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Wiki source code of KerberosAndLDAP

Version 29.1 by Sirius Rayner-Karlsson on 2024/05/07 13:43
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1 {{toc/}}
2
3 = Debian =
4
5 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.
6
7 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.
8
9 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.
10
11 **The guide is for illustration. Expectation is that you do not follow it verbatim but adapt it to your needs.**
12
13
14 ===== Install packages: =====
15
16 (% class="wikigeneratedid" %)
17 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.
18
19 (% style="color:#400" %)
20 ##{{{$ sudo apt install krb5-kdc-ldap krb5-admin-server schema2ldif}}}##
21
22
23 ===== Load ##kerberos LDAP## schema: =====
24
25 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
27 (% style="color:#400" %)
28 ##{{{$ zcat /usr/share/doc/krb5-kdc-ldap/kerberos.openldap.ldif.gz | ldapadd -H ldaps://nas.example.com/ -D cn=config -W}}}##
29 ##{{{Enter LDAP Password:}}}##
30 ##{{{adding new entry "cn=kerberos,cn=schema,cn=config"}}}##
31 ##{{{$}}}##
32
33
34 ===== Create Index on krbPrincipalName: =====
35
36 Having an index on the ##krbPrincipalName## improves performance and also suppresses some log messages if ##slapd## is configured to log more than default for the database(s) where you intend to store Kerberos data. As this is OpenLDAP on the Synology, it does not use ##mdb## format, it uses ##bdb##. If you install ##slapd## on Debian, it uses ##mdb## format. It is different database format, but the principle is the same. Again, as you are modifying config, the DN is ##cn=config##. Interestingly, it is still the main password you set for the Synology LDAP server.
37
38 (% style="color:#400" %)
39 ##{{{$ ldapmodify -H ldaps://nas.example.com/ -D cn=config -W <<EOF}}}##
40 ##{{{dn: olcDatabase={1}bdb,cn=config}}}##
41 ##{{{add: olcDbIndex}}}##
42 ##{{{olcDbIndex: krbPrincipalName eq,pres,sub}}}##
43 ##{{{EOF}}}##
44 ##{{{Enter LDAP Password:}}}##
45 ##{{{modifying entry "olcDatabase={1}bdb,cn=config"}}}##
46 ##{{{$}}}##
47
48
49 ===== Create principals kadmin and kdc: =====
50
51 Next, you create and configure two entries which will be used by the Kerberos servers to connect to OpenLDAP. As you will not run the Kerberos KDC and Admin Server on the same host as OpenLDAP, these steps are required. In order to keep things nicely separated, everything will be created under a separate ##organizationalUnit##. I diverge from the official Debian guide here as I do not agree with the DN they use. I also had to make changes to the DNs of ##kdc## and ##kadmin## due to ##pwdPolicy## applied by Synology to their LDAP server. The official guide will have you use placeholder passwords and that does not work with the Synology LDAP server. You need to generate them upfront with ##slappasswd -h {SSHA}##.
52
53 (% style="color:#400" %)
54 ##{{{$ ldapadd -H ldap://nas.example.com/ -D uid=root,cn=users,dc=example,dc=com -W <<EOF}}}##
55 ##{{{dn: ou=kerberos,dc=example,dc=com}}}##
56 ##{{{objectClass: organizationalUnit}}}##
57 ##{{{objectClass: top}}}##
58 ##{{{ou: kerberos}}}##
59
60 (% style="color:#400" %)
61 ##{{{dn: cn=kdc,ou=kerberos,dc=example,dc=com}}}##
62 ##{{{cn: kdc}}}##
63 ##{{{sn: kdc}}}##
64 ##{{{objectClass: person}}}##
65 ##{{{objectClass: pwdPolicy}}}##
66 ##{{{pwdAttribute: userPassword}}}##
67 ##{{{pwdMinLength: 8}}}##
68 ##{{{pwdCheckQuality: 2}}}##
69 ##{{{pwdPolicySubentry: cn=kdc,ou=kerberos,dc=example,dc=com}}}##
70 ##{{{userPassword: {SSHA}<password-hash>}}}##
71 ##{{{description: Kerberos KDC Account}}}##
72
73 (% style="color:#400" %)
74 ##{{{dn: cn=kadmin,ou=kerberos,dc=example,dc=com}}}##
75 ##{{{cn: kadmin}}}##
76 ##{{{sn: kadmin}}}##
77 ##{{{objectClass: person}}}##
78 ##{{{objectClass: pwdPolicy}}}##
79 ##{{{pwdAttribute: userPassword}}}##
80 ##{{{pwdMinLength: 8}}}##
81 ##{{{pwdCheckQuality: 2}}}##
82 ##{{{pwdPolicySubentry: cn=kadmin,ou=kerberos,dc=example,dc=com}}}##
83 ##{{{userPassword: {SSHA}<password-hash>}}}##
84 ##{{{description: Kerberos KDC Account}}}##
85 ##{{{EOF}}}##
86 ##{{{Enter LDAP Password:}}}##
87
88 (% style="color:#400" %)
89 ##{{{adding new entry "ou=kerberos,dc=example,dc=com"}}}##
90
91 (% style="color:#400" %)
92 ##{{{adding new entry "cn=kdc,ou=kerberos,dc=example,dc=com"}}}##
93
94 (% style="color:#400" %)
95 ##{{{adding new entry "cn=kadmin,ou=kerberos,dc=example,dc=com"}}}##
96
97
98 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.
99
100
101 ===== Grant kdc and kadmin permissions: =====
102
103 This switches back to the ##cn=config## DN as you are changing the permissions.
104
105 $ ldapmodify -H ldaps:~/~/ds723.trudheim.com -W -D cn=config <<EOF
106
107 dn: olcDatabase={1}bdb,cn=config
108 add: olcAccess
109 olcAccess: {0}to attrs=krbPrincipalKey
110 by anonymous auth
111 by dn.exact="cn=kdc,ou=kerberos,dc=trudheim,dc=com" write
112 by dn.exact="cn=kadmin,ou=kerberos,dc=trudheim,dc=com" write
113 by self write
114 by * none
115 -
116 add: olcAccess
117 olcAccess: {1}to dn.subtree="cn=krbContainer,ou=kerberos,dc=example,dc=com"
118 by dn.exact="cn=kdc,ou=kerberos,dc=trudheim,dc=com" write
119 by dn.exact="cn=kadmin,ou=kerberos,dc=trudheim,dc=com" write
120 by * none
121
122 EOF
123
124 Enter LDAP Password:
125 modifying entry "olcDatabase={1}bdb,cn=config"
126
127 $
128
129
130 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.
131
132
133 ===== Create your krb5.conf: =====
134
135 Over to adjusting /etc/krb5.conf so that it will point to the right thing later. It should look something like this:
136
137
138 {{{[libdefaults]
139 default_realm = EXAMPLE.COM
140 dns_lookup_realm = false
141 dns_lookup_kdc = false
142 ticket_lifetime = 24h
143 forwardable = true
144 proxiable = true
145 rdns = false
146
147 [realms]
148 EXAMPLE.COM = {
149 kdc = debian.example.com
150 admin_server = debian.example.com
151 default_domain = example.com
152 }
153 [domain_realm]
154 .example.com = EXAMPLE.COM
155 example.com = EXAMPLE.COM}}}
156
157 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.
158
159 Next, we need to write up /etc/krb5kdc/kdc.conf. Something like this should work
160
161
162 [libdefaults]
163
164 [realms]
165 TRUDHEIM.COM = {
166 database_module = openldap_ldapconf
167 max_life = 7d
168 max_renewable_life = 6d
169 }
170
171 [dbdefaults]
172 ldap_kerberos_container_dn = cn=krbContainer,ou=kerberos,dc=trudheim,dc=com
173
174 [dbmodules]
175 openldap_ldapconf = {
176 db_library = kldap
177 disable_last_success = false
178 disable_lockout = false
179 ldap_conns_per_server = 5
180 ldap_servers = ldaps:~/~/ds723.trudheim.com
181 ldap_kdc_dn = "cn=kdc,ou=kerberos,dc=trudheim,dc=com"
182 ldap_kadmind_dn = "cn=kadmin,ou=kerberos,dc=trudheim,dc=com"
183 ldap_service_password_file = /etc/krb5kdc/service.keyfile
184 }
185
186
187 Then you need to create ##/etc/krb5kdc/kadm5.acl and put in it##
188
189
190 ##*/admin@EXAMPLE.COM *##
191
192
193 so that administrator principals can run kadmin. Now we are ready to create the domain. And that we do with
194
195
196 #
197
198 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
199 Password for "uid=root,cn=users,dc=trudheim,dc=com":
200 Initializing database for realm 'TRUDHEIM.COM'
201 You will be prompted for the database Master Password.
202 It is important that you NOT FORGET this password.
203 Enter KDC database master key:
204 Re-enter KDC database master key to verify:
205
206 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
207 Password for "uid=root,cn=users,dc=trudheim,dc=com":
208 Password for "cn=kdc,ou=kerberos,dc=trudheim,dc=com":
209 Re-enter password for "cn=kdc,ou=kerberos,dc=trudheim,dc=com":
210
211 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
212 Password for "uid=root,cn=users,dc=trudheim,dc=com":
213 Password for "cn=kadmin,ou=kerberos,dc=trudheim,dc=com":
214 Re-enter password for "cn=kadmin,ou=kerberos,dc=trudheim,dc=com":
215
216