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Wiki source code of KerberosAndLDAP

Version 36.1 by Sirius Rayner-Karlsson on 2024/05/09 10:00

version	line-number	content
30.1	1	{{box cssClass="floatinginfobox" title="Contents"}}
22.1	2	{{toc/}}
30.1	3	{{/box}}
22.1	4
1.1	5	= Debian =
	6
26.1	7	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.
23.1	8
26.1	9	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.
14.1	10
26.1	11	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.
2.1	12
26.1	13	The guide is for illustration. Expectation is that you do not follow it verbatim but adapt it to your needs.
20.1	14
23.1	15
34.1	16	=== Install packages ===
26.1	17
24.1	18	(% class="wikigeneratedid" %)
26.1	19	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.
24.1	20
21.1	21	(% style="color:#400" %)
13.1	22	##{{{$ sudo apt install krb5-kdc-ldap krb5-admin-server schema2ldif}}}##
3.1	23
13.1	24
35.1	25	=== Load kerberos LDAP schema ===
3.1	26
35.1	27	Now you need to load the kerberos schema into the LDAP server on the Synology. Use the ##cn=config## DN.
26.1	28
21.1	29	(% style="color:#400" %)
36.1	30	##{{{$ 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" $}}}##
3.1	31
	32
34.1	33	=== Create Index on krbPrincipalName ===
14.1	34
35.1	35	Having an index on the ##krbPrincipalName## improves performance. Synology OpenLDAP does not use ##mdb## format, it uses ##bdb##. Debian ##slapd## uses ##mdb## format. It is different database format, but the principle is the same. Again, as you are modifying config, the DN is ##cn=config##. Use the main password you set for the Synology LDAP server. Create a file ##step1.ldif## with the following content:
23.1	36
21.1	37	(% style="color:#400" %)
36.1	38	##{{{dn: olcDatabase={1}bdb,cn=config add: olcDbIndex olcDbIndex: krbPrincipalName eq,pres,sub}}}##
3.1	39
36.1	40
35.1	41	and apply it with
3.1	42
35.1	43	(% style="color:#400" %)
36.1	44	##{{{$ ldapmodify -H ldaps://nas.example.com/ -D cn=config -W -f step1.ldif Enter LDAP Password: modifying entry "olcDatabase={1}bdb,cn=config" $}}}##
35.1	45
	46
34.1	47	=== Create principals kadmin and kdc ===
23.1	48
35.1	49	Next, you create and configure two entries which will be used by the Kerberos servers to connect to OpenLDAP. Not running the Kerberos KDC and Admin Server on the same host as OpenLDAP, these steps are required. Keeping things confined, everything will be created under a separate ##organizationalUnit##. My guide differs from the official Debian guide here. Due to Synology OpenLDAP having a strict password policy, it was necessary to adjust the DNs of ##kdc## and ##kadmin##. The official guide use placeholder passwords which does not work with the Synology LDAP server.
	50	Generate the passwords upfront with ##slappasswd -h {SSHA}##. Then create a file ##step2.ldif## with the following content:
4.1	51
21.1	52	(% style="color:#400" %)
36.1	53	##{{{dn: ou=kerberos,dc=example,dc=com objectClass: organizationalUnit objectClass: top ou: kerberos dn: cn=kdc,ou=kerberos,dc=example,dc=com cn: kdc sn: kdc objectClass: person objectClass: pwdPolicy pwdAttribute: userPassword pwdMinLength: 8 pwdCheckQuality: 2 pwdPolicySubentry: cn=kdc,ou=kerberos,dc=example,dc=com userPassword: {SSHA}<password-hash> description: Kerberos KDC Account dn: cn=kadmin,ou=kerberos,dc=example,dc=com cn: kadmin sn: kadmin objectClass: person objectClass: pwdPolicy pwdAttribute: userPassword pwdMinLength: 8 pwdCheckQuality: 2 pwdPolicySubentry: cn=kadmin,ou=kerberos,dc=example,dc=com userPassword: {SSHA}<password-hash> description: Kerberos KDC Account}}}##
27.1	54
35.1	55	Apply it with
17.1	56
27.1	57	(% style="color:#400" %)
36.1	58	##{{{$ 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 "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"}}}##
19.1	59
27.1	60
27.2	61
34.1	62	=== Grant kdc and kadmin permissions ===
27.2	63
	64	This switches back to the ##cn=config## DN as you are changing the permissions.
	65
	66	$ ldapmodify -H ldaps:~/~/ds723.trudheim.com -W -D cn=config <<EOF
	67
	68	dn: olcDatabase={1}bdb,cn=config
	69	add: olcAccess
	70	olcAccess: {0}to attrs=krbPrincipalKey
	71	by anonymous auth
	72	by dn.exact="cn=kdc,ou=kerberos,dc=trudheim,dc=com" write
	73	by dn.exact="cn=kadmin,ou=kerberos,dc=trudheim,dc=com" write
	74	by self write
	75	by * none
	76	-
	77	add: olcAccess
	78	olcAccess: {1}to dn.subtree="cn=krbContainer,ou=kerberos,dc=example,dc=com"
	79	by dn.exact="cn=kdc,ou=kerberos,dc=trudheim,dc=com" write
	80	by dn.exact="cn=kadmin,ou=kerberos,dc=trudheim,dc=com" write
	81	by * none
	82
	83	EOF
	84
	85	Enter LDAP Password:
	86	modifying entry "olcDatabase={1}bdb,cn=config"
	87
	88	$
	89
	90
	91	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 login failures. We like security.
	92
29.1	93
34.1	94	=== Create krb5.conf ===
29.1	95
	96	Over to adjusting /etc/krb5.conf so that it will point to the right thing later. It should look something like this:
	97
	98
	99	{{{[libdefaults]
	100	default_realm = EXAMPLE.COM
	101	dns_lookup_realm = false
	102	dns_lookup_kdc = false
	103	ticket_lifetime = 24h
	104	forwardable = true
	105	proxiable = true
	106	rdns = false
	107
	108	[realms]
	109	EXAMPLE.COM = {
	110	kdc = debian.example.com
	111	admin_server = debian.example.com
	112	default_domain = example.com
	113	}
	114	[domain_realm]
	115	.example.com = EXAMPLE.COM
	116	example.com = EXAMPLE.COM}}}
	117
	118	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.
	119
33.1	120
34.1	121	=== Create kdc.conf ===
33.1	122
29.1	123	Next, we need to write up /etc/krb5kdc/kdc.conf. Something like this should work
	124
	125
	126	[libdefaults]
	127
	128	[realms]
	129	TRUDHEIM.COM = {
	130	database_module = openldap_ldapconf
	131	max_life = 7d
	132	max_renewable_life = 6d
	133	}
	134
	135	[dbdefaults]
	136	ldap_kerberos_container_dn = cn=krbContainer,ou=kerberos,dc=trudheim,dc=com
	137
	138	[dbmodules]
	139	openldap_ldapconf = {
	140	db_library = kldap
	141	disable_last_success = false
	142	disable_lockout = false
	143	ldap_conns_per_server = 5
	144	ldap_servers = ldaps:~/~/ds723.trudheim.com
	145	ldap_kdc_dn = "cn=kdc,ou=kerberos,dc=trudheim,dc=com"
	146	ldap_kadmind_dn = "cn=kadmin,ou=kerberos,dc=trudheim,dc=com"
	147	ldap_service_password_file = /etc/krb5kdc/service.keyfile
	148	}
	149
	150
34.1	151	=== Create kadm5.acl ===
33.1	152
29.1	153	Then you need to create ##/etc/krb5kdc/kadm5.acl and put in it##
	154
	155	##/admin@EXAMPLE.COM ##
	156
	157
	158	so that administrator principals can run kadmin. Now we are ready to create the domain. And that we do with
	159
	160
34.1	161	=== Create the kerberos domain ===
33.1	162
29.1	163	#
	164
	165	kdb5_ldap_util -D uid=root,cn=users,dc=trudheim,dc=com -H ldaps:~/~/ds723.trudheim.com -r TRUDHEIM.COM create -subtrees dc=trudheim,dc=com -maxtktlife '7 Days' -maxrenewlife '6 Days' -s
	166	Password for "uid=root,cn=users,dc=trudheim,dc=com":
	167	Initializing database for realm 'TRUDHEIM.COM'
	168	You will be prompted for the database Master Password.
	169	It is important that you NOT FORGET this password.
	170	Enter KDC database master key:
	171	Re-enter KDC database master key to verify:
	172
	173	kdb5_ldap_util -D uid=root,cn=users,dc=trudheim,dc=com -H ldaps:~/~/ds723.trudheim.com stashsrvpw -f /etc/krb5kdc/service.keyfile cn=kdc,ou=kerberos,dc=trudheim,dc=com
	174	Password for "uid=root,cn=users,dc=trudheim,dc=com":
	175	Password for "cn=kdc,ou=kerberos,dc=trudheim,dc=com":
	176	Re-enter password for "cn=kdc,ou=kerberos,dc=trudheim,dc=com":
	177
	178	kdb5_ldap_util -D uid=root,cn=users,dc=trudheim,dc=com -H ldaps:~/~/ds723.trudheim.com stashsrvpw -f /etc/krb5kdc/service.keyfile cn=kadmin,ou=kerberos,dc=trudheim,dc=com
	179	Password for "uid=root,cn=users,dc=trudheim,dc=com":
	180	Password for "cn=kadmin,ou=kerberos,dc=trudheim,dc=com":
	181	Re-enter password for "cn=kadmin,ou=kerberos,dc=trudheim,dc=com":
	182
33.1	183
34.1	184	=== Create the first regular principals ===
33.1	185
34.1	186	Here, you will run kadmin.local to create first a regular user, and then an admin version of that user.
	187
	188	# kadmin.local
	189
	190	Authenticating as principal root/admin@TRUDHEIM.COM with password.
	191	kadmin.local: addprinc user
	192
	193	No policy specified for user@TRUDHEIM.COM; defaulting to no policy
	194	Enter password for principal "user@TRUDHEIM.COM":
	195	Re-enter password for principal "user@TRUDHEIM.COM":
	196	Principal "user@TRUDHEIM.COM" created.
	197
	198	kadmin.local: addprinc user/admin
	199	No policy specified for user/admin@TRUDHEIM.COM; defaulting to no policy
	200	Enter password for principal "user/admin@TRUDHEIM.COM":
	201	Re-enter password for principal "user/admin@TRUDHEIM.COM":
	202	Principal "user/admin@TRUDHEIM.COM" created.
	203	kadmin.local: q
	204
	205	#
	206
	207	Worth to note here is that [[user@EXAMPLE.COM>>mailto:user@EXAMPLE.COM]] and [[user/admin@EXAMPLE.COM>>mailto:user/admin@EXAMPLE.COM]] can have (and should have) different passwords as the admin variant is allowed to do things to the kerberos database. And 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.
	208
	209	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 the share, they see nothing on it without the krbtgt.
	210
	211
	212	=== Test your new principal ===
	213
	214	$ kinit [[user@EXAMPLE.COM>>mailto:user@EXAMPLE.COM]]
	215
	216	Password for user@EXAMPLE.COM:
	217
	218	$ klist
	219	Ticket cache: FILE:/tmp/krb5cc_1000
	220	Default principal: user@EXAMPLE.COM
	221
	222	Valid starting Expires Service principal
	223	09/05/24 08:07:35 10/05/24 08:07:35 krbtgt/EXAMPLE.COM@EXAMPLE.COM
	224
	225	$
	226
	227
	228	=== Set up pam and sssd ===
	229
33.1	230

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