Wiki source code of KerberosAndLDAP
Version 35.1 by Sirius Rayner-Karlsson on 2024/05/09 09:59
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30.1 | 1 | {{box cssClass="floatinginfobox" title="**Contents**"}} |
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22.1 | 2 | {{toc/}} |
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30.1 | 3 | {{/box}} |
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22.1 | 4 | |
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1.1 | 5 | = Debian = |
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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. |
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23.1 | 8 | |
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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. |
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14.1 | 10 | |
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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. |
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2.1 | 12 | |
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26.1 | 13 | **The guide is for illustration. Expectation is that you do not follow it verbatim but adapt it to your needs.** |
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20.1 | 14 | |
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23.1 | 15 | |
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34.1 | 16 | === Install packages === |
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26.1 | 17 | |
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24.1 | 18 | (% class="wikigeneratedid" %) |
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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. |
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24.1 | 20 | |
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21.1 | 21 | (% style="color:#400" %) |
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13.1 | 22 | ##{{{$ sudo apt install krb5-kdc-ldap krb5-admin-server schema2ldif}}}## |
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3.1 | 23 | |
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13.1 | 24 | |
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35.1 | 25 | === Load kerberos LDAP schema === |
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3.1 | 26 | |
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35.1 | 27 | Now you need to load the kerberos schema into the LDAP server on the Synology. Use the ##cn=config## DN. |
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26.1 | 28 | |
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21.1 | 29 | (% style="color:#400" %) |
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35.1 | 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 | }}}## | ||
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3.1 | 36 | |
| 37 | |||
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34.1 | 38 | === Create Index on krbPrincipalName === |
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14.1 | 39 | |
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35.1 | 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: |
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23.1 | 41 | |
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21.1 | 42 | (% style="color:#400" %) |
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35.1 | 43 | ##{{{ |
| 44 | dn: olcDatabase={1}bdb,cn=config | ||
| 45 | add: olcDbIndex | ||
| 46 | olcDbIndex: krbPrincipalName eq,pres,sub | ||
| 47 | }}}## | ||
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3.1 | 48 | |
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35.1 | 49 | and apply it with |
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3.1 | 50 | |
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35.1 | 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 | }}}## | ||
| 58 | |||
| 59 | |||
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34.1 | 60 | === Create principals kadmin and kdc === |
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23.1 | 61 | |
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35.1 | 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: | ||
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4.1 | 64 | |
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21.1 | 65 | (% style="color:#400" %) |
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35.1 | 66 | ##{{{ |
| 67 | dn: ou=kerberos,dc=example,dc=com | ||
| 68 | objectClass: organizationalUnit | ||
| 69 | objectClass: top | ||
| 70 | ou: kerberos | ||
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27.1 | 71 | |
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35.1 | 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 | ||
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4.1 | 83 | |
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35.1 | 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 | }}}## | ||
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16.1 | 96 | |
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35.1 | 97 | Apply it with |
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17.1 | 98 | |
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27.1 | 99 | (% style="color:#400" %) |
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35.1 | 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: | ||
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19.1 | 103 | |
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35.1 | 104 | adding new entry "ou=kerberos,dc=example,dc=com" |
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27.1 | 105 | |
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35.1 | 106 | adding new entry "cn=kdc,ou=kerberos,dc=example,dc=com" |
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27.2 | 107 | |
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35.1 | 108 | adding new entry "cn=kadmin,ou=kerberos,dc=example,dc=com" |
| 109 | }}}## | ||
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27.1 | 110 | |
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27.2 | 111 | |
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35.1 | 112 | |
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34.1 | 113 | === Grant kdc and kadmin permissions === |
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27.2 | 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 | |||
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29.1 | 144 | |
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34.1 | 145 | === Create krb5.conf === |
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29.1 | 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 | |||
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33.1 | 171 | |
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34.1 | 172 | === Create kdc.conf === |
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33.1 | 173 | |
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29.1 | 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 | |||
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34.1 | 202 | === Create kadm5.acl === |
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33.1 | 203 | |
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29.1 | 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 | |||
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34.1 | 212 | === Create the kerberos domain === |
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33.1 | 213 | |
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29.1 | 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 | |||
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33.1 | 234 | |
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34.1 | 235 | === Create the first regular principals === |
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33.1 | 236 | |
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34.1 | 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 | |||
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33.1 | 281 |