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Wiki source code of KerberosAndLDAP

Version 30.1 by Sirius Rayner-Karlsson on 2024/05/09 05:50
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1 {{box cssClass="floatinginfobox" title="**Contents**"}}
2 {{toc/}}
3 {{/box}}
4
5 = Debian =
6
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.
8
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.
10
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.
12
13 **The guide is for illustration. Expectation is that you do not follow it verbatim but adapt it to your needs.**
14
15
16 ===== Install packages: =====
17
18 (% class="wikigeneratedid" %)
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.
20
21 (% style="color:#400" %)
22 ##{{{$ sudo apt install krb5-kdc-ldap krb5-admin-server schema2ldif}}}##
23
24
25 ===== Load ##kerberos LDAP## schema: =====
26
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.
28
29 (% style="color:#400" %)
30 ##{{{$ zcat /usr/share/doc/krb5-kdc-ldap/kerberos.openldap.ldif.gz | ldapadd -H ldaps://nas.example.com/ -D cn=config -W}}}##
31 ##{{{Enter LDAP Password:}}}##
32 ##{{{adding new entry "cn=kerberos,cn=schema,cn=config"}}}##
33 ##{{{$}}}##
34
35
36 ===== Create Index on krbPrincipalName: =====
37
38 Having an index on the ##krbPrincipalName## improves performance and also suppresses some log messages if ##slapd## is configured to log more than default for the database(s) where you intend to store Kerberos data. As this is OpenLDAP on the Synology, it does not use ##mdb## format, it uses ##bdb##. If you install ##slapd## on Debian, it uses ##mdb## format. It is different database format, but the principle is the same. Again, as you are modifying config, the DN is ##cn=config##. Interestingly, it is still the main password you set for the Synology LDAP server.
39
40 (% style="color:#400" %)
41 ##{{{$ ldapmodify -H ldaps://nas.example.com/ -D cn=config -W <<EOF}}}##
42 ##{{{dn: olcDatabase={1}bdb,cn=config}}}##
43 ##{{{add: olcDbIndex}}}##
44 ##{{{olcDbIndex: krbPrincipalName eq,pres,sub}}}##
45 ##{{{EOF}}}##
46 ##{{{Enter LDAP Password:}}}##
47 ##{{{modifying entry "olcDatabase={1}bdb,cn=config"}}}##
48 ##{{{$}}}##
49
50
51 ===== Create principals kadmin and kdc: =====
52
53 Next, you create and configure two entries which will be used by the Kerberos servers to connect to OpenLDAP. As you will not run the Kerberos KDC and Admin Server on the same host as OpenLDAP, these steps are required. In order to keep things nicely separated, everything will be created under a separate ##organizationalUnit##. I diverge from the official Debian guide here as I do not agree with the DN they use. I also had to make changes to the DNs of ##kdc## and ##kadmin## due to ##pwdPolicy## applied by Synology to their LDAP server. The official guide will have you use placeholder passwords and that does not work with the Synology LDAP server. You need to generate them upfront with ##slappasswd -h {SSHA}##.
54
55 (% style="color:#400" %)
56 ##{{{$ 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}}}##
58 ##{{{objectClass: organizationalUnit}}}##
59 ##{{{objectClass: top}}}##
60 ##{{{ou: kerberos}}}##
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>}}}##
73 ##{{{description: Kerberos KDC Account}}}##
74
75 (% style="color:#400" %)
76 ##{{{dn: cn=kadmin,ou=kerberos,dc=example,dc=com}}}##
77 ##{{{cn: kadmin}}}##
78 ##{{{sn: kadmin}}}##
79 ##{{{objectClass: person}}}##
80 ##{{{objectClass: pwdPolicy}}}##
81 ##{{{pwdAttribute: userPassword}}}##
82 ##{{{pwdMinLength: 8}}}##
83 ##{{{pwdCheckQuality: 2}}}##
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:}}}##
89
90 (% style="color:#400" %)
91 ##{{{adding new entry "ou=kerberos,dc=example,dc=com"}}}##
92
93 (% style="color:#400" %)
94 ##{{{adding new entry "cn=kdc,ou=kerberos,dc=example,dc=com"}}}##
95
96 (% style="color:#400" %)
97 ##{{{adding new entry "cn=kadmin,ou=kerberos,dc=example,dc=com"}}}##
98
99
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
102
103 ===== Grant kdc and kadmin permissions: =====
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
134
135 ===== Create your krb5.conf: =====
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
161 Next, we need to write up /etc/krb5kdc/kdc.conf. Something like this should work
162
163
164 [libdefaults]
165
166 [realms]
167 TRUDHEIM.COM = {
168 database_module = openldap_ldapconf
169 max_life = 7d
170 max_renewable_life = 6d
171 }
172
173 [dbdefaults]
174 ldap_kerberos_container_dn = cn=krbContainer,ou=kerberos,dc=trudheim,dc=com
175
176 [dbmodules]
177 openldap_ldapconf = {
178 db_library = kldap
179 disable_last_success = false
180 disable_lockout = false
181 ldap_conns_per_server = 5
182 ldap_servers = ldaps:~/~/ds723.trudheim.com
183 ldap_kdc_dn = "cn=kdc,ou=kerberos,dc=trudheim,dc=com"
184 ldap_kadmind_dn = "cn=kadmin,ou=kerberos,dc=trudheim,dc=com"
185 ldap_service_password_file = /etc/krb5kdc/service.keyfile
186 }
187
188
189 Then you need to create ##/etc/krb5kdc/kadm5.acl and put in it##
190
191
192 ##*/admin@EXAMPLE.COM *##
193
194
195 so that administrator principals can run kadmin. Now we are ready to create the domain. And that we do with
196
197
198 #
199
200 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
201 Password for "uid=root,cn=users,dc=trudheim,dc=com":
202 Initializing database for realm 'TRUDHEIM.COM'
203 You will be prompted for the database Master Password.
204 It is important that you NOT FORGET this password.
205 Enter KDC database master key:
206 Re-enter KDC database master key to verify:
207
208 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
209 Password for "uid=root,cn=users,dc=trudheim,dc=com":
210 Password for "cn=kdc,ou=kerberos,dc=trudheim,dc=com":
211 Re-enter password for "cn=kdc,ou=kerberos,dc=trudheim,dc=com":
212
213 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
214 Password for "uid=root,cn=users,dc=trudheim,dc=com":
215 Password for "cn=kadmin,ou=kerberos,dc=trudheim,dc=com":
216 Re-enter password for "cn=kadmin,ou=kerberos,dc=trudheim,dc=com":
217
218