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pam_namespace — PAM module for configuring namespace for a session
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
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.
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.
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. Special entry $HOME is supported to designate 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>. 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 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.
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.
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.
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