Setting up an LDAP server with OpenLDAP

FixMe: update for current (Jessie) defaults and recommendations

ToDo: update for Jessie; review, organize, refactor; consider moving specific topics (e.g. Samba) to separate pages

most of this page does not easily apply to ldap in squeeze. as of slapd 2.4.23 things changed a lot. I've found that most of the docs available in searches for ldap setup are for an older set up.

so this page and others need to be updated for Squeeze , Wheezy and the future.

Install the OpenLDAP package slapd

Install the package with:

  # apt-get install slapd

answering the prompts as follows:

Note: if you don't get these options use dpkg-reconfigure -plow slapd after installation. With the latest version, it only asks you for admin user password and none of the rest, because the DNS domain name is taken from configured machine FQDN name.

• For the DNS domain name, enter your domain name. This will be translated to an LDAP DN (for example, 'example.com' would become 'dc=example, dc=com'). This becomes what is known as your BaseDN, the root of your database.

• For your organization you can enter any string; this becomes associated to the 'o' field of your BaseDN record.

• Next enter your LDAP administrator password twice. This will set the password for 'cn=admin, BaseDN' and give 'cn=admin, BaseDN' write access to everything in your LDAP tree.

• Accept the default of No to the question Allow LDAPv2 protocol.

• Use the default database backend.

For querying the LDAP server utilities like ldapsearch are available. See the LDAP/LDAPUtils topic for more details.

Missing slapd.conf?

Since version 2.4.23-3 the configuration of OpenLDAP has been changed to /etc/ldap/slapd.d by default. The OpenLDAP packages in Debian provide an automatic migration to the new configuration style. With the new configuration style it is possible to change values on the fly without restarting slapd. Changes are made through the use of ldif files and ldap{add,modify}. In Debian you can use the following command to search the configuration:

• ldapsearch -Y EXTERNAL -H ldapi:/// -b "cn=config"

To modify configuration use the command:

• ldapmodify -Y EXTERNAL -H ldapi:/// -f <file.ldif>

For configuration options see the several manpages that exist or the documentation provided upstream.

The use of slapd.conf remains possible (optional).

Indexes

For better performance do more indexing than the default.

with slapd.conf

Modify /etc/ldap/slapd.conf to contain the following:

index   objectClass             eq
index   cn                      pres,sub,eq
index   sn                      pres,sub,eq
index   uid                     pres,sub,eq
index   displayName             pres,sub,eq
index   default                 sub
index   uidNumber               eq
index   gidNumber               eq
index   mail,givenName          eq,subinitial
index   dc                      eq

After any new indexes have been defined or other major database changes have been made (e.g. slapadd was used) it is best to recreate the indexes. Note that you should stop slapd before recreating the indexes and should fix the permissions afterward.

  # /etc/init.d/slapd stop
  # slapindex
  # chown -R openldap:openldap /var/lib/ldap
  # /etc/init.d/slapd start

with cn=config

Create a LDIF file : olcDbIndex.ldif

dn: olcDatabase={1}mdb,cn=config
changetype: modify
add: olcDbIndex
olcDbIndex: cn pres,sub,eq
-
add: olcDbIndex
olcDbIndex: sn pres,sub,eq
-
add: olcDbIndex
olcDbIndex: uid pres,sub,eq
-
add: olcDbIndex
olcDbIndex: displayName pres,sub,eq
-
add: olcDbIndex
olcDbIndex: default sub
-
add: olcDbIndex
olcDbIndex: uidNumber eq
-
add: olcDbIndex
olcDbIndex: gidNumber eq
-
add: olcDbIndex
olcDbIndex: mail,givenName eq,subinitial
-
add: olcDbIndex
olcDbIndex: dc eq

Note: use the correct database format in the first line, the default type during installation of slapd is mdb.

Use ldapmodify to add this settings to the ldap :

ldapmodify -Y EXTERNAL -H ldapi:/// -f ./olcDbIndex.ldif

Don't forget the - ! After the execution, slapd will launch a internal task to create indexes. Don't stop slapd during this indexation.

Access control

Configuring 'chsh' and 'chfn' to work with LDAP

via static configuration

Edit '/etc/ldap/slapd.conf' to allow access for users to update their loginShell and gecos entries by adding the following before the 'access to *' entry:

access to attrs=loginShell,gecos
      by dn="cn=admin,dc=example,dc=com" write
      by self write
      by * read

via dynamic configuration

Create a LDIF file olcAccess.ldif with access permissions to loginShell and gecos entries for the user and admins :

dn: olcDatabase={1}hdb,cn=config
changetype: modify
add: olcAccess
olcAccess: {1}to attrs=loginShell,gecos
  by dn="cn=admin,dc=example,dc=com" write
  by self write
  by * read

Instanty apply these new permissions to ldap with :

ldapmodify -Y EXTERNAL -H ldapi:/// -f ./olcAccess.ldif

For SAMBA LDAP support

For Samba LDAP, slapd needs the Samba schema. The Debian package seems to have a samba.schema file which is old and out of date, and a samba.schema.gz file which is actually the correct one. Do the following (as root):

 # this package contains samba.schema.gz :
 aptitude install samba-doc

Copy example samba.schema to ldap configuration directory:

 zcat /usr/share/doc/samba-doc/examples/LDAP/samba.schema.gz > /etc/ldap/schema/samba.schema

with slapd.conf (old style, still possible in squeeze)

Add the following line to /etc/ldap/slapd.conf after the other includes.

include /etc/ldap/schema/samba.schema

And restart slapd:

  # /etc/init.d/slapd restart

with cn=config, slapd.d (default in Squeeze):

Create a temporary config file samba.conf:

  include          /etc/ldap/schema/core.schema
  include          /etc/ldap/schema/cosine.schema
  include          /etc/ldap/schema/nis.schema
  include          /etc/ldap/schema/inetorgperson.schema
  include          /etc/ldap/schema/samba.schema

Convert samba.schema into samba.ldif with slaptest:

  # mkdir /tmp/slapd.d
  # slaptest -f samba.conf -F /tmp/slapd.d/

Load the /tmp/slapd.d/cn=config/cn=schema/cn={4}samba.ldif into your cn=config using:

  # cp "/tmp/slapd.d/cn=config/cn=schema/cn={4}samba.ldif" "/etc/ldap/slapd.d/cn=config/cn=schema"
  # chown openldap: '/etc/ldap/slapd.d/cn=config/cn=schema/cn={4}samba.ldif'
  # /etc/init.d/slapd stop
  # /etc/init.d/slapd start

and check you now see the new samba schema:

# ldapsearch -LLLQY EXTERNAL -H ldapi:/// -b cn=schema,cn=config "(objectClass=olcSchemaConfig)" dn
dn: cn=schema,cn=config

dn: cn={0}core,cn=schema,cn=config

dn: cn={1}cosine,cn=schema,cn=config

dn: cn={2}nis,cn=schema,cn=config

dn: cn={3}inetorgperson,cn=schema,cn=config

dn: cn={4}samba,cn=schema,cn=config

Access controls for subtree-specific LDAP Admins

If you choose to use LDAP for many functions, such as having a single server for DNS, Authentication, and networking flat file database replacement, you may wish to have LDAP administrative users for each subtree in addition to the global admin (dn="cn=admin, dc=example, dc=com). The following example is useful when using a separate authentication tree which includes Samba.

 # The manager dn has full write access to the auth subtree
 # Everyone else has read access to not otherwise protected fields and entries
 access to dn.sub="ou=auth,dc=example,dc=com"
         by dn="cn=Manager,ou=auth,dc=example,dc=com" write
         by * read

Configuring LDAPS

Once your LDAP server is up and running, be sure to backup your configuration before trying to configure LDAPS. If you break your configuration with the "cn=config" style, the LDAP server will not restart.

Now, first, you must enable ldaps port in /etc/default/slapd :

SLAPD_SERVICES="ldap://127.0.0.1:389/ ldaps:/// ldapi:///"

Configuring the certificate (and possibly the CA used) in slapd config :

in /etc/ldap/slapd.conf:

TLSCACertificateFile    /etc/ssl/certs/server-intermediate.pem
TLSCertificateKeyFile   /etc/ssl/private/server-key.pem
TLSCertificateFile      /etc/ssl/certs/server-cert.pem

or add attributes to cn=config (for Debian Squeeze or later). Create a olcSSL.ldif file with:

dn: cn=config
add: olcTLSCACertificateFile
olcTLSCACertificateFile: /etc/ssl/certs/server-intermediate.pem
-
add: olcTLSCertificateKeyFile
olcTLSCertificateKeyFile: /etc/ssl/private/server-key.pem
-
add: olcTLSCertificateFile
olcTLSCertificateFile: /etc/ssl/certs/server-cert.pem

and import the settings with ldapmodify:

  # ldapmodify -Y EXTERNAL -H ldapi:/// -f ./olcSSL.ldif

By default, slapd runs as user/group openldap, so it can't read the key file. On Debian Lenny, the preferred solution to this dilemma seems to be to chown the key to root:ssl-cert, set permissions to 640 and add the user openldap to group ssl-cert:

usermod -a -G ssl-cert openldap

• In Wheezy, not adding openldap to the ssl-cert group caused this in logs:

main: TLS init def ctx failed: -1

Symptoms:

In slapd debug output:

[...] TLS: could not set cipher list HIGH:MEDIUM:-SSLv2.  (or similar)

In /var/log/syslog:

[...] main: TLS init def ctx failed: -1

Diagnosis:

If you try to install the OpenLDAP server (slapd) with Debian Lenny, it comes compiled against the GnuTLS library. It means you cannot use an OpenSSL style directive like TLSCipherSuite HIGH:MEDIUM:-SSLv2 in slapd.conf.

Cure:

In /etc/ldap/slapd.conf, either comment out TLSCipherSuite option to let gnutls choose rather sane default for you, or use something like:

TLSCipherSuite NORMAL

To get all the supported GnuTLS cipher suite names:

# aptitude install gnutls-bin
# man gnutls-cli

And skip to TLS/SSL control options section of man page.

To use only 256 bit cyphers, use this (paranoiac?) setting:

TLSCipherSuite SECURE256:!AES-128-CBC:!ARCFOUR-128:!CAMELLIA-128-CBC:!3DES-CBC:!CAMELLIA-128-CBC

Another useful tool to test server-supported TLS options is to use gnutls-cli-debug. First add ldaps:/// string to the SLAPD_SERVICES option in /etc/default/slapd, restart slapd and then run

gnutls-cli-debug -p 636 <fqdn_of_you_ldap_host>

That will show you cryptographic suits your LDAP server supports.

Symptoms (round 2)

If you are getting messages such as

slapd TLS: can't connect: A TLS packet with unexpected length was received..

or

Could not negotiate a supported cipher suite.

take a wander by this.

Diagnosis:

How did you generate your certificates? If you generated them using OpenSSL, you're going to run into problems. Debian switched over to using gnutls a while ago, and it doesn't play nice with OpenSSL certificates. So, to fix this, check out the next section.

NOTE: On Debian Squeeze openldap is linked with gnutls as well, but works just fine with certificate generated by openssl.

NOTE about the above note: I don't find it to be the case, except for the CA cert. I ended up having to generate a new key & csr to sign with gnutls's certtool and then signing it with my existing openssl created CA like so:

certtool --generate-privkey --outfile ldap.gnutls.key
certtool --generate-certificate --load-privkey ldap.gnutls.key --outfile ldap.gnutls.crt --load-ca-certificate ca.crt --load-ca-privkey ca.key

Again, this allows you to keep your existing OpenSSL CA.

Procedure:

You're going to need the gnutls certificate generator: certtool available in gnutls-bin

Run these two commands to generate a new self-signed key (into the current working directory):

certtool --generate-privkey --outfile ca-key.pem
certtool --generate-self-signed --load-privkey ca-key.pem --outfile ca-cert.pem

Then, update your certificate locations in /etc/ldap/slapd.conf (TLSCertificateFile points to ca-cert.pem and TLSCertificateKeyFile points to ca-key.pem), comment out TLSCACertificateFile, and change TLSVerifyClient to never.

In /etc/ldap/ldap.conf, comment out TLS_CACERT and change TLS_REQCERT to never.

Since the certificate is self-signed, we can't have gnutls trying to verify it (hence the never), otherwise it will never run.

Then restart your services, and you're good (assuming all your links point properly to ldaps://url/).

Configuring MirrorMode LDAP Sync Replication (syncrepl)

See http://www.openldap.org/doc/admin24/replication.html for a clear explanation of OpenLDAP Replication. Several types of replication are possible, this section focusses on how to configure MirrorMode Replication.

with slapd.conf

See the aforementioned http://www.openldap.org/doc/admin24/replication.html for a clear explanation on how to configure MirrorMode LDAP Sync Replication (syncrepl) using the old slapd.conf syntax. No need to repeat this here.

with cn=config

MirrorMode LDAP Sync Replication (syncrepl) is achieved by following the seven small steps below.

1: Create a special user for the replication of the data. This by default can't be done using the SASL/EXTERNAL authentication, since you will get a 'no write access to parent' error. Please use a basedn suited to your situation, in example change the "dc=nodomain" to the basedn for your server. Please see step 7 for the password chosen and use slappasswd command to format it.

$ ldapmodify -D "cn=admin,dc=nodomain" -W<<EOT
> dn: cn=mirrormode,dc=nodomain
> changetype: add
> objectClass: simpleSecurityObject
> objectClass: organizationalRole
> cn: mirrormode
> description: Syncrepl user for mirrormode operation
> userPassword: e1NTSEF9SktNQmpPV29zOEtPSCtaWmdDeTVUa056U3c5NWF5bis=
> EOT
Enter LDAP Password:
adding new entry "cn=mirrormode,dc=nodomain"

$

All the other steps can easily be done using the SASL/EXTERNAL authentication as explained in Missing slapd.conf. Just save the given information in a file and load it with: $ ldapmodify -Y EXTERNAL -H ldapi:/// -f <file.ldif>

2: Load the syncrepl module:

dn: cn=module{0},cn=config
changetype: modify
add: olcModuleLoad
olcModuleLoad: syncprov

3: Make sure the newly created replication user can read the data to be replicated:

dn: olcDatabase={1}hdb,cn=config
changetype: modify
delete: olcAccess
olcAccess: {0}to attrs=userPassword,shadowLastChange by self write by anonymous auth by dn="cn=admin,dc=nodomain" write by * none
-
add: olcAccess
olcAccess: {0}to attrs=userPassword,shadowLastChange by self write by anonymous auth by dn="cn=admin,dc=nodomain" write by dn="cn=mirrormode,dc=nodomain" read by * none
-

4: Set up the provider slapd:

dn: olcOverlay=syncprov,olcDatabase={1}hdb,cn=config
changeType: add
objectClass: olcOverlayConfig
objectClass: olcSyncProvConfig
olcOverlay: syncprov
olcSpCheckpoint: 100 10
olcSpSessionLog: 100

5: Note that using the session log requires searching on the entryUUID attribute. Setting an eq index on this attribute will greatly benefit the performance of the session log on the provider:

dn: olcDatabase={1}hdb,cn=config
changeType: modify
delete: olcDbIndex
olcDbIndex: objectClass eq
-
add: olcDbIndex
olcDbIndex: objectClass,entryCSN,entryUUID eq
-

6: Set the server ID. Make sure you use different ID's for different servers, in example 0, 1, etc...:

dn: cn=config
changeType: modify
add: olcServerID
olcServerID: 0
-

7: Enable the replication. Make sure you use the correct IP number for each ldap server and make sure they point to each other! Also, the credentials are just an example. Choose a password of your own of course:

dn: olcDatabase={1}hdb,cn=config
changeType: modify
add: olcSyncrepl
olcSyncrepl: rid=001 provider=ldap://172.16.42.74:389 bindmethod=simple binddn="cn=mirrormode,dc=nodomain" credentials=_ei7N8o.gh=o44 searchbase="dc=nodomain" schemachecking=on type=refreshAndPersist retry="60 +"
-
add: olcMirrorMode
olcMirrorMode: TRUE
-

And you're up and running. Try adding something to one of the LDAP servers and see it appear automagically at the other. Well done my friend!

CategorySystemAdministration