13. Access Control Lists (ACLs)

By default, the root user or any user in the haclient group can modify Pacemaker’s CIB without restriction. Pacemaker offers access control lists (ACLs) to provide more fine-grained authorization.

Important

Being able to modify the CIB’s resource section allows a user to run any executable file as root, by configuring it as an LSB resource with a full path.

13.1. ACL Prerequisites

In order to use ACLs:

  • The Pacemaker software must have been built with ACL support. If the output of the command pacemakerd --features contains acls, your installation supports ACLs.
  • Desired users must have user accounts in the haclient group on all cluster nodes in the cluster.
  • If your CIB was created before Pacemaker 1.1.12, it might need to be updated to the current schema (using cibadmin --upgrade or a higher-level tool equivalent) in order to use the syntax documented here.
  • The enable-acl cluster option must be set to true.

13.2. ACL Configuration

ACLs are specified within an acls element of the CIB. The acls element may contain any number of acl_role, acl_target, and acl_group elements.

13.3. ACL Roles

An ACL role is a collection of permissions allowing or denying access to particular portions of the CIB. A role is configured with an acl_role element in the CIB acls section.

Properties of an acl_role element
Attribute Description
id

A unique name for the role (required)

description

Arbitrary text (not used by Pacemaker)

An acl_role element may contain any number of acl_permission elements.

Properties of an acl_permission element
Attribute Description
id

A unique name for the permission (required)

description

Arbitrary text (not used by Pacemaker)

kind

The access being granted. Allowed values are read, write, and deny. A value of write grants both read and write access.

object-type

The name of an XML element in the CIB to which the permission applies. (Exactly one of object-type, xpath, and reference must be specified for a permission.)

attribute

If specified, the permission applies only to object-type elements that have this attribute set (to any value). If not specified, the permission applies to all object-type elements. May only be used with object-type.

reference

The ID of an XML element in the CIB to which the permission applies. (Exactly one of object-type, xpath, and reference must be specified for a permission.)

xpath

An XPath specification selecting an XML element in the CIB to which the permission applies. Attributes may be specified in the XPath to select particular elements, but the permissions apply to the entire element. (Exactly one of object-type, xpath, and reference must be specified for a permission.)

Important

  • Permissions are applied to the selected XML element’s entire XML subtree (all elements enclosed within it).
  • Write permission grants the ability to create, modify, or remove the element and its subtree, and also the ability to create any “scaffolding” elements (enclosing elements that do not have attributes other than an ID).
  • Permissions for more specific matches (more deeply nested elements) take precedence over more general ones.
  • If multiple permissions are configured for the same match (for example, in different roles applied to the same user), any deny permission takes precedence, then write, then lastly read.

13.4. ACL Targets and Groups

ACL targets correspond to user accounts on the system.

Properties of an acl_target element
Attribute Description
id

The name of a user on the system (required)

ACL groups may be specified, but are not currently used by Pacemaker. This is expected to change in a future version.

Properties of an acl_group element
Attribute Description
id

The name of a group on the system (required)

Each acl_target and acl_group element may contain any number of role elements.

Properties of a role element
Attribute Description
id

The id of an acl_role element that specifies permissions granted to the enclosing target or group.

Important

The root and hacluster user accounts always have full access to the CIB, regardless of ACLs. For all other user accounts, when enable-acl is true, permission to all parts of the CIB is denied by default (permissions must be explicitly granted).

13.5. ACL Examples

<acls>

   <acl_role id="read_all">
       <acl_permission id="read_all-cib" kind="read" xpath="/cib" />
   </acl_role>

   <acl_role id="operator">

       <acl_permission id="operator-maintenance-mode" kind="write"
           xpath="//crm_config//nvpair[@name='maintenance-mode']" />

       <acl_permission id="operator-maintenance-attr" kind="write"
           xpath="//nvpair[@name='maintenance']" />

       <acl_permission id="operator-target-role" kind="write"
           xpath="//resources//meta_attributes/nvpair[@name='target-role']" />

       <acl_permission id="operator-is-managed" kind="write"
           xpath="//resources//nvpair[@name='is-managed']" />

       <acl_permission id="operator-rsc_location" kind="write"
           object-type="rsc_location" />

   </acl_role>

   <acl_role id="administrator">
       <acl_permission id="administrator-cib" kind="write" xpath="/cib" />
   </acl_role>

   <acl_role id="minimal">

       <acl_permission id="minimal-standby" kind="read"
           description="allow reading standby node attribute (permanent or transient)"
           xpath="//instance_attributes/nvpair[@name='standby']"/>

       <acl_permission id="minimal-maintenance" kind="read"
           description="allow reading maintenance node attribute (permanent or transient)"
           xpath="//nvpair[@name='maintenance']"/>

       <acl_permission id="minimal-target-role" kind="read"
           description="allow reading resource target roles"
           xpath="//resources//meta_attributes/nvpair[@name='target-role']"/>

       <acl_permission id="minimal-is-managed" kind="read"
           description="allow reading resource managed status"
           xpath="//resources//meta_attributes/nvpair[@name='is-managed']"/>

       <acl_permission id="minimal-deny-instance-attributes" kind="deny"
           xpath="//instance_attributes"/>

       <acl_permission id="minimal-deny-meta-attributes" kind="deny"
           xpath="//meta_attributes"/>

       <acl_permission id="minimal-deny-operations" kind="deny"
           xpath="//operations"/>

       <acl_permission id="minimal-deny-utilization" kind="deny"
           xpath="//utilization"/>

       <acl_permission id="minimal-nodes" kind="read"
           description="allow reading node names/IDs (attributes are denied separately)"
           xpath="/cib/configuration/nodes"/>

       <acl_permission id="minimal-resources" kind="read"
           description="allow reading resource names/agents (parameters are denied separately)"
           xpath="/cib/configuration/resources"/>

       <acl_permission id="minimal-deny-constraints" kind="deny"
           xpath="/cib/configuration/constraints"/>

       <acl_permission id="minimal-deny-topology" kind="deny"
           xpath="/cib/configuration/fencing-topology"/>

       <acl_permission id="minimal-deny-op_defaults" kind="deny"
           xpath="/cib/configuration/op_defaults"/>

       <acl_permission id="minimal-deny-rsc_defaults" kind="deny"
           xpath="/cib/configuration/rsc_defaults"/>

       <acl_permission id="minimal-deny-alerts" kind="deny"
           xpath="/cib/configuration/alerts"/>

       <acl_permission id="minimal-deny-acls" kind="deny"
           xpath="/cib/configuration/acls"/>

       <acl_permission id="minimal-cib" kind="read"
           description="allow reading cib element and crm_config/status sections"
           xpath="/cib"/>

   </acl_role>

   <acl_target id="alice">
      <role id="minimal"/>
   </acl_target>

   <acl_target id="bob">
      <role id="read_all"/>
   </acl_target>

   <acl_target id="carol">
      <role id="read_all"/>
      <role id="operator"/>
   </acl_target>

   <acl_target id="dave">
      <role id="administrator"/>
   </acl_target>

</acls>

In the above example, the user alice has the minimal permissions necessary to run basic Pacemaker CLI tools, including using crm_mon to view the cluster status, without being able to modify anything. The user bob can view the entire configuration and status of the cluster, but not make any changes. The user carol can read everything, and change selected cluster properties as well as resource roles and location constraints. Finally, dave has full read and write access to the entire CIB.

Looking at the minimal role in more depth, it is designed to allow read access to the cib tag itself, while denying access to particular portions of its subtree (which is the entire CIB).

This is because the DC node is indicated in the cib tag, so crm_mon will not be able to report the DC otherwise. However, this does change the security model to allow by default, since any portions of the CIB not explicitly denied will be readable. The cib read access could be removed and replaced with read access to just the crm_config and status sections, for a safer approach at the cost of not seeing the DC in status output.

For a simpler configuration, the minimal role allows read access to the entire crm_config section, which contains cluster properties. It would be possible to allow read access to specific properties instead (such as stonith-enabled, dc-uuid, have-quorum, and cluster-name) to restrict access further while still allowing status output, but cluster properties are unlikely to be considered sensitive.

13.6. ACL Limitations

13.6.1. Actions performed via IPC rather than the CIB

ACLs apply only to the CIB.

That means ACLs apply to command-line tools that operate by reading or writing the CIB, such as crm_attribute when managing permanent node attributes, crm_mon, and cibadmin.

However, command-line tools that communicate directly with Pacemaker daemons via IPC are not affected by ACLs. For example, users in the haclient group may still do the following, regardless of ACLs:

  • Query transient node attribute values using crm_attribute and attrd_updater.
  • Query basic node information using crm_node.
  • Erase resource operation history using crm_resource.
  • Query fencing configuration information, and execute fencing against nodes, using stonith_admin.

13.6.2. ACLs and Pacemaker Remote

ACLs apply to commands run on Pacemaker Remote nodes using the Pacemaker Remote node’s name as the ACL user name.

The idea is that Pacemaker Remote nodes (especially virtual machines and containers) are likely to be purpose-built and have different user accounts from full cluster nodes.