samba-mirror/docs-xml/Samba3-HOWTO/TOSHARG-PAM.xml

<?xml version="1.0" encoding="iso-8859-1"?>
<!DOCTYPE chapter PUBLIC "-//Samba-Team//DTD DocBook V4.2-Based Variant V1.0//EN" "http://www.samba.org/samba/DTD/samba-doc">
<chapter id="pam">
<chapterinfo>
	&author.jht;
	<author>
		<firstname>Stephen</firstname><surname>Langasek</surname>
		<affiliation>
			<address><email>vorlon@netexpress.net</email></address>
		</affiliation>
	</author>
    <pubdate>May 31, 2003</pubdate>
</chapterinfo>
 
<title>PAM-Based Distributed Authentication</title>

<para>
<indexterm><primary>PAM-enabled</primary></indexterm>
<indexterm><primary>Winbind</primary></indexterm>
<indexterm><primary>ADS</primary></indexterm>
<indexterm><primary>Winbind-based authentication</primary></indexterm>
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.
</para>

<para>
<indexterm><primary>PAM management</primary></indexterm>
<indexterm><primary>pam_smbpass.so</primary></indexterm>
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 <filename>pam_smbpass.so</filename> to your advantage.
</para>

<note><para>
The use of Winbind requires more than PAM configuration alone.
Please refer to <link linkend="winbind">Winbind: Use of Domain Accounts</link>, for further information regarding Winbind.
</para></note>

<sect1>
<title>Features and Benefits</title>

<para>
<indexterm><primary>Sun Solaris</primary></indexterm>
<indexterm><primary>xxxxBSD</primary></indexterm>
<indexterm><primary>Linux</primary></indexterm>
<indexterm><primary>Pluggable Authentication Modules</primary><see>PAM</see></indexterm>
<indexterm><primary>/etc/passwd</primary></indexterm>
<indexterm><primary>login</primary></indexterm>
<indexterm><primary>passwd</primary></indexterm>
<indexterm><primary>chown</primary></indexterm>
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 (<filename>/etc/passwd</filename>) 
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 <command>login</command>, 
<command>passwd</command>, <command>chown</command>, and so on.
</para>

<para>
<indexterm><primary>PAM</primary></indexterm>
<indexterm><primary>/etc/pam.conf</primary></indexterm>
<indexterm><primary>Solaris</primary></indexterm>
<indexterm><primary>/etc/pam.d</primary></indexterm>
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,
<filename>/etc/pam.conf</filename> (Solaris), or by editing individual control files that are
located in <filename>/etc/pam.d</filename>.
</para>

<para>
<indexterm><primary>PAM-enabled</primary></indexterm>
<indexterm><primary>dynamically loadable library modules</primary></indexterm>
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.
</para>

<para>
PAM support modules are available for:
</para>

<variablelist>
	<varlistentry><term><filename>/etc/passwd</filename></term><listitem>
		<para>
<indexterm><primary>/etc/passwd</primary></indexterm>
<indexterm><primary>PAM modules</primary></indexterm>
<indexterm><primary>pam_unix.so</primary></indexterm>
<indexterm><primary>pam_unix2.so</primary></indexterm>
<indexterm><primary>pam_pwdb.so</primary></indexterm>
<indexterm><primary>pam_userdb.so</primary></indexterm>
		There are several PAM modules that interact with this standard UNIX user database. The most common are called
		<filename>pam_unix.so</filename>, <filename>pam_unix2.so</filename>, <filename>pam_pwdb.so</filename> and
		<filename>pam_userdb.so</filename>.
		</para>
	</listitem></varlistentry>

	<varlistentry><term>Kerberos</term><listitem>
		<para>
<indexterm><primary>pam_krb5.so</primary></indexterm>
<indexterm><primary>Kerberos</primary></indexterm>
<indexterm><primary>Heimdal</primary></indexterm>
<indexterm><primary>MIT Kerberos</primary></indexterm>
<indexterm><primary>ADS</primary></indexterm>
		The <filename>pam_krb5.so</filename> 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).
		</para>
	</listitem></varlistentry>

	<varlistentry><term>LDAP</term><listitem>
		<para>
<indexterm><primary>LDAP</primary></indexterm>
<indexterm><primary>pam_ldap.so</primary></indexterm>
<indexterm><primary>OpenLDAP</primary></indexterm>
<indexterm><primary>Sun ONE iDentity server</primary></indexterm>
<indexterm><primary>Novell eDirectory server</primary></indexterm>
<indexterm><primary>Microsoft Active Directory</primary></indexterm>
		The <filename>pam_ldap.so</filename> 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, and Microsoft Active Directory.
		</para>
	</listitem></varlistentry>

	<varlistentry><term>NetWare Bindery</term><listitem>
		<para>
<indexterm><primary>NetWare Bindery</primary></indexterm>
<indexterm><primary>pam_ncp_auth.so</primary></indexterm>
<indexterm><primary>bindery-enabled</primary></indexterm>
<indexterm><primary>NetWare Core Protocol-based server</primary></indexterm>
		The <filename>pam_ncp_auth.so</filename> module allows authentication off any bindery-enabled
		NetWare Core Protocol-based server.
		</para>
	</listitem></varlistentry>

	<varlistentry><term>SMB Password</term><listitem>
		<para>
<indexterm><primary>SMB Password</primary></indexterm>
<indexterm><primary>pam_smbpass.so</primary></indexterm>
<indexterm><primary>passdb backend</primary></indexterm>
		This module, called <filename>pam_smbpass.so</filename>, allows user authentication of
		the passdb backend that is configured in the Samba &smb.conf; file.
		</para>
	</listitem></varlistentry>

	<varlistentry><term>SMB Server</term><listitem>
		<para>
<indexterm><primary>SMB Server</primary></indexterm>
<indexterm><primary>pam_smb_auth.so</primary></indexterm>
		The <filename>pam_smb_auth.so</filename> module is the original MS Windows networking authentication
		tool. This module has been somewhat outdated by the Winbind module.
		</para>
	</listitem></varlistentry>

	<varlistentry><term>Winbind</term><listitem>
		<para>
<indexterm><primary>Winbind</primary></indexterm>
<indexterm><primary>pam_winbind.so</primary></indexterm>
<indexterm><primary>domain controller</primary></indexterm>
<indexterm><primary>authentication</primary></indexterm>
		The <filename>pam_winbind.so</filename> 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.
		</para>
	</listitem></varlistentry>

	<varlistentry><term>RADIUS</term><listitem>
		<para>
<indexterm><primary>Remote Access Dial-In User Service</primary><see>RADIUS</see></indexterm>
		There is a PAM RADIUS (Remote Access Dial-In User Service) authentication
		module. In most cases, administrators 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.
		</para>
	</listitem></varlistentry>
</variablelist>

<para>
<indexterm><primary>pam_smbpasswd.so</primary></indexterm>
<indexterm><primary>pam_winbind.so</primary></indexterm>
Of the modules listed, Samba provides the <filename>pam_smbpasswd.so</filename> and the
<filename>pam_winbind.so</filename> modules alone.
</para>

<para>
<indexterm><primary>wide-area network bandwidth</primary></indexterm>
<indexterm><primary>efficient authentication</primary></indexterm>
<indexterm><primary>PAM-capable</primary></indexterm>
<indexterm><primary>centrally managed</primary></indexterm>
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.
</para>

</sect1>

<sect1>
<title>Technical Discussion</title>

<para>
<indexterm><primary>PAM</primary></indexterm>
<indexterm><primary>privilege-granting applications</primary></indexterm>
<indexterm><primary>/etc/pam.conf</primary></indexterm>
<indexterm><primary>/etc/pam.d/</primary></indexterm>
PAM is designed to provide system administrators 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 <filename>/etc/pam.conf</filename> or the
<filename>/etc/pam.d/</filename> directory.
</para>

<sect2>
<title>PAM Configuration Syntax</title>

<para>
<indexterm><primary>PAM-specific tokens</primary></indexterm>
<indexterm><primary>case sensitivity</primary></indexterm>
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.
</para>

<para>
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 <quote>#</quote> and extend to the next end-of-line; also,
module specification lines may be extended with a <quote>\</quote>-escaped newline. 
</para>

<para>
<indexterm><primary>PAM authentication module</primary></indexterm>
<indexterm><primary>/lib/security</primary></indexterm>
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 <filename>/lib/security</filename>. If the module
is located outside the default, then the path must be specified as:
<programlisting>
auth  required  /other_path/pam_strange_module.so
</programlisting>
</para>

<sect3>
<title>Anatomy of <filename>/etc/pam.d</filename> Entries</title>

<para>
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>.
</para>

<para>
<indexterm><primary>/etc/pam.conf</primary></indexterm>
A general configuration line of the <filename>/etc/pam.conf</filename> file has the following form:
<programlisting>
service-name   module-type   control-flag   module-path   args
</programlisting>
</para>

<para>
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 <filename>/etc/pam.d/</filename> directory.
Once we have explained the meaning of the tokens, we describe this method.
</para>

<variablelist>
	<varlistentry><term>service-name</term><listitem>
		<para>
<indexterm><primary>ftpd</primary></indexterm>
<indexterm><primary>rlogind</primary></indexterm>
<indexterm><primary>su</primary></indexterm>
		The name of the service associated with this entry. Frequently, the service-name is the conventional
		name of the given application &smbmdash; for example, <command>ftpd</command>, <command>rlogind</command> and
		<command>su</command>, and so on.
		</para>

		<para>
		There is a special service-name reserved for defining a default authentication mechanism. It has
		the name <parameter>OTHER</parameter> and may be specified in either lower- or uppercase characters.
		Note, when there is a module specified for a named service, the <parameter>OTHER</parameter>
		entries are ignored.
		</para>
		</listitem>
	</varlistentry>

	<varlistentry><term>module-type</term><listitem>
                <para>
		One of (currently) four types of module. The four types are as follows:
		</para>

		<itemizedlist>
			<listitem><para>
<indexterm><primary>auth</primary></indexterm>
<indexterm><primary>/etc/groups</primary></indexterm>
			<parameter>auth:</parameter> This module type provides two aspects of authenticating the user.
			It establishes that the user is who he or she claims to be by instructing the application
			to prompt the user for a password or other means of identification. Second, the module can
			grant group membership (independently of the <filename>/etc/groups</filename> file)
			or other privileges through its credential-granting properties.
			</para></listitem>

			<listitem><para>
<indexterm><primary>account</primary></indexterm>
<indexterm><primary>non-authentication-based account management</primary></indexterm>
			<parameter>account:</parameter> 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 user 
			login. For example, the <quote>root</quote> login may be permitted only on the console.
			</para></listitem>

			<listitem><para>
<indexterm><primary>session</primary></indexterm>
			<parameter>session:</parameter> Primarily, this module is associated with doing things that need
			to be done for the user before and after he or she can be given service. Such things include logging
			information concerning the opening and closing of some data exchange with a user, mounting
			directories, and so on.
			</para></listitem>

			<listitem><para>
<indexterm><primary>password</primary></indexterm>
			<parameter>password:</parameter> This last module type is required for updating the authentication
			token associated with the user. Typically, there is one module for each
			<quote>challenge/response</quote> authentication <parameter>(auth)</parameter> module type.
			</para></listitem>
		</itemizedlist>
		</listitem>
	</varlistentry>

	<varlistentry><term>control-flag</term><listitem>
		<para>
		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
		<filename>/etc/pam.conf</filename> 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
		<filename>/etc/pam.conf</filename> 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.
		</para>

		<para>
<indexterm><primary>required</primary></indexterm>
<indexterm><primary>requisite</primary></indexterm>
<indexterm><primary>sufficient</primary></indexterm>
<indexterm><primary>optional</primary></indexterm>
		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: <parameter>required</parameter>, <parameter>requisite</parameter>,
		<parameter>sufficient</parameter>, and <parameter>optional</parameter>.
		</para>

		<para>
		The Linux-PAM library interprets these keywords in the following manner:
		</para>

		<itemizedlist>
			<listitem><para>
			<parameter>required:</parameter> 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.
			</para></listitem>

			<listitem><para>
			<parameter>requisite:</parameter> Like required, except that if 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.
			</para></listitem>

			<listitem><para>
			<parameter>sufficient:</parameter> The success of this module is deemed <parameter>sufficient</parameter> 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 <quote>stacked</quote> 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.
			</para></listitem>

            <listitem><para>
            <parameter>optional:</parameter> 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.
			</para></listitem>
		</itemizedlist>

		<para>
		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 <parameter>value=action</parameter> tokens:
		</para>

<para><programlisting>
[value1=action1 value2=action2 ...]
</programlisting></para>

		<para>
		Here, <parameter>value1</parameter> is one of the following return values:
<screen>
<parameter>success; open_err; symbol_err; service_err; system_err; buf_err;</parameter>
<parameter>perm_denied; auth_err; cred_insufficient; authinfo_unavail;</parameter>
<parameter>user_unknown; maxtries; new_authtok_reqd; acct_expired; session_err;</parameter>
<parameter>cred_unavail; cred_expired; cred_err; no_module_data; conv_err;</parameter>
<parameter>authtok_err; authtok_recover_err; authtok_lock_busy;</parameter>
<parameter>authtok_disable_aging; try_again; ignore; abort; authtok_expired;</parameter>
<parameter>module_unknown; bad_item;</parameter> and <parameter>default</parameter>.
</screen>
</para>

		<para>
		The last of these (<parameter>default</parameter>) can be used to set the action for those return values that are not explicitly defined.
		</para>

		<para>
		The <parameter>action1</parameter> can be a positive integer or one of the following tokens: 
		<parameter>ignore</parameter>; <parameter>ok</parameter>; <parameter>done</parameter>;
		<parameter>bad</parameter>; <parameter>die</parameter>; and <parameter>reset</parameter>.
		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.
		</para>

		<itemizedlist>
			<listitem><para>
			<parameter>ignore:</parameter> When used with a stack of modules, the module's return status will not
			contribute to the return code the application obtains.
			</para></listitem>

			<listitem><para>
            <parameter>bad:</parameter> 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.
			</para></listitem>

            <listitem><para>
            <parameter>die:</parameter> Equivalent to bad with the side effect of terminating the module stack and
			PAM immediately returning to the application.
			</para></listitem>

           <listitem><para>
           <parameter>ok:</parameter> 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 module's
			failure, this <parameter>ok</parameter> value will not be used to override that value.
			</para></listitem>

            <listitem><para>
            <parameter>done:</parameter> Equivalent to <parameter>ok</parameter> with the side effect of terminating the module stack and
			PAM immediately returning to the application.
                        </para></listitem>

           <listitem><para>
           <parameter>reset:</parameter> Clears all memory of the state of the module stack and starts again with
			the next stacked module.
			</para></listitem>
		</itemizedlist>

		<para>
		Each of the four keywords, <parameter>required</parameter>; <parameter>requisite</parameter>;
		<parameter>sufficient</parameter>; and <parameter>optional</parameter>, have an equivalent expression in terms
		of the [...] syntax. They are as follows:
		</para>

		<para>
		<itemizedlist>
			<listitem><para>
			<parameter>required</parameter> is equivalent to <parameter>[success=ok new_authtok_reqd=ok ignore=ignore default=bad]</parameter>.
			</para></listitem>

			<listitem><para>
			<parameter>requisite</parameter> is equivalent to <parameter>[success=ok new_authtok_reqd=ok ignore=ignore default=die]</parameter>.
			</para></listitem>

			<listitem><para>
			<parameter>sufficient</parameter> is equivalent to <parameter>[success=done  new_authtok_reqd=done  default=ignore]</parameter>.
			</para></listitem>

			<listitem><para>
			<parameter>optional</parameter> is equivalent to <parameter>[success=ok new_authtok_reqd=ok default=ignore]</parameter>.
			</para></listitem>
		</itemizedlist>
		</para>

		<para>
		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 makes it possible for PAM to support
		machine-machine authentication using the transport protocol inherent to the client/server application. With the
		<parameter>[ ... value=action ... ]</parameter> control syntax, it is possible for an application to be configured
		to support binary prompts with compliant clients, but to gracefully fail over into an alternative authentication
		mode for legacy applications.
		</para>
		</listitem>
	</varlistentry>

	<varlistentry><term>module-path</term><listitem>
		<para>
		The pathname of the dynamically loadable object file; the pluggable module itself. If the first character of the
		module path is <quote>/</quote>, 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: <filename>/lib/security</filename> (but see the previous notes).
		</para>

		<para>
		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.
		</para>

		<para>
		If you wish to include spaces in an argument, you should surround that argument with square brackets. For example:
		</para>

<para><programlisting>
squid auth required pam_mysql.so user=passwd_query passwd=mada \
db=eminence [query=select user_name from internet_service where \
user_name=<quote>%u</quote> and password=PASSWORD(<quote>%p</quote>) and service=<quote>web_proxy</quote>]
</programlisting></para>

		<para>
		When using this convention, you can include <quote>[</quote> characters inside the string, and if you wish to have a <quote>]</quote>
		character inside the string that will survive the argument parsing, you should use <quote>\[</quote>. In other words,
		</para>

<para><programlisting>
[..[..\]..]    -->   ..[..]..
</programlisting></para>

		<para>
		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). 
		</para>
		</listitem>
	</varlistentry>
</variablelist>

</sect3>

</sect2>

<sect2>
<title>Example System Configurations</title>

<para>
The following is an example <filename>/etc/pam.d/login</filename> 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 <filename>pam_pwdb.so</filename>.
</para>

<sect3>
<title>PAM: Original Login Config</title>

<para>
	<programlisting>
#%PAM-1.0
# The PAM configuration file for the <quote>login</quote> 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
</programlisting>
</para>

</sect3>

<sect3>
<title>PAM: Login Using <filename>pam_smbpass</filename></title>

<para>
PAM allows use of replaceable modules. Those available on a sample system include:
</para>

<para><prompt>$</prompt><userinput>/bin/ls /lib/security</userinput>
<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
</programlisting></para>

<para>
The following example for the login program replaces the use of 
the <filename>pam_pwdb.so</filename> module that uses the system 
password database (<filename>/etc/passwd</filename>,
<filename>/etc/shadow</filename>, <filename>/etc/group</filename>) with 
the module <filename>pam_smbpass.so</filename>, which uses the Samba 
database containing the Microsoft MD4 encrypted password 
hashes. This database is stored either in 
<filename>/usr/local/samba/private/smbpasswd</filename>, 
<filename>/etc/samba/smbpasswd</filename> or in 
<filename>/etc/samba.d/smbpasswd</filename>, depending on the 
Samba implementation for your UNIX/Linux system. The 
<filename>pam_smbpass.so</filename> module is provided by 
Samba version 2.2.1 or later. It can be compiled by specifying the 
<option>--with-pam_smbpass</option> options when running Samba's
<command>configure</command> script. For more information
on the <filename>pam_smbpass</filename> module, see the documentation
in the <filename>source/pam_smbpass</filename> directory of the Samba 
source distribution.
</para>

<para>
	<programlisting>
#%PAM-1.0
# The PAM configuration file for the <quote>login</quote> 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
</programlisting></para>

<para>
The following is the PAM configuration file for a particular 
Linux system. The default condition uses <filename>pam_pwdb.so</filename>.
</para>

<para>
	<programlisting>
#%PAM-1.0
# The PAM configuration file for the <quote>samba</quote> 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
</programlisting></para>

<para>
In the following example, the decision has been made to use the 
<command>smbpasswd</command> database even for basic Samba authentication. Such a 
decision could also be made for the <command>passwd</command> program and would 
thus allow the <command>smbpasswd</command> passwords to be changed using the
<command>passwd</command> program:
</para>

<para>
		<programlisting>
#%PAM-1.0
# The PAM configuration file for the <quote>samba</quote> 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
</programlisting>
</para>

<note><para>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 <filename>pam_stack.so</filename> module that allows all 
authentication to be configured in a single central file. The 
<filename>pam_stack.so</filename> method has some devoted followers 
on the basis that it allows for easier administration. As with all issues in 
life, though, every decision has trade-offs, so you may want to examine the 
PAM documentation for further helpful information.
</para></note>

</sect3>

</sect2>

<sect2>
<title>&smb.conf; PAM Configuration</title>

<para>
There is an option in &smb.conf; called <smbconfoption name="obey pam restrictions"/>.
The following is from the online help for this option in SWAT:
</para>

<blockquote>
<para>
When Samba is configured to enable PAM support (i.e., <option>--with-pam</option>), 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 <smbconfoption name="encrypt passwords">yes</smbconfoption>. 
The reason is that PAM modules cannot support the challenge/response authentication mechanism needed in the presence of SMB 
password encryption. 
</para>

<para>Default: <smbconfoption name="obey pam restrictions">no</smbconfoption></para>
</blockquote>

</sect2>

<sect2>
<title>Remote CIFS Authentication Using <filename>winbindd.so</filename></title>

<para>
All operating systems depend on the provision of user 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 numbers that are obtained from a password backend such
as <filename>/etc/passwd</filename>.
</para>

<para>
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.
</para>

<para>
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.
</para>

<para>
The astute administrator will realize from this that the combination of <filename>pam_smbpass.so</filename>, 
<command>winbindd</command>, and a distributed <smbconfoption name="passdb backend"></smbconfoption>
such as <parameter>ldap</parameter> 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) insofar as
the reduction of wide-area network authentication traffic.
</para>

<warning><para>
The RID to UNIX ID database is the only location where the user and group  mappings are 
stored by <command>winbindd</command>. If this file is deleted or corrupted, there is no way for <command>winbindd</command>
to determine which user and group IDs correspond to Windows NT user and group RIDs.
</para></warning>

</sect2>

<sect2>
<title>Password Synchronization Using <filename>pam_smbpass.so</filename></title>

<para>
<filename>pam_smbpass</filename> is a PAM module that can be used on conforming systems to
keep the <filename>smbpasswd</filename> (Samba password) database in sync with the UNIX
password file. PAM is an API supported
under some UNIX operating systems, such as Solaris, HPUX, and Linux, that provides a
generic interface to authentication mechanisms.
</para>

<para>
This module authenticates a local <filename>smbpasswd</filename> 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 <filename>pam_winbind</filename> instead.
</para>

<para>
Options recognized by this module are shown in <link linkend="smbpassoptions">next table</link>.
<table frame="all" id="smbpassoptions">
	<title>Options recognized by <parameter>pam_smbpass</parameter></title>
	<tgroup cols="2" align="left">
		<colspec align="left"/>
		<colspec align="justify" colwidth="1*"/>
	<tbody>
		<row><entry>debug</entry><entry>Log more debugging info.</entry></row>
		<row><entry>audit</entry><entry>Like debug, but also logs unknown usernames.</entry></row>
		<row><entry>use_first_pass</entry><entry>Do not prompt the user for passwords; take them from PAM_ items instead.</entry></row>
		<row><entry>try_first_pass</entry><entry>Try to get the password from a previous PAM module; fall back to prompting the user.</entry></row>
		<row><entry>use_authtok</entry>
			<entry>Like try_first_pass, but *fail* if the new PAM_AUTHTOK has not been previously set (intended for stacking password modules only).</entry></row>
		<row><entry>not_set_pass</entry><entry>Do not make passwords used by this module available to other modules.</entry></row>
		<row><entry>nodelay</entry><entry>dDo not insert ~1-second delays on authentication failure.</entry></row>
		<row><entry>nullok</entry><entry>Null passwords are allowed.</entry></row>
		<row><entry>nonull</entry><entry>Null passwords are not allowed. Used to override the Samba configuration.</entry></row>
		<row><entry>migrate</entry><entry>Only meaningful in an <quote>auth</quote> context; used to update smbpasswd file with a password used for successful authentication.</entry></row>
		<row><entry>smbconf=<replaceable>file</replaceable></entry><entry>Specify an alternate path to the &smb.conf; file.</entry></row>
	</tbody>
</tgroup>
</table>
</para>

<para>
The following are examples of the use of <filename>pam_smbpass.so</filename> in the format of the Linux
<filename>/etc/pam.d/</filename> files structure. Those wishing to implement this
tool on other platforms will need to adapt this appropriately.
</para>

<sect3>
<title>Password Synchronization Configuration</title>

<para>
The following is a sample PAM configuration that shows the use of pam_smbpass to make
sure <filename>private/smbpasswd</filename> is kept in sync when <filename>/etc/passwd (/etc/shadow)</filename>
is changed. It is useful when an expired password might be changed by an
application (such as <command>ssh</command>).
</para>

<para>
	<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
</programlisting></para>
</sect3>

<sect3>
<title>Password Migration Configuration</title>

<para>
The following PAM configuration shows the use of <filename>pam_smbpass</filename> 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 <command>ftp</command> in, login using <command>ssh</command>, pop
their mail, and so on.
</para>

<para>
	<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
</programlisting></para>
</sect3>

<sect3>
<title>Mature Password Configuration</title>

<para>
The following is a sample PAM configuration for a mature <filename>smbpasswd</filename> installation.
<filename>private/smbpasswd</filename> is fully populated, and we consider it an error if
the SMB password does not exist or does not match the UNIX password.
</para>

<para>
<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
</programlisting></para>
</sect3>

<sect3>
<title>Kerberos Password Integration Configuration</title>

<para>
The following is a sample PAM configuration that shows <parameter>pam_smbpass</parameter> used together with
<parameter>pam_krb5</parameter>. This could be useful on a Samba PDC that is also a member of
a Kerberos realm.
</para>

<para>
		<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
</programlisting></para>

</sect3>

</sect2>

</sect1>

<sect1>
<title>Common Errors</title>

<para>
PAM can be fickle and sensitive to configuration glitches. Here we look at a few cases from
the Samba mailing list.
</para>

	<sect2>
	<title>pam_winbind Problem</title>

	<para>
	A user reported, <emphasis>I have the following PAM configuration</emphasis>:
	</para>

<para>
<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
</programlisting>
</para>

	<para>
	<emphasis>When I open a new console with [ctrl][alt][F1], I can't log in with my user <quote>pitie.</quote>
	I have tried with user <quote>scienceu\pitie</quote> also.</emphasis>
	</para>

	<para>
	The problem may lie with the inclusion of <parameter>pam_stack.so
	service=system-auth</parameter>. That file often contains a lot of stuff that may
	duplicate what you are already doing. Try commenting out the <parameter>pam_stack</parameter> lines
	for <parameter>auth</parameter> and <parameter>account</parameter> and see if things work. If they do, look at
	<filename>/etc/pam.d/system-auth</filename> and copy only what you need from it into your
	<filename>/etc/pam.d/login</filename> file. Alternatively, if you want all services to use
	Winbind, you can put the Winbind-specific stuff in <filename>/etc/pam.d/system-auth</filename>.
	</para>

	</sect2>

	<sect2>
	<title>Winbind Is Not Resolving Users and Groups</title>

	<para>
	<quote>
	My &smb.conf; file is correctly configured. I have specified 
	<smbconfoption name="idmap uid">12000</smbconfoption> 
	and <smbconfoption name="idmap gid">3000-3500,</smbconfoption>
	and <command>winbind</command> is running. When I do the following it all works fine.
	</quote>
	</para>

<para><screen>
&rootprompt;<userinput>wbinfo -u</userinput>
MIDEARTH\maryo
MIDEARTH\jackb
MIDEARTH\ameds
...
MIDEARTH\root

&rootprompt;<userinput>wbinfo -g</userinput>
MIDEARTH\Domain Users
MIDEARTH\Domain Admins
MIDEARTH\Domain Guests
...
MIDEARTH\Accounts

&rootprompt;<userinput>getent passwd</userinput>
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
</screen></para>

	<para>
	<quote>
	But this command fails:
	</quote>
<screen>
&rootprompt;<userinput>chown maryo a_file</userinput>
chown: 'maryo': invalid user
</screen>
	<quote>This is driving me nuts! What can be wrong?</quote>
	</para>

	<para>
	Your system is likely running <command>nscd</command>, the name service
	caching daemon. Shut it down, do not restart it! You will find your problem resolved.
	</para>

	</sect2>
</sect1>

</chapter>