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LDAP Additions in GitLab EE

This is a continuation of the main LDAP documentation, detailing LDAP features specific to GitLab Enterprise Edition.

Overview

LDAP stands for Lightweight Directory Access Protocol, which is a standard application protocol for accessing and maintaining distributed directory information services over an Internet Protocol (IP) network.

GitLab integrates with LDAP to support user authentication. This integration works with most LDAP-compliant directory servers, including Microsoft Active Directory, Apple Open Directory, Open LDAP, and 389 Server. GitLab Enterprise Edition includes enhanced integration, including group membership syncing.

Use-cases

  • User Sync: Once a day, GitLab will update users against LDAP
  • Group Sync: Once an hour, GitLab will update group membership based on LDAP group members

User Sync

Once per day, GitLab will run a worker to check and update GitLab users against LDAP.

The process will execute the following access checks:

  1. Ensure the user is still present in LDAP
  2. If the LDAP server is Active Directory, ensure the user is active (not blocked/disabled state). This will only be checked if active_directory: true is set in the LDAP configuration 1

The user will be set to ldap_blocked state in GitLab if the above conditions fail. This means the user will not be able to login or push/pull code.

The process will also update the following user information:

  1. Email address
  2. If sync_ssh_keys is set, SSH public keys
  3. If Kerberos is enabled, Kerberos identity

Note: The LDAP sync process updates existing users while new users will be created on first sign in.

Group Sync

If your LDAP supports the memberof property, GitLab will add the user to any new groups they might be added to when the user logs in. That way they don't need to wait for the hourly sync to be granted access to the groups that they are in in LDAP.

In GitLab Enterprise Edition Premium, we can also add a GitLab group to sync with one or multiple LDAP groups or we can also add a filter. The filter must comply with the syntax defined in RFC 2254.

A group sync process will run every hour on the hour, and group_base must be set in LDAP configuration for LDAP synchronizations based on group CN to work. This allows GitLab group membership to be automatically updated based on LDAP group members.

The group_base configuration should be a base LDAP 'container', such as an 'organization' or 'organizational unit', that contains LDAP groups that should be available to GitLab. For example, group_base could be ou=groups,dc=example,dc=com. In the config file it will look like the following.

Omnibus configuration

Edit /etc/gitlab/gitlab.rb:

gitlab_rails['ldap_servers'] = YAML.load <<-EOS
main:
  # snip...
  group_base: ou=groups,dc=example,dc=com
EOS

Reconfigure GitLab for the changes to take effect.

Source configuration

Edit /home/git/gitlab/config/gitlab.yml:

production:
  ldap:
    servers:
      main:
        # snip...
        group_base: ou=groups,dc=example,dc=com

Restart GitLab for the changes to take effect.

To take advantage of group sync, group owners or masters will need to create an LDAP group link in their group Settings -> LDAP Groups page. Multiple LDAP groups and/or filters can be linked with a single GitLab group. When the link is created, an access level/role is specified (Guest, Reporter, Developer, Master, or Owner).

Administrator Sync

As an extension of group sync, you can automatically manage your global GitLab administrators. Specify a group CN for admin_group and all members of the LDAP group will be given administrator privileges. The configuration will look like the following.

Note: Administrators will not be synced unless group_base is also specified alongside admin_group. Also, only specify the CN of the admin group, as opposed to the full DN.

Omnibus configuration

Edit /etc/gitlab/gitlab.rb:

gitlab_rails['ldap_servers'] = YAML.load <<-EOS
main:
  # snip...
  group_base: ou=groups,dc=example,dc=com
  admin_group: my_admin_group
EOS

Reconfigure GitLab for the changes to take effect.

Source configuration

Edit /home/git/gitlab/config/gitlab.yml:

production:
  ldap:
    servers:
      main:
        # snip...
        group_base: ou=groups,dc=example,dc=com
        admin_group: my_admin_group

Restart GitLab for the changes to take effect.

External Groups

Note: External Groups configuration is only available in GitLab EE Version 8.9 and above.

Using the external_groups setting will allow you to mark all users belonging to these groups as external users. Group membership is checked periodically through the LdapGroupSync background task.

Omnibus configuration

gitlab_rails['ldap_servers'] = YAML.load <<-EOS
main:
  # snip...
  external_groups: ['interns', 'contractors']
EOS

Reconfigure GitLab for the changes to take effect.

Source configuration

production:
  ldap:
    servers:
      main:
        # snip...
        external_groups: ['interns', 'contractors']

Restart GitLab for the changes to take effect.

Group Sync Technical Details

There is a lot going on with group sync 'under the hood'. This section outlines what LDAP queries are executed and what behavior you can expect from group sync.

Group member access will be downgraded from a higher level if their LDAP group membership changes. For example, if a user has 'Owner' rights in a group and the next group sync reveals they should only have 'Developer' privileges, their access will be adjusted accordingly. The only exception is if the user is the last owner in a group. Groups need at least one owner to fulfill administrative duties.

Supported LDAP Group Types/Attributes

GitLab supports LDAP groups that use member attributes member, submember, uniquemember, memberof and memberuid. This means group sync supports, at least, LDAP groups with object class groupOfNames, posixGroup, and groupOfUniqueName. Other object classes should work fine as long as members are defined as one of the mentioned attributes. This also means GitLab supports Microsoft Active Directory, Apple Open Directory, Open LDAP, and 389 Server. Other LDAP servers should work, too.

Active Directory also supports nested groups. Group sync will recursively resolve membership if active_directory: true is set in the configuration file.

Note: Nested group membership will only be resolved if the nested group also falls within the configured group_base. For example, if GitLab sees a nested group with DN cn=nested_group,ou=special_groups,dc=example,dc=com but the configured group_base is ou=groups,dc=example,dc=com, cn=nested_group will be ignored.

Queries

  • Each LDAP group is queried a maximum of one time with base group_base and filter (cn=<cn_from_group_link>).
  • If the LDAP group has the memberuid attribute, GitLab will execute another LDAP query per member to obtain each user's full DN. These queries are executed with base base, scope 'base object', and a filter depending on whether user_filter is set. Filter may be (uid=<uid_from_group>) or a joining of user_filter.

Benchmarks

Group sync was written to be as performant as possible. Data is cached, database queries are optimized, and LDAP queries are minimized. The last benchmark run revealed the following metrics:

For 20,000 LDAP users, 11,000 LDAP groups and 1,000 GitLab groups with 10 LDAP group links each:

  • Initial sync (no existing members assigned in GitLab) took 1.8 hours
  • Subsequent syncs (checking membership, no writes) took 15 minutes

These metrics are meant to provide a baseline and performance may vary based on any number of factors. This was a pretty extreme benchmark and most instances will not have near this many users or groups. Disk speed, database performance, network and LDAP server response time will affect these metrics.

Troubleshooting

Referral Error

If you see LDAP search error: Referral in the logs, or when troubleshooting LDAP Group Sync, this error may indicate a configuration problem. The LDAP configuration /etc/gitlab/gitlab.rb (Omnibus) or config/gitlab.yml (source) is in YAML format and is sensitive to indentation. Check that group_base and admin_group configuration keys are indented 2 spaces past the server identifier. The default identifier is main and an example snippet looks like the following:

main: # 'main' is the GitLab 'provider ID' of this LDAP server
  label: 'LDAP'
  host: 'ldap.example.com'
  ...
  group_base: 'cn=my_group,ou=groups,dc=example,dc=com'
  admin_group: 'my_admin_group'

User DN has changed

When an LDAP user is created in GitLab, their LDAP DN is stored for later reference.

If GitLab cannot find a user by their DN, it will attempt to fallback to finding the user by their email. If the lookup is successful, GitLab will update the stored DN to the new value.

User is not being added to a group

Sometimes you may think a particular user should be added to a GitLab group via LDAP group sync, but for some reason it's not happening. There are several things to check to debug the situation.

  • Ensure LDAP configuration has a group_base specified. This configuration is required for group sync to work properly.
  • Ensure the correct LDAP group link is added to the GitLab group. Check group links by visiting the GitLab group, then Settings dropdown -> LDAP groups.
  • Check that the user has an LDAP identity
    1. Sign in to GitLab as an administrator user.
    2. Navigate to Admin area -> Users.
    3. Search for the user
    4. Open the user, by clicking on their name. Do not click 'Edit'.
    5. Navigate to the Identities tab. There should be an LDAP identity with an LDAP DN as the 'Identifier'.

If all of the above looks good, jump in to a little more advanced debugging. Often, the best way to learn more about why group sync is behaving a certain way is to enable debug logging. There is verbose output that details every step of the sync.

  1. Start a Rails console

    # For Omnibus installations
sudo gitlab-rails console

# For installations from source
sudo -u git -H bundle exec rails console production

  2. Set the log level to debug (only for this session):

    Rails.logger.level = Logger::DEBUG

  3. Choose a GitLab group to test with. This group should have an LDAP group link already configured. If the output is nil, the group could not be found. If a bunch of group attributes are output, your group was found successfully.

    group = Group.find_by(name: 'my_group')

# Output
=> #<Group:0x007fe825196558 id: 1234, name: "my_group"...>

  4. Run a group sync for this particular group.

    EE::Gitlab::LDAP::Sync::Group.execute_all_providers(group)

  5. Look through the output of the sync. See example log output below for more information about the output.

  6. If you still aren't able to see why the user isn't being added, query the LDAP group directly to see what members are listed. Still in the Rails console, run the following query:

    adapter = Gitlab::LDAP::Adapter.new('ldapmain') # If `main` is the LDAP provider
ldap_group = EE::Gitlab::LDAP::Group.find_by_cn('group_cn_here', adapter)

# Output
=> #<EE::Gitlab::LDAP::Group:0x007fcbdd0bb6d8

  7. Query the LDAP group's member DNs and see if the user's DN is in the list. One of the DNs here should match the 'Identifier' from the LDAP identity checked earlier. If it doesn't, the user does not appear to be in the LDAP group.

    ldap_group.member_dns

# Output
=> ["uid=john,ou=people,dc=example,dc=com", "uid=mary,ou=people,dc=example,dc=com"]

  8. Some LDAP servers don't store members by DN. Rather, they use UIDs instead. If you didn't see results from the last query, try querying by UIDs instead.

    ldap_group.member_uids

# Output
=> ['john','mary']

Example log output

The output of the last command will be very verbose, but contains lots of helpful information. For the most part you can ignore log entries that are SQL statements.

Indicates the point where syncing actually begins:

Started syncing all providers for 'my_group' group

The follow entry shows an array of all user DNs GitLab sees in the LDAP server. Note that these are the users for a single LDAP group, not a GitLab group. If you have multiple LDAP groups linked to this GitLab group, you will see multiple log entries like this - one for each LDAP group. If you don't see an LDAP user DN in this log entry, LDAP is not returning the user when we do the lookup. Verify the user is actually in the LDAP group.

Members in 'ldap_group_1' LDAP group: ["uid=john0,ou=people,dc=example,dc=com",
"uid=mary0,ou=people,dc=example,dc=com", "uid=john1,ou=people,dc=example,dc=com",
"uid=mary1,ou=people,dc=example,dc=com", "uid=john2,ou=people,dc=example,dc=com",
"uid=mary2,ou=people,dc=example,dc=com", "uid=john3,ou=people,dc=example,dc=com",
"uid=mary3,ou=people,dc=example,dc=com", "uid=john4,ou=people,dc=example,dc=com",
"uid=mary4,ou=people,dc=example,dc=com"]

Shortly after each of the above entries, you will see a hash of resolved member access levels. This hash represents all user DNs GitLab thinks should have access to this group, and at which access level (role). This hash is additive, and more DNs may be added, or existing entries modified, based on additional LDAP group lookups. The very last occurrence of this entry should indicate exactly which users GitLab believes should be added to the group.

Note: 10 is 'Guest', 20 is 'Reporter', 30 is 'Developer', 40 is 'Master' and 50 is 'Owner'

Resolved 'my_group' group member access: {"uid=john0,ou=people,dc=example,dc=com"=>30,
"uid=mary0,ou=people,dc=example,dc=com"=>30, "uid=john1,ou=people,dc=example,dc=com"=>30,
"uid=mary1,ou=people,dc=example,dc=com"=>30, "uid=john2,ou=people,dc=example,dc=com"=>30,
"uid=mary2,ou=people,dc=example,dc=com"=>30, "uid=john3,ou=people,dc=example,dc=com"=>30,
"uid=mary3,ou=people,dc=example,dc=com"=>30, "uid=john4,ou=people,dc=example,dc=com"=>30,
"uid=mary4,ou=people,dc=example,dc=com"=>30}

It's not uncommon to see warnings like the following. These indicate that GitLab would have added the user to a group, but the user could not be found in GitLab. Usually this is not a cause for concern.

If you think a particular user should already exist in GitLab, but you're seeing this entry, it could be due to a mismatched DN stored in GitLab. See User DN has changed to update the user's LDAP identity.

User with DN `uid=john0,ou=people,dc=example,dc=com` should have access
to 'my_group' group but there is no user in GitLab with that
identity. Membership will be updated once the user signs in for
the first time.

Finally, the following entry says syncing has finished for this group:

Finished syncing all providers for 'my_group' group

  1. In Active Directory, a user is marked as disabled/blocked if the user account control attribute (userAccountControl:1.2.840.113556.1.4.803) has bit 2 set. See https://ctogonewild.com/2009/09/03/bitmask-searches-in-ldap/ for more information. ↩