debian-mirror-gitlab/doc/development/permissions.md

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Implementing permissions

There are multiple types of permissions across GitLab, and when implementing anything that deals with permissions, all of them should be considered.

Instance

User types

Each user can be one of the following types:

• Regular.
• External - access to groups and projects only if direct member.
• Internal users - system created.
• Auditor:
  • No access to projects or groups settings menu.
  • No access to Admin Area.
  • Read-only access to everything else.
• Administrator - read-write access.

See the permissions page for details on how each user type is used.

Groups and Projects

General permissions

Groups and projects can have the following visibility levels:

• public (20) - an entity is visible to everyone
• internal (10) - an entity is visible to logged in users
• private (0) - an entity is visible only to the approved members of the entity

By default, subgroups can not have higher visibility levels. For example, if you create a new private group, it can not include a public subgroup.

The visibility level of a group can be changed only if all subgroups and sub-projects have the same or lower visibility level. For example, a group can be set to internal only if all subgroups and projects are internal or private.

WARNING: If you migrate an existing group to a lower visibility level, that action does not migrate subgroups in the same way. This is a known issue.

Visibility levels can be found in the Gitlab::VisibilityLevel module.

Feature specific permissions

Additionally, the following project features can have different visibility levels:

• Issues
• Repository
  • Merge request
  • Forks
  • Pipelines
• Analytics
• Requirements
• Security & Compliance
• Wiki
• Snippets
• Pages
• Operations
• Metrics Dashboard

These features can be set to "Everyone with Access" or "Only Project Members". They make sense only for public or internal projects because private projects can be accessed only by project members by default.

Members

Users can be members of multiple groups and projects. The following access levels are available (defined in the Gitlab::Access module):

• No access (0)
• Minimal access (5)
• Guest (10)
• Reporter (20)
• Developer (30)
• Maintainer (40)
• Owner (50)

If a user is the member of both a project and the project parent groups, the highest permission is the applied access level for the project.

If a user is the member of a project, but not the parent groups, they can still view the groups and their entities (like epics).

Project membership (where the group membership is already taken into account) is stored in the project_authorizations table.

NOTE: In GitLab 14.9 and later, projects in personal namespaces have a maximum role of Owner. Because of a known issue in GitLab 14.8 and earlier, projects in personal namespaces have a maximum role of Maintainer.

Confidential issues

Confidential issues can be accessed only by project members who are at least reporters (they can't be accessed by guests). Additionally they can be accessed by their authors and assignees.

Licensed features

Some features can be accessed only if the user has the correct license plan.

Permission dependencies

Feature policies can be quite complex and consist of multiple rules. Quite often, one permission can be based on another.

Designing good permissions means reusing existing permissions as much as possible and making access to features granular.

In the case of a complex resource, it should be broken into smaller pieces of information and each piece should be granted a different permission.

A good example in this case is the Merge Request widget and the Security reports. Depending on the visibility level of the Pipelines, the Security reports are either visible in the widget or not. So, the Merge Request widget, the Pipelines, and the Security reports, have separate permissions. Moreover, the permissions for the Merge Request widget and the Pipelines are dependencies of the Security reports.

Permission dependencies of Secure features

Secure features have complex permissions since these features are integrated into different features like Merge Requests and CI flow.

Here is a list of some permission dependencies.

Activity level	Resource	Locations	Permission dependency
View	License information	Dependency list, License Compliance	Can view repository
View	Dependency information	Dependency list, License Compliance	Can view repository
View	Vulnerabilities information	Dependency list	Can view security findings
View	Black/Whitelisted licenses for the project	License Compliance, merge request	Can view repository
View	Security findings	merge request, CI job page, Pipeline security tab	Can read the project and CI jobs
View	Vulnerability feedback	merge request	Can read security findings
View	Dependency List page	Project	Can access Dependency information
View	License Compliance page	Project	Can access License information

Where should permissions be checked?

We should typically apply defense-in-depth (implementing multiple checks at various layers) starting with low-level layers, such as finders and services, followed by high-level layers, such as GraphQL, public REST API, and controllers.

See Guidelines for reusing abstractions.

Protecting the same resources at many points means that if one layer of defense is compromised or missing, customer data is still protected by the additional layers.

See the permissions section in the Secure Coding Guidelines.

Considerations

Services or finders are appropriate locations because:

• Multiple endpoints share services or finders so downstream logic is more likely to be re-used.
• Sometimes authorization logic must be incorporated in DB queries to filter records.
• Permission checks at the display layer should be avoided except to provide better UX and not as a security check. For example, showing and hiding non-data elements like buttons.

The downsides to defense-in-depth are:

• DeclarativePolicy rules are relatively performant, but conditions may perform database calls.
• Higher maintenance costs.

Exceptions

Developers can choose to do authorization in only a single area after weighing the risks and drawbacks for their specific case.

Prefer domain logic (services or finders) as the source of truth when making exceptions.

Logic, like backend worker logic, might not need authorization based on the current user. If the service or finder's constructor does not expect current_user, then it typically won't check permissions.

Tips

If a class accepts current_user, then it may be responsible for authorization.

Example: Adding a new API endpoint

By default, we authorize at the endpoint. Checking an existing ability may make sense; if not, then we probably need to add one.

As an aside, most endpoints can be cleanly categorized as a CRUD (create, read, update, destroy) action on a resource. The services and abilities follow suit, which is why many are named like Projects::CreateService or :read_project.

Say, for example, we extract the whole endpoint into a service. The can? check will now be in the service. Say the service reuses an existing finder, which we are modifying for our purposes. Should we make the finder check an ability?

• If the finder doesn't accept current_user, and therefore doesn't check permissions, then probably no.
• If the finder accepts current_user, and doesn't check permissions, then it would be a good idea to double check other usages of the finder, and we might consider adding authorization.
• If the finder accepts current_user, and already checks permissions, then either we need to add our case, or the existing checks are appropriate.