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Changes for page KerberosAndLDAP

Last modified by Sirius Rayner-Karlsson on 2024/05/09 10:54
From version 35.1
edited by Sirius Rayner-Karlsson
on 2024/05/09 09:59
Change comment: There is no comment for this version
To version 25.1
edited by Sirius Rayner-Karlsson
on 2024/05/06 03:06
Change comment: There is no comment for this version

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1 -{{box cssClass="floatinginfobox" title="**Contents**"}}
2 2  {{toc/}}
3 -{{/box}}
4 4  
5 5  = Debian =
6 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.
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.
8 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.
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.
10 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.
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.
12 12  
13 -**The guide is for illustration. Expectation is that you do not follow it verbatim but adapt it to your needs.**
14 14  
12 +===== Install the packages containing the LDAP-enabled Kerberos servers: =====
15 15  
16 -=== Install packages ===
17 -
18 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.
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~#~#.
20 20  
21 21  (% style="color:#400" %)
22 22  ##{{{$ sudo apt install krb5-kdc-ldap krb5-admin-server schema2ldif}}}##
23 23  
24 24  
25 -=== Load kerberos LDAP schema ===
21 +===== Load the ##kerberos## schema into the LDAP server on your Synology: =====
26 26  
27 -Now you need to load the kerberos schema into the LDAP server on the Synology. Use the ##cn=config## DN.
28 -
29 29  (% style="color:#400" %)
30 -##{{{
31 -$ zcat /usr/share/doc/krb5-kdc-ldap/kerberos.openldap.ldif.gz | ldapadd -H ldaps://nas.example.com/ -D cn=config -W
32 -Enter LDAP Password:
33 -adding new entry "cn=kerberos,cn=schema,cn=config"
34 -$
35 -}}}##
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 +##{{{$}}}##
36 36  
37 37  
38 -=== Create Index on krbPrincipalName ===
30 +===== Create Index on krbPrincipalName: =====
39 39  
40 -Having an index on the ##krbPrincipalName## improves performance. Synology OpenLDAP does not use ##mdb## format, it uses ##bdb##. Debian ##slapd## uses ##mdb## format. It is different database format, but the principle is the same. Again, as you are modifying config, the DN is ##cn=config##. Use the main password you set for the Synology LDAP server. Create a file ##step1.ldif## with the following content:
32 +Having an index on the ##krbPrincipalName## improves performance and also suppresses some log messages if ##slapd## is configured to log more than default for the database(s) where you intend to store Kerberos data. As this is OpenLDAP on the Synology, it does not use ~#~###mdb~#~### format, it uses ##~#~#bdb~#~###. If you install ~#~#slapd~#~# on Debian, it uses ~#~#mdb~#~# format.
41 41  
42 42  (% style="color:#400" %)
43 -##{{{
44 -dn: olcDatabase={1}bdb,cn=config
45 -add: olcDbIndex
46 -olcDbIndex: krbPrincipalName eq,pres,sub
47 -}}}##
35 +##{{{$ 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 +##{{{$}}}##
48 48  
49 -and apply it with
50 50  
51 -(% style="color:#400" %)
52 -##{{{
53 -$ ldapmodify -H ldaps://nas.example.com/ -D cn=config -W -f step1.ldif
54 -Enter LDAP Password:
55 -modifying entry "olcDatabase={1}bdb,cn=config"
56 -$
57 -}}}##
45 +===== Create the two principals kadmin and kdc: =====
58 58  
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~#~#.
59 59  
60 -=== Create principals kadmin and kdc ===
61 -
62 -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.
63 -Generate the passwords upfront with ##slappasswd -h {SSHA}##. Then create a file ##step2.ldif## with the following content:
64 -
65 65  (% style="color:#400" %)
66 -##{{{
67 -dn: ou=kerberos,dc=example,dc=com
68 -objectClass: organizationalUnit
69 -objectClass: top
70 -ou: kerberos
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"}}}##
71 71  
72 -dn: cn=kdc,ou=kerberos,dc=example,dc=com
73 -cn: kdc
74 -sn: kdc
75 -objectClass: person
76 -objectClass: pwdPolicy
77 -pwdAttribute: userPassword
78 -pwdMinLength: 8
79 -pwdCheckQuality: 2
80 -pwdPolicySubentry: cn=kdc,ou=kerberos,dc=example,dc=com
81 -userPassword: {SSHA}<password-hash>
82 -description: Kerberos KDC Account
83 83  
84 -dn: cn=kadmin,ou=kerberos,dc=example,dc=com
85 -cn: kadmin
86 -sn: kadmin
87 -objectClass: person
88 -objectClass: pwdPolicy
89 -pwdAttribute: userPassword
90 -pwdMinLength: 8
91 -pwdCheckQuality: 2
92 -pwdPolicySubentry: cn=kadmin,ou=kerberos,dc=example,dc=com
93 -userPassword: {SSHA}<password-hash>
94 -description: Kerberos KDC Account
95 -}}}##
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:
96 96  
97 -Apply it with
98 -
99 99  (% style="color:#400" %)
100 -##{{{
101 -$ ldapadd -H ldaps://nas.example.com/ -D uid=root,cn=users,dc=example,dc=com -W -f step2.ldif
102 -Enter LDAP Password:
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}}}##
103 103  
104 -adding new entry "ou=kerberos,dc=example,dc=com"
94 +and that seems to have worked out fine as my KDC is fully functioning.
105 105  
106 -adding new entry "cn=kdc,ou=kerberos,dc=example,dc=com"
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.
107 107  
108 -adding new entry "cn=kadmin,ou=kerberos,dc=example,dc=com"
109 -}}}##
110 -
111 -
112 -
113 -=== Grant kdc and kadmin permissions ===
114 -
115 -This switches back to the ##cn=config## DN as you are changing the permissions.
116 -
117 -$ ldapmodify -H ldaps:~/~/ds723.trudheim.com -W -D cn=config <<EOF
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=trudheim,dc=com" write
124 - by dn.exact="cn=kadmin,ou=kerberos,dc=trudheim,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=trudheim,dc=com" write
131 - by dn.exact="cn=kadmin,ou=kerberos,dc=trudheim,dc=com" write
132 - by * none
133 -
134 -EOF
135 -
136 -Enter LDAP Password:
137 -modifying entry "olcDatabase={1}bdb,cn=config"
138 -
139 -$
140 -
141 -
142 -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.
143 -
144 -
145 -=== Create krb5.conf ===
146 -
147 -Over to adjusting /etc/krb5.conf so that it will point to the right thing later. It should look something like this:
148 -
149 -
150 -{{{[libdefaults]
151 - default_realm = EXAMPLE.COM
152 - dns_lookup_realm = false
153 - dns_lookup_kdc = false
154 - ticket_lifetime = 24h
155 - forwardable = true
156 - proxiable = true
157 - rdns = false
158 -
159 -[realms]
160 - EXAMPLE.COM = {
161 - kdc = debian.example.com
162 - admin_server = debian.example.com
163 - default_domain = example.com
164 - }
165 - [domain_realm]
166 - .example.com = EXAMPLE.COM
167 - example.com = EXAMPLE.COM}}}
168 -
169 -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.
170 -
171 -
172 -=== Create kdc.conf ===
173 -
174 -Next, we need to write up /etc/krb5kdc/kdc.conf. Something like this should work
175 -
176 -
177 -[libdefaults]
178 -
179 -[realms]
180 - TRUDHEIM.COM = {
181 - database_module = openldap_ldapconf
182 - max_life = 7d
183 - max_renewable_life = 6d
184 - }
185 -
186 -[dbdefaults]
187 - ldap_kerberos_container_dn = cn=krbContainer,ou=kerberos,dc=trudheim,dc=com
188 -
189 -[dbmodules]
190 - openldap_ldapconf = {
191 - db_library = kldap
192 - disable_last_success = false
193 - disable_lockout = false
194 - ldap_conns_per_server = 5
195 - ldap_servers = ldaps:~/~/ds723.trudheim.com
196 - ldap_kdc_dn = "cn=kdc,ou=kerberos,dc=trudheim,dc=com"
197 - ldap_kadmind_dn = "cn=kadmin,ou=kerberos,dc=trudheim,dc=com"
198 - ldap_service_password_file = /etc/krb5kdc/service.keyfile
199 - }
200 -
201 -
202 -=== Create kadm5.acl ===
203 -
204 -Then you need to create ##/etc/krb5kdc/kadm5.acl and put in it##
205 -
206 -##*/admin@EXAMPLE.COM *##
207 -
208 -
209 -so that administrator principals can run kadmin. Now we are ready to create the domain. And that we do with
210 -
211 -
212 -=== Create the kerberos domain ===
213 -
214 -#
215 -
216 -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
217 -Password for "uid=root,cn=users,dc=trudheim,dc=com":
218 -Initializing database for realm 'TRUDHEIM.COM'
219 -You will be prompted for the database Master Password.
220 -It is important that you NOT FORGET this password.
221 -Enter KDC database master key:
222 -Re-enter KDC database master key to verify:
223 -
224 -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
225 -Password for "uid=root,cn=users,dc=trudheim,dc=com":
226 -Password for "cn=kdc,ou=kerberos,dc=trudheim,dc=com":
227 -Re-enter password for "cn=kdc,ou=kerberos,dc=trudheim,dc=com":
228 -
229 -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
230 -Password for "uid=root,cn=users,dc=trudheim,dc=com":
231 -Password for "cn=kadmin,ou=kerberos,dc=trudheim,dc=com":
232 -Re-enter password for "cn=kadmin,ou=kerberos,dc=trudheim,dc=com":
233 -
234 -
235 -=== Create the first regular principals ===
236 -
237 -Here, you will run kadmin.local to create first a regular user, and then an admin version of that user.
238 -
239 -# kadmin.local
240 -
241 -Authenticating as principal root/admin@TRUDHEIM.COM with password.
242 -kadmin.local:  addprinc user
243 -
244 -No policy specified for user@TRUDHEIM.COM; defaulting to no policy
245 -Enter password for principal "user@TRUDHEIM.COM":
246 -Re-enter password for principal "user@TRUDHEIM.COM":
247 -Principal "user@TRUDHEIM.COM" created.
248 -
249 -kadmin.local:  addprinc user/admin
250 -No policy specified for user/admin@TRUDHEIM.COM; defaulting to no policy
251 -Enter password for principal "user/admin@TRUDHEIM.COM":
252 -Re-enter password for principal "user/admin@TRUDHEIM.COM":
253 -Principal "user/admin@TRUDHEIM.COM" created.
254 -kadmin.local:  q
255 -
256 -#
257 -
258 -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.
259 -
260 -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.
261 -
262 -
263 -=== Test your new principal ===
264 -
265 -$ kinit [[user@EXAMPLE.COM>>mailto:user@EXAMPLE.COM]]
266 -
267 -Password for user@EXAMPLE.COM:
268 -
269 -$ klist
270 -Ticket cache: FILE:/tmp/krb5cc_1000
271 -Default principal: user@EXAMPLE.COM
272 -
273 -Valid starting     Expires            Service principal
274 -09/05/24 08:07:35  10/05/24 08:07:35  krbtgt/EXAMPLE.COM@EXAMPLE.COM
275 -
276 -$
277 -
278 -
279 -=== Set up pam and sssd ===
280 -
281 -
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.