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+<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>
+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>
+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>
+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>
+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>
+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>
+ 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>
+ 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>
+ 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, Microsoft Active Directory.
+ </para>
+ </listitem></varlistentry>
+
+ <varlistentry><term>NetWare Bindery</term><listitem>
+ <para>
+ 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>
+ This module, called <filename>pam_smbpass.so</filename>, will allow user authentication off
+ the passdb backend that is configured in the Samba &smb.conf; file.
+ </para>
+ </listitem></varlistentry>
+
+ <varlistentry><term>SMB Server</term><listitem>
+ <para>
+ 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>
+ 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>
+ 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.
+ </para>
+ </listitem></varlistentry>
+</variablelist>
+
+<para>
+Of the above, Samba provides the <filename>pam_smbpasswd.so</filename> and the <filename>pam_winbind.so</filename> modules alone.
+</para>
+
+<para>
+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>
+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, <filename>/etc/pam.conf</filename>, or the
+<filename>/etc/pam.d/</filename> directory.
+</para>
+
+<sect2>
+<title>PAM Configuration Syntax</title>
+
+<para>
+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>
+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:
+</para>
+
+<para>
+<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>
+A general configuration line of the <filename>/etc/pam.conf</filename> file has the following form:
+</para>
+
+<para>
+<programlisting>
+service-name module-type control-flag module-path args
+</programlisting>
+</para>
+
+<para>
+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 <filename>/etc/pam.d/</filename> directory.
+Once we have explained the meaning of the above tokens, we will describe this method.
+</para>
+
+<variablelist>
+ <varlistentry><term>service-name</term><listitem>
+ <para>
+ The name of the service associated with this entry. Frequently, the service name is the conventional
+ name of the given application. 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 upper-case 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>
+ <parameter>auth:</parameter> 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 <filename>/etc/groups</filename> file discussed
+ above) or other privileges through its credential granting properties.
+ </para></listitem>
+
+ <listitem><para>
+ <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 applicant
+ user <quote>root</quote> login only on the console.
+ </para></listitem>
+
+ <listitem><para>
+ <parameter>session:</parameter> 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.
+ </para></listitem>
+
+ <listitem><para>
+ <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>
+ -based 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>
+ 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, requisite, sufficient and 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, 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.
+ </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; ok; done; bad; 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 modules
+ 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; requisite; 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<?latex \linebreak ?> 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 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
+ <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 fall over into an alternative authentication
+ mode for older, legacy applications.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry><term>module-path</term><listitem>
+ <para>
+ The path-name 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 notes above).
+ </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>
+ <smbfile name="pam-login-default">
+ <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>
+</smbfile></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 which contains the Microsoft MD4 encrypted password
+hashes. This database is stored in either
+<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>
+ <smbfile name="pam-login-smbpass">
+ <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></smbfile></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>
+ <smbfile name="pam-samba-default">
+ <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></smbfile></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><smbfile name="pam-samba-smbpass">
+ <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>
+</smbfile></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 makes 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</name></smbconfoption>.
+The following is from the online help for this option in SWAT;
+</para>
+
+<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</name><value>yes</value></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</name><value>no</value></smbconfoption></para>
+
+</sect2>
+
+<sect2>
+<title>Remote CIFS Authentication Using <filename>winbindd.so</filename></title>
+
+<para>
+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 <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</name><value></value></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) in so far 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 (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.
+</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>do 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 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>
+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. Useful when an expired password might be changed by an
+application (such as <command>ssh</command>).
+</para>
+
+<para>
+ <smbfile name="pam-synchronised-password">
+ <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></smbfile></para>
+</sect3>
+
+<sect3>
+<title>Password Migration Configuration</title>
+
+<para>
+A sample PAM configuration that 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><smbfile name="pam-password-migration">
+ <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></smbfile></para>
+</sect3>
+
+<sect3>
+<title>Mature Password Configuration</title>
+
+<para>
+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><smbfile name="pam-fallback">
+<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></smbfile></para>
+</sect3>
+
+<sect3>
+<title>Kerberos Password Integration Configuration</title>
+
+<para>
+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><smbfile name="pam-krb">
+ <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></smbfile></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>
+
+<!-- shouldn't this be in the Winbind chapter - Jelmer -->
+ <sect2>
+ <title>pam_winbind Problem</title>
+
+ <para>
+ A user reported: I have the following PAM configuration:
+ </para>
+
+<para>
+ <smbfile name="pam-winbind-erratic">
+<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></smbfile>
+</para>
+
+ <para>
+ 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.
+ </para>
+
+ <para>
+ <emphasis>Answer:</emphasis> The problem may lie with your 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. Alternately, 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</name><value>12000</value></smbconfoption>,
+ and <smbconfoption><name>idmap gid</name><value>3000-3500</value></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>
+ <emphasis>Answer:</emphasis> 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>