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<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 V1.60.1"><link rel="home" href="index.html" title="SAMBA Project Documentation"><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#id2958910">Features and Benefits</a></dt><dt><a href="pam.html#id2959235">Technical Discussion</a></dt><dd><dl><dt><a href="pam.html#id2959266">PAM Configuration Syntax</a></dt><dt><a href="pam.html#id2960262">Example System Configurations</a></dt><dt><a href="pam.html#id2960612">smb.conf PAM Configuration</a></dt><dt><a href="pam.html#id2960701">Remote CIFS Authentication Using winbindd.so</a></dt><dt><a href="pam.html#id2960824">Password Synchronization Using pam_smbpass.so</a></dt></dl></dd><dt><a href="pam.html#id2961283">Common Errors</a></dt><dd><dl><dt><a href="pam.html#id2961296">pam_winbind Problem</a></dt><dt><a href="pam.html#id2961406">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 <link linkend="winbind">, 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="id2958910"></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="id2959235"></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="id2959266"></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>” and extend to the next end-of-line; also,
module specification lines may be extended with a “<span class="quote">\</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="id2959332"></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
<ulink url="http://ftp.kernel.org/pub/linux/libs/pam/">The Official Linux-PAM home page.</ulink>
</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">root</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">challenge/response</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">stacked</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>”, 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">%u</span>” and password=PASSWORD(“<span class="quote">%p</span>”) and service=“<span class="quote">web_proxy</span>”]
</pre><p>
When using this convention, you can include “<span class="quote">[</span>” characters inside the string, and if you wish to have a “<span class="quote">]</span>”
character inside the string that will survive the argument parsing, you should use “<span class="quote">\[</span>”. In other words:
</p><pre class="programlisting">
[..[..\]..] --> ..[..]..
</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="id2960262"></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="id2960294"></a>PAM: Original Login Config</h4></div></div><div></div></div><pre class="programlisting">
#%PAM-1.0
# The PAM configuration file for the “<span class="quote">login</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></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2960324"></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><pre class="programlisting">
#%PAM-1.0
# The PAM configuration file for the “<span class="quote">login</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><pre class="programlisting">
#%PAM-1.0
# The PAM configuration file for the “<span class="quote">samba</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><pre class="programlisting">
#%PAM-1.0
# The PAM configuration file for the “<span class="quote">samba</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><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="id2960612"></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="id2960633"></a><i class="parameter"><tt>obey pam restrictions</tt></i>.
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 cleartext authentication only and to ignore any account or session management. Samba always
ignores PAM for authentication in the case of <a class="indexterm" name="id2960663"></a><i class="parameter"><tt>encrypt passwords</tt></i> = 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="id2960684"></a><i class="parameter"><tt>obey pam restrictions</tt></i> = no</p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2960701"></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="id2960770"></a><i class="parameter"><tt>passdb backend</tt></i>,
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="id2960824"></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 <link linkend="smbpassoptions">.
</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">auth</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="id2961083"></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><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="id2961136"></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><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="id2961191"></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><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="id2961236"></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><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="id2961283"></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="id2961296"></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">pitie</span>”.
I have tried with user “<span class="quote">scienceu+pitie</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="id2961406"></a>Winbind Is Not Resolving Users and Groups</h3></div></div><div></div></div><p>
“<span class="quote">
My <tt class="filename">smb.conf</tt> file is correctly configured. I have specified
<a class="indexterm" name="id2961428"></a><i class="parameter"><tt>idmap uid</tt></i> = 12000,
and <a class="indexterm" name="id2961442"></a><i class="parameter"><tt>idmap gid</tt></i> = 3000-3500
and <b class="command">winbind</b> is running. When I do the following it all works fine.
</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">
But this command fails:
</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">This is driving me nuts! What can be wrong?</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>
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