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PAM_NAMESPACE(8) Linux-PAM Manual PAM_NAMESPACE(8)
NAME
pam_namespace - PAM module for configuring namespace for a session
SYNOPSIS
pam_namespace.so [debug] [unmnt_remnt] [unmnt_only] [require_selinux] [gen_hash]
[ignore_config_error] [ignore_instance_parent_mode] [no_unmount_on_close]
[use_current_context] [use_default_context]
DESCRIPTION
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 /etc/security/namespace.init exists, it is used to initialize the
namespace every time a new instance directory is setup. 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.
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.
OPTIONS
debug
A lot of debug information is logged using syslog
unmnt_remnt
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
unmnt_only
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
require_selinux
If selinux is not enabled, return failure
gen_hash
Instead of using the security context string for the instance name, generate and use
its md5 hash.
ignore_config_error
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.
ignore_instance_parent_mode
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.
no_unmount_on_close
For certain trusted programs such as newrole, open session is called from a child
process while the parent perfoms close session and pam end functions. For these
commands use this option to instruct pam_close_session to not unmount the bind mounted
polyinstantiated directory in the parent.
use_current_context
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.
use_default_context
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.
MODULE SERVICES PROVIDED
The session service is supported. The module must not be called from multithreaded
processes.
RETURN VALUES
PAM_SUCCESS
Namespace setup was successful.
PAM_SERVICE_ERR
Unexpected system error occurred while setting up namespace.
PAM_SESSION_ERR
Unexpected namespace configuration error occurred.
FILES
/etc/security/namespace.conf
Main configuration file
/etc/security/namespace.d
Directory for additional configuration files
/etc/security/namespace.init
Init script for instance directories
EXAMPLES
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:
session required pam_namespace.so [arguments]
To use polyinstantiation with graphical display manager gdm, insert the following line,
before exit 0, in /etc/gdm/PostSession/Default:
/usr/sbin/gdm-safe-restart
This allows gdm to restart after each session and appropriately adjust namespaces of
display manager and the X server. If polyinstantiation of /tmp is desired along with the
graphical environment, then additional configuration changes are needed to address the
interaction of X server and font server namespaces with their use of /tmp to create
communication sockets. Please use the initialization script /etc/security/namespace.init
to ensure that the X server and its clients can appropriately access the communication
socket X0. Please refer to the sample instructions provided in the comment section of the
instance initialization script /etc/security/namespace.init. In addition, perform the
following changes to use graphical environment with polyinstantiation of /tmp:
1. Disable the use of font server by commenting out "FontPath"
line in /etc/X11/xorg.conf. If you do want to use the font server
then you will have to augment the instance initialization
script to appropriately provide /tmp/.font-unix from the
polyinstantiated /tmp.
2. Ensure that the gdm service is setup to use pam_namespace,
as described above, by modifying /etc/pam.d/gdm.
3. Ensure that the display manager is configured to restart X server
with each new session. This default setup can be verified by
making sure that /usr/share/gdm/defaults.conf contains
"AlwaysRestartServer=true", and it is not overridden by
/etc/gdm/custom.conf.
SEE ALSO
namespace.conf(5), pam.d(5), mount(8), pam(7).
AUTHORS
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 AT us.com>, Chad Sellers
<csellers AT tresys.com> and Steve Grubb <sgrubb AT redhat.com>. Additional improvements by
Xavier Toth <txtoth AT gmail.com> and Tomas Mraz <tmraz AT redhat.com>.
Linux-PAM Manual 07/27/2008 PAM_NAMESPACE(8)
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