EVOLUTION-MANAGER
Edit File: sag-pam_namespace.html
<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>6.22. pam_namespace - setup a private namespace</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_motd.html" title="6.21. pam_motd - display the motd file"><link rel="next" href="sag-pam_nologin.html" title="6.23. pam_nologin - prevent non-root users from login"></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">6.22. pam_namespace - setup a private namespace</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="sag-pam_motd.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_nologin.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_namespace"></a>6.22. pam_namespace - setup a private namespace</h2></div></div></div><div class="cmdsynopsis"><p><code class="command">pam_namespace.so</code> [ debug ] [ unmnt_remnt ] [ unmnt_only ] [ require_selinux ] [ gen_hash ] [ ignore_config_error ] [ ignore_instance_parent_mode ] [ unmount_on_close ] [ use_current_context ] [ use_default_context ] [ mount_private ]</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="sag-pam_namespace-description"></a>6.22.1. DESCRIPTION</h3></div></div></div><p> The pam_namespace PAM module sets up a private namespace for a session with polyinstantiated directories. A polyinstantiated directory provides a different instance of itself based on user name, or when using SELinux, user name, security context or both. If an executable script <code class="filename">/etc/security/namespace.init</code> exists, it is used to initialize the instance directory after it is set up and mounted on the polyinstantiated directory. The script receives the polyinstantiated directory path, the instance directory path, flag whether the instance directory was newly created (0 for no, 1 for yes), and the user name as its arguments. </p><p> The pam_namespace module disassociates the session namespace from the parent namespace. Any mounts/unmounts performed in the parent namespace, such as mounting of devices, are not reflected in the session namespace. To propagate selected mount/unmount events from the parent namespace into the disassociated session namespace, an administrator may use the special shared-subtree feature. For additional information on shared-subtree feature, please refer to the mount(8) man page and the shared-subtree description at http://lwn.net/Articles/159077 and http://lwn.net/Articles/159092. </p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="sag-namespace.conf-description"></a>6.22.2. DESCRIPTION</h3></div></div></div><p> The <span class="emphasis"><em>pam_namespace.so</em></span> module allows setup of private namespaces with polyinstantiated directories. Directories can be polyinstantiated based on user name or, in the case of SELinux, user name, sensitivity level or complete security context. If an executable script <code class="filename">/etc/security/namespace.init</code> exists, it is used to initialize the namespace every time an instance directory is set up and mounted. The script receives the polyinstantiated directory path and the instance directory path as its arguments. </p><p> The <code class="filename">/etc/security/namespace.conf</code> file specifies which directories are polyinstantiated, how they are polyinstantiated, how instance directories would be named, and any users for whom polyinstantiation would not be performed. </p><p> When someone logs in, the file <code class="filename">namespace.conf</code> is scanned. Comments are marked by <span class="emphasis"><em>#</em></span> characters. Each non comment line represents one polyinstantiated directory. The fields are separated by spaces but can be quoted by <span class="emphasis"><em>"</em></span> characters also escape sequences <span class="emphasis"><em>\b</em></span>, <span class="emphasis"><em>\n</em></span>, and <span class="emphasis"><em>\t</em></span> are recognized. The fields are as follows: </p><p><em class="replaceable"><code>polydir</code></em> <em class="replaceable"><code>instance_prefix</code></em> <em class="replaceable"><code>method</code></em> <em class="replaceable"><code>list_of_uids</code></em> </p><p> The first field, <em class="replaceable"><code>polydir</code></em>, is the absolute pathname of the directory to polyinstantiate. The special string <span class="emphasis"><em>$HOME</em></span> is replaced with the user's home directory, and <span class="emphasis"><em>$USER</em></span> with the username. This field cannot be blank. </p><p> The second field, <em class="replaceable"><code>instance_prefix</code></em> is the string prefix used to build the pathname for the instantiation of <polydir>. Depending on the polyinstantiation <em class="replaceable"><code>method</code></em> it is then appended with "instance differentiation string" to generate the final instance directory path. This directory is created if it did not exist already, and is then bind mounted on the <polydir> to provide an instance of <polydir> based on the <method> column. The special string <span class="emphasis"><em>$HOME</em></span> is replaced with the user's home directory, and <span class="emphasis"><em>$USER</em></span> with the username. This field cannot be blank. </p><p> The third field, <em class="replaceable"><code>method</code></em>, is the method used for polyinstantiation. It can take these values; "user" for polyinstantiation based on user name, "level" for polyinstantiation based on process MLS level and user name, "context" for polyinstantiation based on process security context and user name, "tmpfs" for mounting tmpfs filesystem as an instance dir, and "tmpdir" for creating temporary directory as an instance dir which is removed when the user's session is closed. Methods "context" and "level" are only available with SELinux. This field cannot be blank. </p><p> The fourth field, <em class="replaceable"><code>list_of_uids</code></em>, is a comma separated list of user names for whom the polyinstantiation is not performed. If left blank, polyinstantiation will be performed for all users. If the list is preceded with a single "~" character, polyinstantiation is performed only for users in the list. </p><p> The <em class="replaceable"><code>method</code></em> field can contain also following optional flags separated by <span class="emphasis"><em>:</em></span> characters. </p><p><span class="emphasis"><em>create</em></span>=<em class="replaceable"><code>mode</code></em>,<em class="replaceable"><code>owner</code></em>,<em class="replaceable"><code>group</code></em> - create the polyinstantiated directory. The mode, owner and group parameters are optional. The default for mode is determined by umask, the default owner is the user whose session is opened, the default group is the primary group of the user. </p><p><span class="emphasis"><em>iscript</em></span>=<em class="replaceable"><code>path</code></em> - path to the instance directory init script. The base directory for relative paths is <code class="filename">/etc/security/namespace.d</code>. </p><p><span class="emphasis"><em>noinit</em></span> - instance directory init script will not be executed. </p><p><span class="emphasis"><em>shared</em></span> - the instance directories for "context" and "level" methods will not contain the user name and will be shared among all users. </p><p><span class="emphasis"><em>mntopts</em></span>=<em class="replaceable"><code>value</code></em> - value of this flag is passed to the mount call when the tmpfs mount is done. It allows for example the specification of the maximum size of the tmpfs instance that is created by the mount call. See <span class="citerefentry"><span class="refentrytitle">mount</span>(8)</span> for details. </p><p> The directory where polyinstantiated instances are to be created, must exist and must have, by default, the mode of 0000. The requirement that the instance parent be of mode 0000 can be overridden with the command line option <span class="emphasis"><em>ignore_instance_parent_mode</em></span> </p><p> In case of context or level polyinstantiation the SELinux context which is used for polyinstantiation is the context used for executing a new process as obtained by getexeccon. This context must be set by the calling application or <code class="filename">pam_selinux.so</code> module. If this context is not set the polyinstatiation will be based just on user name. </p><p> The "instance differentiation string" is <user name> for "user" method and <user name>_<raw directory context> for "context" and "level" methods. If the whole string is too long the end of it is replaced with md5sum of itself. Also when command line option <span class="emphasis"><em>gen_hash</em></span> is used the whole string is replaced with md5sum of itself. </p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="sag-pam_namespace-options"></a>6.22.3. OPTIONS</h3></div></div></div><div class="variablelist"><dl class="variablelist"><dt><span class="term"> <code class="option">debug</code> </span></dt><dd><p> A lot of debug information is logged using syslog </p></dd><dt><span class="term"> <code class="option">unmnt_remnt</code> </span></dt><dd><p> For programs such as su and newrole, the login session has already setup a polyinstantiated namespace. For these programs, polyinstantiation is performed based on new user id or security context, however the command first needs to undo the polyinstantiation performed by login. This argument instructs the command to first undo previous polyinstantiation before proceeding with new polyinstantiation based on new id/context </p></dd><dt><span class="term"> <code class="option">unmnt_only</code> </span></dt><dd><p> For trusted programs that want to undo any existing bind mounts and process instance directories on their own, this argument allows them to unmount currently mounted instance directories </p></dd><dt><span class="term"> <code class="option">require_selinux</code> </span></dt><dd><p> If selinux is not enabled, return failure </p></dd><dt><span class="term"> <code class="option">gen_hash</code> </span></dt><dd><p> Instead of using the security context string for the instance name, generate and use its md5 hash. </p></dd><dt><span class="term"> <code class="option">ignore_config_error</code> </span></dt><dd><p> If a line in the configuration file corresponding to a polyinstantiated directory contains format error, skip that line process the next line. Without this option, pam will return an error to the calling program resulting in termination of the session. </p></dd><dt><span class="term"> <code class="option">ignore_instance_parent_mode</code> </span></dt><dd><p> Instance parent directories by default are expected to have the restrictive mode of 000. Using this option, an administrator can choose to ignore the mode of the instance parent. This option should be used with caution as it will reduce security and isolation goals of the polyinstantiation mechanism. </p></dd><dt><span class="term"> <code class="option">unmount_on_close</code> </span></dt><dd><p> Explicitly unmount the polyinstantiated directories instead of relying on automatic namespace destruction after the last process in a namespace exits. This option should be used only in case it is ensured by other means that there cannot be any processes running in the private namespace left after the session close. It is also useful only in case there are multiple pam session calls in sequence from the same process. </p></dd><dt><span class="term"> <code class="option">use_current_context</code> </span></dt><dd><p> Useful for services which do not change the SELinux context with setexeccon call. The module will use the current SELinux context of the calling process for the level and context polyinstantiation. </p></dd><dt><span class="term"> <code class="option">use_default_context</code> </span></dt><dd><p> Useful for services which do not use pam_selinux for changing the SELinux context with setexeccon call. The module will use the default SELinux context of the user for the level and context polyinstantiation. </p></dd><dt><span class="term"> <code class="option">mount_private</code> </span></dt><dd><p> This option can be used on systems where the / mount point or its submounts are made shared (for example with a <span class="command"><strong>mount --make-rshared /</strong></span> command). The module will mark the whole directory tree so any mount and unmount operations in the polyinstantiation namespace are private. Normally the pam_namespace will try to detect the shared / mount point and make the polyinstantiated directories private automatically. This option has to be used just when only a subtree is shared and / is not. </p><p> Note that mounts and unmounts done in the private namespace will not affect the parent namespace if this option is used or when the shared / mount point is autodetected. </p></dd></dl></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="sag-pam_namespace-types"></a>6.22.4. MODULE TYPES PROVIDED</h3></div></div></div><p> Only the <code class="option">session</code> module type is provided. The module must not be called from multithreaded processes. </p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="sag-pam_namespace-return_values"></a>6.22.5. RETURN VALUES</h3></div></div></div><div class="variablelist"><dl class="variablelist"><dt><span class="term">PAM_SUCCESS</span></dt><dd><p> Namespace setup was successful. </p></dd><dt><span class="term">PAM_SERVICE_ERR</span></dt><dd><p> Unexpected system error occurred while setting up namespace. </p></dd><dt><span class="term">PAM_SESSION_ERR</span></dt><dd><p> Unexpected namespace configuration error occurred. </p></dd></dl></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="sag-pam_namespace-files"></a>6.22.6. FILES</h3></div></div></div><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="filename">/etc/security/namespace.conf</code></span></dt><dd><p>Main configuration file</p></dd><dt><span class="term"><code class="filename">/etc/security/namespace.d</code></span></dt><dd><p>Directory for additional configuration files</p></dd><dt><span class="term"><code class="filename">/etc/security/namespace.init</code></span></dt><dd><p>Init script for instance directories</p></dd></dl></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="sag-namespace.conf-examples"></a>6.22.7. EXAMPLES</h3></div></div></div><p> These are some example lines which might be specified in <code class="filename">/etc/security/namespace.conf</code>. </p><div class="literallayout"><p><br> # The following three lines will polyinstantiate /tmp,<br> # /var/tmp and user's home directories. /tmp and /var/tmp<br> # will be polyinstantiated based on the security level<br> # as well as user name, whereas home directory will be<br> # polyinstantiated based on the full security context and user name.<br> # Polyinstantiation will not be performed for user root<br> # and adm for directories /tmp and /var/tmp, whereas home<br> # directories will be polyinstantiated for all users.<br> #<br> # Note that instance directories do not have to reside inside<br> # the polyinstantiated directory. In the examples below,<br> # instances of /tmp will be created in /tmp-inst directory,<br> # where as instances of /var/tmp and users home directories<br> # will reside within the directories that are being<br> # polyinstantiated.<br> #<br> /tmp /tmp-inst/ level root,adm<br> /var/tmp /var/tmp/tmp-inst/ level root,adm<br> $HOME $HOME/$USER.inst/inst- context<br> </p></div><p> For the <service>s you need polyinstantiation (login for example) put the following line in /etc/pam.d/<service> as the last line for session group: </p><p> session required pam_namespace.so [arguments] </p><p> This module also depends on pam_selinux.so setting the context. </p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="sag-pam_namespace-authors"></a>6.22.8. AUTHORS</h3></div></div></div><p> The namespace setup scheme was designed by Stephen Smalley, Janak Desai and Chad Sellers. The pam_namespace PAM module was developed by Janak Desai <janak@us.ibm.com>, Chad Sellers <csellers@tresys.com> and Steve Grubb <sgrubb@redhat.com>. Additional improvements by Xavier Toth <txtoth@gmail.com> and Tomas Mraz <tmraz@redhat.com>. </p></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="sag-pam_motd.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="sag-module-reference.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="sag-pam_nologin.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">6.21. pam_motd - display the motd file </td><td width="20%" align="center"><a accesskey="h" href="Linux-PAM_SAG.html">Home</a></td><td width="40%" align="right" valign="top"> 6.23. pam_nologin - prevent non-root users from login</td></tr></table></div></body></html>