• Custom roles vs default roles
• Technical overview
• Refactoring abilities
  • Finding existing abilities checks
  • Understanding logic for individual abilities
  • Abilities consolidation
• How to add support for an ability to custom roles
  • Step 1. Generate a configuration file
  • Step 2: Create a spec file and update validation schema
  • Step 3: Update policies
  • Step 4: Verify
  • Step 5: Add specs
  • Step 6: Update documentation
  • Privilege escalation consideration
  • Consuming seats
  • Modular Policies

Custom Roles

Ultimate customers can create custom roles and define those roles by assigning specific abilities.

For example, a user could create an “Engineer” role with read code and admin merge requests abilities, but without abilities like admin issues.

In this context, the terms “permission” and “ability” are often used interchangeably.

• “Ability” is an action a user can do. These map to Declarative Policy abilities and live in Policy classes in ee/app/policies/*.
• “Permission” is how we refer to an ability in user-facing documentation. The documentation of permissions is manually generated so there is not necessarily a 1:1 mapping of the permissions listed in documentation and the abilities defined in Policy classes.

Custom roles vs default roles

In GitLab 15.9 and earlier, GitLab only had default roles as a permission system. In this system, there are a few predefined roles that are statically assigned to certain abilities. These default roles are not customizable by customers.

With custom roles, the customers can decide which abilities they want to assign to certain user groups. For example:

• In the default role system, reading of vulnerabilities is limited to a Developer role.
• In the custom role system, a customer can assign this ability to a new custom role based on any default role.

Like default roles, custom roles are inherited within a group hierarchy. If a user has custom role for a group, that user will also have a custom role for any projects or subgroups within the group.

Technical overview

• Individual custom roles are stored in the member_roles table (MemberRole model).
• A member_roles record is associated with top-level groups (not subgroups) via the namespace_id foreign key.
• A Group or project membership (members record) is associated with a custom role via the member_role_id foreign key.
• A Group or project membership can be associated with any custom role that is defined on the root-level group of the group or project.
• The member_roles table includes individual permissions and a base_access_level value.
• The base_access_level must be a valid access level. The base_access_level determines which abilities are included in the custom role. For example, if the base_access_level is 10, the custom role will include any abilities that a default Guest role would receive, plus any additional abilities that are enabled by the member_roles record by setting an attribute, such as read_code, to true.
• A custom role can enable additional abilities for a base_access_level but it cannot disable a permission. As a result, custom roles are “additive only”. The rationale for this choice is in this comment.
• Custom role abilities are supported at project level and group level.

Refactoring abilities

Finding existing abilities checks

Abilities are often checked in multiple locations for a single endpoint or web request. Therefore, it can be difficult to find the list of authorization checks that are run for a given endpoint.

To assist with this, you can locally set GITLAB_DEBUG_POLICIES=true.

This outputs information about which abilities are checked in the requests made in any specs that you run. The output also includes the line of code where the authorization check was made. Caller information is especially helpful in cases where there is metaprogramming used because those cases are difficult to find by grepping for ability name strings.

For example:

# example spec run

GITLAB_DEBUG_POLICIES=true bundle exec rspec spec/controllers/groups_controller_spec.rb:162

# permissions debug output when spec is run; if multiple policy checks are run they will all be in the debug output.

POLICY CHECK DEBUG -> policy: GlobalPolicy, ability: create_group, called_from: ["/gitlab/app/controllers/application_controller.rb:245:in `can?'", "/gitlab/app/controllers/groups_controller.rb:255:in `authorize_create_group!'"]

Use this setting to learn more about authorization checks while refactoring. You should not keep this setting enabled for any specs on the default branch.

Understanding logic for individual abilities

References to an ability may appear in a DeclarativePolicy class many times and depend on conditions and rules which reference other abilities. As a result, it can be challenging to know exactly which conditions apply to a particular ability.

DeclarativePolicy provides a ability_map for each policy class, which pulls all rules for an ability into an array.

For example:

> GroupPolicy.ability_map.map.select { |k,v| k == :read_group_member }
=> {:read_group_member=>[[:enable, #<Rule can?(:read_group)>], [:prevent, #<Rule ~can_read_group_member>]]}

> GroupPolicy.ability_map.map.select { |k,v| k == :read_group }
=> {:read_group=>
  [[:enable, #<Rule public_group>],
   [:enable, #<Rule logged_in_viewable>],
   [:enable, #<Rule guest>],
   [:enable, #<Rule admin>],
   [:enable, #<Rule has_projects>],
   [:enable, #<Rule read_package_registry_deploy_token>],
   [:enable, #<Rule write_package_registry_deploy_token>],
   [:prevent, #<Rule all?(~public_group, ~admin, user_banned_from_group)>],
   [:enable, #<Rule auditor>],
   [:prevent, #<Rule needs_new_sso_session>],
   [:prevent, #<Rule all?(ip_enforcement_prevents_access, ~owner, ~auditor)>]]}

DeclarativePolicy also provides a debug method that can be used to understand the logic tree for a specific object and actor. The output is similar to the list of rules from ability_map. But, DeclarativePolicy stops evaluating rules after you prevent an ability, so it is possible that not all conditions are called.

Example:

policy = GroupPolicy.new(User.last,  Group.last)
policy.debug(:read_group)

- [0] enable when public_group ((@custom_guest_user1 : Group/139))
- [0] enable when logged_in_viewable ((@custom_guest_user1 : Group/139))
- [0] enable when admin ((@custom_guest_user1 : Group/139))
- [0] enable when auditor ((@custom_guest_user1 : Group/139))
- [14] prevent when all?(~public_group, ~admin, user_banned_from_group) ((@custom_guest_user1 : Group/139))
- [14] prevent when needs_new_sso_session ((@custom_guest_user1 : Group/139))
- [16] enable when guest ((@custom_guest_user1 : Group/139))
- [16] enable when has_projects ((@custom_guest_user1 : Group/139))
- [16] enable when read_package_registry_deploy_token ((@custom_guest_user1 : Group/139))
- [16] enable when write_package_registry_deploy_token ((@custom_guest_user1 : Group/139))
  [21] prevent when all?(ip_enforcement_prevents_access, ~owner, ~auditor) ((@custom_guest_user1 : Group/139))

=> #<DeclarativePolicy::Runner::State:0x000000015c665050
 @called_conditions=
  #<Set: {
   "/dp/condition/GroupPolicy/public_group/Group:139",
   "/dp/condition/GroupPolicy/logged_in_viewable/User:83,Group:139",
   "/dp/condition/BasePolicy/admin/User:83",
   "/dp/condition/BasePolicy/auditor/User:83",
   "/dp/condition/GroupPolicy/user_banned_from_group/User:83,Group:139",
   "/dp/condition/GroupPolicy/needs_new_sso_session/User:83,Group:139",
   "/dp/condition/GroupPolicy/guest/User:83,Group:139",
   "/dp/condition/GroupPolicy/has_projects/User:83,Group:139",
   "/dp/condition/GroupPolicy/read_package_registry_deploy_token/User:83,Group:139",
   "/dp/condition/GroupPolicy/write_package_registry_deploy_token/User:83,Group:139"}>,
 @enabled=false,
 @prevented=true>

Abilities consolidation

Every feature added to custom roles should have minimal abilities. For most features, having read_* and admin_* should be enough. You should consolidate all:

• View-related abilities under read_*. For example, viewing a list or detail.
• Object updates under admin_*. For example, updating an object, adding assignees or closing it that object. Usually, a role that enables admin_ has to have also read_ abilities enabled. This is defined in requirement option in the ALL_CUSTOMIZABLE_PERMISSIONS hash on MemberRole model.

There might be features that require additional abilities but try to minimize those. You can always ask members of the Authentication and Authorization group for their opinion or help.

This is also where your work should begin. Take all the abilities for the feature you work on, and consolidate those abilities into read_, admin_, or additional abilities if necessary.

Many abilities in the GroupPolicy and ProjectPolicy classes have many redundant policies. There is an epic for consolidating these Policy classes. If you encounter similar permissions in these classes, consider refactoring so that they have the same name.

For example, you see in GroupPolicy that there is an ability called read_group_security_dashboard and in ProjectPolicy has an ability called read_project_security_dashboard. You’d like to make both customizable. Rather than adding a row to the member_roles table for each ability, consider renaming them to read_security_dashboard and adding read_security_dashboard to the member_roles table. Enabling read_security_dashboard on the parent group will allow the custom role to access the group security dashboard and the project security dashboard for each project in that group. Enabling the same permission on a specific project will allow access to that projects’ security dashboard.

How to add support for an ability to custom roles

If adding an existing ability, consider refactoring & consolidating abilities for the feature before in a separate merge request, before completing the below.

Step 1. Generate a configuration file

• Run ./ee/bin/custom-ability <ABILITY_NAME> to generate a configuration file for the new ability.
• This will generate a YAML file in ee/config/custom_abilities which follows the following schema:

Step 2: Create a spec file and update validation schema

• Run bundle exec rails generate gitlab:custom_roles:code --ability <ABILITY_NAME> which will update the permissions validation schema file and create an empty spec file.

Step 3: Update policies

• If the ability is checked on a group level, add rule(s) to GroupPolicy to enable the ability.
• For example: if the ability we would like to add is read_dependency, then an update to ee/app/policies/ee/group_policy.rb would look like as follows:

rule { custom_role_enables_read_dependency }.enable(:read_dependency)

• Similarly, If the ability is checked on a project level, add rule(s) to ProjectPolicy to enable the ability.
• For example: if the ability we would like to add is read_dependency, then an update to ee/app/policies/ee/project_policy.rb would look like as follows:

rule { custom_role_enables_read_dependency }.enable(:read_dependency)

• Not all abilities need to be enabled on both levels, for instance admin_terraform_state allows users to manage a project’s terraform state. It only needs to be enabled on the project level and not the group level, and thus only needs to be configured in ee/app/policies/ee/project_policy.rb.

Step 4: Verify

• Ensure SaaS mode is enabled with GITLAB_SIMULATE_SAAS=1.
• Go to any Group that you are an owner of, then go to Settings -> Roles and Permissions.
• Select New role and create a custom role with the permission you have just created.
• Go to the Group’s Manage -> Members page and assign a member to this newly created custom role.
• Next, sign in as that member and ensure that you are able to access the page that the custom ability is intended for.

Step 5: Add specs

• Add the ability as a trait in the MemberRoles factory, ee/spec/factories/member_roles.rb.
• Add tests to ee/spec/requests/custom_roles/<ABILITY_NAME>/request_spec.rb to ensure that once the user has been assigned the custom ability, they can successfully access the controllers, REST API endpoints and GraphQL API endpoints.
• Below is an example of the typical setup that is required to test a Rails Controller endpoint.

  let_it_be(:user) { create(:user) }
  let_it_be(:project) { create(:project, :repository, :in_group) }
  let_it_be(:role) { create(:member_role, :guest, namespace: project.group, custom_permission: true) }
  let_it_be(:membership) { create(:project_member, :guest, member_role: role, user: user, project: project) }

  before do
    stub_licensed_features(custom_roles: true)

    sign_in(user)
  end

  describe MyController do
    describe '#show' do
      it 'allows access' do
        get my_controller_path(project)

        expect(response).to have_gitlab_http_status(:ok)
        expect(response).to render_template(:show)
      end
    end
  end

• Below is an example of the typical setup that is required to test a GraphQL mutation.

  let_it_be(:user) { create(:user) }
  let_it_be(:project) { create(:project, :repository, :in_group) }
  let_it_be(:role) { create(:member_role, :guest, namespace: project.group, custom_permission: true) }
  let_it_be(:membership) { create(:project_member, :guest, member_role: role, user: user, project: project) }

  before do
    stub_licensed_features(custom_roles: true)

    sign_in(user)
  end

  describe MyMutation do
    include GraphqlHelpers

    describe '#show' do
      let(:mutation) { graphql_mutation(:my_mutation) }

      it_behaves_like 'a working graphql query'
    end
  end

• Add tests to ProjectPolicy and/or GroupPolicy. Below is an example for testing ProjectPolicy related changes.

  context 'for a member role with read_dependency true' do
    let(:member_role_abilities) { { read_dependency: true } }
    let(:allowed_abilities) { [:read_dependency] }

    it_behaves_like 'custom roles abilities'
  end

Step 6: Update documentation

• Update the list of custom abilities by running bundle exec rake gitlab:custom_roles:compile_docs
• Update the GraphQL documentation by running bundle exec rake gitlab:graphql:compile_docs

Privilege escalation consideration

A base role typically has permissions that allow creation or management of artifacts corresponding to the base role when interacting with that artifact. For example, when a Developer creates an access token for a project, it is created with Developer access encoded into that credential. It is important to keep in mind that as new custom permissions are created, there might be a risk of elevated privileges when interacting with GitLab artifacts, and appropriate safeguards or base role checks should be added.

Consuming seats

If a new user with a role Guest is added to a member role that includes enablement of an ability that is not in the CUSTOMIZABLE_PERMISSIONS_EXEMPT_FROM_CONSUMING_SEAT array, a seat is consumed. We simply want to make sure we are charging Ultimate customers for guest users, who have “elevated” abilities. This only applies to billable users on SaaS (billable users that are counted towards namespace subscription). More details about this topic can be found in this issue.

Modular Policies

In an effort to support the GitLab Modular Monolith design document the Authorization group is collaborating with the Create:IDE group. Once a POC is implemented, the findings will be discussed and the Authorization group will make a decision of what the modular design of policies will be going forward.