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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 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.
DESCRIPTION
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. In addition to options
specified in the tmpfs(5) manual the nosuid, noexec, and nodev flags can be
used to respectively disable setuid bit effect, disable running executables,
and disable devices to be interpreted on the mounted tmpfs filesystem.
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.
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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