LDAP

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Project: LDAP
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Members Stuiterveer
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Description LDAP server for central logins using passwords or keypairs
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LDAP installation so we can use space-wide logins instead of seperate logins for every computer/server.


Server

Server IP is 192.168.1.177. The server uses an installation of OpenLDAP with phpLDAPAdmin. The following settings were applied:

OpenLDAP

  • DNS domain name: ackspace.nl ("dc=ackspace,dc=nl")
  • Database backend: HDB

phpLDAPAdmin

/etc/phpldapadmin/config.php

The following values were set/changed in /etc/phpldapadmin/config.php:

$servers->setValue('server','host','0.0.0.0');
$servers->setValue('server','base',array('dc=ackspace,dc=nl'));
$config->custom->appearance['hide_template_warning'] = true;
$servers->setValue('login','bind_id','cn=admin,dc=ackspace,dc=nl');

SSH keys

A field to insert SSH keys for users is not present in OpenLDAP/phpLDAPAdmin by default, for this I created a file called openssh-lpk.ldif with the following content:

dn: cn=openssh-lpk,cn=schema,cn=config
objectClass: olcSchemaConfig
cn: openssh-lpk
olcAttributeTypes: ( 1.3.6.1.4.1.24552.500.1.1.1.13 NAME 'sshPublicKey'
  DESC 'MANDATORY: OpenSSH Public key'
  EQUALITY octetStringMatch
  SYNTAX 1.3.6.1.4.1.1466.115.121.1.40 )
olcObjectClasses: ( 1.3.6.1.4.1.24552.500.1.1.2.0 NAME 'ldapPublicKey' SUP top AUXILIARY
  DESC 'MANDATORY: OpenSSH LPK objectclass'
  MAY ( sshPublicKey $ uid )
  )

The following command was then used to add support (make sure ldapscripts is installed):

ldapadd -Y EXTERNAL -H ldapi:/// -f openssh-lpk.ldif

/etc/phpldapadmin/templates/creation/posixAccount.xml

Finally the User Account creation template was changed to add an SSH public key input field to the form by default. For this, /etc/phpldapadmin/templates/creation/posixAccount.xml was changed to the following:

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE template SYSTEM "template.dtd">

<template>
<askcontainer>1</askcontainer>
<description>New User Account</description>
<icon>ldap-user.png</icon>
<invalid>0</invalid>
<rdn>cn</rdn>
<title>Generic: User Account</title>
<visible>1</visible>

<objectClasses>
<objectClass id="inetOrgPerson"></objectClass>
<objectClass id="posixAccount"></objectClass>
<objectClass id="ldapPublicKey"></objectClass>
</objectClasses>

<attributes>
<attribute id="givenName">
    <display>First name</display>
    <icon>ldap-uid.png</icon>
    <onchange>=autoFill(cn;%givenName% %sn%)</onchange>
    <onchange>=autoFill(uid;%givenName|0-1/l%%sn/l%)</onchange>
    <order>1</order>
    <page>1</page>
</attribute>
<attribute id="sn">
    <display>Last name</display>
    <onchange>=autoFill(cn;%givenName% %sn%)</onchange>
    <onchange>=autoFill(uid;%givenName|0-1/l%%sn/l%)</onchange>
    <order>2</order>
    <page>1</page>
</attribute>
<attribute id="cn">
    <display>Common Name</display>
    <order>3</order>
    <page>1</page>
</attribute>
<attribute id="uid">
    <display>User ID</display>
    <onchange>=autoFill(homeDirectory;/home/users/%uid%)</onchange>
    <order>4</order>
    <page>1</page>
    <spacer>1</spacer>
</attribute>
<attribute id="homeDirectory">
    <display>Home directory</display>
    <order>8</order>
    <page>1</page>
</attribute>
<attribute id="uidNumber">
    <display>UID Number</display>
    <icon>terminal.png</icon>
    <order>6</order>
    <page>1</page>
    <readonly>1</readonly>
    <value>=php.GetNextNumber(/;uidNumber)</value>
</attribute>
<attribute id="gidNumber">
    <display>GID Number</display>
    <order>7</order>
    <page>1</page>
    <value><![CDATA[=php.PickList(/;(&(objectClass=posixGroup));gidNumber;%cn%;;;;cn)]]></value>
</attribute>
<attribute id="loginShell">
    <display>Login shell</display>
    <order>9</order>
    <page>1</page>
    <type>select</type>
    <value id="/bin/bash">/bin/bash</value>
    <value id="/bin/sh">/bin/sh</value>
    <value id="/bin/csh">/bin/csh</value>
    <value id="/bin/tsh">/bin/tsh</value>
</attribute>
<attribute id="userPassword">
    <display>Password</display>
    <icon>lock.png</icon>
    <order>5</order>
    <page>1</page>
    <post>=php.PasswordEncrypt(%enc%;%userPassword%)</post>
    <spacer>1</spacer>
    <verify>1</verify>
</attribute>
<attribute id="sshPublicKey">
        <display>SSH public key</display>
        <icon>lock.png</icon>
        <order>10</order>
        <page>1</page>
</attribute>
</attributes>

</template>

Sudoers

Sudo roles are not included in LDAP by default. For this we need to create a few files.

/etc/ldap/schema/sudo.schema

First of all, a schema was added called /etc/ldap/schema/sudo.schema. It contains the following:

attributetype ( 1.3.6.1.4.1.15953.9.1.1
    NAME 'sudoUser'
    DESC 'User(s) who may  run sudo'
    EQUALITY caseExactIA5Match
    SUBSTR caseExactIA5SubstringsMatch
    SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )

attributetype ( 1.3.6.1.4.1.15953.9.1.2
    NAME 'sudoHost'
    DESC 'Host(s) who may run sudo'
    EQUALITY caseExactIA5Match
    SUBSTR caseExactIA5SubstringsMatch
    SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )

attributetype ( 1.3.6.1.4.1.15953.9.1.3
    NAME 'sudoCommand'
    DESC 'Command(s) to be executed by sudo'
    EQUALITY caseExactIA5Match
    SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )

attributetype ( 1.3.6.1.4.1.15953.9.1.4
    NAME 'sudoRunAs'
    DESC 'User(s) impersonated by sudo (deprecated)'
    EQUALITY caseExactIA5Match
    SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )

attributetype ( 1.3.6.1.4.1.15953.9.1.5
    NAME 'sudoOption'
    DESC 'Options(s) followed by sudo'
    EQUALITY caseExactIA5Match
    SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )

attributetype ( 1.3.6.1.4.1.15953.9.1.6
    NAME 'sudoRunAsUser'
    DESC 'User(s) impersonated by sudo'
    EQUALITY caseExactIA5Match
    SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )

attributetype ( 1.3.6.1.4.1.15953.9.1.7
    NAME 'sudoRunAsGroup'
    DESC 'Group(s) impersonated by sudo'
    EQUALITY caseExactIA5Match
    SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )

attributetype ( 1.3.6.1.4.1.15953.9.1.8
    NAME 'sudoNotBefore'
    DESC 'Start of time interval for which the entry is valid'
    EQUALITY generalizedTimeMatch
    ORDERING generalizedTimeOrderingMatch
    SYNTAX 1.3.6.1.4.1.1466.115.121.1.24 )

attributetype ( 1.3.6.1.4.1.15953.9.1.9
    NAME 'sudoNotAfter'
    DESC 'End of time interval for which the entry is valid'
    EQUALITY generalizedTimeMatch
    ORDERING generalizedTimeOrderingMatch
    SYNTAX 1.3.6.1.4.1.1466.115.121.1.24 )

attributeTypes ( 1.3.6.1.4.1.15953.9.1.10
    NAME 'sudoOrder'
    DESC 'an integer to order the sudoRole entries'
    EQUALITY integerMatch
    ORDERING integerOrderingMatch
    SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 )

objectclass ( 1.3.6.1.4.1.15953.9.2.1 NAME 'sudoRole' SUP top STRUCTURAL
    DESC 'Sudoer Entries'
    MUST ( cn )
    MAY ( sudoUser $ sudoHost $ sudoCommand $ sudoRunAs $ sudoRunAsUser $ sudoRunAsGroup $ sudoOption $ sudoOrder $ sudoNotBefore $ sudoNotAfter $
            description )
    )

/etc/ldap/slapd.conf

If /etc/ldap/slapd.conf exists, make sure you place the following at the top (where you find other includes as well):

include         /etc/ldap/schema/sudo.schema

Note that slapd.conf is deprecated and should be replaced by the use of slapd-config[1].

Restart service

Restart the slapd service to make sure the schema is loaded.

LDIF file

Last, a file was created called sudo.ldif that contains the following:

dn: cn=sudo,cn=schema,cn=config
objectClass: olcSchemaConfig
cn: sudo
olcAttributeTypes: ( 1.3.6.1.4.1.15953.9.1.1 NAME 'sudoUser' DESC 'User(s) who may  run sudo' EQUALITY caseExactIA5Match SUBSTR caseExactIA5SubstringsMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )
olcAttributeTypes: ( 1.3.6.1.4.1.15953.9.1.2 NAME 'sudoHost' DESC 'Host(s) who may run sudo' EQUALITY caseExactIA5Match SUBSTR caseExactIA5SubstringsMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )
olcAttributeTypes: ( 1.3.6.1.4.1.15953.9.1.3 NAME 'sudoCommand' DESC 'Command(s) to be executed by sudo' EQUALITY caseExactIA5Match SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )
olcAttributeTypes: ( 1.3.6.1.4.1.15953.9.1.4 NAME 'sudoRunAs' DESC 'User(s) impersonated by sudo (deprecated)' EQUALITY caseExactIA5Match SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )
olcAttributeTypes: ( 1.3.6.1.4.1.15953.9.1.5 NAME 'sudoOption' DESC 'Options(s) followed by sudo' EQUALITY caseExactIA5Match SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )
olcAttributeTypes: ( 1.3.6.1.4.1.15953.9.1.6 NAME 'sudoRunAsUser' DESC 'User(s) impersonated by sudo' EQUALITY caseExactIA5Match SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )
olcAttributeTypes: ( 1.3.6.1.4.1.15953.9.1.7 NAME 'sudoRunAsGroup' DESC 'Group(s) impersonated by sudo' EQUALITY caseExactIA5Match SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )
olcObjectClasses: ( 1.3.6.1.4.1.15953.9.2.1 NAME 'sudoRole' SUP top STRUCTURAL DESC 'Sudoer Entries' MUST ( cn ) MAY ( sudoUser $ sudoHost $ sudoCommand $ sudoRunAs $ sudoRunAsUser $ sudoRunAsGroup $ sudoOption $ description ) )

You can import this file to LDAP using:

ldapadd -Y EXTERNAL -H ldapi:/// -f openssh-lpk.ldif

Client

To obtain a user on the LDAP server, contact Stuiterveer.

PAM

To use LDAP to sign in to Linux, install libpam-ldapd. When asked, fill in the details mentioned in LDAP#OpenLDAP.

/etc/nsswitch.conf

Make sure LDAP is enabled for passwd, group and shadow. To verify, check to see if the following is present (edit the existing entries if needed) in /etc/nsswitch.conf:

passwd:         ldap compat
group:          ldap compat
shadow:         ldap compat

This will first check LDAP for entries, otherwise it will check locally. If preferred, you can switch around compat and ldap to first check locally and revert to LDAP on failure.

Home folder creation

If you want to make sure a user folder is created upon login, add the following to the end of /etc/pam.d/common-session:

session required        pam_mkhomedir.so skel=/etc/skel umask=0022

SSH key login

Create a file that has the following content:

#!/bin/bash
ldapsearch -h 192.168.1.177 -b "dc=ackspace,dc=nl" -x '(&(objectClass=posixAccount)(uid='"$1"'))' 'sshPublicKey' | sed -n '/^ /{H;d};/sshPublicKey:/x;$g;s/\n *//g;s/sshPublicKey: //gp'

Make sure the file and all folders above it are owned by root:root and have umask 022.[2]

Then edit sshd_config to include the following:

AuthorizedKeysCommand /path/to/file
AuthorizedKeysCommandUser nobody

Sudoers

In order to make sure you can use LDAP for sudoers, make sure your installation of sudo has support for LDAP. If it doesn't you can try installing sudo-ldap which will replace the existing sudo installation.

/etc/ldap.conf

If /etc/ldap.conf doesn't exist yet, create it. Make sure it has at least the following lines in it:

URI     ldap://192.168.1.177
sudoers_base    ou=sudoers,dc=ackspace,dc=nl

/etc/nsswitch.conf

Make sure /etc/nssswitch.conf has the following line in it:

sudoers:        ldap files

Be aware that any matches found in LDAP will be overwritten if they are found in the regular files.

Restart services

When you restart the nscd and ssh services you will be up and running. Sign in to the computer/VM with your LDAP account to verify that it works.

References

  1. https://www.openldap.org/doc/admin24/slapdconfig.html
  2. https://stackoverflow.com/a/27638306