&author.jelmer; &author.jerry; &author.jeremy; &author.jht; Olivier (lem)Lemaire IDEALX

olem@IDEALX.org

February 2003 Old windows clients send plain text passwords over the wire. Samba can check these passwords by crypting them and comparing them to the hash stored in the unix user database. Newer windows clients send encrypted passwords (so-called Lanman and NT hashes) over the wire, instead of plain text passwords. The newest clients will only send encrypted passwords and refuse to send plain text passwords, unless their registry is tweaked. These passwords can't be converted to unix style encrypted passwords. Because of that you can't use the standard unix user database, and you have to store the Lanman and NT hashes somewhere else. Next to a differently encrypted passwords, windows also stores certain data for each user that is not stored in a unix user database, e.g. workstations the user may logon from, the location where his/her profile is stored, etc. Samba retrieves and stores this information using a "passdb backend". Commonly available backends are LDAP, plain text file, MySQL and nisplus. For more information, see the documentation about the passdb backend = parameter. The unix and SMB password encryption techniques seem similar on the surface. This similarity is, however, only skin deep. The unix scheme typically sends clear text passwords over the network when logging in. This is bad. The SMB encryption scheme never sends the cleartext password over the network but it does store the 16 byte hashed values on disk. This is also bad. Why? Because the 16 byte hashed values are a "password equivalent". You cannot derive the user's password from them, but they could potentially be used in a modified client to gain access to a server. This would require considerable technical knowledge on behalf of the attacker but is perfectly possible. You should thus treat the data stored in whatever passdb backend you use (smbpasswd file, ldap, mysql) as though it contained the cleartext passwords of all your users. Its contents must be kept secret, and the file should be protected accordingly. Ideally we would like a password scheme which neither requires plain text passwords on the net or on disk. Unfortunately this is not available as Samba is stuck with being compatible with other SMB systems (WinNT, WfWg, Win95 etc). Note that Windows NT 4.0 Service pack 3 changed the default for permissible authentication so that plaintext passwords are never sent over the wire. The solution to this is either to switch to encrypted passwords with Samba or edit the Windows NT registry to re-enable plaintext passwords. See the document WinNT.txt for details on how to do this. Other Microsoft operating systems which also exhibit this behavior includes These versions of MS Windows do not support full domain security protocols, although they may log onto a domain environment. Of these Only MS Windows XP Home does NOT support domain logons. MS DOS Network client 3.0 with the basic network redirector installed Windows 95 with the network redirector update installed Windows 98 [se] Windows Me Windows XP Home The following versions of MS Windows fully support domain security protocols. Windows NT 3.5x Windows NT 4.0 Windows 2000 Professional Windows 200x Server/Advanced Server Windows XP Professional All current release of Microsoft SMB/CIFS clients support authentication via the SMB Challenge/Response mechanism described here. Enabling clear text authentication does not disable the ability of the client to participate in encrypted authentication. MS Windows clients will cache the encrypted password alone. Even when plain text passwords are re-enabled, through the appropriate registry change, the plain text password is NEVER cached. This means that in the event that a network connections should become disconnected (broken) only the cached (encrypted) password will be sent to the resource server to affect a auto-reconnect. If the resource server does not support encrypted passwords the auto-reconnect will fail. USE OF ENCRYPTED PASSWORDS IS STRONGLY ADVISED. Plain text passwords are not passed across the network. Someone using a network sniffer cannot just record passwords going to the SMB server. WinNT doesn't like talking to a server that does not support encrypted passwords. It will refuse to browse the server if the server is also in user level security mode. It will insist on prompting the user for the password on each connection, which is very annoying. The only things you can do to stop this is to use SMB encryption. Encrypted password support allows automatic share (resource) reconnects. Plain text passwords are not kept on disk, and are NOT cached in memory. Uses same password file as other unix services such as login and ftp Use of other services (such as telnet and ftp) which send plain text passwords over the net, so sending them for SMB isn't such a big deal. The smbpasswd utility is a utility similar to the passwd or yppasswd programs. It maintains the two 32 byte password fields in the passdb backend. smbpasswd works in a client-server mode where it contacts the local smbd to change the user's password on its behalf. This has enormous benefits - as follows. smbpasswd has the capability to change passwords on Windows NT servers (this only works when the request is sent to the NT Primary Domain Controller if you are changing an NT Domain user's password). To run smbpasswd as a normal user just type : $ smbpasswd Old SMB password: <type old value here - or hit return if there was no old password> New SMB Password: <type new value> Repeat New SMB Password: <re-type new value If the old value does not match the current value stored for that user, or the two new values do not match each other, then the password will not be changed. If invoked by an ordinary user it will only allow the user to change his or her own Samba password. If run by the root user smbpasswd may take an optional argument, specifying the user name whose SMB password you wish to change. Note that when run as root smbpasswd does not prompt for or check the old password value, thus allowing root to set passwords for users who have forgotten their passwords. smbpasswd is designed to work in the same way and be familiar to UNIX users who use the passwd or yppasswd commands. For more details on using smbpasswd refer to the man page which will always be the definitive reference. Older versions of samba retrieved user information from the unix user database and eventually some other fields from the file /etc/samba/smbpasswd or /etc/smbpasswd. When password encryption is disabled, no data is stored at all. Samba can also store the user data in a "TDB" (Trivial Database). Using this backend doesn't require any additional configuration. This backend is recommended for new installations that don not require LDAP. 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. 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 large 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). There are a few points to stress about that the 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/). More information about the configuration of these packages may be found at "LDAP, System Administration; Gerald Carter, O'Reilly; Chapter 6: Replacing NIS". The LDAP samdb code in 2.2.3 (and later) 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. Samba 3.0 includes the necessary schema file for OpenLDAP 2.0 in examples/LDAP/samba.schema. The sambaAccount objectclass is given here: objectclass ( 1.3.1.5.1.4.1.7165.2.2.2 NAME 'sambaAccount' SUP top AUXILIARY 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 meant 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. 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 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 # (both fetched via ldapsearch): index primaryGroupID eq index displayName pres,eq The following parameters are available in smb.conf only with --with-ldapsam was included when compiling Samba. passdb backend [ldapsam|ldapsam_nua]:url ldap ssl ldap admin dn ldap suffix ldap filter ldap port ldap machine suffix ldap user suffix ldap delete dn 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 # change, this password will need to be reset. ldap admin dn = "cn=Samba Manager,ou=people,dc=samba,dc=org" # Define the SSL option when connecting to the directory # ('off', 'start tls', or 'on' (default)) ldap ssl = start tls passdb backend ldapsam:ldap://ahab.samba.org # smbpasswd -x delete the entire dn-entry ldap delete dn = no # the machine and user suffix added to the base suffix # wrote WITHOUT quotes. NULL siffixes by default ldap user suffix = ou=People ldap machine suffix = ou=Systems # 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))" As users accounts are managed thru the sambaAccount objectclass, you should modify your 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 store 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 3.0, the group management system is based on posix groups. This means that Samba makes usage of the posixGroup objectclass. For now, there is no NT-like group system management (global and local groups). 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 User Database 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 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), I(Domain trust account), H(Home dir required), S(Server trust account), N(Password not required) 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 if the value is something other than the default (e.g. \\MOBY\becky). 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 You either can set up your own table and specify the field names to pdb_mysql (see below for the column names) or use the default table. The file examples/pdb/mysql/mysql.dump contains the correct queries to create the required tables. Use the command : mysql -uusername -hhostname -ppassword databasename > /path/to/samba/examples/pdb/mysql/mysql.dump This plugin lacks some good documentation, but here is some short info: Add a the following to the passdb backend variable in your smb.conf: passdb backend = [other-plugins] mysql:identifier [other-plugins] The identifier can be any string you like, as long as it doesn't collide with the identifiers of other plugins or other instances of pdb_mysql. If you specify multiple pdb_mysql.so entries in 'passdb backend', you also need to use different identifiers! Additional options can be given thru the smb.conf file in the [global] section. identifier:mysql host - host name, defaults to 'localhost' identifier:mysql password identifier:mysql user - defaults to 'samba' identifier:mysql database - defaults to 'samba' identifier:mysql port - defaults to 3306 identifier:table - Name of the table containing users Since the password for the mysql user is stored in the smb.conf file, you should make the the smb.conf file readable only to the user that runs samba. This is considered a security bug and will be fixed soon. Names of the columns in this table(I've added column types those columns should have first): identifier:logon time column - int(9) identifier:logoff time column - int(9) identifier:kickoff time column - int(9) identifier:pass last set time column - int(9) identifier:pass can change time column - int(9) identifier:pass must change time column - int(9) identifier:username column - varchar(255) - unix username identifier:domain column - varchar(255) - NT domain user is part of identifier:nt username column - varchar(255) - NT username identifier:fullname column - varchar(255) - Full name of user identifier:home dir column - varchar(255) - Unix homedir path identifier:dir drive column - varchar(2) - Directory drive path (eg: 'H:') identifier:logon script column - varchar(255) - Batch file to run on client side when logging on identifier:profile path column - varchar(255) - Path of profile identifier:acct desc column - varchar(255) - Some ASCII NT user data identifier:workstations column - varchar(255) - Workstations user can logon to (or NULL for all) identifier:unknown string column - varchar(255) - unknown string identifier:munged dial column - varchar(255) - ? identifier:user sid column - varchar(255) - NT user SID identifier:group sid column - varchar(255) - NT group ID identifier:lanman pass column - varchar(255) - encrypted lanman password identifier:nt pass column - varchar(255) - encrypted nt passwd identifier:plain pass column - varchar(255) - plaintext password identifier:acct control column - int(9) - nt user data identifier:unknown 3 column - int(9) - unknown identifier:logon divs column - int(9) - ? identifier:hours len column - int(9) - ? identifier:unknown 5 column - int(9) - unknown identifier:unknown 6 column - int(9) - unknown Eventually, you can put a colon (:) after the name of each column, which should specify the column to update when updating the table. You can also specify nothing behind the colon - then the data from the field will not be updated. I strongly discourage the use of plaintext passwords, however, you can use them: If you would like to use plaintext passwords, set 'identifier:lanman pass column' and 'identifier:nt pass column' to 'NULL' (without the quotes) and 'identifier:plain pass column' to the name of the column containing the plaintext passwords. If you use encrypted passwords, set the 'identifier:plain pass column' to 'NULL' (without the quotes). This is the default. It is possible to have not all data in the database and making some 'constant'. For example, you can set 'identifier:fullname column' to : CONCAT(First_name,' ',Sur_name) Or, set 'identifier:workstations column' to : NULL See the MySQL documentation for more language constructs. This module requires libxml2 to be installed. The usage of pdb_xml is pretty straightforward. To export data, use: pdbedit -e xml:filename (where filename is the name of the file to put the data in) To import data, use: pdbedit -i xml:filename -e current-pdb Where filename is the name to read the data from and current-pdb to put it in.