Storing Samba's User/Machine Account information in an LDAP Directory

Purpose

This document describes how to use an LDAP directory for storing Samba user -account information traditionally stored in the smbpasswd(5) file. It is -assumed that the reader already has a basic understanding of LDAP concepts -and has a working directory server already installed. For more information -on LDAP architectures and Directories, please refer to the following sites.

OpenLDAP - http://www.openldap.org/
iPlanet Directory Server - http://iplanet.netscape.com/directory

Note that O'Reilly Publishing is working on -a guide to LDAP for System Administrators which has a planned release date of -early summer, 2002.

Two additional Samba resources which may prove to be helpful are

The Samba-PDC-LDAP-HOWTO - maintained by Ignacio Coupeau.
The NT migration scripts from IDEALX that are - geared to manage users and group in such a Samba-LDAP Domain Controller configuration. -

Introduction

Traditionally, when configuring "encrypt -passwords = yes" in Samba's smb.conf file, user account -information such as username, LM/NT password hashes, password change times, and account -flags have been stored in the smbpasswd(5) file. There are several -disadvantages to this approach for sites with very large numbers of users (counted -in the thousands).

The first is that all lookups must be performed sequentially. Given that -there are approximately two lookups per domain logon (one for a normal -session connection such as when mapping a network drive or printer), this -is a performance bottleneck for lareg sites. What is needed is an indexed approach -such as is used in databases.
The second problem is that administrators who desired to replicate a -smbpasswd file to more than one Samba server were left to use external -tools such as rsync(1) and ssh(1) -and wrote custom, in-house scripts.
And finally, the amount of information which is stored in an -smbpasswd entry leaves no room for additional attributes such as -a home directory, password expiration time, or even a Relative -Identified (RID).

As a result of these defeciencies, a more robust means of storing user attributes -used by smbd was developed. The API which defines access to user accounts -is commonly referred to as the samdb interface (previously this was called the passdb -API, and is still so named in the CVS trees). In Samba 2.2.3, enabling support -for a samdb backend (e.g. --with-ldapsam or ---with-tdbsam) requires compile time support.

When compiling Samba to include the --with-ldapsam autoconf -option, smbd (and associated tools) will store and lookup user accounts in -an LDAP directory. In reality, this is very easy to understand. If you are -comfortable with using an smbpasswd file, simply replace "smbpasswd" with -"LDAP directory" in all the documentation.

There are a few points to stress about what the --with-ldapsam -does not provide. The LDAP support referred to in the this documentation does not -include:

A means of retrieving user account information from - an Windows 2000 Active Directory server.
A means of replacing /etc/passwd.

The second item can be accomplished by using LDAP NSS and PAM modules. LGPL -versions of these libraries can be obtained from PADL Software -(http://www.padl.com/). However, -the details of configuring these packages are beyond the scope of this document.

Supported LDAP Servers

The LDAP samdb code in 2.2.3 has been developed and tested using the OpenLDAP -2.0 server and client libraries. The same code should be able to work with -Netscape's Directory Server and client SDK. However, due to lack of testing -so far, there are bound to be compile errors and bugs. These should not be -hard to fix. If you are so inclined, please be sure to forward all patches to -samba-patches@samba.org and -jerry@samba.org.

Schema and Relationship to the RFC 2307 posixAccount

Samba 2.2.3 includes the necessary schema file for OpenLDAP 2.0 in -examples/LDAP/samba.schema. (Note that this schema -file has been modified since the experimental support initially included -in 2.2.2). The sambaAccount objectclass is given here:

objectclass ( 1.3.1.5.1.4.1.7165.2.2.2 NAME 'sambaAccount' SUP top STRUCTURAL
-     DESC 'Samba Account'
-     MUST ( uid $ rid )
-     MAY  ( cn $ lmPassword $ ntPassword $ pwdLastSet $ logonTime $
-            logoffTime $ kickoffTime $ pwdCanChange $ pwdMustChange $ acctFlags $
-            displayName $ smbHome $ homeDrive $ scriptPath $ profilePath $
-            description $ userWorkstations $ primaryGroupID $ domain ))

The samba.schema file has been formatted for OpenLDAP 2.0. The OID's are -owned by the Samba Team and as such is legal to be openly published. -If you translate the schema to be used with Netscape DS, please -submit the modified schema file as a patch to jerry@samba.org

Just as the smbpasswd file is mean to store information which supplements a -user's /etc/passwd entry, so is the sambaAccount object -meant to supplement the UNIX user account information. A sambaAccount is a -STRUCTURAL objectclass so it can be stored individually -in the directory. However, there are several fields (e.g. uid) which overlap -with the posixAccount objectclass outlined in RFC2307. This is by design.

In order to store all user account information (UNIX and Samba) in the directory, -it is necessary to use the sambaAccount and posixAccount objectclasses in -combination. However, smbd will still obtain the user's UNIX account -information via the standard C library calls (e.g. getpwnam(), et. al.). -This means that the Samba server must also have the LDAP NSS library installed -and functioning correctly. This division of information makes it possible to -store all Samba account information in LDAP, but still maintain UNIX account -information in NIS while the network is transitioning to a full LDAP infrastructure.

Configuring Samba with LDAP

OpenLDAP configuration

To include support for the sambaAccount object in an OpenLDAP directory -server, first copy the samba.schema file to slapd's configuration directory.

root# cp samba.schema /etc/openldap/schema/

Next, include the samba.schema file in slapd.conf. -The sambaAccount object contains two attributes which depend upon other schema -files. The 'uid' attribute is defined in cosine.schema and -the 'displayName' attribute is defined in the inetorgperson.schema -file. Both of these must be included before the samba.schema file.

## /etc/openldap/slapd.conf
-
-## schema files (core.schema is required by default)
-include	           /etc/openldap/schema/core.schema
-
-## needed for sambaAccount
-include            /etc/openldap/schema/cosine.schema
-include            /etc/openldap/schema/inetorgperson.schema
-include            /etc/openldap/schema/samba.schema
-
-## uncomment this line if you want to support the RFC2307 (NIS) schema
-## include         /etc/openldap/schema/nis.schema
-
-....

It is recommended that you maintain some indices on some of the most usefull attributes, -like in the following example, to speed up searches made on sambaAccount objectclasses -(and possibly posixAccount and posixGroup as well).

# Indices to maintain
-## required by OpenLDAP 2.0
-index objectclass   eq
-
-## support pb_getsampwnam()
-index uid           pres,eq
-## support pdb_getsambapwrid()
-index rid           eq
-
-## uncomment these if you are storing posixAccount and
-## posixGroup entries in the directory as well
-##index uidNumber     eq
-##index gidNumber     eq
-##index cn            eq
-##index memberUid     eq

Configuring Samba

The following parameters are available in smb.conf only with --with-ldapsam -was included with compiling Samba.

ldap ssl
ldap server
ldap admin dn
ldap suffix
ldap filter
ldap port

These are described in the smb.conf(5) man -page and so will not be repeated here. However, a sample smb.conf file for -use with an LDAP directory could appear as

## /usr/local/samba/lib/smb.conf
-[global]
-     security = user
-     encrypt passwords = yes
-
-     netbios name = TASHTEGO
-     workgroup = NARNIA
-
-     # ldap related parameters
-
-     # define the DN to use when binding to the directory servers
-     # The password for this DN is not stored in smb.conf.  Rather it
-     # must be set by using 'smbpasswd -w secretpw' to store the
-     # passphrase in the secrets.tdb file.  If the "ldap admin dn" values
-     # changes, this password will need to be reset.
-     ldap admin dn = "cn=Samba Manager,ou=people,dc=samba,dc=org"
-
-     #  specify the LDAP server's hostname (defaults to locahost)
-     ldap server = ahab.samba.org
-
-     # Define the SSL option when connecting to the directory
-     # ('off', 'start tls', or 'on' (default))
-     ldap ssl = start tls
-
-     # define the port to use in the LDAP session (defaults to 636 when
-     # "ldap ssl = on")
-     ldap port = 389
-
-     # specify the base DN to use when searching the directory
-     ldap suffix = "ou=people,dc=samba,dc=org"
-
-     # generally the default ldap search filter is ok
-     # ldap filter = "(&(uid=%u)(objectclass=sambaAccount))"

Accounts and Groups management

As users accounts are managed thru the sambaAccount objectclass, you should -modify you existing administration tools to deal with sambaAccount attributes.

Machines accounts are managed with the sambaAccount objectclass, just -like users accounts. However, it's up to you to stored thoses accounts -in a different tree of you LDAP namespace: you should use -"ou=Groups,dc=plainjoe,dc=org" to store groups and -"ou=People,dc=plainjoe,dc=org" to store users. Just configure your -NSS and PAM accordingly (usually, in the /etc/ldap.conf configuration -file).

In Samba release 2.2.3, the group management system is based on posix -groups. This meand that Samba make usage of the posixGroup objectclass. -For now, there is no NT-like group system management (global and local -groups).

Security and sambaAccount

There are two important points to remember when discussing the security -of sambaAccount entries in the directory.

Never retrieve the lmPassword or - ntPassword attribute values over an unencrypted LDAP session.
Never allow non-admin users to - view the lmPassword or ntPassword attribute values.

These password hashes are clear text equivalents and can be used to impersonate -the user without deriving the original clear text strings. For more information -on the details of LM/NT password hashes, refer to the ENCRYPTION chapter of the Samba-HOWTO-Collection.

To remedy the first security issue, the "ldap ssl" smb.conf parameter defaults -to require an encrypted session (ldap ssl = on) using -the default port of 636 -when contacting the directory server. When using an OpenLDAP 2.0 server, it -is possible to use the use the StartTLS LDAP extended operation in the place of -LDAPS. In either case, you are strongly discouraged to disable this security -(ldap ssl = off).

Note that the LDAPS protocol is deprecated in favor of the LDAPv3 StartTLS -extended operation. However, the OpenLDAP library still provides support for -the older method of securing communication between clients and servers.

The second security precaution is to prevent non-administrative users from -harvesting password hashes from the directory. This can be done using the -following ACL in slapd.conf:

## allow the "ldap admin dn" access, but deny everyone else
-access to attrs=lmPassword,ntPassword
-     by dn="cn=Samba Admin,ou=people,dc=plainjoe,dc=org" write
-     by * none

LDAP specials attributes for sambaAccounts

The sambaAccount objectclass is composed of the following attributes:

lmPassword: the LANMAN password 16-byte hash stored as a character - representation of a hexidecimal string.
ntPassword: the NT password hash 16-byte stored as a character - representation of a hexidecimal string.
pwdLastSet: The integer time in seconds since 1970 when the - lmPassword and ntPassword attributes were last set. -
acctFlags: string of 11 characters surrounded by square brackets [] - representing account flags such as U (user), W(workstation), X(no password expiration), and - D(disabled).
logonTime: Integer value currently unused
logoffTime: Integer value currently unused
kickoffTime: Integer value currently unused
pwdCanChange: Integer value currently unused
pwdMustChange: Integer value currently unused
homeDrive: specifies the drive letter to which to map the - UNC path specified by homeDirectory. The drive letter must be specified in the form "X:" - where X is the letter of the drive to map. Refer to the "logon drive" parameter in the - smb.conf(5) man page for more information.
scriptPath: The scriptPath property specifies the path of - the user's logon script, .CMD, .EXE, or .BAT file. The string can be null. The path - is relative to the netlogon share. Refer to the "logon script" parameter in the - smb.conf(5) man page for more information.
profilePath: specifies a path to the user's profile. - This value can be a null string, a local absolute path, or a UNC path. Refer to the - "logon path" parameter in the smb.conf(5) man page for more information.
smbHome: The homeDirectory property specifies the path of - the home directory for the user. The string can be null. If homeDrive is set and specifies - a drive letter, homeDirectory should be a UNC path. The path must be a network - UNC path of the form \\server\share\directory. This value can be a null string. - Refer to the "logon home" parameter in the smb.conf(5) man page for more information. -
userWorkstation: character string value currently unused. -
rid: the integer representation of the user's relative identifier - (RID).
primaryGroupID: the relative identifier (RID) of the primary group - of the user.

The majority of these parameters are only used when Samba is acting as a PDC of -a domain (refer to the Samba-PDC-HOWTO for details on -how to configure Samba as a Primary Domain Controller). The following four attributes -are only stored with the sambaAccount entry if the values are non-default values:

smbHome
scriptPath
logonPath
homeDrive

These attributes are only stored with the sambaAccount entry if -the values are non-default values. For example, assume TASHTEGO has now been -configured as a PDC and that logon home = \\%L\%u was defined in -its smb.conf file. When a user named "becky" logons to the domain, -the logon home string is expanded to \\TASHTEGO\becky. -If the smbHome attribute exists in the entry "uid=becky,ou=people,dc=samba,dc=org", -this value is used. However, if this attribute does not exist, then the value -of the logon home parameter is used in its place. Samba -will only write the attribute value to the directory entry is the value is -something other than the default (e.g. \\MOBY\becky).

Example LDIF Entries for a sambaAccount

The following is a working LDIF with the inclusion of the posixAccount objectclass:

dn: uid=guest2, ou=people,dc=plainjoe,dc=org
-ntPassword: 878D8014606CDA29677A44EFA1353FC7
-pwdMustChange: 2147483647
-primaryGroupID: 1201
-lmPassword: 552902031BEDE9EFAAD3B435B51404EE
-pwdLastSet: 1010179124
-logonTime: 0
-objectClass: sambaAccount
-uid: guest2
-kickoffTime: 2147483647
-acctFlags: [UX         ]
-logoffTime: 2147483647
-rid: 19006
-pwdCanChange: 0

The following is an LDIF entry for using both the sambaAccount and -posixAccount objectclasses:

dn: uid=gcarter, ou=people,dc=plainjoe,dc=org
-logonTime: 0
-displayName: Gerald Carter
-lmPassword: 552902031BEDE9EFAAD3B435B51404EE
-primaryGroupID: 1201
-objectClass: posixAccount
-objectClass: sambaAccount
-acctFlags: [UX         ]
-userPassword: {crypt}BpM2ej8Rkzogo
-uid: gcarter
-uidNumber: 9000
-cn: Gerald Carter
-loginShell: /bin/bash
-logoffTime: 2147483647
-gidNumber: 100
-kickoffTime: 2147483647
-pwdLastSet: 1010179230
-rid: 19000
-homeDirectory: /home/tashtego/gcarter
-pwdCanChange: 0
-pwdMustChange: 2147483647
-ntPassword: 878D8014606CDA29677A44EFA1353FC7

Comments

Please mail all comments regarding this HOWTO to jerry@samba.org. This documents was -last updated to reflect the Samba 2.2.3 release.