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<html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Chapter 20. PAM Configuration for Centrally Managed Authentication</title><link rel="stylesheet" href="samba.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.59.1"><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="InterdomainTrusts.html" title="Chapter 19. Interdomain Trust Relationships"><link rel="next" href="VFS.html" title="Chapter 21. Stackable VFS modules"></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 20. PAM Configuration for Centrally Managed Authentication</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="InterdomainTrusts.html">Prev</a> </td><th width="60%" align="center">Part III. Advanced Configuration</th><td width="20%" align="right"> <a accesskey="n" href="VFS.html">Next</a></td></tr></table><hr></div><div class="chapter" lang="en"><div class="titlepage"><div><h2 class="title"><a name="pam"></a>Chapter 20. PAM Configuration for Centrally Managed Authentication</h2></div><div><div class="author"><h3 class="author">John H. Terpstra</h3><div class="affiliation"><span class="orgname">Samba Team<br></span><div class="address"><p><tt><<a href="mailto:jht@samba.org">jht@samba.org</a>></tt></p></div></div></div></div><div><p class="pubdate"> (Jun 21 2001) </p></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><a href="pam.html#id2897853">Samba and PAM</a></dt><dd><dl><dt><a href="pam.html#id2898634">PAM Configuration in smb.conf</a></dt><dt><a href="pam.html#id2898691">Password Synchronisation using pam_smbpass.so</a></dt></dl></dd><dt><a href="pam.html#id2898943">Distributed Authentication</a></dt></dl></div><div class="sect1" lang="en"><div class="titlepage"><div><h2 class="title" style="clear: both"><a name="id2897853"></a>Samba and PAM</h2></div></div><p>
A number of Unix systems (eg: 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>/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 such programs as: <b>login</b>,
<b>passwd</b>, <b>chown</b>, etc.
</p><p>
PAM provides a mechanism that disconnects these security programs
from the underlying authentication/authorization infrastructure.
PAM is configured either through one file <tt>/etc/pam.conf</tt> (Solaris),
or by editing individual files that are located in <tt>/etc/pam.d</tt>.
</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><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>/lib/security</tt>. If the module
is located outside the default then the path must be specified as:
</p><pre class="programlisting">
auth required /other_path/pam_strange_module.so
</pre><p>
</p></div><p>
The following is an example <tt>/etc/pam.d/login</tt> configuration file.
This example had all options been uncommented is probably not usable
as 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>pam_pwdb.so</tt>.
</p><pre class="programlisting">
#%PAM-1.0
# The PAM configuration file for the `login' service
#
auth required pam_securetty.so
auth required pam_nologin.so
# auth required pam_dialup.so
# auth optional pam_mail.so
auth required pam_pwdb.so shadow md5
# account requisite pam_time.so
account required pam_pwdb.so
session required pam_pwdb.so
# session optional pam_lastlog.so
# password required pam_cracklib.so retry=3
password required pam_pwdb.so shadow md5
</pre><p>
PAM allows use of replacable modules. Those available on a
sample system include:
</p><p><tt>$</tt><b><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>pam_pwdb.so</tt> module which uses the system
password database (<tt>/etc/passwd</tt>,
<tt>/etc/shadow</tt>, <tt>/etc/group</tt>) with
the module <tt>pam_smbpass.so</tt> which uses the Samba
database which contains the Microsoft MD4 encrypted password
hashes. This database is stored in either
<tt>/usr/local/samba/private/smbpasswd</tt>,
<tt>/etc/samba/smbpasswd</tt>, or in
<tt>/etc/samba.d/smbpasswd</tt>, depending on the
Samba implementation for your Unix/Linux system. The
<tt>pam_smbpass.so</tt> module is provided by
Samba version 2.2.1 or later. It can be compiled by specifying the
<b>--with-pam_smbpass</b> options when running Samba's
<tt>configure</tt> script. For more information
on the <tt>pam_smbpass</tt> module, see the documentation
in the <tt>source/pam_smbpass</tt> directory of the Samba
source distribution.
</p><pre class="programlisting">
#%PAM-1.0
# The PAM configuration file for the `login' 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>pam_pwdb.so</tt>.
</p><pre class="programlisting">
#%PAM-1.0
# The PAM configuration file for the `samba' 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
smbpasswd database even for basic samba authentication. Such a
decision could also be made for the passwd program and would
thus allow the smbpasswd passwords to be changed using the passwd
program.
</p><pre class="programlisting">
#%PAM-1.0
# The PAM configuration file for the `samba' 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 implmentations also
provide the <tt>pam_stack.so</tt> module that allows all
authentication to be configured in a single central file. The
<tt>pam_stack.so</tt> method has some very 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 examine the
PAM documentation for further helpful information.
</p></div><div class="sect2" lang="en"><div class="titlepage"><div><h3 class="title"><a name="id2898634"></a>PAM Configuration in smb.conf</h3></div></div><p>
There is an option in smb.conf called <a href="smb.conf.5.html#OBEYPAMRESTRICTIONS" target="_top">obey pam restrictions</a>.
The following is from the on-line help for this option in SWAT;
</p><p>
When Samba is configured to enable PAM support (i.e.
<tt>--with-pam</tt>), this parameter will
control whether or not Samba should obey PAM's account
and session management directives. The default behavior
is to use PAM for clear text authentication only and to
ignore any account or session management. Note that Samba always
ignores PAM for authentication in the case of
<a href="smb.conf.5.html#ENCRYPTPASSWORDS" target="_top">encrypt passwords = yes</a>.
The reason is that PAM modules cannot support the challenge/response
authentication mechanism needed in the presence of SMB
password encryption.
</p><p>Default: <b>obey pam restrictions = no</b></p></div><div class="sect2" lang="en"><div class="titlepage"><div><h3 class="title"><a name="id2898691"></a>Password Synchronisation using pam_smbpass.so</h3></div></div><p>
pam_smbpass is a PAM module which can be used on conforming systems to
keep the smbpasswd (Samba password) database in sync with the unix
password file. PAM (Pluggable Authentication Modules) is an API supported
under some Unices, such as Solaris, HPUX and Linux, that provides a
generic interface to authentication mechanisms.
</p><p>
For more information on PAM, see http://ftp.kernel.org/pub/linux/libs/pam/
</p><p>
This module authenticates a local smbpasswd user database. If you require
support for authenticating against a remote SMB server, or if you're
concerned about the presence of suid root binaries on your system, it is
recommended that you use pam_winbind instead.
</p><pre class="programlisting">
Options recognized by this module are as follows:
debug - log more debugging info
audit - like debug, but also logs unknown usernames
use_first_pass - don't prompt the user for passwords;
take them from PAM_ items instead
try_first_pass - try to get the password from a previous
PAM module, fall back to prompting the user
use_authtok - like try_first_pass, but *fail* if the new
PAM_AUTHTOK has not been previously set.
(intended for stacking password modules only)
not_set_pass - don't make passwords used by this module
available to other modules.
nodelay - don't insert ~1 second delays on authentication
failure.
nullok - null passwords are allowed.
nonull - null passwords are not allowed. Used to
override the Samba configuration.
migrate - only meaningful in an "auth" context;
used to update smbpasswd file with a
password used for successful authentication.
smbconf=< file > - specify an alternate path to the smb.conf
file.
</pre><pre class="programlisting">
Thanks go to the following people:
* Andrew Morgan < morgan@transmeta.com >, for providing the Linux-PAM
framework, without which none of this would have happened
* Christian Gafton < gafton@redhat.com > and Andrew Morgan again, for the
pam_pwdb module upon which pam_smbpass was originally based
* Luke Leighton < lkcl@switchboard.net > for being receptive to the idea,
and for the occasional good-natured complaint about the project's status
that keep me working on it :)
* and of course, all the other members of the Samba team
<http://www.samba.org/samba/team.html>, for creating a great product
and for giving this project a purpose
---------------------
Stephen Langasek < vorlon@netexpress.net >
</pre><p>
The following are examples of the use of pam_smbpass.so in the format of Linux
<tt>/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><h4 class="title"><a name="id2898803"></a>Password Synchonisation Configuration</h4></div></div><p>
A sample PAM configuration that shows the use of pam_smbpass to make
sure private/smbpasswd is kept in sync when /etc/passwd (/etc/shadow)
is changed. Useful when an expired password might be changed by an
application (such as ssh).
</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><h4 class="title"><a name="id2898838"></a>Password Migration Configuration</h4></div></div><p>
A sample PAM configuration that shows the use of pam_smbpass 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 ftp in, login using ssh, pop
their mail, etc.
</p><pre class="programlisting">
#%PAM-1.0
# password-migration
#
auth requisite pam_nologin.so
# pam_smbpass is called IFF 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><h4 class="title"><a name="id2898875"></a>Mature Password Configuration</h4></div></div><p>
A sample PAM configuration for a 'mature' smbpasswd installation.
private/smbpasswd is fully populated, and we consider it an error if
the smbpasswd doesn't exist or doesn't 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><h4 class="title"><a name="id2898908"></a>Kerberos Password Integration Configuration</h4></div></div><p>
A sample PAM configuration that shows pam_smbpass used together with
pam_krb5. 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><h2 class="title" style="clear: both"><a name="id2898943"></a>Distributed Authentication</h2></div></div><p>
The astute administrator will realize from this that the
combination of <tt>pam_smbpass.so</tt>,
<b>winbindd</b>, and a distributed
passdb backend, such as ldap, will allow the establishment of a
centrally managed, distributed
user/password database that can also be used by all
PAM (eg: Linux) aware programs and applications. This arrangement
can have particularly potent advantages compared with the
use of Microsoft Active Directory Service (ADS) in so far as
reduction of wide area network authentication traffic.
</p></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="InterdomainTrusts.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="VFS.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 19. Interdomain Trust Relationships </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 21. Stackable VFS modules</td></tr></table></div></body></html>
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