13.2.22. Creating Domains: Access Control
SSSD provides a rudimentary access control for domain configuration, allowing either simple user allow/deny lists or using the LDAP back end itself.
Using the Simple Access Provider
The Simple Access Provider allows or denies access based on a list of user names or groups.
The Simple Access Provider is a way to restrict access to certain, specific machines. For example, if a company uses laptops, the Simple Access Provider can be used to restrict access to only a specific user or a specific group, even if a different user authenticated successfully against the same authentication provider.
The most common options are
simple_allow_users and simple_allow_groups, which grant access explicitly to specific users (either the given users or group members) and deny access to everyone else. It is also possible to create deny lists (which deny access only to explicit people and implicitly allow everyone else access).
The Simple Access Provider adheres to the following four rules to determine which users should or should not be granted access:
- If both the allow and deny lists are empty, access is granted.
- If any list is provided, allow rules are evaluated first, and then deny rules. Practically, this means that deny rules supersede allow rules.
- If an allowed list is provided, then all users are denied access unless they are in the list.
- If only deny lists are provided, then all users are allowed access unless they are in the list.
This example grants access to two users and anyone who belongs to the IT group; implicitly, all other users are denied:
[domain/example.com] access_provider = simple simple_allow_users = jsmith,bjensen simple_allow_groups = itgroup
Note
The LOCAL domain in SSSD does not support
simple as an access provider.
Other options are listed in the
sssd-simple man page, but these are rarely used.
Using the Access Filters
An LDAP, Active Directory, or Identity Management server can provide access control rules for a domain. The associated options (
ldap_access_filter for LDAP and IdM and ad_access_filter for AD) specify which users are granted access to the specified host. The user filter must be used or all users are denied access. See the examples below:
[domain/example.com] access_provider = ldap ldap_access_filter = memberOf=cn=allowedusers,ou=Groups,dc=example,dc=com
[domain/example.com] access_provider = ad ad_access_filter = memberOf=cn=allowedusers,ou=Groups,dc=example,dc=com
Note
Offline caching for LDAP access providers is limited to determining whether the user's last online login attempt was successful. Users that were granted access during their last login will continue to be granted access while offline.
SSSD can also check results by the
authorizedService or host attribute in an entry. In fact, all options — LDAP filter, authorizedService, and host — can be evaluated, depending on the user entry and the configuration. The ldap_access_order parameter lists all access control methods to use, in order of how they should be evaluated.
[domain/example.com] access_provider = ldap ldap_access_filter = memberOf=cn=allowedusers,ou=Groups,dc=example,dc=com ldap_access_order = filter, host, authorized_service
The attributes in the user entry to use to evaluate authorized services or allowed hosts can be customized. Additional access control parameters are listed in the
sssd-ldap(5) man page.
