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
]
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.
The pam_namespace.so 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 /etc/security/namespace.init
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.
The /etc/security/namespace.conf 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.
When someone logs in, the file namespace.conf is
scanned. Comments are marked by # characters.
Each non comment line represents one polyinstantiated
directory. The fields are separated by spaces but can be quoted by
" characters also escape
sequences \b, \n, and
\t are recognized. The fields are as follows:
polydir instance_prefix method list_of_uids
The first field, polydir, is the absolute
pathname of the directory to polyinstantiate. The special string
$HOME is replaced with the user's home directory,
and $USER with the username. This field cannot
be blank.
The second field, instance_prefix is
the string prefix used to build the pathname for the instantiation
of <polydir>. Depending on the polyinstantiation
method 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 $HOME is replaced with the
user's home directory, and $USER with the username.
This field cannot be blank.
The third field, method, 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.
The fourth field, list_of_uids, 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.
The method field can contain also following
optional flags separated by : characters.
create=mode,owner,group
- 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.
iscript=path
- path to the instance directory init script. The base directory for relative
paths is /etc/security/namespace.d.
noinit - instance directory init script will not be executed.
shared - the instance directories for "context" and "level" methods will not contain the user name and will be shared among all users.
mntopts=value
- 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 mount(8) for details.
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 ignore_instance_parent_mode
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 pam_selinux.so
module. If this context is not set the polyinstatiation will be
based just on user name.
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 gen_hash is used the whole string is replaced with md5sum of itself.
-
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.
Only the session module type is provided.
The module must not be called from multithreaded processes.
- 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.
/etc/security/namespace.confMain configuration file
/etc/security/namespace.dDirectory for additional configuration files
/etc/security/namespace.initInit script for instance directories
These are some example lines which might be specified in
/etc/security/namespace.conf.
# The following three lines will polyinstantiate /tmp,
# /var/tmp and user's home directories. /tmp and /var/tmp
# will be polyinstantiated based on the security level
# as well as user name, whereas home directory will be
# polyinstantiated based on the full security context and user name.
# Polyinstantiation will not be performed for user root
# and adm for directories /tmp and /var/tmp, whereas home
# directories will be polyinstantiated for all users.
#
# Note that instance directories do not have to reside inside
# the polyinstantiated directory. In the examples below,
# instances of /tmp will be created in /tmp-inst directory,
# where as instances of /var/tmp and users home directories
# will reside within the directories that are being
# polyinstantiated.
#
/tmp /tmp-inst/ level root,adm
/var/tmp /var/tmp/tmp-inst/ level root,adm
$HOME $HOME/$USER.inst/inst- context
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]
This module also depends on pam_selinux.so setting the context.
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>.