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V4/Certificate profile update mechanism

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Work in progress
This design is not complete yet.

Name: V4/Certificate profile update mechanism
Ticket: #5323
Target version: 4.6.0
Author: Ftweedal
Incomplete.png Pending review
Last updated: 2017-06-29 by Ftweedal

Overview

FreeIPA includes a variety of certificate profiles for various use cases. The profile primarily consists of a Dogtag profile configuration, and a small amount of FreeIPA-specific configuration. Occasionally we need to update the Dogtag configuration for a profile, typically to make use of new profile policy components in Dogtag, to improve usable, increase the range of supported use cases, and/or improve the compatibility of issued certificates with server and client software.

FreeIPA configures Dogtag to use LDAP-based storage for profiles, so that profile configuration changes made on one CA master are automatically replicated to the other CA masters in the topology.

When updating a profile to use a profile component that is only available from a particular version of Dogtag, we hit a problem. Because FreeIPA can run in a mixed-version topology (i.e. different replicas, including CA replicas, at different releases), updating a profile to include a policy component only avaiabile in a newer release of Dogtag potentially breaks certificate issuance on older releases of Dogtag in the topology. This is undesirable.

Until now, our approach has been to ship the updated profile to be included in new installations, but to leave the profile unchanged on existing deployments to avoid potential breakage. This is also undesirable, because it leaves the topology with a suboptimal profile configuration, even when all CA masters in the topology are at a version that could support the updated configuration.

The purpose of this design is to introduce a general, topology-aware profile update mechanism that ensures that the latest version of a profile that can be supported by the topology gets used, providing safe, automatic profile updates.

Terminology

included profile
A profile that is included with FreeIPA
profile (configuration) template
The profile template that is shipped with FreeIPA, containing various installation-specific substitutions to be performed to produce a valid Dogtag profile configuration
profile configuration
A complete Dogtag profile configuration.

Feature Management

There is no user or administrator interaction involved in this mechanism (modulo conflict resolution; see Dealing with modified profiles below).

From a development perspective, updating a profile will involve the following:

  • If the updated profile configuration will require a higher minimum version of FreeIPA than the current profile configuration, copy the profile template to a new file, with the new ipa-lower-bound in the filename.
  • Modify the profile configuration template, and increment the template-version.

See Profile template versioning below for a discussion of these requirements.

Design

Design at a glance

Each profile configuration shall now be accompanied by a version of that profile. FreeIPA certprofile objects shall be updated to include the profile configuration version that is currently active.

Each profile configuration shall now also be accompanied by the minimum version of FreeIPA that supports that profile. Each profile may have multiple configurations available, with different lower bounds.

FreeIPA master entries shall be updated to include the version of FreeIPA that the master is currently at.

During server upgrade, the highest version of the profile configuration that is supported by all CA masters in the topology shall be selected. If the current version of that profile is lower than the selected version, the profile shall be updated in Dogtag.

Profile template versioning

Each profile template shall have a version consisting of two parts.

The ipa-lower-bound part shall be the earliest version of FreeIPA that supports that version of the profile template. When a profile template update requires a newer version of FreeIPA, a copy of the profile template is made, and the ipa-lower-bound of that copy shall be the version of FreeIPA it requires. The older version of the profile template is kept. An example ipa-lower-bound value is 4.5.3.

The template-version part shall be a non-negative integer. Whenever a profile template is updated, whether or not it requires a newer version of FreeIPA, the template-version is incremented. If the profile does not require a newer version of FreeIPA, the changes are performed in-place (i.e. no copy of the profile template is made).

Filesystem storage

Profile templates are currently stored as:

/usr/share/ipa/profiles/<profile-name>.cfg

Now that we need to store multiple versions of a profile template, we shall use the following schema:

/usr/share/ipa/profiles/<profile-name>.<ipa-lower-bound>

Each template file shall contain a template-version directive asserting the template version.

Schema changes

Certificate profile objects

The ipaCertProfile object class shall be updated with a new optional integer attribute for storing the version of the profile:

# New attribute
attributeTypes: ( 2.16.840.1.113730.3.8.21.1.9
  NAME 'ipaCertProfileVersion'
  DESC 'Profile version'
  SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
  EQUALITY integerMatch
  ORDERING integerOrderingMatch
  SINGLE-VALUE
  X-ORIGIN 'IPA v4.6 Profile update mechanism' )

objectClasses: ( 2.16.840.1.113730.3.8.21.2.1
  NAME 'ipaCertProfile' SUP top STRUCTURAL
  MUST ( cn $ description $ ipaCertProfileStoreIssued )
  MAY ipaCertProfileVersion
  X-ORIGIN 'IPA v4.2' )

The absense of the ipaCertProfile attribute value implies the starting value of 0.

IPA master entries

Information about IPA masters is stored in entries cn=$FQDN,cn=masters,cn=ipa,cn=etc,$SUFFIX. These entries shall be updated to assert the version of FreeIPA currently installed on that master.

QUESTION the master entries have auxiliary object classes ipaConfigObject and ipaSupportedDomainLevelConfig. Should we...

  1. Use ipaConfigString: ipa-version $VERSION to indicate the current IPA version of the master?
  2. Add a new attribute to the ipaSupportedDomainLevelConfig to indicate the IPA version of the master?
  3. Define a new auxiliary object class and an associated attribute for the purpose of indicating the IPA version of the master, and add this object class and attribute to master entries.

I lean towards 3, or 2.

Changes to ipa-server-upgrade

IPA version update

The /usr/share/ipa/master-entry.ldif template shall be updated to include the current IPA version information, according to the IPA master entries schema changes outlined above. The template substitution dictionary shall be updated to include this datum.

This is small enhancement to the domain level bounds update already performed by ipa-server-upgrade.

Profile update

Note that the IPA version update_ must be performed before profile updates.

During upgrade, the right template for the topology must be chosen and, if not the version currently in use, the profile must be updated in Dogtag.

Find all CA masters in the topology (search base cn=masters,cn=ipa,cn=etc,$SUFFIX with filter (cn=CA)).

For each CA master entry returned, query the IPA version of the parent entry, according to the IPA master entries schema changes outlined above. Choose the lowest version (denoted the target IPA version).

For each included profile, glob /usr/share/ipa/profiles/<profile-name>.* to find templates for that profile. Each template file is suffixed with the ipa-lower-bound. Eliminate templates with an ipa-lower-bound that exceeds the target IPA version. Then choose the template with the highest ipa-lower-bound (denoted the target template).

Read the target template to discover its template-version. Read the LDAP certprofile object to discover its current version. If the template-version exceeds the current profile version, format the template and update the profile.

Dealing with modified profiles

The certprofile plugin currently allows included profiles to be modified. Admins may have modified the configurations of included profiles (e.g. to change the validity period of issued certificates). The main question to answer here is:

QUESTION

Should we try to detect customisations and incorporate them in the updated profile configuration?

Implications of yes to the question:

  • More complexity and more data to retain so that we can detect user modifications and attempt to merge them into the new profile configuration. For example, it may be necessary to retain every version of a profile that has been shipped, rather than just versions for each ipa-lower-bound, so that diffs against the "pristine" version of the current profile version can be performed. Essentially a 3-way diff must be performed.
  • The possibility of merge conflicts, therefore the need of a conflict resolution process of some kind, possibly requiring the involvement of an admin, or explicit and clear reporting of the conflicts that were encountered and how they were resolved.
  • The possibility of configuration choices made by admins resulting in invalid or otherwise problematic configurations or problematic issued certificates, even where there were not merge conflicts.

Implications of no to the question:

  • Profile configuration customisations will be reverted, possibly resulting in changed profile behaviour that is is contrary to user expectations.
  • Profile configurations should be backed up, so that admins can easily restore custom configurations (preferably as a separate profile).
  • Release notes will have to prominently notify of this change and discuss its implications.
  • The certprofile-mod command should be updated to prohibit future modification of included profile configurations.

Implementation

Upgrade

How to Use

There is no user or administrator action required to use this mechanism.

Test Plan