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· 4 min read

Understanding roles is integral to applying the principal of least privilege to GCP environments.

A quick primer on roles in GCP

A Role in GCP is a collection of permissions to services and APIs on the platform. Roles are "bound" to principals or members (users, groups and service accounts).

These bindings are referred to as "policies" which are scoped at a particular level - organisation, folder, project, resource.

There are three types of roles - Primitive Roles, Predefined Roles and Custom Roles.

Primitive (or Basic) Roles

These are legacy roles set at a GCP project level which include Owner, Editor, and Viewer. These are generally considered to be excessive in terms of permissions and their use should be minimised if not avoided altogether.

Predefined Roles

These are roles with fine grained access to discrete services in GCP. Google has put these together for your convenience. In most cases predefined roles are the preferred mechanism to assign permissions to members.

Custom Roles

Custom roles can be created with a curated collection of permissions if required, reasons for doing so include:

  • if the permissions in predefined roles are excessive for your security posture
  • if you want to combine permissions across different services, and cannot find a suitable predefined role although it is preferred to assign multiple predefined roles to a given member

Anatomy of an IAM Policy

An IAM Policy is a collection of bindings of one or more members (user, group or service account) to a role (primitive, predefined or custom). Policies are normally expressed as JSON objects as shown here:

{
"bindings": [
{
"members": [
"group:project-admins@my-cloud-identity-domain.com"
],
"role": "roles/owner"
},
{
"members": [
"serviceAccount:provisioner@my-project.iam.gserviceaccount.com",
"user:javen@avensolutions.com"
],
"role": "roles/resourcemanager.folderViewer"
}
]
}

Groups are Google Groups created in Cloud Identity or Google Workspace (formerly known as G-Suite)

Application of policies is an atomic operation, which will overwrite any existing policy attached to an entity (org, folder, project, resource).

Querying Roles with StackQL

Predefined and primitive roles are defined in the roles resource in StackQL (google.iam.roles) - which returns the following fields (as returned by DESCRIBE google.iam.roles):

NameDescription
nameName of the role in the format roles/[{service}.]{role}
for predefined or basic roles, or qualified for custom roles,
e.g. organizations/{org_id}/roles/[{service}.]{role}
descriptionAn optional, human-readable description for the role
includedPermissionsAn array of permissions this role grants (only displayed with
VIEW = 'full')
etagOutput only, used internally for consistency
titleAn optional, human-readable title for the role (visible in the
Console)
deletedA read only boolean field showing the current deleted state
of the role
stageThe current launch stage of the role, e.g. ALPHA

Get the name for a role

Often, you may know the "friendly" title for a role like "Logs Bucket Writer", but you need the actual role name to use in an Iam policy - which is roles/logging.bucketWriter. A simple query to find this using StackQL is shown here:

SELECT name
FROM google.iam.roles
WHERE title = 'Logs Bucket Writer';
/* RETURNS:
|----------------------------|
| name |
|----------------------------|
| roles/logging.bucketWriter |
|----------------------------|
*/

Conversely, if you have the name but want the friendly title you could use:

SELECT title
FROM google.iam.roles
WHERE name = 'roles/logging.bucketWriter';
/* RETURNS:
|--------------------|
| title |
|--------------------|
| Logs Bucket Writer |
|--------------------|
*/

Wildcards can also be used with the LIKE operator, for example to get the name and title for each predefined role in the logging service you could run:

SELECT name, title
FROM google.iam.roles
WHERE name LIKE 'roles/logging.%';

Get the permissions for a role

To return the includedPermissions you need to add the following WHERE clause:

WHERE view = 'FULL'

An example query to list the permissions for a given role is shown here:

SELECT includedPermissions
FROM google.iam.roles
WHERE view = 'FULL' AND
name = 'roles/cloudfunctions.viewer';
/* RETURNS
["cloudbuild.builds.get","cloudbuild.builds.list",...]
*/

A more common challenge is that you know a particular permission such as cloudfunctions.functions.get and you want to know which roles contain this permission you could run the following query:

SELECT name, title
FROM google.iam.roles
WHERE view = 'FULL'
AND includedPermissions LIKE '%cloudfunctions.functions.get%';

Creating custom roles and more...

In forthcoming articles, we will demonstrate how you can create custom roles using StackQL INSERT operations, as well as how you can construct a simple IAM framework to manage and provision access to resources in GCP, stay tuned!