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] [unmount_on_close]
[use_current_context] [use_default_context]
[mount_private]
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 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.
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.
unmount_on_close
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.
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.
mount_private
This option can be used on systems where the / mount point or its
submounts are made shared (for example with a mount --make-rshared
/ 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.
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.
MODULE TYPES PROVIDED
Only the session module type is provided. 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@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>.
Linux-PAM Manual 05/18/2017 PAM_NAMESPACE(8)