions for your custom constraints are defined using Common Expression Language (CEL). For more information about how to build conditions in custom constraints using CEL, see the CEL section of Creating and managing custom constraints.

To create a custom constraint, create a YAML file using the following format:

name: organizations/ORGANIZATION_ID/customConstraints/CONSTRAINT_NAME
resourceTypes:
- RESOURCE_NAME
methodTypes:
- CREATE
- UPDATE
condition: "CONDITION"
actionType: ACTION
displayName: DISPLAY_NAME
description: DESCRIPTION

Replace the following:

• ORGANIZATION_ID: your organization ID, such as 123456789.

• CONSTRAINT_NAME: the name you want for your new custom constraint. A custom constraint must start with custom., and can only include uppercase letters, lowercase letters, or numbers. For example, custom.denyProjectIAMAdmin. The maximum length of this field is 70 characters.

• RESOURCE_NAME: the fully qualified name of the Google Cloud resource containing the object and field you want to restrict. For example, iam.googleapis.com/AllowPolicy.

• CONDITION: a CEL condition that is written against a representation of a supported service resource. This field has a maximum length of 1000 characters. See Supported resources for more information about the resources available to write conditions against. For example, resource.bindings.exists(binding, RoleNameMatches(binding.role, ['roles/resourcemanager.projectIamAdmin'])).

• ACTION: the action to take if the condition is met. Possible values are ALLOW and DENY.

• DISPLAY_NAME: a human-friendly name for the constraint. This field has a maximum length of 200 characters.

• DESCRIPTION: a human-friendly description of the constraint to display as an error message when the policy is violated. This field has a maximum length of 2000 characters.

For more information about how to create a custom constraint, see Defining custom constraints.

Set up a custom constraint

gcloud org-policies set-custom-constraint CONSTRAINT_PATH

gcloud org-policies list-custom-constraints --organization=ORGANIZATION_ID

Enforce a custom organization policy

      name: projects/PROJECT_ID/policies/CONSTRAINT_NAME
      spec:
        rules:
        - enforce: true
    

    gcloud org-policies set-policy POLICY_PATH
    

Test the custom organization policy

Optionally, you can test the organization policy by setting the policy and then trying to take an action that the policy should prevent.

Create the constraint

1. Save the following file as constraint-deny-project-iam-admin.

   name: organizations/ORG_ID/customConstraints/custom.denyProjectIAMAdmin
   resourceTypes: iam.googleapis.com/AllowPolicy
   methodTypes:
     - CREATE
     - UPDATE
   condition:
     "resource.bindings.exists(
       binding,
       RoleNameMatches(binding.role, ['roles/resourcemanager.projectIamAdmin']) &&
       binding.members.exists(member,
         MemberSubjectMatches(member, ['user:EMAIL_ADDRESS'])
       )
     )"
   actionType: DENY
   displayName: Do not allow EMAIL_ADDRESS to be granted the Project IAM Admin role.
   

   Replace the following values:

   • ORG_ID: the numeric ID of your Google Cloud organization.
   • MEMBER_EMAIL_ADDRESS: the email address of the principal that you want to use to test the custom constraint. While the constraint is active, this principal won't be able to be granted the Project IAM Admin role (roles/resourcemanager.projectIamAdmin) on the project that you enforce the constraint for.

2. Apply the constraint:

   gcloud org-policies set-custom-constraint ~/constraint-deny-project-iam-admin.yaml
   

3. Verify that the constraint exists:

   gcloud org-policies list-custom-constraints --organization=ORGANIZATION_ID
   

Create the policy

1. Save the following file as policy-deny-project-iam-admin.yaml:

   name: projects/PROJECT_ID/policies/custom.denyProjectIamAdmin
   spec:
     rules:
     - enforce: true
   

   Replace PROJECT_ID with your project ID.

2. Apply the policy:

   gcloud org-policies set-policy ~/policy-deny-project-iam-admin.yaml
   

3. Verify that the policy exists:

   gcloud org-policies list --project=PROJECT_ID
   

After you apply the policy, wait for about two minutes for Google Cloud to start enforcing the policy.

Test the policy

Try to grant the Project IAM Admin role (roles/resourcemanager.projectIamAdmin) to the principal whose email address you included in the custom constraint. Before running the command, replace the following values:

• PROJECT_ID: The ID of the Google Cloud project where you enforced the constraint
• EMAIL_ADDRESS: The email address of the principal that you specified when you created the organization policy constraint.

gcloud projects add-iam-policy-binding PROJECT_ID \
    --member=user:EMAIL_ADDRESS --role=roles/resourcemanager.projectIamAdmin

The output is the following:

Operation denied by custom org policies: ["customConstraints/custom.denyProjectIAMAdmin": "EMAIL_ADDRESS can't be granted the Project IAM Admin role."]

Example custom organization policies for common use cases

The following table provides the syntax of some custom constraints for common use cases.

The following examples use the CEL macros all and exists. For more information about these macros, see Macros.

name: organizations/ORG_ID/customConstraints/custom.denyRole
resourceTypes: iam.googleapis.com/AllowPolicy
methodTypes:
  - CREATE
  - UPDATE
condition:
"resource.bindings.exists(
    binding,
    RoleNameMatches(binding.role, ['ROLE'])
  )"
actionType: DENY
displayName: Do not allow the ROLE role to be granted

name: organizations/ORG_ID/customConstraints/custom.specificRolesOnly
resourceTypes: iam.googleapis.com/AllowPolicy
methodTypes:
  - CREATE
  - UPDATE
condition:
  "resource.bindings.all(
    binding,
    RoleNameMatches(binding.role, ['ROLE_1', 'ROLE_2'])
  )"
actionType: ALLOW
displayName: Only allow the ROLE_1 role and ROLE_2 role to be granted

name: organizations/ORG_ID/customConstraints/custom.dontgrantStorageRoles
resourceTypes: iam.googleapis.com/AllowPolicy
methodTypes:
  - CREATE
  - UPDATE
condition:
  "resource.bindings.exists(
    binding,
    RoleNameStartsWith(binding.role, ['roles/storage.'])
  )"
actionType: DENY
displayName: Prevent roles that start with "roles/storage." from being granted

name: organizations/ORG_ID/customConstraints/custom.dontRevokeAdminRoles
resourceTypes: iam.googleapis.com/AllowPolicy
methodTypes:
  - REMOVE_GRANT
condition:
  "resource.bindings.exists(
    binding,
    RoleNameContains(binding.role, ['admin'])
  )"
actionType: DENY
displayName: Prevent roles with "admin" in their names from being revoked

name: organizations/ORG_ID/customConstraints/custom.allowSpecificPrincipals
resourceTypes: iam.googleapis.com/AllowPolicy
methodTypes:
  - CREATE
  - UPDATE
condition:
  "resource.bindings.all(
    binding,
    binding.members.all(member,
      MemberSubjectMatches(member, ['user:USER','serviceAccount:SERVICE_ACCOUNT'])
    )
  )"
actionType: ALLOW
displayName: Only allow roles to be granted to USER and SERVICE_ACCOUNT

name: organizations/ORG_ID/customConstraints/custom.denyRemovalOfSpecificPrincipals
resourceTypes: iam.googleapis.com/AllowPolicy
methodTypes:
  - REMOVE_GRANT
condition:
  "resource.bindings.exists(
    binding,
    binding.members.exists(member,
      MemberSubjectMatches(member, ['user:USER_1','user:USER_2'])
    )
  )"
actionType: DENY
displayName: Do not allow roles to be revoked from USER_1 or USER_2

name: organizations/ORG_ID/customConstraints/custom.dontGrantToGmail
resourceTypes: iam.googleapis.com/AllowPolicy
methodTypes:
  - CREATE
  - UPDATE
condition:
  "resource.bindings.exists(
    binding,
    binding.members.exists(member,
      MemberSubjectEndsWith(member, ['@gmail.com'])
    )
  )"
actionType: DENY
displayName: Do not allow members whose email addresses end with "@gmail.com" to be granted roles

name: organizations/ORG_ID/customConstraints/custom.allowSpecificRolesAndPrincipals
resourceTypes: iam.googleapis.com/AllowPolicy
methodTypes:
  - CREATE
  - UPDATE
condition:
  "resource.bindings.all(
    binding,
    RoleNameMatches(binding.role, ['ROLE_1', 'ROLE_2'])  &&
    binding.members.all(member,
      MemberSubjectMatches(member, ['serviceAccount:SERVICE_ACCOUNT', 'group:GROUP'])
    )
  )"
actionType: ALLOW
displayName: Only allow ROLE_1 and ROLE_2 to be granted to SERVICE_ACCOUNT and GROUP

name: organizations/ORG_ID/customConstraints/custom.denyStorageRolesForPrincipalAllUsers
resourceTypes: iam.googleapis.com/AllowPolicy
methodTypes:
  - CREATE
  - UPDATE
condition:
  "resource.bindings.exists(
    binding,
    RoleNameStartsWith(binding.role, ['roles/storage.']) &&
    binding.members.exists(member,
      MemberSubjectMatches(member, ['allUsers', 'allAuthenticatedUsers'])
    )
  )"
actionType: DENY
displayName: Do not allow storage roles to be granted to allUsers or allAuthenticatedUsers

name: organizations/ORG_ID/customConstraints/custom.allowInternaldentitiesOnly
resourceTypes: iam.googleapis.com/AllowPolicy
methodTypes:
  - CREATE
  - UPDATE
condition:
  "resource.bindings.all(
    binding,
    binding.members.all(member,
      MemberInPrincipalSet(member, ['//cloudresourcemanager.googleapis.com/organizations/ORG_ID'])
    )
  )"
actionType: ALLOW
displayName: Only allow organization members to be granted roles

name: organizations/ORG_ID/customConstraints/custom.allowServiceAccountsOnly
resourceTypes: iam.googleapis.com/AllowPolicy
methodTypes:
  - CREATE
  - UPDATE
condition:
  "resource.bindings.all(
    binding,
    binding.members.all(member,
      MemberTypeMatches(member, ['iam.googleapis.com/ServiceAccount'])
    )
  )"
actionType: ALLOW
displayName: Only allow service accounts to be granted roles

Identity and Access Management supported resources

IAM supports the AllowPolicy resource. This resource has the attribute resources.bindings attribute, which is returned for all methods that modify a resource's allow policy. All of the methods that modify a resource's allow policy end with setIamPolicy.

The resource.bindings attribute has the following structure, where BINDINGS is an array of role bindings that were modified during a change to an allow policy:

{
  "bindings": {
    BINDINGS
  }
}

Each binding in resource.bindings has the following structure, where ROLE is the name of the role in the role binding and MEMBERS is a list of identifiers for the principals that were added to or removed from the role binding:

{
  "role": "ROLE"
  "members": {
    MEMBERS
  }
}

To see the formats that principal identifiers can have, see Principal identifiers.

You can only evaluate the resource.bindings attribute and its fields using the supported functions. Other operators and functions—like ==, !=, in, contains, startsWith, and endsWith—are not supported.

Supported functions

You can use the following CEL functions to evaluate the role and members fields of binding resources. When using these functions, you can also use the logical operators && (and) and || (or) to write multipart conditions.

Supported principal types for MemberTypeMatches

The MemberTypeMatches function requires you to specify which principal type the specified member must match.

The following table lists the principal types that you can enter and a description of what the principal type represents. It also lists the principal identifiers that correspond with each principal type. These identifiers are the values that are used in IAM policies.

What's next

• Learn more about Organization Policy Service.
• Learn more about how to create and manage organization policies.
• See the full list of predefined organization policy constraints.