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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 29.1
edited by Sirius Rayner-Karlsson
on 2024/05/07 13:43
Change comment: There is no comment for this version

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... ... @@ -22,10 +22,10 @@
22 22  
23 23  ===== Load ##kerberos LDAP## schema: =====
24 24  
25 -Now you need to load the kerberos schema into the LDAP server on the Synology.
25 +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.
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}}}##
28 +##{{{$ zcat /usr/share/doc/krb5-kdc-ldap/kerberos.openldap.ldif.gz | ldapadd -H ldaps://nas.example.com/ -D cn=config -W}}}##
29 29  ##{{{Enter LDAP Password:}}}##
30 30  ##{{{adding new entry "cn=kerberos,cn=schema,cn=config"}}}##
31 31  ##{{{$}}}##
... ... @@ -33,10 +33,10 @@
33 33  
34 34  ===== Create Index on krbPrincipalName: =====
35 35  
36 -Having an index on the ##krbPrincipalName## improves performance and also suppresses some log messages if ##slapd## is configured to log more than default for the database(s) where you intend to store Kerberos data. As this is OpenLDAP on the Synology, it does not use ##mdb## format, it uses ##bdb##. If you install ##slapd## on Debian, it uses ##mdb## format. It is different database format, but the principle is the same.
36 +Having an index on the ##krbPrincipalName## improves performance and also suppresses some log messages if ##slapd## is configured to log more than default for the database(s) where you intend to store Kerberos data. As this is OpenLDAP on the Synology, it does not use ##mdb## format, it uses ##bdb##. If you install ##slapd## on Debian, it uses ##mdb## format. It is different database format, but the principle is the same. Again, as you are modifying config, the DN is ##cn=config##. Interestingly, it is still the main password you set for the Synology LDAP server.
37 37  
38 38  (% style="color:#400" %)
39 -##{{{$ ldapmodify -H ldap://nas.example.com/ -D uid=root,cn=users,dc=example,dc=com -W <<EOF}}}##
39 +##{{{$ ldapmodify -H ldaps://nas.example.com/ -D cn=config -W <<EOF}}}##
40 40  ##{{{dn: olcDatabase={1}bdb,cn=config}}}##
41 41  ##{{{add: olcDbIndex}}}##
42 42  ##{{{olcDbIndex: krbPrincipalName eq,pres,sub}}}##
... ... @@ -48,7 +48,7 @@
48 48  
49 49  ===== Create principals kadmin and kdc: =====
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##.
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 -h {SSHA}##.
52 52  
53 53  (% style="color:#400" %)
54 54  ##{{{$ ldapadd -H ldap://nas.example.com/ -D uid=root,cn=users,dc=example,dc=com -W <<EOF}}}##
... ... @@ -56,47 +56,161 @@
56 56  ##{{{objectClass: organizationalUnit}}}##
57 57  ##{{{objectClass: top}}}##
58 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}}}##
59 +
60 +(% style="color:#400" %)
61 +##{{{dn: cn=kdc,ou=kerberos,dc=example,dc=com}}}##
62 +##{{{cn: kdc}}}##
63 +##{{{sn: kdc}}}##
64 +##{{{objectClass: person}}}##
65 +##{{{objectClass: pwdPolicy}}}##
66 +##{{{pwdAttribute: userPassword}}}##
67 +##{{{pwdMinLength: 8}}}##
68 +##{{{pwdCheckQuality: 2}}}##
69 +##{{{pwdPolicySubentry: cn=kdc,ou=kerberos,dc=example,dc=com}}}##
70 +##{{{userPassword: {SSHA}<password-hash>}}}##
65 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"}}}##
81 81  
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:
84 -
85 85  (% style="color:#400" %)
86 -##{{{dn: cn=kadmin,ou=kerberos,ou=Services,dc=example,dc=com}}}##
87 -##{{{sn: kadmin}}}##
74 +##{{{dn: cn=kadmin,ou=kerberos,dc=example,dc=com}}}##
88 88  ##{{{cn: kadmin}}}##
76 +##{{{sn: kadmin}}}##
89 89  ##{{{objectClass: person}}}##
90 90  ##{{{objectClass: pwdPolicy}}}##
91 91  ##{{{pwdAttribute: userPassword}}}##
92 92  ##{{{pwdMinLength: 8}}}##
93 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}}}##
82 +##{{{pwdPolicySubentry: cn=kadmin,ou=kerberos,dc=example,dc=com}}}##
83 +##{{{userPassword: {SSHA}<password-hash>}}}##
84 +##{{{description: Kerberos KDC Account}}}##
85 +##{{{EOF}}}##
86 +##{{{Enter LDAP Password:}}}##
97 97  
98 -and that seems to have worked out fine as my KDC is fully functioning.
88 +(% style="color:#400" %)
89 +##{{{adding new entry "ou=kerberos,dc=example,dc=com"}}}##
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.
91 +(% style="color:#400" %)
92 +##{{{adding new entry "cn=kdc,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.
94 +(% style="color:#400" %)
95 +##{{{adding new entry "cn=kadmin,ou=kerberos,dc=example,dc=com"}}}##
96 +
97 +
98 +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.
99 +
100 +
101 +===== Grant kdc and kadmin permissions: =====
102 +
103 +This switches back to the ##cn=config## DN as you are changing the permissions.
104 +
105 +$ ldapmodify -H ldaps:~/~/ds723.trudheim.com -W -D cn=config <<EOF
106 +
107 +dn: olcDatabase={1}bdb,cn=config
108 +add: olcAccess
109 +olcAccess: {0}to attrs=krbPrincipalKey
110 + by anonymous auth
111 + by dn.exact="cn=kdc,ou=kerberos,dc=trudheim,dc=com" write
112 + by dn.exact="cn=kadmin,ou=kerberos,dc=trudheim,dc=com" write
113 + by self write
114 + by * none
115 +-
116 +add: olcAccess
117 +olcAccess: {1}to dn.subtree="cn=krbContainer,ou=kerberos,dc=example,dc=com"
118 + by dn.exact="cn=kdc,ou=kerberos,dc=trudheim,dc=com" write
119 + by dn.exact="cn=kadmin,ou=kerberos,dc=trudheim,dc=com" write
120 + by * none
121 +
122 +EOF
123 +
124 +Enter LDAP Password:
125 +modifying entry "olcDatabase={1}bdb,cn=config"
126 +
127 +$
128 +
129 +
130 +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.
131 +
132 +
133 +===== Create your krb5.conf: =====
134 +
135 +Over to adjusting /etc/krb5.conf so that it will point to the right thing later. It should look something like this:
136 +
137 +
138 +{{{[libdefaults]
139 + default_realm = EXAMPLE.COM
140 + dns_lookup_realm = false
141 + dns_lookup_kdc = false
142 + ticket_lifetime = 24h
143 + forwardable = true
144 + proxiable = true
145 + rdns = false
146 +
147 +[realms]
148 + EXAMPLE.COM = {
149 + kdc = debian.example.com
150 + admin_server = debian.example.com
151 + default_domain = example.com
152 + }
153 + [domain_realm]
154 + .example.com = EXAMPLE.COM
155 + example.com = EXAMPLE.COM}}}
156 +
157 +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.
158 +
159 +Next, we need to write up /etc/krb5kdc/kdc.conf. Something like this should work
160 +
161 +
162 +[libdefaults]
163 +
164 +[realms]
165 + TRUDHEIM.COM = {
166 + database_module = openldap_ldapconf
167 + max_life = 7d
168 + max_renewable_life = 6d
169 + }
170 +
171 +[dbdefaults]
172 + ldap_kerberos_container_dn = cn=krbContainer,ou=kerberos,dc=trudheim,dc=com
173 +
174 +[dbmodules]
175 + openldap_ldapconf = {
176 + db_library = kldap
177 + disable_last_success = false
178 + disable_lockout = false
179 + ldap_conns_per_server = 5
180 + ldap_servers = ldaps:~/~/ds723.trudheim.com
181 + ldap_kdc_dn = "cn=kdc,ou=kerberos,dc=trudheim,dc=com"
182 + ldap_kadmind_dn = "cn=kadmin,ou=kerberos,dc=trudheim,dc=com"
183 + ldap_service_password_file = /etc/krb5kdc/service.keyfile
184 + }
185 +
186 +
187 +Then you need to create ##/etc/krb5kdc/kadm5.acl and put in it##
188 +
189 +
190 +##*/admin@EXAMPLE.COM *##
191 +
192 +
193 +so that administrator principals can run kadmin. Now we are ready to create the domain. And that we do with
194 +
195 +
196 +#
197 +
198 +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
199 +Password for "uid=root,cn=users,dc=trudheim,dc=com":
200 +Initializing database for realm 'TRUDHEIM.COM'
201 +You will be prompted for the database Master Password.
202 +It is important that you NOT FORGET this password.
203 +Enter KDC database master key:
204 +Re-enter KDC database master key to verify:
205 +
206 +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
207 +Password for "uid=root,cn=users,dc=trudheim,dc=com":
208 +Password for "cn=kdc,ou=kerberos,dc=trudheim,dc=com":
209 +Re-enter password for "cn=kdc,ou=kerberos,dc=trudheim,dc=com":
210 +
211 +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
212 +Password for "uid=root,cn=users,dc=trudheim,dc=com":
213 +Password for "cn=kadmin,ou=kerberos,dc=trudheim,dc=com":
214 +Re-enter password for "cn=kadmin,ou=kerberos,dc=trudheim,dc=com":
215 +
216 +