6.20. pam_namespace - setup a private namespace
Prev | Chapter 6. A reference guide for available modules | Next

## 6.20. pam_namespace - setup a private namespace

`pam_namespace.so` [ debug ] [ unmnt_remnt ] [ unmnt_only ] [ require_selinux ] [ gen_hash ] [ ignore_config_error ] [ ignore_instance_parent_mode ] [ no_unmount_on_close ]

### 6.20.1. 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 and the instance directory path 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.

### 6.20.2. DESCRIPTION

This 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 a new instance directory is setup. 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 where each non comment line represents one polyinstantiated directory with space separated fields 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 in entry is replaced with user's home directory. This field cannot be blank.

The second field, `instance_prefix` is the string prefix used to build the pathname for the instantiation of <polydir>. The directory security context, or optionally its md5sum string (32 hex characters), is appended to the prefix 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 directory where polyinstantiated instances are to be created, must exist and must have, by default, the mode of 000. The requirement that the instance parent be of mode 000 can be overridden with the command line option <ignore_instance_parent_mode>

The third field, `method`, is the method used for polyinstantiation. It can take 3 different values; "user" for polyinstantiation based on user name, "level" for polyinstantiation based on process MLS level and user name, and "context" for polyinstantiation based on process security context and user name 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.

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.

### 6.20.3. 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.

### 6.20.4. MODULE SERVICES PROVIDED

The `session` service is supported.

### 6.20.5. 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.

### 6.20.6. FILES

`/etc/security/namespace.conf`

  Configuration file

### 6.20.7. EXAMPLES

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.

### 6.20.8. 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>.

Prev | Up | Next
6.19. pam_motd - display the motd file | Home | 6.21. pam_nologin - prevent non-root users from login