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.
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.
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.