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Changes for page KerberosAndLDAP

Last modified by Sirius Rayner-Karlsson on 2024/05/09 10:54

From 9.1 to 10.1

From version 10.1

edited by Sirius Rayner-Karlsson
on 2024/05/01 17:04

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To version 37.1

edited by Sirius Rayner-Karlsson
on 2024/05/09 10:54

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++{{box cssClass="floatinginfobox" title="**Contents**"}}
++{{toc/}}
++{{/box}}
++
  = Debian =
--The guide I followed was [[https:~~/~~/wiki.debian.org/LDAP/OpenLDAPSetup#Kerberos>>https://wiki.debian.org/LDAP/OpenLDAPSetup#Kerberos]] which while it worked required some minor tweaks. I obtained edit privileges for the Debian Wiki and updated the guide with the fixes that I found. I however have a Synology NAS and that can run an LDAP Server. So this guide differs a little from the upstream Debian Guide.
++The guide I followed was https://wiki.debian.org/LDAP/OpenLDAPSetup#Kerberos which while it worked required some minor tweaks. I obtained edit privileges for the Debian Wiki and updated the guide with the fixes that I found. I however have a Synology NAS and that can run an LDAP Server. So this guide differs from the upstream Debian Guide.
--{{{
--First, install the packages containing the LDAP-enabled Kerberos servers ([[krb5-kdc-ldap>>url:https://packages.debian.org/krb5-kdc-ldap]] and [[krb5-admin-server>>url:https://packages.debian.org/krb5-admin-server]]) and the [[schema2ldif>>url:https://packages.debian.org/schema2ldif]] tool:
++Assumption is that you have installed the LDAP Server package on your NAS and gone through initial configuration steps, so it has a domain, there is a DN you can bind as and so forth. It is also assumed you have a Debian system (12.5 or later, though this guide should work with 11.x and likely 10.x as well) that will become your KDC and KAdmin server.
--##$ sudo apt install krb5-kdc-ldap krb5-admin-server schema2ldif##
--}}}
++Recommendation is that you create actual ##.ldif## files rather than use here-documents as used in this guide. It is far easier to make adjustments to things if you have a file to edit rather than having to type it all out again or paste it and then have to try and make edits to it without making mistakes.
--{{{
--Then load the ##kerberos## schema:
++**The guide is for illustration. Expectation is that you do not follow it verbatim but adapt it to your needs.**
--##$ zcat /usr/share/doc/krb5-kdc-ldap/kerberos.openldap.ldif.gz | ldapadd -H ldap:~/~/nas.fqdn/ -D uid=root,cn=users,dc=example,dc=com##
--##Password:##
--##adding new entry "cn=kerberos,cn=schema,cn=config"##
--}}}
++=== Install packages ===
++(% class="wikigeneratedid" %)
++The packages you need are [[krb5-kdc-ldap>>url:https://packages.debian.org/krb5-kdc-ldap]], [[krb5-admin-server>>url:https://packages.debian.org/krb5-admin-server]] for the actual KDC and [[schema2ldif>>url:https://packages.debian.org/schema2ldif]]  plus [[slapd>>https://packages.debian.org/search?keywords=slapd]] for adding the schema and ##slappasswd##. They are to be installed on your designated Debian host.
--And add an index on the ##krbPrincipalName## (improves performance and also suppresses some log messages if ##slapd## is configured to log more than default) for the database(s) where you intend to store Kerberos data:
++(% style="color:#400" %)
++##{{{$ sudo apt install krb5-kdc-ldap krb5-admin-server schema2ldif}}}##
--{{{# ldapmodify -H ldap:~/~/nas.fqhn <<EOF
--dn: olcDatabase={1}bdb,cn=config
++=== Load kerberos LDAP schema ===
++Now you need to load the kerberos schema into the LDAP server on the Synology. Use the ##cn=config## DN.
++
++(% style="color:#400" %)
++##{{{$ zcat /usr/share/doc/krb5-kdc-ldap/kerberos.openldap.ldif.gz | ldapadd -H ldaps://nas.example.com/ -D cn=config -W Enter LDAP Password: adding new entry "cn=kerberos,cn=schema,cn=config" $}}}##
++
++
++=== Create Index on krbPrincipalName ===
++
++Having an index on the ##krbPrincipalName## improves performance. Synology OpenLDAP does not use ##mdb## format, it uses ##bdb##. Debian ##slapd## uses ##mdb## format. It is different database format, but the principle is the same. Again, as you are modifying config, the DN is ##cn=config##. Use the main password you set for the Synology LDAP server. Create a file ##step1.ldif## with the following content:
++
++(% style="color:#400" %)
++##{{{
++dn: olcDatabase={1}bdb,cn=config
  add: olcDbIndex
++olcDbIndex: krbPrincipalName eq,pres,sub}}}##
--olcDbIndex: krbPrincipalName eq,pres,sub
--EOF
++and apply it with
++(% style="color:#400" %)
++##{{{$ ldapmodify -H ldaps://nas.example.com/ -D cn=config -W -f step1.ldif
++Enter LDAP Password:
++
  modifying entry "olcDatabase={1}bdb,cn=config"
--}}}
++$ }}}##
--Next, you need to create and configure two entries which will be used by the Kerberos servers to connect to OpenLDAP. If you are running Kerberos and OpenLDAP on the same system, these steps are optional, but recommended. In order to keep things nicely separated, everything will be created under a separate ##organizationalUnit##. Note that a simple bind (##-x -D##) is used instead of an ##EXTERNAL## bind since write access to the dc=example,dc=com DIT is necessary:
++=== Create principals kadmin and kdc ===
++Next, you create and configure two entries which will be used by the Kerberos servers to connect to OpenLDAP. Not running the Kerberos KDC and Admin Server on the same host as OpenLDAP, these steps are required. Keeping things confined, everything will be created under a separate ##organizationalUnit##. My guide differs from the official Debian guide here. Due to Synology OpenLDAP having a strict password policy, it was necessary to adjust the DNs of ##kdc## and ##kadmin##. The official guide use placeholder passwords which does not work with the Synology LDAP server.
++Generate the passwords upfront with ##slappasswd -h {SSHA}##. Then create a file ##step2.ldif## with the following content:
--{{{# ldapadd -x -D cn=admin,dc=example,dc=com -W <<EOF
--dn: ou=Services,dc=example,dc=com
++(% style="color:#400" %)
++##{{{
++dn: ou=kerberos,dc=example,dc=com
  objectClass: organizationalUnit
  objectClass: top
--ou: Services
--
--dn: ou=kerberos,ou=Services,dc=example,dc=com
--objectClass: organizationalUnit
--objectClass: top
  ou: kerberos
--dn: uid=kdc,ou=kerberos,ou=Services,dc=example,dc=com
--uid: kdc
--objectClass: account
--objectClass: simpleSecurityObject
--userPassword: {CRYPT}x
++dn: cn=kdc,ou=kerberos,dc=example,dc=com
++cn: kdc
++sn: kdc
++objectClass: person
++objectClass: pwdPolicy
++pwdAttribute: userPassword
++pwdMinLength: 8
++pwdCheckQuality: 2
++pwdPolicySubentry: cn=kdc,ou=kerberos,dc=example,dc=com
++userPassword: {SSHA}<password-hash>
  description: Kerberos KDC Account
--dn: uid=kadmin,ou=kerberos,ou=Services,dc=example,dc=com
--uid: kadmin
--objectClass: account
--objectClass: simpleSecurityObject
--userPassword: {CRYPT}x
--description: Kerberos Admin Server Account
--EOF
--Enter LDAP Password: SECRET
++dn: cn=kadmin,ou=kerberos,dc=example,dc=com
++cn: kadmin
++sn: kadmin
++objectClass: person
++objectClass: pwdPolicy
++pwdAttribute: userPassword
++pwdMinLength: 8
++pwdCheckQuality: 2
++pwdPolicySubentry: cn=kadmin,ou=kerberos,dc=example,dc=com
++userPassword: {SSHA}<password-hash>
++description: Kerberos KDC Account}}}##
--adding new entry "ou=Services,dc=example,dc=com"
--adding new entry "ou=kerberos,ou=Services,dc=example,dc=com"
++Apply it with
--adding new entry "uid=kdc,ou=kerberos,ou=Services,dc=example,dc=com"
++(% style="color:#400" %)
++##{{{$ ldapadd -H ldaps://nas.example.com/ -D uid=root,cn=users,dc=example,dc=com -W -f step2.ldif
++Enter LDAP Password:
--adding new entry "uid=kadmin,ou=kerberos,ou=Services,dc=example,dc=com"}}}
++adding new entry "ou=kerberos,dc=example,dc=com"
++adding new entry "cn=kdc,ou=kerberos,dc=example,dc=com"
--
++adding new entry "cn=kadmin,ou=kerberos,dc=example,dc=com"
++
++$ }}}##
++
++
++A small note on this section:
++The ##objectClass: pwdPolicy## must be added to a, to LDAP, physical thing. ##objectClass: person## fits the criteria, but can not have ##uid##. So to make it work, the ##uid## is replaced with ##sn## and ##cn## (yes, both are needed). Then you can set the other four attributes and add the hashed password you got from ##slappasswd##.
++
++
++=== Grant kdc and kadmin permissions ===
++
++This switches back to the ##cn=config## DN as you are changing the permissions. Note that we now reference our kdc and kadmin accounts and we grant them permission to the krbContainer which will house all our kerberos principals. Give both of them write access, because we do want to have the ability to track last login and lock accounts if there are  too many login failures. We like security.
++
++Create ##step3.ldif## with the following content:
++
++(% style="color:#400" %)
++##{{{
++dn: olcDatabase={1}bdb,cn=config
++add: olcAccess
++olcAccess: {0}to attrs=krbPrincipalKey
++  by anonymous auth
++  by dn.exact="cn=kdc,ou=kerberos,dc=example,dc=com" write
++  by dn.exact="cn=kadmin,ou=kerberos,dc=example,dc=com" write
++  by self write
++  by * none
++-
++add: olcAccess
++olcAccess: {1}to dn.subtree="cn=krbContainer,ou=kerberos,dc=example,dc=com"
++  by dn.exact="cn=kdc,ou=kerberos,dc=example,dc=com" write
++  by dn.exact="cn=kadmin,ou=kerberos,dc=example,dc=com" write
++  by * none
++}}}##
++
++
++**Do not get the domain part above wrong. If you do, you may not be able to use ##kadmin## or ##kinit## and fixing the permissions without breaking something else is a nervous task. Trust me on this (as I screwed them up).**
++
++Apply it with
++
++(% style="color:#400" %)
++##{{{
++$ ldapmodify -H ldaps://nas.example.com -W -D cn=config -f step3.ldif
++Enter LDAP Password:
++
++modifying entry "olcDatabase={1}bdb,cn=config"
++
++$ }}}##
++
++
++=== Create krb5.conf ===
++
++Next we create (or modify)  ##/etc/krb5.conf## so that it will point to the right thing later. It should look something like this:
++
++(% style="color:#400" %)
++##{{{
++[libdefaults]
++    default_realm = EXAMPLE.COM
++    dns_lookup_realm = false
++    dns_lookup_kdc = false
++    ticket_lifetime = 24h
++    forwardable = true
++    proxiable = true
++    rdns = false
++
++[realms]
++    EXAMPLE.COM = {
++        kdc = debian.example.com
++        admin_server = debian.example.com
++        default_domain = example.com
++    }
++[domain_realm]
++    .example.com = EXAMPLE.COM
++    example.com = EXAMPLE.COM
++}}}##
++
++
++Make sure your designated debian server have ports **88**, **464** and **749** open, both for TCP and UDP, in its firewall. 88 is for the kdc, 464 and 749 is for kadmin.
++
++
++=== Create kdc.conf ===
++
++Now we do /etc/krb5kdc/kdc.conf. Something like this should work
++
++(% style="color:#400" %)
++##{{{
++[libdefaults]
++
++[realms]
++    EXAMPLE.COM = {
++        database_module = openldap_ldapconf
++        max_life = 7d
++        max_renewable_life = 6d
++    }
++
++[dbdefaults]
++    ldap_kerberos_container_dn = cn=krbContainer,ou=kerberos,dc=example,dc=com
++
++[dbmodules]
++    openldap_ldapconf = {
++        db_library = kldap
++        disable_last_success = false
++        disable_lockout = false
++        ldap_conns_per_server = 5
++        ldap_servers = ldaps:~/~/nas.example.com
++        ldap_kdc_dn = "cn=kdc,ou=kerberos,dc=example,dc=com"
++        ldap_kadmind_dn = "cn=kadmin,ou=kerberos,dc=example,dc=com"
++        ldap_service_password_file = /etc/krb5kdc/service.keyfile
++    }
++}}}##
++
++
++=== Create kadm5.acl ===
++
++Create ##/etc/krb5kdc/kadm5.acl with the following content so that kerberos administrator principals can run ##kadmin##
++
++(% style="color:#400" %)
++##{{{
++*/admin@EXAMPLE.COM *
++}}}##
++
++
++=== Create the kerberos domain ===
++
++Now we are ready to create the domain. And that we do with ##kdb5_ldap_util## as ##root##. Note that this commandline is deceptive and you need all of it.
++
++(% style="color:#400" %)
++##{{{
++# kdb5_ldap_util -D uid=root,cn=users,dc=example,dc=com -H ldaps://nas.example.com -r EXAMPLE.COM create -subtrees dc=example,dc=com -maxtktlife '7 Days' -maxrenewlife '6 Days' -s
++Password for "uid=root,cn=users,dc=trudheim,dc=com":
++Initializing database for realm 'EXAMPLE.COM'
++You will be prompted for the database Master Password.
++It is important that you NOT FORGET this password.
++Enter KDC database master key:
++Re-enter KDC database master key to verify:
++# }}}##
++
++
++=== Stash the passwords for ##kdc## and ##kadmin## ===
++
++Most likely, you will want your KDC and KAdmin server to start at boot, and for that, we can stash the passwords (into LDAP) for ##cn=kdc,ou=kerberos,dc=example,dc=com## and ##cn=kdc,ou=kerberos,dc=example,dc=com## using the same tool as in the previous step.
++
++(% style="color:#400" %)
++##{{{
++# kdb5_ldap_util -D uid=root,cn=users,dc=example,dc=com -H ldaps://nas.example.com stashsrvpw -f /etc/krb5kdc/service.keyfile cn=kdc,ou=kerberos,dc=example,dc=com
++Password for "uid=root,cn=users,dc=example,dc=com":
++Password for "cn=kdc,ou=kerberos,dc=example,dc=com":
++Re-enter password for "cn=kdc,ou=kerberos,dc=example,dc=com":
++# kdb5_ldap_util -D uid=root,cn=users,dc=example,dc=com -H ldaps://nas.example.com stashsrvpw -f /etc/krb5kdc/service.keyfile cn=kadmin,ou=kerberos,dc=example,dc=com
++Password for "uid=root,cn=users,dc=example,dc=com":
++Password for "cn=kadmin,ou=kerberos,dc=example,dc=com":
++Re-enter password for "cn=kadmin,ou=kerberos,dc=example,dc=com":
++# }}}##
++
++
++=== Start the services ===
++
++We are now ready to start the services. If this does not work, you need to backtrack and find out where you made a mistake, rectify it, and then walk forward again.
++
++(% style="color:#400" %)
++##{{{
++# systemctl enable --now krb5-kdc krb5-admin-server
++#
++}}}##
++
++
++Check that they are running and not giving off errors with ##systemctl status krb5-kdc## and ##systemctl status krb5-admin-server##.
++
++
++=== Create the first regular principals ===
++
++Providing you got to here without issues it is now time to generate your principals that you will use to authenticate into systems with. Run ##kadmin.local## as root to create first a regular user, and then an admin version of that user.
++
++(% style="color:#400" %)
++##{{{
++# kadmin.local
++
++Authenticating as principal root/admin@EXAMPLE.COM with password.
++kadmin.local:  addprinc user
++
++No policy specified for user@EXAMPLE.COM; defaulting to no policy
++Enter password for principal "user@EXAMPLE.COM":
++Re-enter password for principal "user@EXAMPLE.COM":
++Principal "user@EXAMPLE.COM" created.
++
++kadmin.local:  addprinc user/admin
++No policy specified for user/admin@EXAMPLE.COM; defaulting to no policy
++Enter password for principal "user/admin@EXAMPLE.COM":
++Re-enter password for principal "user/admin@EXAMPLE.COM":
++Principal "user/admin@EXAMPLE.COM" created.
++kadmin.local:  q
++
++# }}}##
++
++
++Worth to note here is that ##user@EXAMPLE.COM## and ##user/admin@EXAMPLE.COM## can have (and probably should have) different passwords. The admin variant is allowed to do things to the kerberos database and should therefore have greater security. This is why you want to have the registering of failures to login enabled. Should you have the system exposed to the internet, you can and should expect intrusion attempts. Having Kerberos deployed makes it harder for perpetrators to gain access, but not impossible.
++
++If you later kerberise your storage and leverage it for NFS4 mounts from your NAS, you can have NFS exposed to the internet as well. Unless someone has a valid kerberos ticket, even if they somehow could mount a share, they see nothing on it without the krbtgt.
++
++
++=== Test your new principal ===
++
++Acid test is, can you authenticate with kinit?
++
++(% style="color:#400" %)
++##{{{
++$ kinit user@EXAMPLE.COM
++
++Password for user@EXAMPLE.COM:
++
++$ klist
++Ticket cache: FILE:/tmp/krb5cc_1000
++Default principal: user@EXAMPLE.COM
++
++Valid starting     Expires            Service principal
++09/05/24 08:07:35  10/05/24 08:07:35  krbtgt/EXAMPLE.COM@EXAMPLE.COM
++
++$ }}}##
++
++
++Congratulations - you now have Kerberos working, and to boot, the database sits in LDAP. Which you can inspect with something like:
++
++(% style="color:#400" %)
++##{{{
++$ ldapsearch -H ldaps://nas.example.com -D uid=root,cn=users,dc=example,dc=com -W -b ou=kerberos,dc=example,dc=com
++}}}##
++
++
++=== Set up pam and sssd ===
++
++ To fully leverage your shiny new KDC, you will want to install the Kerberos authentication pieces for ##PAM## and also ##sssd## to facilitate caching of authentication, in case your KDC is offline for some reason when you try to authenticate into another system.
++
++(% style="color:#400" %)
++##{{{
++$ sudo apt install krb5-user libpam-krb5 sssd-krb5
++...
++$ sudo pam-auth-update
++}}}##
++
++
++With ##pam-auth-update## you want to enable Kerberos and SSS authentication (and flip on the auto-creation of home directories while you are there). If you now want to test login on another system with kerberos, you need ##/etc/krb5.conf## and the ##krb5-user##, ##libpam-krb5## and ##sssd-krb5## packages installed on this new system and you need to run ##pam-auth-update## to enable Kerberos and SSS. After that, the system does not need local ##user## (in /etc/passwd) - the kerberos ##user## will work instead.
++
++/S

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