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   $Id: pam_pwdb.sgml 274 2005-07-13 09:52:25Z vorlon $
   
   This file was written by Andrew G. Morgan <morgan@kernel.org>
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<sect1>The Password-Database module

<sect2>Synopsis

<p>
<descrip>

<tag><bf>Module Name:</bf></tag>
pam_pwdb

<tag><bf>Author:</bf></tag>
Cristian Gafton &lt;gafton@redhat.com&gt; <newline>
and Andrew G. Morgan &lt;morgan@kernel.org&gt;

<tag><bf>Maintainer:</bf></tag>
Red Hat.

<tag><bf>Management groups provided:</bf></tag>
account; authentication; password; session

<tag><bf>Cryptographically sensitive:</bf></tag>
	
<tag><bf>Security rating:</bf></tag>

<tag><bf>Clean code base:</bf></tag>

<tag><bf>System dependencies:</bf></tag>
Requires properly configured <tt/libpwdb/

<tag><bf>Network aware:</bf></tag>

</descrip>

<sect2>Overview of module

<p>
This module is a pluggable replacement for the <tt/pam_unix_../
modules. It uses the generic interface of the <em/Password Database/
library <tt>libpwdb</tt>.

<sect2>Account component

<p>
<descrip>

<tag><bf>Recognized arguments:</bf></tag>
<tt/debug/

<tag><bf>Description:</bf></tag>

The <tt/debug/ argument makes the accounting functions of this module
<tt/syslog(3)/ more information on its actions. (Remaining arguments
supported by the other functions of this module are silently ignored,
but others are logged as errors through <tt/syslog(3)/).

Based on the following <tt/pwdb_element/s:
<tt/expire/;
<tt/last_change/;
<tt/max_change/;
<tt/defer_change/;
<tt/warn_change/,
this module performs the task of establishing the status of the user's
account and password. In the case of the latter, it may offer advice
to the user on changing their password or, through the
<tt/PAM_AUTHTOKEN_REQD/ return, delay giving service to the user until
they have established a new password. The entries listed above are
documented in the <em/Password Database Library Guide/ (see pointer
above). Should the user's record not contain one or more of these
entries, the corresponding <em/shadow/ check is not performed.

<tag><bf>Examples/suggested usage:</bf></tag>

In its accounting mode, this module can be inserted as follows:
<tscreen>
<verb>
#
# Ensure users account and password are still active
#
login	account	 required	pam_pwdb.so
</verb>
</tscreen>

</descrip>

<sect2>Authentication component

<p>
<descrip>

<tag><bf>Recognized arguments:</bf></tag>
<tt/debug/;
<tt/use_first_pass/;
<tt/try_first_pass/;
<tt/nullok/;
<tt/nodelay/;
<tt/likeauth/;
<tt/noreap/

<tag><bf>Description:</bf></tag>

The <tt/debug/ argument makes the authentication functions of this
module <tt/syslog(3)/ more information on its actions.

<p>
The default action of this module is to not permit the user access to
a service if their <em/official/ password is blank. The <tt/nullok/
argument overrides this default.

<p>
When given the argument <tt/try_first_pass/, before prompting the user
for their password, the module first tries the previous stacked
<tt/auth/-module's password in case that satisfies this module as
well. The argument <tt/use_first_pass/ forces the module to use such a
recalled password and will never prompt the user - if no password is
available or the password is not appropriate, the user will be denied
access.

<p>
The argument, <tt>nodelay</tt>, can be used to discourage the
authentication component from requesting a delay should the
authentication as a whole fail.  The default action is for the module
to request a delay-on-failure of the order of one second.

<p>
Remaining arguments, supported by the other functions of this module,
are silently ignored. Other arguments are logged as errors through
<tt/syslog(3)/.

<p>
A helper binary, <tt>pwdb_chkpwd</tt>, is provided to check the user's
password when it is stored in a read protected database.  This binary
is very simple and will only check the password of the user invoking
it.  It is called transparently on behalf of the user by the
authenticating component of this module.  In this way it is possible
for applications like <em>xlock</em> to work without being
setuid-root. The module, by default, will temporarily turn off
<tt/SIGCHLD/ handling for the duration of execution of the helper
binary. This is generally the right thing to do, as many applications
are not prepared to handle this signal from a child they didn't know
was <tt/fork()/d. The <tt/noreap/ module argument can be used to
suppress this temporary shielding and may be needed for use with
certain applications.

<p>
The <tt>likeauth</tt> argument makes the module return the same value
when called as a credential setting module and an authentication
module.  This will help libpam take a sane path through the auth
component of your configuration file.

<tag><bf>Examples/suggested usage:</bf></tag>

The correct functionality of this module is dictated by having an
appropriate <tt>/etc/pwdb.conf</tt> file, the user
databases specified there dictate the source of the authenticated
user's record.

</descrip>

<sect2>Password component

<p>
<descrip>

<tag><bf>Recognized arguments:</bf></tag>
<tt/debug/; <tt/nullok/; <tt/not_set_pass/; <tt/use_authtok/;
<tt/try_first_pass/; <tt/use_first_pass/; <tt/md5/; <tt/bigcrypt/;
<tt/shadow/; <tt/radius/; <tt/unix/

<tag><bf>Description:</bf></tag>

This part of the <tt/pam_pwdb/ module performs the task of updating
the user's password.  Thanks to the flexibility of <tt/libpwdb/ this
module is able to move the user's password from one database to
another, perhaps securing the user's database entry in a dynamic
manner (<em/this is very ALPHA code at the moment!/) - this is the
purpose of the <tt/shadow/, <tt/radius/ and <tt/unix/ arguments.

<p>
In the case of conventional unix databases (which store the password
encrypted) the <tt/md5/ argument is used to do the encryption with the
MD5 function as opposed to the <em/conventional/ <tt/crypt(3)/ call.
As an alternative to this, the <tt/bigcrypt/ argument can be used to
encrypt more than the first 8 characters of a password with DEC's
(Digital Equipment Cooperation) `C2' extension to the standard UNIX
<tt/crypt()/ algorithm.

<p>
The <tt/nullok/ module is used to permit the changing of a password
<em/from/ an empty one. Without this argument, empty passwords are
treated as account-locking ones.

<p>
The argument <tt/use_first_pass/ is used to lock the choice of old and
new passwords to that dictated by the previously stacked <tt/password/
module.  The <tt/try_first_pass/ argument is used to avoid the user
having to re-enter an old password when <tt/pam_pwdb/ follows a module
that possibly shared the user's old password - if this old password is
not correct the user will be prompted for the correct one.  The
argument <tt/use_authtok/ is used to <em/force/ this module to set the
new password to the one provided by the previously stacked
<tt/password/ module (this is used in an example of the stacking of
the <em/Cracklib/ module documented above).

<p>
The <tt/not_set_pass/ argument is used to inform the module that it is
not to pay attention to/make available the old or new passwords from/to
other (stacked) password modules.

<p>
The <tt/debug/ argument makes the password functions of this module
<tt/syslog(3)/ more information on its actions. Other arguments may be
logged as erroneous to <tt/syslog(3)/.

<tag><bf>Examples/suggested usage:</bf></tag>

An example of the stacking of this module with respect to the
pluggable password checking module, <tt/pam_cracklib/, is given in
that modules section above.
</descrip>

<sect2>Session component

<p>
<descrip>

<tag><bf>Recognized arguments:</bf></tag>

<tag><bf>Description:</bf></tag>

No arguments are recognized by this module component. Its action is
simply to log the username and the service-type to
<tt/syslog(3)/. Messages are logged at the beginning and end of the
user's session.

<tag><bf>Examples/suggested usage:</bf></tag>

The use of the session modules is straightforward:
<tscreen>
<verb>
#
# pwdb - unix like session opening and closing
#
login	session	 required	pam_pwdb.so
</verb>
</tscreen>

</descrip>

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