<html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Chapter 25. PAM-Based Distributed Authentication</title><link rel="stylesheet" href="samba.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.61.2"><link rel="home" href="index.html" title="Samba HOWTO Collection"><link rel="up" href="optional.html" title="Part III. Advanced Configuration"><link rel="previous" href="ProfileMgmt.html" title="Chapter 24. Desktop Profile Management"><link rel="next" href="integrate-ms-networks.html" title="Chapter 26. Integrating MS Windows Networks with Samba"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 25. PAM-Based Distributed Authentication</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ProfileMgmt.html">Prev</a> </td><th width="60%" align="center">Part III. Advanced Configuration</th><td width="20%" align="right"> <a accesskey="n" href="integrate-ms-networks.html">Next</a></td></tr></table><hr></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="pam"></a>Chapter 25. PAM-Based Distributed Authentication</h2></div><div><div class="author"><h3 class="author"><span class="firstname">John</span> <span class="othername">H.</span> <span class="surname">Terpstra</span></h3><div class="affiliation"><span class="orgname">Samba Team<br></span><div class="address"><p><tt class="email"><<a href="mailto:jht@samba.org">jht@samba.org</a>></tt></p></div></div></div></div><div><div class="author"><h3 class="author"><span class="firstname">Stephen</span> <span class="surname">Langasek</span></h3><div class="affiliation"><div class="address"><p><tt class="email"><<a href="mailto:vorlon@netexpress.net">vorlon@netexpress.net</a>></tt></p></div></div></div></div><div><p class="pubdate">May 31, 2003</p></div></div><div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><a href="pam.html#id2962814">Features and Benefits</a></dt><dt><a href="pam.html#id2963140">Technical Discussion</a></dt><dd><dl><dt><a href="pam.html#id2963171">PAM Configuration Syntax</a></dt><dt><a href="pam.html#id2964188">Example System Configurations</a></dt><dt><a href="pam.html#id2964555">smb.conf PAM Configuration</a></dt><dt><a href="pam.html#id2964629">Remote CIFS Authentication Using winbindd.so</a></dt><dt><a href="pam.html#id2964747">Password Synchronization Using pam_smbpass.so</a></dt></dl></dd><dt><a href="pam.html#id2965218">Common Errors</a></dt><dd><dl><dt><a href="pam.html#id2965234">pam_winbind Problem</a></dt><dt><a href="pam.html#id2965349">Winbind Is Not Resolving Users and Groups</a></dt></dl></dd></dl></div><p> This chapter should help you to deploy Winbind-based authentication on any PAM-enabled UNIX/Linux system. Winbind can be used to enable User-Level application access authentication from any MS Windows NT Domain, MS Windows 200x Active Directory-based domain, or any Samba-based domain environment. It will also help you to configure PAM-based local host access controls that are appropriate to your Samba configuration. </p><p> In addition to knowing how to configure Winbind into PAM, you will learn generic PAM management possibilities and in particular how to deploy tools like <tt class="filename">pam_smbpass.so</tt> to your advantage. </p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p> The use of Winbind requires more than PAM configuration alone. Please refer to <a href="winbind.html" title="Chapter 21. Winbind: Use of Domain Accounts">Winbind: Use of Domain Accounts</a>, for further information regarding Winbind. </p></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2962814"></a>Features and Benefits</h2></div></div><div></div></div><p> A number of UNIX systems (e.g., Sun Solaris), as well as the xxxxBSD family and Linux, now utilize the Pluggable Authentication Modules (PAM) facility to provide all authentication, authorization and resource control services. Prior to the introduction of PAM, a decision to use an alternative to the system password database (<tt class="filename">/etc/passwd</tt>) would require the provision of alternatives for all programs that provide security services. Such a choice would involve provision of alternatives to programs such as: <b class="command">login</b>, <b class="command">passwd</b>, <b class="command">chown</b>, and so on. </p><p> PAM provides a mechanism that disconnects these security programs from the underlying authentication/authorization infrastructure. PAM is configured by making appropriate modifications to one file <tt class="filename">/etc/pam.conf</tt> (Solaris), or by editing individual control files that are located in <tt class="filename">/etc/pam.d</tt>. </p><p> On PAM-enabled UNIX/Linux systems, it is an easy matter to configure the system to use any authentication backend so long as the appropriate dynamically loadable library modules are available for it. The backend may be local to the system, or may be centralized on a remote server. </p><p> PAM support modules are available for: </p><div class="variablelist"><dl><dt><span class="term"><tt class="filename">/etc/passwd</tt></span></dt><dd><p> There are several PAM modules that interact with this standard UNIX user database. The most common are called: <tt class="filename">pam_unix.so</tt>, <tt class="filename">pam_unix2.so</tt>, <tt class="filename">pam_pwdb.so</tt> and <tt class="filename">pam_userdb.so</tt>. </p></dd><dt><span class="term">Kerberos</span></dt><dd><p> The <tt class="filename">pam_krb5.so</tt> module allows the use of any Kerberos compliant server. This tool is used to access MIT Kerberos, Heimdal Kerberos, and potentially Microsoft Active Directory (if enabled). </p></dd><dt><span class="term">LDAP</span></dt><dd><p> The <tt class="filename">pam_ldap.so</tt> module allows the use of any LDAP v2 or v3 compatible backend server. Commonly used LDAP backend servers include: OpenLDAP v2.0 and v2.1, Sun ONE iDentity server, Novell eDirectory server, Microsoft Active Directory. </p></dd><dt><span class="term">NetWare Bindery</span></dt><dd><p> The <tt class="filename">pam_ncp_auth.so</tt> module allows authentication off any bindery-enabled NetWare Core Protocol-based server. </p></dd><dt><span class="term">SMB Password</span></dt><dd><p> This module, called <tt class="filename">pam_smbpass.so</tt>, will allow user authentication off the passdb backend that is configured in the Samba <tt class="filename">smb.conf</tt> file. </p></dd><dt><span class="term">SMB Server</span></dt><dd><p> The <tt class="filename">pam_smb_auth.so</tt> module is the original MS Windows networking authentication tool. This module has been somewhat outdated by the Winbind module. </p></dd><dt><span class="term">Winbind</span></dt><dd><p> The <tt class="filename">pam_winbind.so</tt> module allows Samba to obtain authentication from any MS Windows Domain Controller. It can just as easily be used to authenticate users for access to any PAM-enabled application. </p></dd><dt><span class="term">RADIUS</span></dt><dd><p> There is a PAM RADIUS (Remote Access Dial-In User Service) authentication module. In most cases, administrators will need to locate the source code for this tool and compile and install it themselves. RADIUS protocols are used by many routers and terminal servers. </p></dd></dl></div><p> Of the above, Samba provides the <tt class="filename">pam_smbpasswd.so</tt> and the <tt class="filename">pam_winbind.so</tt> modules alone. </p><p> Once configured, these permit a remarkable level of flexibility in the location and use of distributed Samba Domain Controllers that can provide wide area network bandwidth efficient authentication services for PAM-capable systems. In effect, this allows the deployment of centrally managed and maintained distributed authentication from a single-user account database. </p></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2963140"></a>Technical Discussion</h2></div></div><div></div></div><p> PAM is designed to provide the system administrator with a great deal of flexibility in configuration of the privilege granting applications of their system. The local configuration of system security controlled by PAM is contained in one of two places: either the single system file, <tt class="filename">/etc/pam.conf</tt>, or the <tt class="filename">/etc/pam.d/</tt> directory. </p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2963171"></a>PAM Configuration Syntax</h3></div></div><div></div></div><p> In this section we discuss the correct syntax of and generic options respected by entries to these files. PAM-specific tokens in the configuration file are case insensitive. The module paths, however, are case sensitive since they indicate a file's name and reflect the case dependence of typical file systems. The case-sensitivity of the arguments to any given module is defined for each module in turn. </p><p> In addition to the lines described below, there are two special characters provided for the convenience of the system administrator: comments are preceded by a “<span class="quote"><span class="emphasis"><em>#</em></span></span>” and extend to the next end-of-line; also, module specification lines may be extended with a “<span class="quote"><span class="emphasis"><em>\</em></span></span>” escaped newline. </p><p> If the PAM authentication module (loadable link library file) is located in the default location, then it is not necessary to specify the path. In the case of Linux, the default location is <tt class="filename">/lib/security</tt>. If the module is located outside the default, then the path must be specified as: </p><p> </p><pre class="programlisting"> auth required /other_path/pam_strange_module.so </pre><p> </p><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2963239"></a>Anatomy of <tt class="filename">/etc/pam.d</tt> Entries</h4></div></div><div></div></div><p> The remaining information in this subsection was taken from the documentation of the Linux-PAM project. For more information on PAM, see <a href="http://ftp.kernel.org/pub/linux/libs/pam/" target="_top">The Official Linux-PAM home page.</a> </p><p> A general configuration line of the <tt class="filename">/etc/pam.conf</tt> file has the following form: </p><p> </p><pre class="programlisting"> service-name module-type control-flag module-path args </pre><p> </p><p> Below, we explain the meaning of each of these tokens. The second (and more recently adopted) way of configuring Linux-PAM is via the contents of the <tt class="filename">/etc/pam.d/</tt> directory. Once we have explained the meaning of the above tokens, we will describe this method. </p><div class="variablelist"><dl><dt><span class="term">service-name</span></dt><dd><p> The name of the service associated with this entry. Frequently, the service name is the conventional name of the given application. For example, <b class="command">ftpd</b>, <b class="command">rlogind</b> and <b class="command">su</b>, and so on. </p><p> There is a special service-name reserved for defining a default authentication mechanism. It has the name <i class="parameter"><tt>OTHER</tt></i> and may be specified in either lower- or upper-case characters. Note, when there is a module specified for a named service, the <i class="parameter"><tt>OTHER</tt></i> entries are ignored. </p></dd><dt><span class="term">module-type</span></dt><dd><p> One of (currently) four types of module. The four types are as follows: </p><div class="itemizedlist"><ul type="disc"><li><p> <i class="parameter"><tt>auth:</tt></i> This module type provides two aspects of authenticating the user. It establishes that the user is who he claims to be by instructing the application to prompt the user for a password or other means of identification. Secondly, the module can grant group membership (independently of the <tt class="filename">/etc/groups</tt> file discussed above) or other privileges through its credential granting properties. </p></li><li><p> <i class="parameter"><tt>account:</tt></i> This module performs non-authentication-based account management. It is typically used to restrict/permit access to a service based on the time of day, currently available system resources (maximum number of users) or perhaps the location of the applicant user “<span class="quote"><span class="emphasis"><em>root</em></span></span>” login only on the console. </p></li><li><p> <i class="parameter"><tt>session:</tt></i> Primarily, this module is associated with doing things that need to be done for the user before and after they can be given service. Such things include the logging of information concerning the opening and closing of some data exchange with a user, mounting directories, and so on. </p></li><li><p> <i class="parameter"><tt>password:</tt></i> This last module type is required for updating the authentication token associated with the user. Typically, there is one module for each “<span class="quote"><span class="emphasis"><em>challenge/response</em></span></span>” -based authentication <i class="parameter"><tt>(auth)</tt></i> module type. </p></li></ul></div></dd><dt><span class="term">control-flag</span></dt><dd><p> The control-flag is used to indicate how the PAM library will react to the success or failure of the module it is associated with. Since modules can be stacked (modules of the same type execute in series, one after another), the control-flags determine the relative importance of each module. The application is not made aware of the individual success or failure of modules listed in the <tt class="filename">/etc/pam.conf</tt> file. Instead, it receives a summary success or fail response from the Linux-PAM library. The order of execution of these modules is that of the entries in the <tt class="filename">/etc/pam.conf</tt> file; earlier entries are executed before later ones. As of Linux-PAM v0.60, this control-flag can be defined with one of two syntaxes. </p><p> The simpler (and historical) syntax for the control-flag is a single keyword defined to indicate the severity of concern associated with the success or failure of a specific module. There are four such keywords: <i class="parameter"><tt>required, requisite, sufficient and optional</tt></i>. </p><p> The Linux-PAM library interprets these keywords in the following manner: </p><div class="itemizedlist"><ul type="disc"><li><p> <i class="parameter"><tt>required:</tt></i> This indicates that the success of the module is required for the module-type facility to succeed. Failure of this module will not be apparent to the user until all of the remaining modules (of the same module-type) have been executed. </p></li><li><p> <i class="parameter"><tt>requisite:</tt></i> Like required, however, in the case that such a module returns a failure, control is directly returned to the application. The return value is that associated with the first required or requisite module to fail. This flag can be used to protect against the possibility of a user getting the opportunity to enter a password over an unsafe medium. It is conceivable that such behavior might inform an attacker of valid accounts on a system. This possibility should be weighed against the not insignificant concerns of exposing a sensitive password in a hostile environment. </p></li><li><p> <i class="parameter"><tt>sufficient:</tt></i> The success of this module is deemed <i class="parameter"><tt>sufficient</tt></i> to satisfy the Linux-PAM library that this module-type has succeeded in its purpose. In the event that no previous required module has failed, no more “<span class="quote"><span class="emphasis"><em>stacked</em></span></span>” modules of this type are invoked. (In this case, subsequent required modules are not invoked). A failure of this module is not deemed as fatal to satisfying the application that this module-type has succeeded. </p></li><li><p> <i class="parameter"><tt>optional:</tt></i> As its name suggests, this control-flag marks the module as not being critical to the success or failure of the user's application for service. In general, Linux-PAM ignores such a module when determining if the module stack will succeed or fail. However, in the absence of any definite successes or failures of previous or subsequent stacked modules, this module will determine the nature of the response to the application. One example of this latter case, is when the other modules return something like PAM_IGNORE. </p></li></ul></div><p> The more elaborate (newer) syntax is much more specific and gives the administrator a great deal of control over how the user is authenticated. This form of the control flag is delimited with square brackets and consists of a series of <i class="parameter"><tt>value=action</tt></i> tokens: </p><pre class="programlisting"> [value1=action1 value2=action2 ...] </pre><p> Here, <i class="parameter"><tt>value1</tt></i> is one of the following return values: </p><pre class="screen"> <i class="parameter"><tt>success; open_err; symbol_err; service_err; system_err; buf_err;</tt></i> <i class="parameter"><tt>perm_denied; auth_err; cred_insufficient; authinfo_unavail;</tt></i> <i class="parameter"><tt>user_unknown; maxtries; new_authtok_reqd; acct_expired; session_err;</tt></i> <i class="parameter"><tt>cred_unavail; cred_expired; cred_err; no_module_data; conv_err;</tt></i> <i class="parameter"><tt>authtok_err; authtok_recover_err; authtok_lock_busy;</tt></i> <i class="parameter"><tt>authtok_disable_aging; try_again; ignore; abort; authtok_expired;</tt></i> <i class="parameter"><tt>module_unknown; bad_item;</tt></i> and <i class="parameter"><tt>default</tt></i>. </pre><p> </p><p> The last of these <i class="parameter"><tt>(default)</tt></i> can be used to set the action for those return values that are not explicitly defined. </p><p> The <i class="parameter"><tt>action1</tt></i> can be a positive integer or one of the following tokens: <i class="parameter"><tt>ignore; ok; done; bad; die;</tt></i> and <i class="parameter"><tt>reset</tt></i>. A positive integer, J, when specified as the action, can be used to indicate that the next J modules of the current module-type will be skipped. In this way, the administrator can develop a moderately sophisticated stack of modules with a number of different paths of execution. Which path is taken can be determined by the reactions of individual modules. </p><div class="itemizedlist"><ul type="disc"><li><p> <i class="parameter"><tt>ignore:</tt></i> When used with a stack of modules, the module's return status will not contribute to the return code the application obtains. </p></li><li><p> <i class="parameter"><tt>bad:</tt></i> This action indicates that the return code should be thought of as indicative of the module failing. If this module is the first in the stack to fail, its status value will be used for that of the whole stack. </p></li><li><p> <i class="parameter"><tt>die:</tt></i> Equivalent to bad with the side effect of terminating the module stack and PAM immediately returning to the application. </p></li><li><p> <i class="parameter"><tt>ok:</tt></i> This tells PAM that the administrator thinks this return code should contribute directly to the return code of the full stack of modules. In other words, if the former state of the stack would lead to a return of PAM_SUCCESS, the module's return code will override this value. Note, if the former state of the stack holds some value that is indicative of a modules failure, this <i class="parameter"><tt>ok</tt></i> value will not be used to override that value. </p></li><li><p> <i class="parameter"><tt>done:</tt></i> Equivalent to <i class="parameter"><tt>ok</tt></i> with the side effect of terminating the module stack and PAM immediately returning to the application. </p></li><li><p> <i class="parameter"><tt>reset:</tt></i> Clears all memory of the state of the module stack and starts again with the next stacked module. </p></li></ul></div><p> Each of the four keywords: <i class="parameter"><tt>required; requisite; sufficient;</tt></i> and <i class="parameter"><tt>optional</tt></i>, have an equivalent expression in terms of the [...] syntax. They are as follows: </p><p> </p><div class="itemizedlist"><ul type="disc"><li><p> <i class="parameter"><tt>required</tt></i> is equivalent to <i class="parameter"><tt>[success=ok new_authtok_reqd=ok ignore=ignore default=bad]</tt></i>. </p></li><li><p> <i class="parameter"><tt>requisite</tt></i> is equivalent to <i class="parameter"><tt>[success=ok new_authtok_reqd=ok ignore=ignore default=die]</tt></i>. </p></li><li><p> <i class="parameter"><tt>sufficient</tt></i> is equivalent to <i class="parameter"><tt>[success=done new_authtok_reqd=done default=ignore]</tt></i>. </p></li><li><p> <i class="parameter"><tt>optional</tt></i> is equivalent to <i class="parameter"><tt>[success=ok new_authtok_reqd=ok default=ignore]</tt></i>. </p></li></ul></div><p> </p><p> Just to get a feel for the power of this new syntax, here is a taste of what you can do with it. With Linux-PAM-0.63, the notion of client plug-in agents was introduced. This is something that makes it possible for PAM to support machine-machine authentication using the transport protocol inherent to the client/server application. With the <i class="parameter"><tt>[ ... value=action ... ]</tt></i> control syntax, it is possible for an application to be configured to support binary prompts with compliant clients, but to gracefully fall over into an alternative authentication mode for older, legacy applications. </p></dd><dt><span class="term">module-path</span></dt><dd><p> The path-name of the dynamically loadable object file; the pluggable module itself. If the first character of the module path is “<span class="quote"><span class="emphasis"><em>/</em></span></span>”, it is assumed to be a complete path. If this is not the case, the given module path is appended to the default module path: <tt class="filename">/lib/security</tt> (but see the notes above). </p><p> The arguments are a list of tokens that are passed to the module when it is invoked, much like arguments to a typical Linux shell command. Generally, valid arguments are optional and are specific to any given module. Invalid arguments are ignored by a module, however, when encountering an invalid argument, the module is required to write an error to syslog(3). For a list of generic options, see the next section. </p><p> If you wish to include spaces in an argument, you should surround that argument with square brackets. For example: </p><pre class="programlisting"> squid auth required pam_mysql.so user=passwd_query passwd=mada \ db=eminence [query=select user_name from internet_service where \ user_name=“<span class="quote"><span class="emphasis"><em>%u</em></span></span>” and password=PASSWORD(“<span class="quote"><span class="emphasis"><em>%p</em></span></span>”) and service=“<span class="quote"><span class="emphasis"><em>web_proxy</em></span></span>”] </pre><p> When using this convention, you can include “<span class="quote"><span class="emphasis"><em>[</em></span></span>” characters inside the string, and if you wish to have a “<span class="quote"><span class="emphasis"><em>]</em></span></span>” character inside the string that will survive the argument parsing, you should use “<span class="quote"><span class="emphasis"><em>\[</em></span></span>”. In other words: </p><pre class="programlisting"> [..[..\]..] --> ..[..].. </pre><p> Any line in one of the configuration files that is not formatted correctly will generally tend (erring on the side of caution) to make the authentication process fail. A corresponding error is written to the system log files with a call to syslog(3). </p></dd></dl></div></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2964188"></a>Example System Configurations</h3></div></div><div></div></div><p> The following is an example <tt class="filename">/etc/pam.d/login</tt> configuration file. This example had all options uncommented and is probably not usable because it stacks many conditions before allowing successful completion of the login process. Essentially all conditions can be disabled by commenting them out, except the calls to <tt class="filename">pam_pwdb.so</tt>. </p><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2964219"></a>PAM: Original Login Config</h4></div></div><div></div></div><p> </p><pre class="programlisting"> #%PAM-1.0 # The PAM configuration file for the “<span class="quote"><span class="emphasis"><em>login</em></span></span>” service # auth required pam_securetty.so auth required pam_nologin.so # auth required pam_dialup.so # auth optional pam_mail.so auth required pam_pwdb.so shadow md5 # account requisite pam_time.so account required pam_pwdb.so session required pam_pwdb.so # session optional pam_lastlog.so # password required pam_cracklib.so retry=3 password required pam_pwdb.so shadow md5 </pre><p> </p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2964254"></a>PAM: Login Using <tt class="filename">pam_smbpass</tt></h4></div></div><div></div></div><p> PAM allows use of replaceable modules. Those available on a sample system include: </p><p><tt class="prompt">$</tt><b class="userinput"><tt>/bin/ls /lib/security</tt></b> </p><pre class="programlisting"> pam_access.so pam_ftp.so pam_limits.so pam_ncp_auth.so pam_rhosts_auth.so pam_stress.so pam_cracklib.so pam_group.so pam_listfile.so pam_nologin.so pam_rootok.so pam_tally.so pam_deny.so pam_issue.so pam_mail.so pam_permit.so pam_securetty.so pam_time.so pam_dialup.so pam_lastlog.so pam_mkhomedir.so pam_pwdb.so pam_shells.so pam_unix.so pam_env.so pam_ldap.so pam_motd.so pam_radius.so pam_smbpass.so pam_unix_acct.so pam_wheel.so pam_unix_auth.so pam_unix_passwd.so pam_userdb.so pam_warn.so pam_unix_session.so </pre><p> The following example for the login program replaces the use of the <tt class="filename">pam_pwdb.so</tt> module that uses the system password database (<tt class="filename">/etc/passwd</tt>, <tt class="filename">/etc/shadow</tt>, <tt class="filename">/etc/group</tt>) with the module <tt class="filename">pam_smbpass.so</tt>, which uses the Samba database which contains the Microsoft MD4 encrypted password hashes. This database is stored in either <tt class="filename">/usr/local/samba/private/smbpasswd</tt>, <tt class="filename">/etc/samba/smbpasswd</tt>, or in <tt class="filename">/etc/samba.d/smbpasswd</tt>, depending on the Samba implementation for your UNIX/Linux system. The <tt class="filename">pam_smbpass.so</tt> module is provided by Samba version 2.2.1 or later. It can be compiled by specifying the <tt class="option">--with-pam_smbpass</tt> options when running Samba's <b class="command">configure</b> script. For more information on the <tt class="filename">pam_smbpass</tt> module, see the documentation in the <tt class="filename">source/pam_smbpass</tt> directory of the Samba source distribution. </p><p> </p><pre class="programlisting"> #%PAM-1.0 # The PAM configuration file for the “<span class="quote"><span class="emphasis"><em>login</em></span></span>” service # auth required pam_smbpass.so nodelay account required pam_smbpass.so nodelay session required pam_smbpass.so nodelay password required pam_smbpass.so nodelay </pre><p> The following is the PAM configuration file for a particular Linux system. The default condition uses <tt class="filename">pam_pwdb.so</tt>. </p><p> </p><pre class="programlisting"> #%PAM-1.0 # The PAM configuration file for the “<span class="quote"><span class="emphasis"><em>samba</em></span></span>” service # auth required pam_pwdb.so nullok nodelay shadow audit account required pam_pwdb.so audit nodelay session required pam_pwdb.so nodelay password required pam_pwdb.so shadow md5 </pre><p> In the following example, the decision has been made to use the <b class="command">smbpasswd</b> database even for basic Samba authentication. Such a decision could also be made for the <b class="command">passwd</b> program and would thus allow the <b class="command">smbpasswd</b> passwords to be changed using the <b class="command">passwd</b> program: </p><p> </p><pre class="programlisting"> #%PAM-1.0 # The PAM configuration file for the “<span class="quote"><span class="emphasis"><em>samba</em></span></span>” service # auth required pam_smbpass.so nodelay account required pam_pwdb.so audit nodelay session required pam_pwdb.so nodelay password required pam_smbpass.so nodelay smbconf=/etc/samba.d/smb.conf </pre><p> </p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>PAM allows stacking of authentication mechanisms. It is also possible to pass information obtained within one PAM module through to the next module in the PAM stack. Please refer to the documentation for your particular system implementation for details regarding the specific capabilities of PAM in this environment. Some Linux implementations also provide the <tt class="filename">pam_stack.so</tt> module that allows all authentication to be configured in a single central file. The <tt class="filename">pam_stack.so</tt> method has some devoted followers on the basis that it allows for easier administration. As with all issues in life though, every decision makes trade-offs, so you may want to examine the PAM documentation for further helpful information. </p></div></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2964555"></a><tt class="filename">smb.conf</tt> PAM Configuration</h3></div></div><div></div></div><p> There is an option in <tt class="filename">smb.conf</tt> called <a class="indexterm" name="id2964577"></a>obey pam restrictions. The following is from the online help for this option in SWAT; </p><p> When Samba is configured to enable PAM support (i.e., <tt class="option">--with-pam</tt>), this parameter will control whether or not Samba should obey PAM's account and session management directives. The default behavior is to use PAM for clear-text authentication only and to ignore any account or session management. Samba always ignores PAM for authentication in the case of <a class="indexterm" name="id2964602"></a>encrypt passwords = yes. The reason is that PAM modules cannot support the challenge/response authentication mechanism needed in the presence of SMB password encryption. </p><p>Default: <a class="indexterm" name="id2964618"></a>obey pam restrictions = no</p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2964629"></a>Remote CIFS Authentication Using <tt class="filename">winbindd.so</tt></h3></div></div><div></div></div><p> All operating systems depend on the provision of users credentials acceptable to the platform. UNIX requires the provision of a user identifier (UID) as well as a group identifier (GID). These are both simple integer type numbers that are obtained from a password backend such as <tt class="filename">/etc/passwd</tt>. </p><p> Users and groups on a Windows NT server are assigned a relative ID (RID) which is unique for the domain when the user or group is created. To convert the Windows NT user or group into a UNIX user or group, a mapping between RIDs and UNIX user and group IDs is required. This is one of the jobs that winbind performs. </p><p> As Winbind users and groups are resolved from a server, user and group IDs are allocated from a specified range. This is done on a first come, first served basis, although all existing users and groups will be mapped as soon as a client performs a user or group enumeration command. The allocated UNIX IDs are stored in a database file under the Samba lock directory and will be remembered. </p><p> The astute administrator will realize from this that the combination of <tt class="filename">pam_smbpass.so</tt>, <b class="command">winbindd</b> and a distributed <a class="indexterm" name="id2964698"></a>passdb backend, such as <i class="parameter"><tt>ldap</tt></i>, will allow the establishment of a centrally managed, distributed user/password database that can also be used by all PAM-aware (e.g., Linux) programs and applications. This arrangement can have particularly potent advantages compared with the use of Microsoft Active Directory Service (ADS) in so far as the reduction of wide area network authentication traffic. </p><div class="warning" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Warning</h3><p> The RID to UNIX ID database is the only location where the user and group mappings are stored by <b class="command">winbindd</b>. If this file is deleted or corrupted, there is no way for <b class="command">winbindd</b> to determine which user and group IDs correspond to Windows NT user and group RIDs. </p></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2964747"></a>Password Synchronization Using <tt class="filename">pam_smbpass.so</tt></h3></div></div><div></div></div><p> <tt class="filename">pam_smbpass</tt> is a PAM module that can be used on conforming systems to keep the <tt class="filename">smbpasswd</tt> (Samba password) database in sync with the UNIX password file. PAM (Pluggable Authentication Modules) is an API supported under some UNIX operating systems, such as Solaris, HPUX and Linux, that provides a generic interface to authentication mechanisms. </p><p> This module authenticates a local <tt class="filename">smbpasswd</tt> user database. If you require support for authenticating against a remote SMB server, or if you are concerned about the presence of SUID root binaries on your system, it is recommended that you use <tt class="filename">pam_winbind</tt> instead. </p><p> Options recognized by this module are shown in <a href="pam.html#smbpassoptions" title="Table 25.1. Options recognized by pam_smbpass">next table</a>. </p><div class="table"><a name="smbpassoptions"></a><p class="title"><b>Table 25.1. Options recognized by <i class="parameter"><tt>pam_smbpass</tt></i></b></p><table summary="Options recognized by pam_smbpass" border="1"><colgroup><col align="left"><col align="justify"></colgroup><tbody><tr><td align="left">debug</td><td align="justify">log more debugging info.</td></tr><tr><td align="left">audit</td><td align="justify">like debug, but also logs unknown usernames.</td></tr><tr><td align="left">use_first_pass</td><td align="justify">do not prompt the user for passwords; take them from PAM_ items instead.</td></tr><tr><td align="left">try_first_pass</td><td align="justify">try to get the password from a previous PAM module fall back to prompting the user.</td></tr><tr><td align="left">use_authtok</td><td align="justify">like try_first_pass, but *fail* if the new PAM_AUTHTOK has not been previously set (intended for stacking password modules only).</td></tr><tr><td align="left">not_set_pass</td><td align="justify">do not make passwords used by this module available to other modules.</td></tr><tr><td align="left">nodelay</td><td align="justify">do not insert ~1 second delays on authentication failure.</td></tr><tr><td align="left">nullok</td><td align="justify">null passwords are allowed.</td></tr><tr><td align="left">nonull</td><td align="justify">null passwords are not allowed. Used to override the Samba configuration.</td></tr><tr><td align="left">migrate</td><td align="justify">only meaningful in an “<span class="quote"><span class="emphasis"><em>auth</em></span></span>” context; used to update smbpasswd file with a password used for successful authentication.</td></tr><tr><td align="left">smbconf=<i class="replaceable"><tt>file</tt></i></td><td align="justify">specify an alternate path to the <tt class="filename">smb.conf</tt> file.</td></tr></tbody></table></div><p> </p><p> The following are examples of the use of <tt class="filename">pam_smbpass.so</tt> in the format of Linux <tt class="filename">/etc/pam.d/</tt> files structure. Those wishing to implement this tool on other platforms will need to adapt this appropriately. </p><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2965010"></a>Password Synchronization Configuration</h4></div></div><div></div></div><p> A sample PAM configuration that shows the use of pam_smbpass to make sure <tt class="filename">private/smbpasswd</tt> is kept in sync when <tt class="filename">/etc/passwd (/etc/shadow)</tt> is changed. Useful when an expired password might be changed by an application (such as <b class="command">ssh</b>). </p><p> </p><pre class="programlisting"> #%PAM-1.0 # password-sync # auth requisite pam_nologin.so auth required pam_unix.so account required pam_unix.so password requisite pam_cracklib.so retry=3 password requisite pam_unix.so shadow md5 use_authtok try_first_pass password required pam_smbpass.so nullok use_authtok try_first_pass session required pam_unix.so </pre></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2965065"></a>Password Migration Configuration</h4></div></div><div></div></div><p> A sample PAM configuration that shows the use of <tt class="filename">pam_smbpass</tt> to migrate from plaintext to encrypted passwords for Samba. Unlike other methods, this can be used for users who have never connected to Samba shares: password migration takes place when users <b class="command">ftp</b> in, login using <b class="command">ssh</b>, pop their mail, and so on. </p><p> </p><pre class="programlisting"> #%PAM-1.0 # password-migration # auth requisite pam_nologin.so # pam_smbpass is called IF pam_unix succeeds. auth requisite pam_unix.so auth optional pam_smbpass.so migrate account required pam_unix.so password requisite pam_cracklib.so retry=3 password requisite pam_unix.so shadow md5 use_authtok try_first_pass password optional pam_smbpass.so nullok use_authtok try_first_pass session required pam_unix.so </pre></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2965122"></a>Mature Password Configuration</h4></div></div><div></div></div><p> A sample PAM configuration for a mature <tt class="filename">smbpasswd</tt> installation. <tt class="filename">private/smbpasswd</tt> is fully populated, and we consider it an error if the SMB password does not exist or does not match the UNIX password. </p><p> </p><pre class="programlisting"> #%PAM-1.0 # password-mature # auth requisite pam_nologin.so auth required pam_unix.so account required pam_unix.so password requisite pam_cracklib.so retry=3 password requisite pam_unix.so shadow md5 use_authtok try_first_pass password required pam_smbpass.so use_authtok use_first_pass session required pam_unix.so </pre></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2965169"></a>Kerberos Password Integration Configuration</h4></div></div><div></div></div><p> A sample PAM configuration that shows <i class="parameter"><tt>pam_smbpass</tt></i> used together with <i class="parameter"><tt>pam_krb5</tt></i>. This could be useful on a Samba PDC that is also a member of a Kerberos realm. </p><p> </p><pre class="programlisting"> #%PAM-1.0 # kdc-pdc # auth requisite pam_nologin.so auth requisite pam_krb5.so auth optional pam_smbpass.so migrate account required pam_krb5.so password requisite pam_cracklib.so retry=3 password optional pam_smbpass.so nullok use_authtok try_first_pass password required pam_krb5.so use_authtok try_first_pass session required pam_krb5.so </pre></div></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2965218"></a>Common Errors</h2></div></div><div></div></div><p> PAM can be fickle and sensitive to configuration glitches. Here we look at a few cases from the Samba mailing list. </p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2965234"></a>pam_winbind Problem</h3></div></div><div></div></div><p> A user reported: I have the following PAM configuration: </p><p> </p><pre class="programlisting"> auth required /lib/security/pam_securetty.so auth sufficient /lib/security/pam_winbind.so auth sufficient /lib/security/pam_unix.so use_first_pass nullok auth required /lib/security/pam_stack.so service=system-auth auth required /lib/security/pam_nologin.so account required /lib/security/pam_stack.so service=system-auth account required /lib/security/pam_winbind.so password required /lib/security/pam_stack.so service=system-auth </pre><p> </p><p> When I open a new console with [ctrl][alt][F1], I can't log in with my user “<span class="quote"><span class="emphasis"><em>pitie</em></span></span>”. I have tried with user “<span class="quote"><span class="emphasis"><em>scienceu+pitie</em></span></span>” also. </p><p> <span class="emphasis"><em>Answer:</em></span> The problem may lie with your inclusion of <i class="parameter"><tt>pam_stack.so service=system-auth</tt></i>. That file often contains a lot of stuff that may duplicate what you are already doing. Try commenting out the <i class="parameter"><tt>pam_stack</tt></i> lines for <i class="parameter"><tt>auth</tt></i> and <i class="parameter"><tt>account</tt></i> and see if things work. If they do, look at <tt class="filename">/etc/pam.d/system-auth</tt> and copy only what you need from it into your <tt class="filename">/etc/pam.d/login</tt> file. Alternately, if you want all services to use Winbind, you can put the Winbind-specific stuff in <tt class="filename">/etc/pam.d/system-auth</tt>. </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2965349"></a>Winbind Is Not Resolving Users and Groups</h3></div></div><div></div></div><p> “<span class="quote"><span class="emphasis"><em> My <tt class="filename">smb.conf</tt> file is correctly configured. I have specified <a class="indexterm" name="id2965372"></a>idmap uid = 12000, and <a class="indexterm" name="id2965380"></a>idmap gid = 3000-3500 and <b class="command">winbind</b> is running. When I do the following it all works fine. </em></span></span>” </p><pre class="screen"> <tt class="prompt">root# </tt><b class="userinput"><tt>wbinfo -u</tt></b> MIDEARTH+maryo MIDEARTH+jackb MIDEARTH+ameds ... MIDEARTH+root <tt class="prompt">root# </tt><b class="userinput"><tt>wbinfo -g</tt></b> MIDEARTH+Domain Users MIDEARTH+Domain Admins MIDEARTH+Domain Guests ... MIDEARTH+Accounts <tt class="prompt">root# </tt><b class="userinput"><tt>getent passwd</tt></b> root:x:0:0:root:/root:/bin/bash bin:x:1:1:bin:/bin:/bin/bash ... maryo:x:15000:15003:Mary Orville:/home/MIDEARTH/maryo:/bin/false </pre><p> “<span class="quote"><span class="emphasis"><em> But this command fails: </em></span></span>” </p><pre class="screen"> <tt class="prompt">root# </tt><b class="userinput"><tt>chown maryo a_file</tt></b> chown: 'maryo': invalid user </pre><p> “<span class="quote"><span class="emphasis"><em>This is driving me nuts! What can be wrong?</em></span></span>” </p><p> <span class="emphasis"><em>Answer:</em></span> Your system is likely running <b class="command">nscd</b>, the name service caching daemon. Shut it down, do not restart it! You will find your problem resolved. </p></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ProfileMgmt.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="optional.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="integrate-ms-networks.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 24. Desktop Profile Management </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 26. Integrating MS Windows Networks with Samba</td></tr></table></div></body></html>