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Changes for page KerberosAndLDAP

Last modified by Sirius Rayner-Karlsson on 2024/05/09 10:54
From version 25.1
edited by Sirius Rayner-Karlsson
on 2024/05/06 03:06
Change comment: There is no comment for this version
To version 37.1
edited by Sirius Rayner-Karlsson
on 2024/05/09 10:54
Change comment: There is no comment for this version

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1 +{{box cssClass="floatinginfobox" title="**Contents**"}}
1 1  {{toc/}}
3 +{{/box}}
2 2  
3 3  = Debian =
4 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 a little from the upstream Debian Guide.
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.
6 6  
7 -I will assume 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. The Synology NAS can be leveraged for a multitude of things, and running DNS, DHCP, WebServices and Containers are but a few. I will also assume 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.
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.
8 8  
9 -I also recommend 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. The guide is for illustration and expectation is that you do not follow it verbatim but adapt it to your needs.
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.
10 10  
13 +**The guide is for illustration. Expectation is that you do not follow it verbatim but adapt it to your needs.**
11 11  
12 -===== Install the packages containing the LDAP-enabled Kerberos servers: =====
13 13  
16 +=== Install packages ===
17 +
14 14  (% class="wikigeneratedid" %)
15 -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~#~#.
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.
16 16  
17 17  (% style="color:#400" %)
18 18  ##{{{$ sudo apt install krb5-kdc-ldap krb5-admin-server schema2ldif}}}##
19 19  
20 20  
21 -===== Load the ##kerberos## schema into the LDAP server on your Synology: =====
25 +=== Load kerberos LDAP schema ===
22 22  
27 +Now you need to load the kerberos schema into the LDAP server on the Synology. Use the ##cn=config## DN.
28 +
23 23  (% style="color:#400" %)
24 -##{{{$ zcat /usr/share/doc/krb5-kdc-ldap/kerberos.openldap.ldif.gz | ldapadd -H ldap://nas.example.com/ -D uid=root,cn=users,dc=example,dc=com -W}}}##
25 -##{{{Enter LDAP Password:}}}##
26 -##{{{adding new entry "cn=kerberos,cn=schema,cn=config"}}}##
27 -##{{{$}}}##
30 +##{{{$ 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" $}}}##
28 28  
29 29  
30 -===== Create Index on krbPrincipalName: =====
33 +=== Create Index on krbPrincipalName ===
31 31  
32 -Having an index on the ##krbPrincipalName## improves performance and also suppresses some log messages if ##slapd## is configured to log more than default for the database(s) where you intend to store Kerberos data. As this is OpenLDAP on the Synology, it does not use ~#~###mdb~#~### format, it uses ##~#~#bdb~#~###. If you install ~#~#slapd~#~# on Debian, it uses ~#~#mdb~#~# format.
35 +Having an index on the ##krbPrincipalName## improves performance. Synology OpenLDAP does not use ##mdb## format, it uses ##bdb##. Debian ##slapd## uses ##mdb## format. It is different database format, but the principle is the same. Again, as you are modifying config, the DN is ##cn=config##. Use the main password you set for the Synology LDAP server. Create a file ##step1.ldif## with the following content:
33 33  
34 34  (% style="color:#400" %)
35 -##{{{$ ldapmodify -H ldap://nas.example.com/ -D uid=root,cn=users,dc=example,dc=com -W <<EOF}}}##
36 -##{{{dn: olcDatabase={1}bdb,cn=config}}}##
37 -##{{{add: olcDbIndex}}}##
38 -##{{{olcDbIndex: krbPrincipalName eq,pres,sub}}}##
39 -##{{{EOF}}}##
40 -##{{{Enter LDAP Password:}}}##
41 -##{{{modifying entry "olcDatabase={1}bdb,cn=config"}}}##
42 -##{{{$}}}##
38 +##{{{
39 +dn: olcDatabase={1}bdb,cn=config
40 +add: olcDbIndex
41 +olcDbIndex: krbPrincipalName eq,pres,sub}}}##
43 43  
44 44  
45 -===== Create the two principals kadmin and kdc: =====
44 +and apply it with
46 46  
47 -Next, you create and configure two entries which will be used by the Kerberos servers to connect to OpenLDAP. As you will not run the Kerberos KDC and Admin Server on the same host as OpenLDAP, these steps are required. In order to keep things nicely separated, everything will be created under a separate ##organizationalUnit##. I diverge from the official Debian guide here as I do not agree with the DN they use. I also had to make changes to the DNs of ~#~#kdc~#~# and ~#~#kadmin~#~# due to ~#~#pwdPolicy~#~# applied by Synology to their LDAP server. The official guide will have you use placeholder passwords and that does not work with the Synology LDAP server. You need to generate them upfront with ~#~#slappasswd~#~#.
46 +(% style="color:#400" %)
47 +##{{{$ ldapmodify -H ldaps://nas.example.com/ -D cn=config -W -f step1.ldif
48 +Enter LDAP Password:
48 48  
50 +modifying entry "olcDatabase={1}bdb,cn=config"
51 +
52 +$ }}}##
53 +
54 +
55 +=== Create principals kadmin and kdc ===
56 +
57 +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.
58 +Generate the passwords upfront with ##slappasswd -h {SSHA}##. Then create a file ##step2.ldif## with the following content:
59 +
49 49  (% style="color:#400" %)
50 -##{{{$ ldapadd -H ldap://nas.example.com/ -D uid=root,cn=users,dc=example,dc=com -W <<EOF}}}##
51 -##{{{dn: ou=kerberos,dc=example,dc=com}}}##
52 -##{{{objectClass: organizationalUnit}}}##
53 -##{{{objectClass: top}}}##
54 -##{{{ou: kerberos}}}##
55 -## ##
56 -##{{{dn: uid=kdc,ou=kerberos,dc=example,dc=com}}}##
57 -##{{{uid: kdc}}}##
58 -##{{{objectClass: account}}}##
59 -##{{{objectClass: simpleSecurityObject}}}##
60 -##{{{userPassword: {CRYPT}x}}}##
61 -##{{{description: Kerberos KDC Account}}}##
62 -## ##
63 -##{{{dn: uid=kadmin,ou=kerberos,dc=example,dc=com}}}##
64 -##{{{uid: kadmin}}}##
65 -##{{{objectClass: account}}}##
66 -##{{{objectClass: simpleSecurityObject}}}##
67 -##{{{userPassword: {CRYPT}x}}}##
68 -##{{{description: Kerberos Admin Server Account}}}##
69 -##{{{EOF}}}##
70 -##{{{Enter LDAP Password:}}}##
71 -## ##
72 -##{{{adding new entry "ou=kerberos,dc=example,dc=com"}}}##
73 -## ##
74 -##{{{adding new entry "uid=kdc,ou=kerberos,dc=example,dc=com"}}}##
75 -## ##
76 -##{{{adding new entry "uid=kadmin,ou=kerberos,dc=example,dc=com"}}}##
61 +##{{{
62 +dn: ou=kerberos,dc=example,dc=com
63 +objectClass: organizationalUnit
64 +objectClass: top
65 +ou: kerberos
77 77  
67 +dn: cn=kdc,ou=kerberos,dc=example,dc=com
68 +cn: kdc
69 +sn: kdc
70 +objectClass: person
71 +objectClass: pwdPolicy
72 +pwdAttribute: userPassword
73 +pwdMinLength: 8
74 +pwdCheckQuality: 2
75 +pwdPolicySubentry: cn=kdc,ou=kerberos,dc=example,dc=com
76 +userPassword: {SSHA}<password-hash>
77 +description: Kerberos KDC Account
78 78  
79 -Now, it was at this point that I had a problem, because the LDAP server on the Synology did not like adding users with placeholder passwords, because Synology puts in place password policies. I ended up working around it using a different construct:
79 +dn: cn=kadmin,ou=kerberos,dc=example,dc=com
80 +cn: kadmin
81 +sn: kadmin
82 +objectClass: person
83 +objectClass: pwdPolicy
84 +pwdAttribute: userPassword
85 +pwdMinLength: 8
86 +pwdCheckQuality: 2
87 +pwdPolicySubentry: cn=kadmin,ou=kerberos,dc=example,dc=com
88 +userPassword: {SSHA}<password-hash>
89 +description: Kerberos KDC Account}}}##
80 80  
91 +
92 +Apply it with
93 +
81 81  (% style="color:#400" %)
82 -##{{{dn: cn=kadmin,ou=kerberos,ou=Services,dc=example,dc=com}}}##
83 -##{{{sn: kadmin}}}##
84 -##{{{cn: kadmin}}}##
85 -##{{{objectClass: person}}}##
86 -##{{{objectClass: pwdPolicy}}}##
87 -##{{{pwdAttribute: userPassword}}}##
88 -##{{{pwdMinLength: 8}}}##
89 -##{{{pwdCheckQuality: 2}}}##
90 -##{{{pwdPolicySubentry: cn=kadmin,ou=kerberos,ou=Services,dc=example,dc=com}}}##
91 -##{{{userPassword: {SSHA}<hashed password>}}}##
92 -##{{{description: Kerberos Admin Server Account}}}##
95 +##{{{$ ldapadd -H ldaps://nas.example.com/ -D uid=root,cn=users,dc=example,dc=com -W -f step2.ldif
96 +Enter LDAP Password:
93 93  
94 -and that seems to have worked out fine as my KDC is fully functioning.
98 +adding new entry "ou=kerberos,dc=example,dc=com"
95 95  
96 -It required modifying the rest of the guide with the fact that it no longer was ##uid=kadmin## and ##uid=kdc##, but rather ##cn=kadmin## and ##cn=kdc##. The most important thing is that it works. As an aside, I am not sure it is required to have two nested Organisation Units, ##Services## and ##kerberos## - so I will likely re-deploy and get rid of the ##Services## Organisational Unit altogether. It shortens the DN's used for binds to LDAP and limits the risk for typos. I also find it highly unlikely that deploying this in a real organisation that there would be an existing Organisational Unit called '##kerberos##' while the risk for there being an existing department called '##Services##' is much more likely.
100 +adding new entry "cn=kdc,ou=kerberos,dc=example,dc=com"
97 97  
98 -A note on the above workaround. In order to add a password policy on ##kadmin## and ##kdc## in LDAP, they have to have an attribute that is "physical". And when adding that object class the entries could no longer be a ##uid##. Hence the ##sn## and ##cn## parts. I spent a fair time looking things up as whenever I thought I made progress, something else turned out to be a blocker. When you create the ##{SSHA}## password hash, use ##slappasswd## from the ##slapd## package.
102 +adding new entry "cn=kadmin,ou=kerberos,dc=example,dc=com"
103 +
104 +$ }}}##
105 +
106 +
107 +A small note on this section:
108 +The ##objectClass: pwdPolicy## must be added to a, to LDAP, physical thing. ##objectClass: person## fits the criteria, but can not have ##uid##. So to make it work, the ##uid## is replaced with ##sn## and ##cn## (yes, both are needed). Then you can set the other four attributes and add the hashed password you got from ##slappasswd##.
109 +
110 +
111 +=== Grant kdc and kadmin permissions ===
112 +
113 +This switches back to the ##cn=config## DN as you are changing the permissions. 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 too many login failures. We like security.
114 +
115 +Create ##step3.ldif## with the following content:
116 +
117 +(% style="color:#400" %)
118 +##{{{
119 +dn: olcDatabase={1}bdb,cn=config
120 +add: olcAccess
121 +olcAccess: {0}to attrs=krbPrincipalKey
122 + by anonymous auth
123 + by dn.exact="cn=kdc,ou=kerberos,dc=example,dc=com" write
124 + by dn.exact="cn=kadmin,ou=kerberos,dc=example,dc=com" write
125 + by self write
126 + by * none
127 +-
128 +add: olcAccess
129 +olcAccess: {1}to dn.subtree="cn=krbContainer,ou=kerberos,dc=example,dc=com"
130 + by dn.exact="cn=kdc,ou=kerberos,dc=example,dc=com" write
131 + by dn.exact="cn=kadmin,ou=kerberos,dc=example,dc=com" write
132 + by * none
133 +}}}##
134 +
135 +
136 +**Do not get the domain part above wrong. If you do, you may not be able to use ##kadmin## or ##kinit## and fixing the permissions without breaking something else is a nervous task. Trust me on this (as I screwed them up).**
137 +
138 +Apply it with
139 +
140 +(% style="color:#400" %)
141 +##{{{
142 +$ ldapmodify -H ldaps://nas.example.com -W -D cn=config -f step3.ldif
143 +Enter LDAP Password:
144 +
145 +modifying entry "olcDatabase={1}bdb,cn=config"
146 +
147 +$ }}}##
148 +
149 +
150 +=== Create krb5.conf ===
151 +
152 +Next we create (or modify) ##/etc/krb5.conf## so that it will point to the right thing later. It should look something like this:
153 +
154 +(% style="color:#400" %)
155 +##{{{
156 +[libdefaults]
157 + default_realm = EXAMPLE.COM
158 + dns_lookup_realm = false
159 + dns_lookup_kdc = false
160 + ticket_lifetime = 24h
161 + forwardable = true
162 + proxiable = true
163 + rdns = false
164 +
165 +[realms]
166 + EXAMPLE.COM = {
167 + kdc = debian.example.com
168 + admin_server = debian.example.com
169 + default_domain = example.com
170 + }
171 +[domain_realm]
172 + .example.com = EXAMPLE.COM
173 + example.com = EXAMPLE.COM
174 +}}}##
175 +
176 +
177 +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.
178 +
179 +
180 +=== Create kdc.conf ===
181 +
182 +Now we do /etc/krb5kdc/kdc.conf. Something like this should work
183 +
184 +(% style="color:#400" %)
185 +##{{{
186 +[libdefaults]
187 +
188 +[realms]
189 + EXAMPLE.COM = {
190 + database_module = openldap_ldapconf
191 + max_life = 7d
192 + max_renewable_life = 6d
193 + }
194 +
195 +[dbdefaults]
196 + ldap_kerberos_container_dn = cn=krbContainer,ou=kerberos,dc=example,dc=com
197 +
198 +[dbmodules]
199 + openldap_ldapconf = {
200 + db_library = kldap
201 + disable_last_success = false
202 + disable_lockout = false
203 + ldap_conns_per_server = 5
204 + ldap_servers = ldaps:~/~/nas.example.com
205 + ldap_kdc_dn = "cn=kdc,ou=kerberos,dc=example,dc=com"
206 + ldap_kadmind_dn = "cn=kadmin,ou=kerberos,dc=example,dc=com"
207 + ldap_service_password_file = /etc/krb5kdc/service.keyfile
208 + }
209 +}}}##
210 +
211 +
212 +=== Create kadm5.acl ===
213 +
214 +Create ##/etc/krb5kdc/kadm5.acl with the following content so that kerberos administrator principals can run ##kadmin##
215 +
216 +(% style="color:#400" %)
217 +##{{{
218 +*/admin@EXAMPLE.COM *
219 +}}}##
220 +
221 +
222 +=== Create the kerberos domain ===
223 +
224 +Now we are ready to create the domain. And that we do with ##kdb5_ldap_util## as ##root##. Note that this commandline is deceptive and you need all of it.
225 +
226 +(% style="color:#400" %)
227 +##{{{
228 +# kdb5_ldap_util -D uid=root,cn=users,dc=example,dc=com -H ldaps://nas.example.com -r EXAMPLE.COM create -subtrees dc=example,dc=com -maxtktlife '7 Days' -maxrenewlife '6 Days' -s
229 +Password for "uid=root,cn=users,dc=trudheim,dc=com":
230 +Initializing database for realm 'EXAMPLE.COM'
231 +You will be prompted for the database Master Password.
232 +It is important that you NOT FORGET this password.
233 +Enter KDC database master key:
234 +Re-enter KDC database master key to verify:
235 +# }}}##
236 +
237 +
238 +=== Stash the passwords for ##kdc## and ##kadmin## ===
239 +
240 +Most likely, you will want your KDC and KAdmin server to start at boot, and for that, we can stash the passwords (into LDAP) for ##cn=kdc,ou=kerberos,dc=example,dc=com## and ##cn=kdc,ou=kerberos,dc=example,dc=com## using the same tool as in the previous step.
241 +
242 +(% style="color:#400" %)
243 +##{{{
244 +# kdb5_ldap_util -D uid=root,cn=users,dc=example,dc=com -H ldaps://nas.example.com stashsrvpw -f /etc/krb5kdc/service.keyfile cn=kdc,ou=kerberos,dc=example,dc=com
245 +Password for "uid=root,cn=users,dc=example,dc=com":
246 +Password for "cn=kdc,ou=kerberos,dc=example,dc=com":
247 +Re-enter password for "cn=kdc,ou=kerberos,dc=example,dc=com":
248 +# kdb5_ldap_util -D uid=root,cn=users,dc=example,dc=com -H ldaps://nas.example.com stashsrvpw -f /etc/krb5kdc/service.keyfile cn=kadmin,ou=kerberos,dc=example,dc=com
249 +Password for "uid=root,cn=users,dc=example,dc=com":
250 +Password for "cn=kadmin,ou=kerberos,dc=example,dc=com":
251 +Re-enter password for "cn=kadmin,ou=kerberos,dc=example,dc=com":
252 +# }}}##
253 +
254 +
255 +=== Start the services ===
256 +
257 +We are now ready to start the services. If this does not work, you need to backtrack and find out where you made a mistake, rectify it, and then walk forward again.
258 +
259 +(% style="color:#400" %)
260 +##{{{
261 +# systemctl enable --now krb5-kdc krb5-admin-server
262 +#
263 +}}}##
264 +
265 +
266 +Check that they are running and not giving off errors with ##systemctl status krb5-kdc## and ##systemctl status krb5-admin-server##.
267 +
268 +
269 +=== Create the first regular principals ===
270 +
271 +Providing you got to here without issues it is now time to generate your principals that you will use to authenticate into systems with. Run ##kadmin.local## as root to create first a regular user, and then an admin version of that user.
272 +
273 +(% style="color:#400" %)
274 +##{{{
275 +# kadmin.local
276 +
277 +Authenticating as principal root/admin@EXAMPLE.COM with password.
278 +kadmin.local:  addprinc user
279 +
280 +No policy specified for user@EXAMPLE.COM; defaulting to no policy
281 +Enter password for principal "user@EXAMPLE.COM":
282 +Re-enter password for principal "user@EXAMPLE.COM":
283 +Principal "user@EXAMPLE.COM" created.
284 +
285 +kadmin.local:  addprinc user/admin
286 +No policy specified for user/admin@EXAMPLE.COM; defaulting to no policy
287 +Enter password for principal "user/admin@EXAMPLE.COM":
288 +Re-enter password for principal "user/admin@EXAMPLE.COM":
289 +Principal "user/admin@EXAMPLE.COM" created.
290 +kadmin.local:  q
291 +
292 +# }}}##
293 +
294 +
295 +Worth to note here is that ##user@EXAMPLE.COM## and ##user/admin@EXAMPLE.COM## can have (and probably should have) different passwords. The admin variant is allowed to do things to the kerberos database and should therefore have greater security. 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.
296 +
297 +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 a share, they see nothing on it without the krbtgt.
298 +
299 +
300 +=== Test your new principal ===
301 +
302 +Acid test is, can you authenticate with kinit?
303 +
304 +(% style="color:#400" %)
305 +##{{{
306 +$ kinit user@EXAMPLE.COM
307 +
308 +Password for user@EXAMPLE.COM:
309 +
310 +$ klist
311 +Ticket cache: FILE:/tmp/krb5cc_1000
312 +Default principal: user@EXAMPLE.COM
313 +
314 +Valid starting     Expires            Service principal
315 +09/05/24 08:07:35  10/05/24 08:07:35  krbtgt/EXAMPLE.COM@EXAMPLE.COM
316 +
317 +$ }}}##
318 +
319 +
320 +Congratulations - you now have Kerberos working, and to boot, the database sits in LDAP. Which you can inspect with something like:
321 +
322 +(% style="color:#400" %)
323 +##{{{
324 +$ ldapsearch -H ldaps://nas.example.com -D uid=root,cn=users,dc=example,dc=com -W -b ou=kerberos,dc=example,dc=com
325 +}}}##
326 +
327 +
328 +=== Set up pam and sssd ===
329 +
330 + To fully leverage your shiny new KDC, you will want to install the Kerberos authentication pieces for ##PAM## and also ##sssd## to facilitate caching of authentication, in case your KDC is offline for some reason when you try to authenticate into another system.
331 +
332 +(% style="color:#400" %)
333 +##{{{
334 +$ sudo apt install krb5-user libpam-krb5 sssd-krb5
335 +...
336 +$ sudo pam-auth-update
337 +}}}##
338 +
339 +
340 +With ##pam-auth-update## you want to enable Kerberos and SSS authentication (and flip on the auto-creation of home directories while you are there). If you now want to test login on another system with kerberos, you need ##/etc/krb5.conf## and the ##krb5-user##, ##libpam-krb5## and ##sssd-krb5## packages installed on this new system and you need to run ##pam-auth-update## to enable Kerberos and SSS. After that, the system does not need local ##user## (in /etc/passwd) - the kerberos ##user## will work instead.
341 +
342 +/S