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Wiki source code of KerberosAndLDAP

Version 34.1 by Sirius Rayner-Karlsson on 2024/05/09 06:09

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
34.1	25	=== Load ##kerberos LDAP## schema ===
3.1	26
27.1	27	Now you need to load the kerberos schema into the LDAP server on the Synology. And here you need to use the ##cn=config## DN.
26.1	28
21.1	29	(% style="color:#400" %)
27.1	30	##{{{$ zcat /usr/share/doc/krb5-kdc-ldap/kerberos.openldap.ldif.gz \| ldapadd -H ldaps://nas.example.com/ -D cn=config -W}}}##
16.1	31	##{{{Enter LDAP Password:}}}##
14.1	32	##{{{adding new entry "cn=kerberos,cn=schema,cn=config"}}}##
	33	##{{{$}}}##
3.1	34
	35
34.1	36	=== Create Index on krbPrincipalName ===
14.1	37
27.1	38	Having an index on the ##krbPrincipalName## improves performance and also suppresses some log messages if ##slapd## is configured to log more than default for the database(s) where you intend to store Kerberos data. As this is OpenLDAP on the Synology, it does not use ##mdb## format, it uses ##bdb##. If you install ##slapd## on Debian, it uses ##mdb## format. It is different database format, but the principle is the same. Again, as you are modifying config, the DN is ##cn=config##. Interestingly, it is still the main password you set for the Synology LDAP server.
23.1	39
21.1	40	(% style="color:#400" %)
27.1	41	##{{{$ ldapmodify -H ldaps://nas.example.com/ -D cn=config -W <<EOF}}}##
15.1	42	##{{{dn: olcDatabase={1}bdb,cn=config}}}##
	43	##{{{add: olcDbIndex}}}##
	44	##{{{olcDbIndex: krbPrincipalName eq,pres,sub}}}##
	45	##{{{EOF}}}##
16.1	46	##{{{Enter LDAP Password:}}}##
15.1	47	##{{{modifying entry "olcDatabase={1}bdb,cn=config"}}}##
	48	##{{{$}}}##
3.1	49
	50
34.1	51	=== Create principals kadmin and kdc ===
23.1	52
27.1	53	Next, you create and configure two entries which will be used by the Kerberos servers to connect to OpenLDAP. As you will not run the Kerberos KDC and Admin Server on the same host as OpenLDAP, these steps are required. In order to keep things nicely separated, everything will be created under a separate ##organizationalUnit##. I diverge from the official Debian guide here as I do not agree with the DN they use. I also had to make changes to the DNs of ##kdc## and ##kadmin## due to ##pwdPolicy## applied by Synology to their LDAP server. The official guide will have you use placeholder passwords and that does not work with the Synology LDAP server. You need to generate them upfront with ##slappasswd -h {SSHA}##.
4.1	54
21.1	55	(% style="color:#400" %)
25.1	56	##{{{$ ldapadd -H ldap://nas.example.com/ -D uid=root,cn=users,dc=example,dc=com -W <<EOF}}}##
	57	##{{{dn: ou=kerberos,dc=example,dc=com}}}##
15.1	58	##{{{objectClass: organizationalUnit}}}##
	59	##{{{objectClass: top}}}##
	60	##{{{ou: kerberos}}}##
27.1	61
	62	(% style="color:#400" %)
	63	##{{{dn: cn=kdc,ou=kerberos,dc=example,dc=com}}}##
	64	##{{{cn: kdc}}}##
	65	##{{{sn: kdc}}}##
	66	##{{{objectClass: person}}}##
	67	##{{{objectClass: pwdPolicy}}}##
	68	##{{{pwdAttribute: userPassword}}}##
	69	##{{{pwdMinLength: 8}}}##
	70	##{{{pwdCheckQuality: 2}}}##
	71	##{{{pwdPolicySubentry: cn=kdc,ou=kerberos,dc=example,dc=com}}}##
	72	##{{{userPassword: {SSHA}<password-hash>}}}##
15.1	73	##{{{description: Kerberos KDC Account}}}##
4.1	74
21.1	75	(% style="color:#400" %)
27.1	76	##{{{dn: cn=kadmin,ou=kerberos,dc=example,dc=com}}}##
	77	##{{{cn: kadmin}}}##
16.1	78	##{{{sn: kadmin}}}##
	79	##{{{objectClass: person}}}##
	80	##{{{objectClass: pwdPolicy}}}##
	81	##{{{pwdAttribute: userPassword}}}##
	82	##{{{pwdMinLength: 8}}}##
	83	##{{{pwdCheckQuality: 2}}}##
27.1	84	##{{{pwdPolicySubentry: cn=kadmin,ou=kerberos,dc=example,dc=com}}}##
	85	##{{{userPassword: {SSHA}<password-hash>}}}##
	86	##{{{description: Kerberos KDC Account}}}##
	87	##{{{EOF}}}##
	88	##{{{Enter LDAP Password:}}}##
16.1	89
27.1	90	(% style="color:#400" %)
	91	##{{{adding new entry "ou=kerberos,dc=example,dc=com"}}}##
17.1	92
27.1	93	(% style="color:#400" %)
	94	##{{{adding new entry "cn=kdc,ou=kerberos,dc=example,dc=com"}}}##
19.1	95
27.1	96	(% style="color:#400" %)
	97	##{{{adding new entry "cn=kadmin,ou=kerberos,dc=example,dc=com"}}}##
	98
27.2	99
27.1	100	Synology LDAP server did not like adding users with placeholder passwords, because Synology puts in place password policies. Hence changing this to a ##cn## instead of a ##uid##. It seems to have worked out fine as my KDC is fully functioning.
	101
27.2	102
34.1	103	=== Grant kdc and kadmin permissions ===
27.2	104
	105	This switches back to the ##cn=config## DN as you are changing the permissions.
	106
	107	$ ldapmodify -H ldaps:~/~/ds723.trudheim.com -W -D cn=config <<EOF
	108
	109	dn: olcDatabase={1}bdb,cn=config
	110	add: olcAccess
	111	olcAccess: {0}to attrs=krbPrincipalKey
	112	by anonymous auth
	113	by dn.exact="cn=kdc,ou=kerberos,dc=trudheim,dc=com" write
	114	by dn.exact="cn=kadmin,ou=kerberos,dc=trudheim,dc=com" write
	115	by self write
	116	by * none
	117	-
	118	add: olcAccess
	119	olcAccess: {1}to dn.subtree="cn=krbContainer,ou=kerberos,dc=example,dc=com"
	120	by dn.exact="cn=kdc,ou=kerberos,dc=trudheim,dc=com" write
	121	by dn.exact="cn=kadmin,ou=kerberos,dc=trudheim,dc=com" write
	122	by * none
	123
	124	EOF
	125
	126	Enter LDAP Password:
	127	modifying entry "olcDatabase={1}bdb,cn=config"
	128
	129	$
	130
	131
	132	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.
	133
29.1	134
34.1	135	=== Create krb5.conf ===
29.1	136
	137	Over to adjusting /etc/krb5.conf so that it will point to the right thing later. It should look something like this:
	138
	139
	140	{{{[libdefaults]
	141	default_realm = EXAMPLE.COM
	142	dns_lookup_realm = false
	143	dns_lookup_kdc = false
	144	ticket_lifetime = 24h
	145	forwardable = true
	146	proxiable = true
	147	rdns = false
	148
	149	[realms]
	150	EXAMPLE.COM = {
	151	kdc = debian.example.com
	152	admin_server = debian.example.com
	153	default_domain = example.com
	154	}
	155	[domain_realm]
	156	.example.com = EXAMPLE.COM
	157	example.com = EXAMPLE.COM}}}
	158
	159	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.
	160
33.1	161
34.1	162	=== Create kdc.conf ===
33.1	163
29.1	164	Next, we need to write up /etc/krb5kdc/kdc.conf. Something like this should work
	165
	166
	167	[libdefaults]
	168
	169	[realms]
	170	TRUDHEIM.COM = {
	171	database_module = openldap_ldapconf
	172	max_life = 7d
	173	max_renewable_life = 6d
	174	}
	175
	176	[dbdefaults]
	177	ldap_kerberos_container_dn = cn=krbContainer,ou=kerberos,dc=trudheim,dc=com
	178
	179	[dbmodules]
	180	openldap_ldapconf = {
	181	db_library = kldap
	182	disable_last_success = false
	183	disable_lockout = false
	184	ldap_conns_per_server = 5
	185	ldap_servers = ldaps:~/~/ds723.trudheim.com
	186	ldap_kdc_dn = "cn=kdc,ou=kerberos,dc=trudheim,dc=com"
	187	ldap_kadmind_dn = "cn=kadmin,ou=kerberos,dc=trudheim,dc=com"
	188	ldap_service_password_file = /etc/krb5kdc/service.keyfile
	189	}
	190
	191
34.1	192	=== Create kadm5.acl ===
33.1	193
29.1	194	Then you need to create ##/etc/krb5kdc/kadm5.acl and put in it##
	195
	196	##/admin@EXAMPLE.COM ##
	197
	198
	199	so that administrator principals can run kadmin. Now we are ready to create the domain. And that we do with
	200
	201
34.1	202	=== Create the kerberos domain ===
33.1	203
29.1	204	#
	205
	206	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
	207	Password for "uid=root,cn=users,dc=trudheim,dc=com":
	208	Initializing database for realm 'TRUDHEIM.COM'
	209	You will be prompted for the database Master Password.
	210	It is important that you NOT FORGET this password.
	211	Enter KDC database master key:
	212	Re-enter KDC database master key to verify:
	213
	214	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
	215	Password for "uid=root,cn=users,dc=trudheim,dc=com":
	216	Password for "cn=kdc,ou=kerberos,dc=trudheim,dc=com":
	217	Re-enter password for "cn=kdc,ou=kerberos,dc=trudheim,dc=com":
	218
	219	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
	220	Password for "uid=root,cn=users,dc=trudheim,dc=com":
	221	Password for "cn=kadmin,ou=kerberos,dc=trudheim,dc=com":
	222	Re-enter password for "cn=kadmin,ou=kerberos,dc=trudheim,dc=com":
	223
33.1	224
34.1	225	=== Create the first regular principals ===
33.1	226
34.1	227	Here, you will run kadmin.local to create first a regular user, and then an admin version of that user.
	228
	229	# kadmin.local
	230
	231	Authenticating as principal root/admin@TRUDHEIM.COM with password.
	232	kadmin.local: addprinc user
	233
	234	No policy specified for user@TRUDHEIM.COM; defaulting to no policy
	235	Enter password for principal "user@TRUDHEIM.COM":
	236	Re-enter password for principal "user@TRUDHEIM.COM":
	237	Principal "user@TRUDHEIM.COM" created.
	238
	239	kadmin.local: addprinc user/admin
	240	No policy specified for user/admin@TRUDHEIM.COM; defaulting to no policy
	241	Enter password for principal "user/admin@TRUDHEIM.COM":
	242	Re-enter password for principal "user/admin@TRUDHEIM.COM":
	243	Principal "user/admin@TRUDHEIM.COM" created.
	244	kadmin.local: q
	245
	246	#
	247
	248	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.
	249
	250	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.
	251
	252
	253	=== Test your new principal ===
	254
	255	$ kinit [[user@EXAMPLE.COM>>mailto:user@EXAMPLE.COM]]
	256
	257	Password for user@EXAMPLE.COM:
	258
	259	$ klist
	260	Ticket cache: FILE:/tmp/krb5cc_1000
	261	Default principal: user@EXAMPLE.COM
	262
	263	Valid starting Expires Service principal
	264	09/05/24 08:07:35 10/05/24 08:07:35 krbtgt/EXAMPLE.COM@EXAMPLE.COM
	265
	266	$
	267
	268
	269	=== Set up pam and sssd ===
	270
33.1	271

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