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Changes for page KerberosAndLDAP

Last modified by Sirius Rayner-Karlsson on 2024/05/09 10:54
From version 26.1
edited by Sirius Rayner-Karlsson
on 2024/05/06 03:16
Change comment: There is no comment for this version
To version 36.1
edited by Sirius Rayner-Karlsson
on 2024/05/09 10:00
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  
... ... @@ -11,7 +11,7 @@
11 11  **The guide is for illustration. Expectation is that you do not follow it verbatim but adapt it to your needs.**
12 12  
13 13  
14 -===== Install packages: =====
16 +=== Install packages ===
15 15  
16 16  (% class="wikigeneratedid" %)
17 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.
... ... @@ -20,83 +20,209 @@
20 20  ##{{{$ sudo apt install krb5-kdc-ldap krb5-admin-server schema2ldif}}}##
21 21  
22 22  
23 -===== Load ##kerberos LDAP## schema: =====
25 +=== Load kerberos LDAP schema ===
24 24  
25 -Now you need to load the kerberos schema into the LDAP server on the Synology.
27 +Now you need to load the kerberos schema into the LDAP server on the Synology. Use the ##cn=config## DN.
26 26  
27 27  (% style="color:#400" %)
28 -##{{{$ 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}}}##
29 -##{{{Enter LDAP Password:}}}##
30 -##{{{adding new entry "cn=kerberos,cn=schema,cn=config"}}}##
31 -##{{{$}}}##
30 +##{{{$ 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" $}}}##
32 32  
33 33  
34 -===== Create Index on krbPrincipalName: =====
33 +=== Create Index on krbPrincipalName ===
35 35  
36 -Having an index on the ##krbPrincipalName## improves performance and also suppresses some log messages if ##slapd## is configured to log more than default for the database(s) where you intend to store Kerberos data. As this is OpenLDAP on the Synology, it does not use ##mdb## format, it uses ##bdb##. If you install ##slapd## on Debian, it uses ##mdb## format. It is different database format, but the principle is the same.
35 +Having an index on the ##krbPrincipalName## improves performance. Synology OpenLDAP does not use ##mdb## format, it uses ##bdb##. Debian ##slapd## uses ##mdb## format. It is different database format, but the principle is the same. Again, as you are modifying config, the DN is ##cn=config##. Use the main password you set for the Synology LDAP server. Create a file ##step1.ldif## with the following content:
37 37  
38 38  (% style="color:#400" %)
39 -##{{{$ ldapmodify -H ldap://nas.example.com/ -D uid=root,cn=users,dc=example,dc=com -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 -##{{{$}}}##
38 +##{{{dn: olcDatabase={1}bdb,cn=config add: olcDbIndex olcDbIndex: krbPrincipalName eq,pres,sub}}}##
47 47  
48 48  
49 -===== Create principals kadmin and kdc: =====
41 +and apply it with
50 50  
51 -Next, you create and configure two entries which will be used by the Kerberos servers to connect to OpenLDAP. As you will not run the Kerberos KDC and Admin Server on the same host as OpenLDAP, these steps are required. In order to keep things nicely separated, everything will be created under a separate ##organizationalUnit##. I diverge from the official Debian guide here as I do not agree with the DN they use. I also had to make changes to the DNs of ##kdc## and ##kadmin## due to ##pwdPolicy## applied by Synology to their LDAP server. The official guide will have you use placeholder passwords and that does not work with the Synology LDAP server. You need to generate them upfront with ##slappasswd##.
52 -
53 53  (% style="color:#400" %)
54 -##{{{$ 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 -##{{{dn: uid=kdc,ou=kerberos,dc=example,dc=com}}}##
61 -##{{{uid: kdc}}}##
62 -##{{{objectClass: account}}}##
63 -##{{{objectClass: simpleSecurityObject}}}##
64 -##{{{userPassword: {CRYPT}x}}}##
65 -##{{{description: Kerberos KDC Account}}}##
66 -## ##
67 -##{{{dn: uid=kadmin,ou=kerberos,dc=example,dc=com}}}##
68 -##{{{uid: kadmin}}}##
69 -##{{{objectClass: account}}}##
70 -##{{{objectClass: simpleSecurityObject}}}##
71 -##{{{userPassword: {CRYPT}x}}}##
72 -##{{{description: Kerberos Admin Server Account}}}##
73 -##{{{EOF}}}##
74 -##{{{Enter LDAP Password:}}}##
75 -## ##
76 -##{{{adding new entry "ou=kerberos,dc=example,dc=com"}}}##
77 -## ##
78 -##{{{adding new entry "uid=kdc,ou=kerberos,dc=example,dc=com"}}}##
79 -## ##
80 -##{{{adding new entry "uid=kadmin,ou=kerberos,dc=example,dc=com"}}}##
44 +##{{{$ ldapmodify -H ldaps://nas.example.com/ -D cn=config -W -f step1.ldif Enter LDAP Password: modifying entry "olcDatabase={1}bdb,cn=config" $}}}##
81 81  
82 82  
83 -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:
47 +=== Create principals kadmin and kdc ===
84 84  
49 +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.
50 +Generate the passwords upfront with ##slappasswd -h {SSHA}##. Then create a file ##step2.ldif## with the following content:
51 +
85 85  (% style="color:#400" %)
86 -##{{{dn: cn=kadmin,ou=kerberos,ou=Services,dc=example,dc=com}}}##
87 -##{{{sn: kadmin}}}##
88 -##{{{cn: kadmin}}}##
89 -##{{{objectClass: person}}}##
90 -##{{{objectClass: pwdPolicy}}}##
91 -##{{{pwdAttribute: userPassword}}}##
92 -##{{{pwdMinLength: 8}}}##
93 -##{{{pwdCheckQuality: 2}}}##
94 -##{{{pwdPolicySubentry: cn=kadmin,ou=kerberos,ou=Services,dc=example,dc=com}}}##
95 -##{{{userPassword: {SSHA}<hashed password>}}}##
96 -##{{{description: Kerberos Admin Server Account}}}##
53 +##{{{dn: ou=kerberos,dc=example,dc=com objectClass: organizationalUnit objectClass: top ou: kerberos dn: cn=kdc,ou=kerberos,dc=example,dc=com cn: kdc sn: kdc objectClass: person objectClass: pwdPolicy pwdAttribute: userPassword pwdMinLength: 8 pwdCheckQuality: 2 pwdPolicySubentry: cn=kdc,ou=kerberos,dc=example,dc=com userPassword: {SSHA}<password-hash> description: Kerberos KDC Account dn: cn=kadmin,ou=kerberos,dc=example,dc=com cn: kadmin sn: kadmin objectClass: person objectClass: pwdPolicy pwdAttribute: userPassword pwdMinLength: 8 pwdCheckQuality: 2 pwdPolicySubentry: cn=kadmin,ou=kerberos,dc=example,dc=com userPassword: {SSHA}<password-hash> description: Kerberos KDC Account}}}##
97 97  
98 -and that seems to have worked out fine as my KDC is fully functioning.
55 +Apply it with
99 99  
100 -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.
57 +(% style="color:#400" %)
58 +##{{{$ ldapadd -H ldaps://nas.example.com/ -D uid=root,cn=users,dc=example,dc=com -W -f step2.ldif Enter LDAP Password: adding new entry "ou=kerberos,dc=example,dc=com" adding new entry "cn=kdc,ou=kerberos,dc=example,dc=com" adding new entry "cn=kadmin,ou=kerberos,dc=example,dc=com"}}}##
101 101  
102 -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.
60 +
61 +
62 +=== Grant kdc and kadmin permissions ===
63 +
64 +This switches back to the ##cn=config## DN as you are changing the permissions.
65 +
66 +$ ldapmodify -H ldaps:~/~/ds723.trudheim.com -W -D cn=config <<EOF
67 +
68 +dn: olcDatabase={1}bdb,cn=config
69 +add: olcAccess
70 +olcAccess: {0}to attrs=krbPrincipalKey
71 + by anonymous auth
72 + by dn.exact="cn=kdc,ou=kerberos,dc=trudheim,dc=com" write
73 + by dn.exact="cn=kadmin,ou=kerberos,dc=trudheim,dc=com" write
74 + by self write
75 + by * none
76 +-
77 +add: olcAccess
78 +olcAccess: {1}to dn.subtree="cn=krbContainer,ou=kerberos,dc=example,dc=com"
79 + by dn.exact="cn=kdc,ou=kerberos,dc=trudheim,dc=com" write
80 + by dn.exact="cn=kadmin,ou=kerberos,dc=trudheim,dc=com" write
81 + by * none
82 +
83 +EOF
84 +
85 +Enter LDAP Password:
86 +modifying entry "olcDatabase={1}bdb,cn=config"
87 +
88 +$
89 +
90 +
91 +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.
92 +
93 +
94 +=== Create krb5.conf ===
95 +
96 +Over to adjusting /etc/krb5.conf so that it will point to the right thing later. It should look something like this:
97 +
98 +
99 +{{{[libdefaults]
100 + default_realm = EXAMPLE.COM
101 + dns_lookup_realm = false
102 + dns_lookup_kdc = false
103 + ticket_lifetime = 24h
104 + forwardable = true
105 + proxiable = true
106 + rdns = false
107 +
108 +[realms]
109 + EXAMPLE.COM = {
110 + kdc = debian.example.com
111 + admin_server = debian.example.com
112 + default_domain = example.com
113 + }
114 + [domain_realm]
115 + .example.com = EXAMPLE.COM
116 + example.com = EXAMPLE.COM}}}
117 +
118 +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.
119 +
120 +
121 +=== Create kdc.conf ===
122 +
123 +Next, we need to write up /etc/krb5kdc/kdc.conf. Something like this should work
124 +
125 +
126 +[libdefaults]
127 +
128 +[realms]
129 + TRUDHEIM.COM = {
130 + database_module = openldap_ldapconf
131 + max_life = 7d
132 + max_renewable_life = 6d
133 + }
134 +
135 +[dbdefaults]
136 + ldap_kerberos_container_dn = cn=krbContainer,ou=kerberos,dc=trudheim,dc=com
137 +
138 +[dbmodules]
139 + openldap_ldapconf = {
140 + db_library = kldap
141 + disable_last_success = false
142 + disable_lockout = false
143 + ldap_conns_per_server = 5
144 + ldap_servers = ldaps:~/~/ds723.trudheim.com
145 + ldap_kdc_dn = "cn=kdc,ou=kerberos,dc=trudheim,dc=com"
146 + ldap_kadmind_dn = "cn=kadmin,ou=kerberos,dc=trudheim,dc=com"
147 + ldap_service_password_file = /etc/krb5kdc/service.keyfile
148 + }
149 +
150 +
151 +=== Create kadm5.acl ===
152 +
153 +Then you need to create ##/etc/krb5kdc/kadm5.acl and put in it##
154 +
155 +##*/admin@EXAMPLE.COM *##
156 +
157 +
158 +so that administrator principals can run kadmin. Now we are ready to create the domain. And that we do with
159 +
160 +
161 +=== Create the kerberos domain ===
162 +
163 +#
164 +
165 +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
166 +Password for "uid=root,cn=users,dc=trudheim,dc=com":
167 +Initializing database for realm 'TRUDHEIM.COM'
168 +You will be prompted for the database Master Password.
169 +It is important that you NOT FORGET this password.
170 +Enter KDC database master key:
171 +Re-enter KDC database master key to verify:
172 +
173 +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
174 +Password for "uid=root,cn=users,dc=trudheim,dc=com":
175 +Password for "cn=kdc,ou=kerberos,dc=trudheim,dc=com":
176 +Re-enter password for "cn=kdc,ou=kerberos,dc=trudheim,dc=com":
177 +
178 +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
179 +Password for "uid=root,cn=users,dc=trudheim,dc=com":
180 +Password for "cn=kadmin,ou=kerberos,dc=trudheim,dc=com":
181 +Re-enter password for "cn=kadmin,ou=kerberos,dc=trudheim,dc=com":
182 +
183 +
184 +=== Create the first regular principals ===
185 +
186 +Here, you will run kadmin.local to create first a regular user, and then an admin version of that user.
187 +
188 +# kadmin.local
189 +
190 +Authenticating as principal root/admin@TRUDHEIM.COM with password.
191 +kadmin.local:  addprinc user
192 +
193 +No policy specified for user@TRUDHEIM.COM; defaulting to no policy
194 +Enter password for principal "user@TRUDHEIM.COM":
195 +Re-enter password for principal "user@TRUDHEIM.COM":
196 +Principal "user@TRUDHEIM.COM" created.
197 +
198 +kadmin.local:  addprinc user/admin
199 +No policy specified for user/admin@TRUDHEIM.COM; defaulting to no policy
200 +Enter password for principal "user/admin@TRUDHEIM.COM":
201 +Re-enter password for principal "user/admin@TRUDHEIM.COM":
202 +Principal "user/admin@TRUDHEIM.COM" created.
203 +kadmin.local:  q
204 +
205 +#
206 +
207 +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.
208 +
209 +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.
210 +
211 +
212 +=== Test your new principal ===
213 +
214 +$ kinit [[user@EXAMPLE.COM>>mailto:user@EXAMPLE.COM]]
215 +
216 +Password for user@EXAMPLE.COM:
217 +
218 +$ klist
219 +Ticket cache: FILE:/tmp/krb5cc_1000
220 +Default principal: user@EXAMPLE.COM
221 +
222 +Valid starting     Expires            Service principal
223 +09/05/24 08:07:35  10/05/24 08:07:35  krbtgt/EXAMPLE.COM@EXAMPLE.COM
224 +
225 +$
226 +
227 +
228 +=== Set up pam and sssd ===
229 +
230 +