vrijdag 18 juni 2010


command line posting 1


command line posting

donderdag 18 juni 2009

SELinux lockdown

Sumaary of things that can be done to lock down SELinux in Fedora 11

1. Use confined users.

By default Fedora maps users to a unconfined user domain. This unconfined user domain was designed to be able to exempt users for most SELinux policy.

Using the unconfined user domain as a primary user environment is not a good idea for security. The same way root logins arent a good idea.

So use the semanage login () command to let new be mapped to a confined user domain of your choosing instead of unconfined_t. Which confined user domain to use depends on the properties of the user.

There are a few profiles to choose from. I map my new users to the guest_u SELinux user.

Guest_u is a unprivileged user that can only log in via SSH. This user has no access to network resources and to setuid/getuid. This user can be denied to execute in the user home space.

Xguest_u is similar to Guest_u except that Xguest cannot log in via SSH but can only login via XWindows.

User_u is similar to Xguest_u except that user_u can log in both via SSH and via XWindows. User_u also has access to network resources.

Staff_u is similar to user_u except that staff_u can use setuid and setgid programs. Staff_u can also stat all processes on the system and has some other minor privileges.

Sysadm_u is a confined root login. root log ins arent recommended so ill skip this user

Unconfined_u login is bad ;)

You can override de default mapping for new users if you use useradd -Z

So if you configured SELinux to map new users to guest_u seuser but want to add a specific user to another SELinux user group (for example add user joe to user_u): useradd -Z user_u joe

You can also change mappings later with the semanage login -m (modify) command

refer to: man useradd and man semanage

2. Configure pam_sepermit

So now were using confined user environment for all our users (except root which should not log on anyways except maybe via TTY in emergencies).

What if the system happens to be in permissive mode? If you run setenforce 0 then all SELinux AVC denials will be allowed (but logged). That means your confined users are no longer restricted by SELinux.

We can mitigate this by using /etc/security/sepermit.conf. You can add users and seusers there and then login will be denied if SELinux is in permissive mode.

For example: putting %user_u in sepermit.conf will disallow user_u seusers the login if getenforce returns: permissive. (try it out)

It should be noted that setenforce (permissive mode) is not recommended or even required anymore on Fedora 11. Fedora 10 instead introduced "permissive domains". The difference between permissive mode and permissive domains is that with permissive domains we can change the state of single processes (domains) to permissive instead of having to put the whole system into a permissive state.

So preferable use permissive domains if you need to troubleshoot some issues. the command semanage permissive -a enable permissive mode for a domain type and the command semanage permissive -d deletes the permissive domain for a domain type.

refer: man semanage

3. You can still use the unconfined user domain as a secundary user role for privileged users.

I will admit sometimes if you want to do some generic sysadmin task you just dont want to be restricted. Thats fine. You can still use the unconfined user environment as a secundary role.

For example. my primary user domain is staff_u as you know this seuser has access to setuid /setgid programs like sudo. I used the semanage user () command to map the unconfined user domain along with the system system domain to the staff_u seuser. Now staff_u can role transition to the unconfined user space if he want to do generic admining.

Just setup /etc/sudoers and of you go:

semanage user -m -L s0 -r s0-s0:c0.c1023 -R "staff_r system_r unconfined_r" -P user staff_u
echo "joe ALL=(ALL) TYPE=unconfined_t ROLE=unconfined_r ALL" >> /etc/sudoers

You do not have to explicitly define your default secundairy role in /etc/sudoers like the example above. You can also define your target role when you run the sudo command like so: sudo -t unconfined_t -r unconfined_r service httpd restart.

Note that only sudo support role transitions. su does not. if you use su (not recommended) then you also need the newrole program (yum list *newrole*)

Also note that besides the unconfined user domain there are other confined user domain designed to be secundairy privileged roles (roles specific to a task) for example the webadm_r role which lets root only manage the webserver. Try it out add the webadmin_r role to staff_u with semanage and use sudo to transition to the webadm environment.

refer: man sudo, man semanage, man su, man newrole

4. More about unconfined

Before F11 unconfined was a space for any process that needed to be unrestricted be it a program or a user. Both programs and users could be run in this unconfined space. During F11 the unconfined domain was split into a unconfined and unconfineduser domain.

What this means to us is that we can uninstall the unconfined domain now but still use the unconfineduser functionality (unconfined user domain) (or vice versa)

So how can this help us lock down SELinux? Well we can now uninstall the unconfined module with semodule -i unconfined so that no system services can run unconfined.

Just like users are by default mapped to a unconfined user environment in Fedora, system services that do not have SElinux policy defined are also automaticly executed in a unconfined environment. What it means is that you might install a system service that has no policy and it will run unstricted. This presents another gaping hole in your security. Because that service can potentially be used to go around selinux.

By uninstalling this unconfined module this can no longer happen. If you install a system service that does not have policy then it just wont run. Youd need to write policy for it first.

5. lock down your booleans

In Fedora some booleans are activated by default. booleans are "tunable policy". Rule that can be enabled on the fly by admin. The more rules are enabled the less fine grained your security becomes. So you need to remove as much policy as possible by toggling booleans on or off.

I say on or off because some booleans may add policy if you turn it on and other when you turn it off.

I cannot explain all booleans here but i will talk about some.

- the secure mode booleans have policy that allow admin to (off is befault. to lock down set to on):
-- put the system into permissive mode
-- inset kernel modules
-- load policy

- xserver object manager has policy that enables the xserver selinux extension (off by default, to lock down set to on)
This is a very powerful feature which lets the admin define selinux policy for X server. This feature (its policy) still has rough edges. If you arent afraid of selinux feel free to experiment and improve the XACE policy like i did)

- nsplugin booleans has policy that defines what access nsplugin has
nsplugin runs you browser plugins. these browser plugins are vulnerable to all kinds of threats.
You can diable network access for nsplugin and you can disable memory execution (execmem) for nsplugin.
if you decide to use unconfined user logins anyway (not recommended) then you can still configure nsplugin selinux security by setting a nsplugin boolean. Needless to say that confined users are subjected to a confined nsplugin by default.

- unconfined login booleanhas policy that allows unconfined logins (enabled by default: to lock down set to off)
Disable unconfined logins. if you use confined users like this guide encourages then disallow unconfined logins.

There are many other booleans. disable as many as possible. keep your configured as least privilege as possible. More rules means less security in general. So play with it and disable as many as possible without losing basic functionality.

refer: man semanage, man setsebool, man getsebool

6. sandbox.
If you decide you you do not want to operate in a restricted space by default. for example if you think your environment does not prefer it then you can still use SELinux in a discretionary way with the sandbox script.

sanbox lets unconfined users run command / programs in a confined space (sandbox) So it is to the discretion of a unconfined user to run a program restricted or unrestricted, unlike confined domains which are mandatory to users (they are mapped to users by admin)

refer: sandbox --help

7. Conclusion
map you users to confined users.
use the unconfined user domain as a secundary environment for superusers.
remove the unconfined module (or unconfineduser or both depending on your security requirements)
lock down you booleans as tight as possible
use permissive domain instead of permissive mode
use pam sepermit if you have confined users

Besides these ways to lock down your selinux enable system there are the basic thing you can do to keep security tight:


vrijdag 25 juli 2008

git and refpolicy

The refpolicy repository is still svn. heres how to use git together with svn.

1. use git svn to clone the refpolicy svn repository:

mkdir ~/git
cd ~/git
git svn clone http://oss.tresys.com/repos/refpolicy/trunk refpolicy
cd ~/git/refpolicy
git branch (to see if master is there)
git branch -r (to see if remote branch (git-svn) is there)

2. create a branch to work on.

git svn checkout -b mybranch git-svn

3. add changes and commit them
git commit

4. create a patch with your modification (your changes from master in this case)
git format-patch master

5. update master and git-svn (remote branche)
git svn fetch

note eclipse-egit is a eclipse plugin that allows you to load, work on a git branch in eclipse and commit.

dinsdag 22 juli 2008

rbac f9

Let us assume we want to make user "joe" our website operator.
"joe" should only be able to operate apache.
To operate apache one traditionally would need a root password.

In fedora 9 root can be confined to specific roles.
Also in Fedora 9 user no longer need a root password to gain root
privileges due to SELinux support built-in sudo.
Pre-Fedora 9 a combination of su and newrole was used to gain root
privileges. This required a user to enter his password for newrole and
then also the root password for su.

Here is how you do it:

1. useradd joe
2. passwd joe
3. /usr/sbin/semanage user -a -L s0 -r s0-s0 -R "staff_r webadm_r" -P
user webadmin
4. /usr/sbin/semanage login -a -s webadmin -r s0-s0 joe
5. echo "joe ALL=(all) TYPE=webadm_t ROLE=webadm_r ALL" >> /etc/sudoers

When joe logs into the system, he will find himself in the staff_t user
domain (id -Z). This is a restricted user domain. The staff_r role is
similar to the user_r with the important exeption that staff_r may
transition to other , maybe more privileged, domain. unlike user_r.
user_r is confined to the user_t user domain, and may not transition.

If joe wants to, for example, restart the webserver, he can just type
sudo service httpd restart. Similar if joe wanted to edit a file that is
owned by apache, joe can edit the file in the webadm_t userdomain by
just typing sudo vi /etc/httpd/conf.d/httpd.conf.

Joe can also open a terminal session in the webadm_t domain by running:
sudo sh. If you would have even more roles, then joe would be able to
define in which user domain he wants to start a new terminal session:
sudo -t webadm_t -r webadm_r sh

Joe can even login to the system directly in the webadm_t domain by
using: ssh joe/webadm_r@localhost

You can delegate very specific administration tasks without having to
share the root password!

a script

# -xv
# Name: loginaccounts.sh
# Description: automate login account management
# Author: Dominick Grift
# Version: 0.0.3

# Copyright (C) 2008 Dominick Grift

# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License as
# published by the Free Software Foundation, either version 3 of the
# License, or (at your option) any later version.

# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# GNU Affero General Public License for more details.

# You should have received a copy of the GNU Affero General Public License
# along with this program. If not, see .

# Report undefined variables
# shopt -s -o nounset

# Global declarations
declare -rx SCRIPT=${0##*/}
declare -rx EXITSTATUS=$?

# My global declarations
declare -r OPTSTRING="-h,-L.-P,-A,-C,-f,-a,-i:,-p:,-c:,-g:,-l:,-n:,-c:,-q:,-e:"
declare UCOMMNT=0 # Optional
declare UGRP="realusers,sshusers" # Tunable
declare USERID # Mandatory
declare RESULT # System
declare UPASSWD # Mandatory
declare ULOGNS=3 # Tunable
declare UNPROC=15 # Tunable
declare ULOCL=0 # Optional
declare UCATGR=0 # Optional
declare UFORWRD=0 # optional
declare UQUOT="10000" # Tunable
declare UEXPR=0 # Optional
declare UPOLY=1 # Optional
declare UCRON=0 # Optional
declare UAT=0 # Optional
declare UAGE=1 # Optional

# Sanity checks

# Requires BASH
if test -z "$BASH" ; then
printf "$SCRIPT:$LINENO: %s\n" "Please run this script with the BASH shell" >&2
exit 192

# Test for input
if test -z "$1" ; then
printf "$SCRIPT:$LINENO: %s\n" "Copyright (C) 2008 Dominick Grift"
printf "$SCRIPT:$LINENO: %s\n" ""
printf "$SCRIPT:$LINENO: %s\n" "This program is free software: you can redistribute it and/or modify"
printf "$SCRIPT:$LINENO: %s\n" "it under the terms of the GNU Affero General Public License as"
printf "$SCRIPT:$LINENO: %s\n" "published by the Free Software Foundation, either version 3 of the"
printf "$SCRIPT:$LINENO: %s\n" "License, or (at your option) any later version."
printf "$SCRIPT:$LINENO: %s\n" ""
printf "$SCRIPT:$LINENO: %s\n" "This program is distributed in the hope that it will be useful,"
printf "$SCRIPT:$LINENO: %s\n" "but WITHOUT ANY WARRANTY; without even the implied warranty of"
printf "$SCRIPT:$LINENO: %s\n" "GNU Affero General Public License for more details."
printf "$SCRIPT:$LINENO: %s\n" ""
printf "$SCRIPT:$LINENO: %s\n" "You should have received a copy of the GNU Affero General Public License"
printf "$SCRIPT:$LINENO: %s\n" "along with this program. If not, see ."
exit 0

# Test for root
if [ `whoami` != "root" ] ; then
printf "$SCRIPT:$LINENO: %s\n" "DAC: Must be root" >&2
exit 192

# Test for unconfined
if [ `id -Z | awk 'BEGIN { FS=":" } { print $3 }'` != unconfined_t ] ; then
printf "$SCRIPT:$LINENO: %s\n" "MAC: Must be unconfined domain" >&2
exit 192

# Check getopt mode
getopt -T
if [ $? -ne 4 ] ; then
printf "$SCRIPT: %s\n" "Getopt is in compatibility mode" >&2
exit 192

# Test parameters
RESULT='getopt --name "$SCRIPT" --options "$OPTSTRING" --longoptions "help" "identity" "password" "comment" "groups" "logins" "nproc" "local" "range" "forward" "quota" "expire" "poly" "cron" "at" "chage" -- "$@"'
if [ $? -gt 0 ] ; then
exit 192

# Functions

add_user() {
/usr/sbin/useradd "$USERID" 1>&2 >/dev/null;

add_user_passwd() {
/bin/echo "$UPASSWD" | /usr/bin/passwd "$USERID" --stdin 1>&2 >/dev/null;

add_comment() {
/usr/sbin/usermod -c "$UCOMMNT" "$USERID" 1>&2 >/dev/null;

add_expire() {
/usr/sbin/usermod -e "$UEXPR" "$USERID" 1>&2 >/dev/null;

add_poly() {
/bin/mkdir /home/"$USERID"/"$USERID".inst && chmod -R 000 /home/"$USERID"/"$USERID".inst 1>&2 >/dev/null;


no_poly() {
/bin/sed '/^\/tmp/s/$/\,$USERID/' /etc/security/namespace.conf > tmpfile && /bin/cp tmpfile /etc/security/namespace.conf; /bin/rm tmpfile;
/bin/sed '/^\/var/s/$/\,$USERID/' /etc/security/namespace.conf > tmpfile && /bin/cp tmpfile /etc/security/namespace.conf; /bin/rm tmpfile;
/bin/sed '/^\$HOME/s/$/\,$USERID/' /etc/security/namespace.conf > tmpfile && /bin/cp tmpfile /etc/security/namespace.conf; /bin/rm tmpfile;

add_forward() {
/bin/echo """
Match User $USERID
X11Forwarding no
AllowTcpForwarding no""" >> /etc/ssh/sshd_config;

add_quota() {
/usr/sbin/setquota -u "$USERID" 0 "$UQUOT" 7500 10000 -a 1>&2 >/dev/null;

add_nproc() {
/bin/echo "$USERID hard nproc $UNPROC" >> /etc/security/limits.conf;

add_logins() {
/bin/echo "$USERID - maxlogins $ULOGNS" >> /etc/security/limits.conf;

add_local() {
/bin/echo "- : $USERID : LOCAL" >> /etc/security/access.conf;

add_cron() {
/bin/echo "$USERID" >> /etc/cron.allow;

add_at() {
/bin/echo "$USERID" >> /etc/at.allow;

add_groups() {
/usr/sbin/usermod -G "$UGRP" "$USERID" 1>&2 >/dev/null;

add_cat() {
/usr/sbin/semanage user -a -L s0 -r "s0-s0$NEWCAT" -R user_r -P user "$USERID" 1>&2 >/dev/null;
/usr/sbin/semanage login -a -s "$USERID" -r "s0-s0$NEWCAT" "$USERID" 1>&2 >/dev/null;

add_seuser() {
/usr/sbin/semanage user -a -L s0 -r "s0-s0" -R user_r -P user "$USERID" 1>&2 >/dev/null;
/usr/sbin/semanage login -a -s "$USERID" -r "s0-s0" "$USERID" 1>&2 >/dev/null;

add_chage() {
/usr/bin/chage -m 7 -M 180 -W 7 "$USERID" 1>&2 >/dev/null;

# Main loop

# Replace the parameters with the results of getopt
eval set -- "$RESULT"

# Process the parameters
while [ $# -gt 0 ] ; do
case "$1" in
-h | --help) # Show help
printf "$SCRIPT:$LINENO: %s\n" "Usage: $SCRIPT [options]"
printf "$SCRIPT:$LINENO: %s\n" ""
printf "$SCRIPT:$LINENO: %s\n" " Options:"
printf "$SCRIPT:$LINENO: %s\n" " [-h][--help] | View this help"
printf "$SCRIPT:$LINENO: %s\n" " [-L][--local] | Optional: Disabled by default"
printf "$SCRIPT:$LINENO: %s\n" " [-f][--forward] | Optional: Disabled by default"
printf "$SCRIPT:$LINENO: %s\n" " [-P][--poly] | Optional: Enabled by default"
printf "$SCRIPT:$LINENO: %s\n" " [-C][--cron] | Optional: Disabled by default"
printf "$SCRIPT:$LINENO: %s\n" " [-A][--at] | Optional: Disabled by default"
printf "$SCRIPT:$LINENO: %s\n" " [-a][--chage] | Optional: Enabled by default"
printf "$SCRIPT:$LINENO: %s\n" " [-i][--identity] identity | Mandatory: User name"
printf "$SCRIPT:$LINENO: %s\n" " [-p][--password] password | Mandatory: Strong password"
printf "$SCRIPT:$LINENO: %s\n" " [-c][--comment] comment | Tunable: Defaults to none"
printf "$SCRIPT:$LINENO: %s\n" " [-g][--groups] groups | Tunable: Defaults to realusers,sshusers"
printf "$SCRIPT:$LINENO: %s\n" " [-l][--logins] number of logins | Tunable: Defaults to 3"
printf "$SCRIPT:$LINENO: %s\n" " [-n][--nproc] number of processes| Tunable: Defaults to 15"
printf "$SCRIPT:$LINENO: %s\n" " [-r][--range] range | Optional: Disabled by default"
printf "$SCRIPT:$LINENO: %s\n" " [-q][--quota] number of blocks | Tunable: Defaults to 10000 blocks"
printf "$SCRIPT:$LINENO: %s\n" " [-e][--expire] date | Optional: Disabled by default"
printf "$SCRIPT:$LINENO: %s\n" ""
printf "$SCRIPT:$LINENO: %s\n" " Examples:"
printf "$SCRIPT:$LINENO: %s\n" " $SCRIPT -i john -c \"John Doe\" -p F000_Bar!!1 -r c2,c4 -e 2010-12-15 -C"
exit 0
-i | --identity) shift
if [ $# -eq 0 ] ; then
printf "$SCRIPT:$LINENO: %s\n" "Identity for [-i][--identity] is missing" >&2
exit 192
-p | --password) shift
if [ $# -eq 0 ] ; then
printf "$SCRIPT:$LINENO: %s\n" "Password for [-p][--password] is missing" >&2
exit 192
-c | --comment) shift
if [ $# -eq 0 ] ; then
printf "$SCRIPT:$LINENO: %s\n" "Comment for [-c][--comment] is missing" >&2
exit 192
-g | --groups) shift
if [ $# -eq 0 ] ; then
printf "$SCRIPT:$LINENO: %s\n" "Groups for [-g][--groups] are missing" >&2
exit 192
-l | --logins) shift
if [ $# -eq 0 ] ; then
printf "$SCRIPT:$LINENO: %s\n" "Number of logins for [-l][--logins] is missing" >&2
exit 192
-n | --nproc) shift
if [ $# -eq 0 ] ; then
printf "$SCRIPT:$LINENO: %s\n" "Number of processes for [-n][--nproc] is missing" >&2
exit 192
-L | --local) shift
-P | --poly) shift
-r | --range) shift
if [ $# -eq 0 ] ; then
printf "$SCRIPT:$LINENO: %s\n" "Range for [-r][--range] is missing" >&2
exit 192
-f | --forward) shift
-C | --cron) shift
-A | --at) shift
-a | --chage) shift
-q | --quota) shift
if [ $# -eq 0 ] ; then
printf "$SCRIPT:$LINENO: %s\n" "Quota for [-q][--quota] is missing" >&2
exit 192
-e | --expire) shift
if [ $# -eq 0 ] ; then
printf "$SCRIPT:$LINENO: %s\n" "Expiration date for [-e][--expire] is missing" >&2
exit 192

if [ -z "$USERID" ] ; then
printf "$SCRIPT:$LINENO: %s\n" "Identity missing" >&2
exit 192

if [ -z "$UPASSWD" ] ; then
printf "$SCRIPT:$LINENO: %s\n" "Password missing" >&2
exit 192

# Processing
if test -n "$USERID" ; then
if [ $? -gt 0 ] ; then
printf "$SCRIPT:$LINENO: %s\n" "add_user: FAIL";
exit 192
printf "$SCRIPT:$LINENO: %s\n" "added user: $USERID";
printf "$SCRIPT:$LINENO: %s\n" "no identity specified: should not be here";
exit 192

sleep 1;

if test -n "$UPASSWD" ; then
if [ $? -gt 0 ] ; then
printf "$SCRIPT:$LINENO: %s\n" "add_passwd: FAIL";
exit 192
printf "$SCRIPT:$LINENO: %s\n" "added passwd: $UPASSWD";
printf "$SCRIPT:$LINENO: %s\n" "no password specified: should not be here";
exit 192

sleep 1;

if test "$UCOMMNT" -ne 0 ; then
if [ $? -gt 0 ] ; then
printf "$SCRIPT:$LINENO: %s\n" "add_comment: FAIL";
exit 192
printf "$SCRIPT:$LINENO: %s\n" "added comment: $UCOMMNT";
printf "$SCRIPT:$LINENO: %s\n" "no comment specified: skipping";

sleep 1;

if [ "$UGRP" != "realusers,sshusers" ] ; then
if [ $? -gt 0 ] ; then
printf "$SCRIPT:$LINENO: %s\n" "add_groups: FAIL";
exit 192
printf "%s\n" "added groups: $UGRP";
if [ $? -gt 0 ] ; then
printf "$SCRIPT:$LINENO: %s\n" "add_groups: FAIL";
exit 192
printf "$SCRIPT:$LINENO: %s\n" "no groups specified: realusers,sshusers";

sleep 1;

if [ "$UEXPR" != "0" ] ; then
if [ $? -gt 0 ] ; then
printf "$SCRIPT:$LINENO: %s\n" "add_expire: FAIL";
exit 192
printf "$SCRIPT:$LINENO: %s\n" "added expire: $UEXPR";
printf "$SCRIPT:$LINENO: %s\n" "no expire specified: skipping";

sleep 1;

if [ "$UPOLY" -eq 1 ] ; then
if [ $? -gt 0 ] ; then
printf "$SCRIPT:$LINENO: %s\n" "add_poly: FAIL";
exit 192
printf "$SCRIPT:$LINENO: %s\n" "poly not specified: enabled poly"
printf "$SCRIPT:$LINENO: %s\n" "poly specified: disabled poly";

sleep 1;

if [ "$UFORWRD" -lt 1 ] ; then
if [ $? -gt 0 ] ; then
printf "$SCRIPT:$LINENO: %s\n" "add forward: FAIL";
exit 192
printf "$SCRIPT:$LINENO: %s\n" "forward not specified: added forward";
printf "$SCRIPT:$LINENO: %s\n" "forward specified: skipping";

sleep 1;

if test "$UQUOT" -ne 10000 && test "$UQUOT" -n 0 ; then
if [ $? -gt 0 ] ; then
printf "$SCRIPT:$LINENO: %s\n" "add_quota: FAIL";
exit 192
printf "$SCRIPT:$LINENO: %s\n" "added quota: $UQUOT"
elif [ "$UQUOT" -ne 0 ] ; then
if [ $? -gt 0 ] ; then
printf "$SCRIPT:$LINENO: %s\n" "add_quota: FAIL";
exit 192
printf "$SCRIPT:$LINENO: %s\n" "quota not specified: 10000";
printf "$SCRIPT:$LINENO: %s\n" "quota disabled: skipping";

sleep 1;

if test "$UNPROC" -ne 15 && test "$UNPROC" -ne 0 ; then
if [ $? -gt 0 ] ; then
printf "$SCRIPT:$LINENO: %s\n" "add_nproc: FAIL";
exit 192
printf "$SCRIPT:$LINENO: %s\n" "nproc specified: added $UNPROC";
elif [ "$UNPROC" -ne 0 ] ; then
if [ $? -gt 0 ] ; then
printf "$SCRIPT:$LINENO: %s\n" "add_nproc: FAIL";
exit 192
printf "$SCRIPT:$LINENO: %s\n" "nproc not specified: 15";
printf "$SCRIPT:$LINENO: %s\n" "nproc disabled: skipping";

sleep 1;

if test "$ULOGNS" -ne 3 && test "$ULOGNG" -ne 0 ; then
if [ $? -gt 0 ] ; then
printf "$SCRIPT:$LINENO: %s\n" "add_logins: FAIL";
exit 192
printf "$SCRIPT:$LINENO: %s\n" "logins specified: added $ULOGNS"
elif [ "$ULOGNS" -ne 0 ] ; then
if [ $? -gt 0 ] ; then
printf "$SCRIPT:$LINENO: %s\n" "add_logins: FAIL";
exit 192
printf "$SCRIPT:$LINENO: %s\n" "logins not specified: 3";
printf "$SCRIPT:$LINENO: %s\n" "logins disabled: skipping";

sleep 1;

if [ "$ULOCL" -eq 0 ] ; then
if [ $? -gt 0 ] ; then
printf "$SCRIPT:$LINENO: %s\n" "add_local: FAIL";
exit 192
printf "$SCRIPT:$LINENO: %s\n" "local not specified: added local";
printf "$SCRIPT:$LINENO: %s\n" "local specified: skipping";

sleep 1;

if [ "$UCRON" -eq 1 ] ; then
if [ $? -gt 0 ] ; then
printf "$SCRIPT:$LINENO: %s\n" "add_cron: FAIL";
exit 192
printf "$SCRIPT:$LINENO: %s\n" "cron specified: adding cron";
printf "$SCRIPT:$LINENO: %s\n" "cron not specified: skipping";

sleep 1;

if [ "$UAT" -gt 0 ] ; then
if [ $? -gt 0 ] ; then
printf "$SCRIPT:$LINENO: %s\n" "add_at: FAIL";
exit 192
printf "$SCRIPT:$LINENO: %s\n" "at specified: adding $UAT";
printf "$SCRIPT:$LINENO: %s\n" "at not specified: skipping";

sleep 1;

if [ "$UAGE" -eq 1 ] ; then
if [ $? -gt 0 ] ; then
printf "$SCRIPT:$LINENO: %s\n" "add_chage: FAIL";
exit 192
printf "$SCRIPT:$LINENO: %s\n" "chage specified: adding $UAGE";
printf "$SCRIPT:$LINENO: %s\n" "chage not specified: skipping";

sleep 1;

if [ "$UCATGR" != "0" ] ; then
if [ $? -gt 0 ] ; then
printf "$SCRIPT:$LINENO: %s\n" "add_cat: FAIL";
exit 192
printf "$SCRIPT:$LINENO: %s\n" "added cat: $UCATGR";
if [ $? -gt 0 ] ; then
printf "$SCRIPT:$LINENO: %s\n" "add_seuser: FAIL";
exit 192
printf "$SCRIPT:$LINENO: %s\n" "added seuser";

# Clean up

#TODO: list, remove, modify, loglevels, interactive

maandag 21 juli 2008


Explain newrole versus sudo to: transition user domain.

in f10 selinux-policy-targeted newrole is no longer encouraged to be used for domain transitions. in policy mls it is still used (but mls is not common)

sudo allows root privileges without actually knowing the root password.

su with newrole still requires a user to enter a root password to gain root privileges.

not needing a root password anymore is a big advantage!


from the wiki:
SELinux and virtualization (relabeling images if images are not in /etc/xen/).

this is not a domain specific issue. customized types. the solution should be man virt_selinux or man xen_selinux like man httpd_selinux. however there is no man xen_selinux yet etc.
this may no longer be an issue in fedora 10 , virt is working on a solution to be implemented in f10


make sure to use proper selinux terminology consequent in an effort to keep it simple.

subject object, security context, domain types, file types, port types, security level, categories, domain transition, executable file types, domain, application domain, user domain, init daemon, classes, attributes, scontext, tcontext, access vector cache, type enforcement, multi level security, multi category security.


from the wiki:

• Do mount points need to be mnt_t?

boolean mount_any_file. this is also kind of a customized type issue. use semanage boolean -l to list all booleans and their explanation. for example:

/usr/sbin/semanage boolean -l | grep mount

sh-3.2# /usr/sbin/semanage boolean -l | grep mount
allow_mount_anyfile -> off Allow the mount command to mount any directory or file.
xguest_mount_media -> off Allow xguest users to mount removable media

consideration: you should consider to not mention get,setsebool. semanage also provides this functionality. keep it simple


from the wiki:
mislabeled files, relabeled but still problems, touch /.autorelabel (Dans journal).
aplain how touch /.autorelabel && reboot relates to fixfiles relabel


different policies:
first there was strict and optional mls (for dod). strict was in fedora2. it was introduced too soon. users were too restricted. targeted was introduced to avoid restriction on users.unconfined domain is a domain exempted fro m most selinux policy. unconfined is a property of targeted policy. targeted policy only targets a select group. strict targets everything on a system. targeted plus multi category security (mcs) which is a (poor) implementation of confidentiality(its discretionary users can chcat aslong as they are member of the cat. mcs in policy mls is part of security level. in policy mls, mcs is mandatory.mls is strict plus BLP, plus MCS, plus MLS. strict no longer maintained, merged with targeted. (strict plus unconfined domain) if you remove the unconfined domain then you use what use to be strict. at the moment there are two selinux policy models maintained: policy targeted and policy-mls. mls aims to enforces confidentiality BLP.

SELinux policy and dependencies.

A policy module has 3 files. Here is the explaination of the 3 files.

mydomain.te (.te) (type enforcement file) it has PRIVATE policy for the "mydomain" policy module.

mydomain.if (.if) (interface file) it has PUBLIC policy for the "mydomain" policy module.

mydomain.fc (.fc) (file context file) it has file contexts for the "mydomain" policy module.

The type enforcement file.

This file has private policy. Policy that is, in my example, related to "mydomain"

for example, you might find a rule like this in the mydomain.te file:

This policy was provided by apache.if to "mydomain". You can look it up in the apache.if file. It is really a template or interface with rules for how to read apaches user content. We are using (instantiating) that interface that apache policy module provides in it's apache.if file, in our mydomain.te file.

Let us refer to interfaces and templates as blocks of public policy. Public policy blocks should be prefixed by the policy module name of the domain that facilitates it in it's .if (interface file).

for example, just by looking at the following interface call in mydomain.te i know: 1. which module provided the interface 2. where to roughly find it. 3. where to find what policy te interface provides. 4. which domain instantiates the block of public policy:


1. provided by the alsa policy module.
2. can be found in alsa.if
3. Summary: Read alsa writable config files

allow $1 alsa_etc_rw_t:dir list_dir_perms;

4. this policy is instantiated by mydomain_t domain.

So you can easily from looking at a .te file know the modules dependencies by parsing each called interface prefix. as each called interface is prefixed by the domain that made it available in its interface file.

important note regarding public policy.

creating a quick policy module package(.pp) can be very handy for implementing quick policy. but it is also limited.

to compile policy one need selinux-devel. it has development files for each module that is used by the compiler to see if the policy that we want to compile is valid.

when you compile and install a seperate policy package with semodule -i mydomain.pp for example. there will not be a devel package installed.

interfaces files are therefore rendered useless for seperate policy module packages. for the reason that other modules will not be able too instantiate any public policy for that module.

the reason is that when you try to compile your module that has a call to a public policy block of a module that was installed with semodule, the compiler will nnot find that interface/ template in its devel files because non were installed!

This is important to know!
do you want to develop and implement much policy, then do not use policy module packages with semodule but instead integrate your module into the selinux-policy source provided upstream, rebuild it and reinstall it.

by rebuilding selinux-policy, a new selinux-policy-devel package is created. this selinux-policy-devel package DOES include the public policy for the domain that you integrated and thus is usable as opposed to using a .pp with semodule.


Basic access control models ( DAC , MAC ) ( not so basic MDAC )

explain discretionary
explain the dac model attributes: user group permission bits
explain why dac acl is not sufficient. example privilege escalation
explain the mac model attributes: security context
explain mandatory
explain that MAC is ACL layer on top of the DAC ACL layer
explain Type enforcement
explain Role Based AC
explain Multi Level Security
Explain Multi Category/Compartment Security

compare a selinux system to a submarine with compartments. if one compartment has a leak, the water will be contained to that compartment and will not be able to spread ( escalate) . submarine will not sink

Security context / SELinux attributes

explain the security context tuple and how to read it (explain the fields)
explain user ( which SELinux user (group) created the object? )
explain type is the attribute for type enforcement (TE)
explain role is the attribute for role enforcement (RBAC)
explain security level is the attribute for security level enforcement (MLS)
explain categories/compartments is the attribute for security level enforcement or category/compartment enforcement (MLS or MCS)

Subjects and objects ( processes and "files" )

explain that everything in a system is a object
explain that even subjects in a system are represented as objects in proc mountpoint
explain subjects and objects
explain subjects are processes (ps auxZ)
explain objects are "files" (ls -alZ)
- file objects ( files , lnk files, dirs, fifo files, sock files etc)
- port objects
- interface objects
- node objects
- objects available by other programs ACE access control extension: XACE, sepostgesql, SEDBUS, mscd, etc.
- explain object is a class defined in kernel :process :file :tcp_socket
example of a class: process. example of a class: file
explain domain type is the attribute of a process ( user_t is (user) domain type/attribute of "user"
explain object type is the attribute of a object or "file". do not mistake files with file objects/file types. a "file" is any object
explain that a object type can never be a scontext ( source context ) in a avc denail
explain that processes (subjects) generally operate on files (objects)
explain that processes (subjects) also operate on other processes (subjects) example: process ( sigchld ) if a user processes spawns a program process.
explain that "files" ( objects ) do not operate. they get operated on by subjects ( processes )
explain permissions that define how to operate on subjects and objects ( classes ) are defined in the kernel and are attributes of classes
explain classes and their attributes are static defined in kernel:
- example of a file object class and its attributes:
+ file read
+ dir write
+ lnk_file getattr
- example of a subject class and its attributes:
+ process sigchld
- example of a object available by other programs ACL
+ dbus send_msg
explain that although classes and their attributes are defined in the kernel, that one can assign "types" to subjects and objects, and that one can define policy for these types can interact using the object classes and their attributes supplied by the kernel.


scontext/domain type/subject | tcontext/file type/object | "object" class | "object" permissions/attributes
user_t | user_home_t | dir | getattr
httpd_t | httpd_sys_content_ra_t | file | read
user_t | mozilla_t | process | sigchld
user_t | self | process | transition
mozilla_t | httpd_port_t | tcp_socket | connect
unconfined_t | cupsd_t | dbus | send_msg

How to find out if selinux is supported /enabled:
supported?: http://domg444.blogspot.com/2007/11/how-to-determine-if-our-system-supports.html
enabled?: getenforce /selinux/config sestatus

explain selinux framework and selinux policy. explain the selinux framework is responsible for enforcing policy.
explain the access vector cache.
perruse selinux packages ( rpm -ql ) and discuss important locations : /etc/selinux , /selinux

How to disable SELinux: i refer to dwalsh blog. some highlights selinux=0 , enforcing=0, setenforce 0, system-config-selinux, semanage

system-config-selinux is a GUI for semanage. semanage is THE central managing point for SELinux administration:
label file objects ( semanage fcontect -a)
label port objects ( semanage port -a) etc
explain each optipn of semanage and system-config-selinux: label interfaces, set booleans, add , modify, delete selinux user (groups) and SELinux logins.
explain translation ( requires mcstransd )
explain what mcstransd does
explain what restorecond does
explain auditd connection to selinux ( explain ausearch /auctl )

show some pratical examples for managing users. add a unconfined user , add a confined user , add a staff users, assign mcs categories to user (ranges)
create custom selinux user groups
create custom selinux logins

explain booleans
explain customizable types
mention manual pages for targeted daemons.

explain audit2allow
explain audit2why
explain sesearch and how you can use this to make decisions
explain semodule, sestatus , restorecon , semanage, setenforce , getenforce
explain limitations of chcon
explain advantage of chcon
explain chcat

explain selinux-policy-devel ( /usr/share/selinux/devel/Makefile )
show example how to make a custom policy module
explain the limitations of a policy module package
explain the advantages of a policy module package

explain role base access control and derrived types.

explain star and selinux tar support (exmaples)

important: Possible problems caused from running in permissive mode, such as having permissions to mislabel files.
important: Copying Vs moving files.

explain avc denials field by field.
explain advantage and limitation of sealert/setroublehoot and how this relates to audit.

explain file_t, unlabeled_t
explain initrc_t
explain unconfined_t
explain sepolgen and gui

explain why /tmp will not be relabled: http://domg444.blogspot.com/2007/11/why-files-with-incompatible-types-in.html

read selinux by example book

explain the MLS vs TARGETED
explain mcs role in targetted versus mcs role in mls

Subjects and object.
a system is really just files. we call files objects. there are different kind of files. There are devices, ports, interfaces, regular files etc. There are also file that can be executed and that spawn a process. A process is also represented as file in the proc file system. processes are called subjects. There are different kind of processes. like there are different kind of files. for example a user process is spawned from a TTY or PTS. these are also represented on a file system as a file. a user program process is spawned from a application executable file and a init daemon is started from a init script which is also represented as a file on the files system. so you see everything just really is a file on your system and processes spawned of these files. files are objects, process are subjects.

SElinux lets us label every file and thus everything in a system. SElinux provides classes and permissions. a class for a subject is process and a permission could be signal, to signal the process. a class for a object could be file or dir or tcp_socket etc each type of file has a class and each class has a set of permission that one can use when enforcing flexible selinux.

so theres everything(files), files are either files or processes.(objects or subjects) then there are different kind of objects (file objects , port objects), and there are also different kind of subjects.(user domains, application domains etc).

these different files have classes defined in the kernel and each class has its own set of permissions. one can assign types to each file and specify how each of these types may interact with the other types.

a real user logins into the system by executing a terminal. we labeled the terminal file with a type: tty_terminal_exec_type. this is a executable file. it spawns a user process. one must specify in which domain the user process should run. lets call the user process, or as we also call process: domains, user_t.

first we should assign the type to the object. we can use chcon or semanage to assign types to file objects and interface objects and port objects. then we should define the rules so that when the user runs the tty terminal file it transition to a user domain.

this is fiction:

file_type tty_terminal_exec_type; # declare a type for your object
userdomain_transition(user_type,tty_terminal_exec_type) # this macro would suggest that when the object with type tty_terminal_type gets executed, the user process (subject) should transtion to the user_type domain.

now we assigned a user domain type (user_type) to a user process. In SElinux world all access between the types is denied by default. so unless there is policy is specified this user domain will not be able to access any other object other then the tty object it executed to get here. lets give this user domain type access to a file type. file type is a name for a set of different kind of files including a general file and a directory file.

lets give directory ~/test a file type of test_dir_type and a file ~/test/file.txt a file type of test_file_type. we use chcon or semanage to assign the file type to the dir and file. and specify how our user domain type may interact with these file types

the class for our user domain type is process. this is static in the kernel. the classes for a file type are dir for the directory file and file for the regular file. also static in the kernel. permissions specific to the file type class are for examples getattr search read write etc. lets write policy

(me executing the tty_terminal with executable file type tty_terminal_exec_t)

allow me to get attribute of class dir with file type test_dir_t
allow user_type test_dir_type:dir getattr;

allow me to manage class dir with file type test_dir_t
allow user_type test_dir_type:dir manage_dir_perms;

the manage_dir_perms is a macro that represents all permissions needed to manage a dir class.

allow me to read class file with file type test_file_type
allow user_type test_file_type:file read;

now we can manage the dir object with file type test_dir_t and class dir and we (subject with a user domain type) can read the file object with file_type test_file_t and class file

can you imagine the flexibility? can you imagine the ammount of rules? how to keep this managable? answer: macros.


explain permissive mode and how that relates to selinux=0. permissive logs would be denials, selinux=0 or the option to disable it in /etc/selinux/config will fully disable selinux.
concentrate on semanage. this is the most important tool for users. if a users knows all options in semanage and how/when to apply them then the user knows alot about selinux. maybe treat semanage as an entrypoint.
if a user knows semanage then the user will have no trouble with system_config_selinux. but focus on semanage and not system config selinux (but ofcourse do mention it)