0 Votes

Wiki source code of KerberosAndLDAP

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

Hide last authors
Sirius Rayner-Karlsson 30.1 1 {{box cssClass="floatinginfobox" title="**Contents**"}}
Sirius Rayner-Karlsson 22.1 2 {{toc/}}
Sirius Rayner-Karlsson 30.1 3 {{/box}}
Sirius Rayner-Karlsson 22.1 4
Sirius Rayner-Karlsson 1.1 5 = Debian =
6
Sirius Rayner-Karlsson 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.
Sirius Rayner-Karlsson 23.1 8
Sirius Rayner-Karlsson 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.
Sirius Rayner-Karlsson 14.1 10
Sirius Rayner-Karlsson 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.
Sirius Rayner-Karlsson 2.1 12
Sirius Rayner-Karlsson 26.1 13 **The guide is for illustration. Expectation is that you do not follow it verbatim but adapt it to your needs.**
Sirius Rayner-Karlsson 20.1 14
Sirius Rayner-Karlsson 23.1 15
Sirius Rayner-Karlsson 34.1 16 === Install packages ===
Sirius Rayner-Karlsson 26.1 17
Sirius Rayner-Karlsson 24.1 18 (% class="wikigeneratedid" %)
Sirius Rayner-Karlsson 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.
Sirius Rayner-Karlsson 24.1 20
Sirius Rayner-Karlsson 21.1 21 (% style="color:#400" %)
Sirius Rayner-Karlsson 13.1 22 ##{{{$ sudo apt install krb5-kdc-ldap krb5-admin-server schema2ldif}}}##
Sirius Rayner-Karlsson 3.1 23
Sirius Rayner-Karlsson 13.1 24
Sirius Rayner-Karlsson 34.1 25 === Load ##kerberos LDAP## schema ===
Sirius Rayner-Karlsson 3.1 26
Sirius Rayner-Karlsson 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.
Sirius Rayner-Karlsson 26.1 28
Sirius Rayner-Karlsson 21.1 29 (% style="color:#400" %)
Sirius Rayner-Karlsson 27.1 30 ##{{{$ zcat /usr/share/doc/krb5-kdc-ldap/kerberos.openldap.ldif.gz | ldapadd -H ldaps://nas.example.com/ -D cn=config -W}}}##
Sirius Rayner-Karlsson 16.1 31 ##{{{Enter LDAP Password:}}}##
Sirius Rayner-Karlsson 14.1 32 ##{{{adding new entry "cn=kerberos,cn=schema,cn=config"}}}##
33 ##{{{$}}}##
Sirius Rayner-Karlsson 3.1 34
35
Sirius Rayner-Karlsson 34.1 36 === Create Index on krbPrincipalName ===
Sirius Rayner-Karlsson 14.1 37
Sirius Rayner-Karlsson 27.1 38 Having an index on the ##krbPrincipalName## improves performance and also suppresses some log messages if ##slapd## is configured to log more than default for the database(s) where you intend to store Kerberos data. As this is OpenLDAP on the Synology, it does not use ##mdb## format, it uses ##bdb##. If you install ##slapd## on Debian, it uses ##mdb## format. It is different database format, but the principle is the same. Again, as you are modifying config, the DN is ##cn=config##. Interestingly, it is still the main password you set for the Synology LDAP server.
Sirius Rayner-Karlsson 23.1 39
Sirius Rayner-Karlsson 21.1 40 (% style="color:#400" %)
Sirius Rayner-Karlsson 27.1 41 ##{{{$ ldapmodify -H ldaps://nas.example.com/ -D cn=config -W <<EOF}}}##
Sirius Rayner-Karlsson 15.1 42 ##{{{dn: olcDatabase={1}bdb,cn=config}}}##
43 ##{{{add: olcDbIndex}}}##
44 ##{{{olcDbIndex: krbPrincipalName eq,pres,sub}}}##
45 ##{{{EOF}}}##
Sirius Rayner-Karlsson 16.1 46 ##{{{Enter LDAP Password:}}}##
Sirius Rayner-Karlsson 15.1 47 ##{{{modifying entry "olcDatabase={1}bdb,cn=config"}}}##
48 ##{{{$}}}##
Sirius Rayner-Karlsson 3.1 49
50
Sirius Rayner-Karlsson 34.1 51 === Create principals kadmin and kdc ===
Sirius Rayner-Karlsson 23.1 52
Sirius Rayner-Karlsson 27.1 53 Next, you create and configure two entries which will be used by the Kerberos servers to connect to OpenLDAP. As you will not run the Kerberos KDC and Admin Server on the same host as OpenLDAP, these steps are required. In order to keep things nicely separated, everything will be created under a separate ##organizationalUnit##. I diverge from the official Debian guide here as I do not agree with the DN they use. I also had to make changes to the DNs of ##kdc## and ##kadmin## due to ##pwdPolicy## applied by Synology to their LDAP server. The official guide will have you use placeholder passwords and that does not work with the Synology LDAP server. You need to generate them upfront with ##slappasswd -h {SSHA}##.
Sirius Rayner-Karlsson 4.1 54
Sirius Rayner-Karlsson 21.1 55 (% style="color:#400" %)
Sirius Rayner-Karlsson 25.1 56 ##{{{$ 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}}}##
Sirius Rayner-Karlsson 15.1 58 ##{{{objectClass: organizationalUnit}}}##
59 ##{{{objectClass: top}}}##
60 ##{{{ou: kerberos}}}##
Sirius Rayner-Karlsson 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>}}}##
Sirius Rayner-Karlsson 15.1 73 ##{{{description: Kerberos KDC Account}}}##
Sirius Rayner-Karlsson 4.1 74
Sirius Rayner-Karlsson 21.1 75 (% style="color:#400" %)
Sirius Rayner-Karlsson 27.1 76 ##{{{dn: cn=kadmin,ou=kerberos,dc=example,dc=com}}}##
77 ##{{{cn: kadmin}}}##
Sirius Rayner-Karlsson 16.1 78 ##{{{sn: kadmin}}}##
79 ##{{{objectClass: person}}}##
80 ##{{{objectClass: pwdPolicy}}}##
81 ##{{{pwdAttribute: userPassword}}}##
82 ##{{{pwdMinLength: 8}}}##
83 ##{{{pwdCheckQuality: 2}}}##
Sirius Rayner-Karlsson 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:}}}##
Sirius Rayner-Karlsson 16.1 89
Sirius Rayner-Karlsson 27.1 90 (% style="color:#400" %)
91 ##{{{adding new entry "ou=kerberos,dc=example,dc=com"}}}##
Sirius Rayner-Karlsson 17.1 92
Sirius Rayner-Karlsson 27.1 93 (% style="color:#400" %)
94 ##{{{adding new entry "cn=kdc,ou=kerberos,dc=example,dc=com"}}}##
Sirius Rayner-Karlsson 19.1 95
Sirius Rayner-Karlsson 27.1 96 (% style="color:#400" %)
97 ##{{{adding new entry "cn=kadmin,ou=kerberos,dc=example,dc=com"}}}##
98
Sirius Rayner-Karlsson 27.2 99
Sirius Rayner-Karlsson 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
Sirius Rayner-Karlsson 27.2 102
Sirius Rayner-Karlsson 34.1 103 === Grant kdc and kadmin permissions ===
Sirius Rayner-Karlsson 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
Sirius Rayner-Karlsson 29.1 134
Sirius Rayner-Karlsson 34.1 135 === Create krb5.conf ===
Sirius Rayner-Karlsson 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
Sirius Rayner-Karlsson 33.1 161
Sirius Rayner-Karlsson 34.1 162 === Create kdc.conf ===
Sirius Rayner-Karlsson 33.1 163
Sirius Rayner-Karlsson 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
Sirius Rayner-Karlsson 34.1 192 === Create kadm5.acl ===
Sirius Rayner-Karlsson 33.1 193
Sirius Rayner-Karlsson 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
Sirius Rayner-Karlsson 34.1 202 === Create the kerberos domain ===
Sirius Rayner-Karlsson 33.1 203
Sirius Rayner-Karlsson 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
Sirius Rayner-Karlsson 33.1 224
Sirius Rayner-Karlsson 34.1 225 === Create the first regular principals ===
Sirius Rayner-Karlsson 33.1 226
Sirius Rayner-Karlsson 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
Sirius Rayner-Karlsson 33.1 271