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<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>6.11. pam_group - module to modify group access</title><meta name="generator" content="DocBook XSL Stylesheets V1.78.1"><link rel="home" href="Linux-PAM_SAG.html" title="The Linux-PAM System Administrators' Guide"><link rel="up" href="sag-module-reference.html" title="Chapter 6. A reference guide for available modules"><link rel="prev" href="sag-pam_ftp.html" title="6.10. pam_ftp - module for anonymous access"><link rel="next" href="sag-pam_issue.html" title="6.12. pam_issue - add issue file to user prompt"></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">6.11. pam_group - module to modify group access</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="sag-pam_ftp.html">Prev</a> </td><th width="60%" align="center">Chapter 6. A reference guide for available modules</th><td width="20%" align="right"> <a accesskey="n" href="sag-pam_issue.html">Next</a></td></tr></table><hr></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="sag-pam_group"></a>6.11. pam_group - module to modify group access</h2></div></div></div><div class="cmdsynopsis"><p><code class="command">pam_group.so</code> </p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="sag-pam_group-description"></a>6.11.1. DESCRIPTION</h3></div></div></div><p>
The pam_group PAM module does not authenticate the user, but instead
it grants group memberships (in the credential setting phase of the
authentication module) to the user. Such memberships are based on the
service they are applying for.
</p><p>
By default rules for group memberships are taken from config file
<code class="filename">/etc/security/group.conf</code>.
</p><p>
This module's usefulness relies on the file-systems
accessible to the user. The point being that once granted the
membership of a group, the user may attempt to create a
<code class="function">setgid</code> binary with a restricted group ownership.
Later, when the user is not given membership to this group, they can
recover group membership with the precompiled binary. The reason that
the file-systems that the user has access to are so significant, is the
fact that when a system is mounted <span class="emphasis"><em>nosuid</em></span> the user
is unable to create or execute such a binary file. For this module to
provide any level of security, all file-systems that the user has write
access to should be mounted <span class="emphasis"><em>nosuid</em></span>.
</p><p>
The pam_group module functions in parallel with the
<code class="filename">/etc/group</code> file. If the user is granted any groups
based on the behavior of this module, they are granted
<span class="emphasis"><em>in addition</em></span> to those entries
<code class="filename">/etc/group</code> (or equivalent).
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="sag-group.conf-description"></a>6.11.2. DESCRIPTION</h3></div></div></div><p>
The pam_group PAM module does not authenticate the user, but instead
it grants group memberships (in the credential setting phase of the
authentication module) to the user. Such memberships are based on the
service they are applying for.
</p><p>
For this module to function correctly there must be a correctly
formatted <code class="filename">/etc/security/group.conf</code> file present.
White spaces are ignored and lines maybe extended with '\' (escaped
newlines). Text following a '#' is ignored to the end of the line.
</p><p>
The syntax of the lines is as follows:
</p><p>
<em class="replaceable"><code>services</code></em>;<em class="replaceable"><code>ttys</code></em>;<em class="replaceable"><code>users</code></em>;<em class="replaceable"><code>times</code></em>;<em class="replaceable"><code>groups</code></em>
</p><p>
The first field, the <em class="replaceable"><code>services</code></em> field, is a logic list
of PAM service names that the rule applies to.
</p><p>
The second field, the <em class="replaceable"><code>tty</code></em>
field, is a logic list of terminal names that this rule applies to.
</p><p>
The third field, the <em class="replaceable"><code>users</code></em>
field, is a logic list of users, or a UNIX group, or a netgroup of
users to whom this rule applies. Group names are preceded by a '%'
symbol, while netgroup names are preceded by a '@' symbol.
</p><p>
For these items the simple wildcard '*' may be used only once.
With UNIX groups or netgroups no wildcards or logic operators
are allowed.
</p><p>
The <em class="replaceable"><code>times</code></em> field is used to indicate "when"
these groups are to be given to the user. The format here is a logic
list of day/time-range entries. The days are specified by a sequence of
two character entries, MoTuSa for example is Monday Tuesday and Saturday.
Note that repeated days are unset MoMo = no day, and MoWk = all weekdays
bar Monday. The two character combinations accepted are Mo Tu We Th Fr Sa
Su Wk Wd Al, the last two being week-end days and all 7 days of the week
respectively. As a final example, AlFr means all days except Friday.
</p><p>
Each day/time-range can be prefixed with a '!' to indicate "anything but".
The time-range part is two 24-hour times HHMM, separated by a hyphen,
indicating the start and finish time (if the finish time is smaller
than the start time it is deemed to apply on the following day).
</p><p>
The <em class="replaceable"><code>groups</code></em> field is a comma or space
separated list of groups that the user inherits membership of. These
groups are added if the previous fields are satisfied by the user's request.
</p><p>
For a rule to be active, ALL of service+ttys+users must be satisfied
by the applying process.
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="sag-pam_group-options"></a>6.11.3. OPTIONS</h3></div></div></div><p>This module does not recognise any options.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="sag-pam_group-types"></a>6.11.4. MODULE TYPES PROVIDED</h3></div></div></div><p>
Only the <code class="option">auth</code> module type is provided.
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="sag-pam_group-return_values"></a>6.11.5. RETURN VALUES</h3></div></div></div><div class="variablelist"><dl class="variablelist"><dt><span class="term">PAM_SUCCESS</span></dt><dd><p>
group membership was granted.
</p></dd><dt><span class="term">PAM_ABORT</span></dt><dd><p>
Not all relevant data could be gotten.
</p></dd><dt><span class="term">PAM_BUF_ERR</span></dt><dd><p>
Memory buffer error.
</p></dd><dt><span class="term">PAM_CRED_ERR</span></dt><dd><p>
Group membership was not granted.
</p></dd><dt><span class="term">PAM_IGNORE</span></dt><dd><p>
<code class="function">pam_sm_authenticate</code> was called which does nothing.
</p></dd><dt><span class="term">PAM_USER_UNKNOWN</span></dt><dd><p>
The user is not known to the system.
</p></dd></dl></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="sag-pam_group-files"></a>6.11.6. FILES</h3></div></div></div><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="filename">/etc/security/group.conf</code></span></dt><dd><p>Default configuration file</p></dd></dl></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="sag-group.conf-examples"></a>6.11.7. EXAMPLES</h3></div></div></div><p>
These are some example lines which might be specified in
<code class="filename">/etc/security/group.conf</code>.
</p><p>
Running 'xsh' on tty* (any ttyXXX device), the user 'us' is given access
to the floppy (through membership of the floppy group)
</p><pre class="programlisting">xsh;tty*&!ttyp*;us;Al0000-2400;floppy</pre><p>
Running 'xsh' on tty* (any ttyXXX device), the user 'sword' is given access
to games (through membership of the floppy group) after work hours.
</p><pre class="programlisting">
xsh; tty* ;sword;!Wk0900-1800;games, sound
xsh; tty* ;*;Al0900-1800;floppy
</pre><p>
Any member of the group 'admin' running 'xsh' on tty*,
is granted access (at any time) to the group 'plugdev'
</p><pre class="programlisting">
xsh; tty* ;%admin;Al0000-2400;plugdev
</pre></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="sag-pam_group-authors"></a>6.11.8. AUTHORS</h3></div></div></div><p>
pam_group was written by Andrew G. Morgan <morgan@kernel.org>.
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