Permissions

NetBox v2.9 introduced a new object-based permissions framework, which replace's Django's built-in permission model. Object-based permissions allow for the assignment of permissions to an arbitrary subset of objects of a certain type, rather than only by type of object. For example, it is possible to grant a user permission to view only sites within a particular region, or to modify only VLANs with a numeric ID within a certain range.

Assigning a permission in NetBox entails defining a relationship among several components:

Object type(s) - One or more types of object in NetBox
User(s) - One or more users or groups of users
Actions - The actions that can be performed (view, add, change, and/or delete)
Constraints - An arbitrary filter used to limit the granted action(s) to a specific subset of objects

At a minimum, a permission assignment must specify one object type, one user or group, and one action. The specification of constraints is optional: A permission without any constraints specified will apply to all instances of the selected model(s).

Actions

There are four core actions that can be permitted for each type of object within NetBox, roughly analogous to the CRUD convention (create, read, update, and delete):

View - Retrieve an object from the database
Add - Create a new object
Change - Modify an existing object
Delete - Delete an existing object

Some models introduce additional permissions that can be granted to allow other actions. For example, the napalm_read permission on the device model allows a user to execute NAPALM queries on a device via NetBox's REST API. These can be specified when granting a permission in the "additional actions" field.

Constraints

Constraints are defined as a JSON object representing a Django query filter. This is the same syntax that you would pass to the QuerySet filter() method when performing a query using the Django ORM. As with query filters, double underscores can be used to traverse related objects or invoke lookup expressions. Some example queries and their corresponding definitions are shown below.

All constraints defined on a permission are applied with a logic AND. For example, suppose you assign a permission for the site model with the following constraints.

{
  "status": "active",
  "region__name": "Americas"
}

The permission will grant access only to sites which have a status of "active" and which are assigned to the "Americas" region. To achieve a logical OR with a different set of constraints, simply create another permission assignment for the same model and user/group.

Example Constraint Definitions

Query Filter	Permission Constraints
`filter(status='active')`	`{"status": "active"}`
`filter(status='active', role='testing')`	`{"status": "active", "role": "testing"}`
`filter(status__in=['planned', 'reserved'])`	`{"status__in": ["planned", "reserved"]}`
`filter(name__startswith('Foo')`	`{"name__startswith": "Foo"}`
`filter(vid__gte=100, vid__lt=200)`	`{"vid__gte": 100, "vid__lt": 200}`

Permissions Enforcement

Viewing Objects

Object-based permissions work by filtering the database query generated by a user's request to restrict the set of objects returned. When a request is received, NetBox first determines whether the user is authenticated and has been granted to perform the requested action. For example, if the requested URL is /dcim/devices/, NetBox will check for the dcim.view_device permission. If the user has not been assigned this permission (either directly or via a group assignment), NetBox will return a 403 (forbidden) HTTP response.

If the permission has been granted, NetBox will compile any specified constraints for the model and action. For example, suppose two permissions have been assigned to the user granting view access to the device model, with the following constraints:

[
    {"site__name__in":  ["NYC1", "NYC2"]},
    {"status":  "offline", "tenant__isnull":  true}
]

This grants the user access to view any device that is in NYC1 or NYC2, or which has a status of "offline" and has no tenant assigned. These constraints will result in the following ORM query:

Site.objects.filter(
    Q(site__name__in=['NYC1', 'NYC2']),
    Q(status='active', tenant__isnull=True)
)

Creating and Modifying Objects

The same sort of logic is in play when a user attempts to create or modify an object in NetBox, with a twist. Once validation has completed, NetBox starts an atomic database transaction to facilitate the change, and the object is created or saved normally. Next, still within the transaction, NetBox issues a second query to retrieve the newly created/updated object, filtering the restricted queryset with the object's primary key. If this query fails to return the object, NetBox knows that the new revision does not match the constraints imposed by the permission. The transaction is then aborted, and the database is left in its original state.

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