17.14. Nagios in a MAC Jail

The following demonstration will implement a secure environment using various MAC modules with properly configured policies. This is only a test and should not be considered the complete answer to everyone's security woes. Just implementing a policy and ignoring it never works and could be disastrous in a production environment.

Before beginning this process, the multilabel option must be set on each file system as stated at the beginning of this chapter. Not doing so will result in errors. While at it, ensure that the net-mngt/nagios-plugins, net-mngt/nagios, and www/apache13 ports are all installed, configured, and working correctly.

17.14.1. Create an insecure User Class

Begin the procedure by adding the following user class to the /etc/login.conf file:

insecure:\
:copyright=/etc/COPYRIGHT:\
:welcome=/etc/motd:\
:setenv=MAIL=/var/mail/$,BLOCKSIZE=K:\
:path=~/bin:/sbin:/bin:/usr/sbin:/usr/bin:/usr/local/sbin:/usr/local/bin
:manpath=/usr/share/man /usr/local/man:\
:nologin=/usr/sbin/nologin:\
:cputime=1h30m:\
:datasize=8M:\
:vmemoryuse=100M:\
:stacksize=2M:\
:memorylocked=4M:\
:memoryuse=8M:\
:filesize=8M:\
:coredumpsize=8M:\
:openfiles=24:\
:maxproc=32:\
:priority=0:\
:requirehome:\
:passwordtime=91d:\
:umask=022:\
:ignoretime@:\
:label=biba/10(10-10):

And adding the following line to the default user class:

:label=biba/high:

Once this is completed, the following command must be issued to rebuild the database:

# cap_mkdb /etc/login.conf

17.14.2. Boot Configuration

Do not reboot yet, just add the following lines to /boot/loader.conf so the required modules will load during system initialization:

mac_biba_load="YES"
mac_seeotheruids_load="YES"

17.14.3. Configure Users

Set the root user to the default class using:

# pw usermod root -L default

All user accounts that are not root or system users will now require a login class. The login class is required otherwise users will be refused access to common commands such as vi(1). The following sh script should do the trick:

# for x in `awk -F: '($3 >= 1001) && ($3 != 65534) { print $1 }' \
	/etc/passwd`; do pw usermod $x -L default; done;

Drop the nagios and www users into the insecure class:

# pw usermod nagios -L insecure
# pw usermod www -L insecure

17.14.4. Create the Contexts File

A contexts file should now be created; the following example file should be placed in /etc/policy.contexts.

# This is the default BIBA policy for this system.

# System:
/var/run                        biba/equal
/var/run/*                      biba/equal

/dev                            biba/equal
/dev/*                          biba/equal

/var				biba/equal
/var/spool                      biba/equal
/var/spool/*                    biba/equal

/var/log                        biba/equal
/var/log/*                      biba/equal

/tmp				biba/equal
/tmp/*				biba/equal
/var/tmp			biba/equal
/var/tmp/*			biba/equal

/var/spool/mqueue		biba/equal
/var/spool/clientmqueue		biba/equal

# For Nagios:
/usr/local/etc/nagios
/usr/local/etc/nagios/*         biba/10

/var/spool/nagios               biba/10
/var/spool/nagios/*             biba/10

# For apache
/usr/local/etc/apache           biba/10
/usr/local/etc/apache/*         biba/10

This policy will enforce security by setting restrictions on the flow of information. In this specific configuration, users, root and others, should never be allowed to access Nagios. Configuration files and processes that are a part of Nagios will be completely self contained or jailed.

This file may now be read into our system by issuing the following command:

# setfsmac -ef /etc/policy.contexts /
# setfsmac -ef /etc/policy.contexts /

Σημείωση:

The above file system layout may be different depending on environment; however, it must be run on every single file system.

The /etc/mac.conf file requires the following modifications in the main section:

default_labels file ?biba
default_labels ifnet ?biba
default_labels process ?biba
default_labels socket ?biba

17.14.5. Enable Networking

Add the following line to /boot/loader.conf:

security.mac.biba.trust_all_interfaces=1

And the following to the network card configuration stored in rc.conf. If the primary Internet configuration is done via DHCP, this may need to be configured manually after every system boot:

maclabel biba/equal

17.14.6. Testing the Configuration

Ensure that the web server and Nagios will not be started on system initialization, and reboot. Ensure the root user cannot access any of the files in the Nagios configuration directory. If root can issue an ls(1) command on /var/spool/nagios, then something is wrong. Otherwise a «permission denied» error should be returned.

If all seems well, Nagios, Apache, and Sendmail can now be started in a way fitting of the security policy. The following commands will make this happen:

# cd /etc/mail && make stop && \
setpmac biba/equal make start && setpmac biba/10\(10-10\) apachectl start && \
setpmac biba/10\(10-10\) /usr/local/etc/rc.d/nagios.sh forcestart

Double check to ensure that everything is working properly. If not, check the log files or error messages. Use the sysctl(8) utility to disable the mac_biba(4) security policy module enforcement and try starting everything again, like normal.

Σημείωση:

The root user can change the security enforcement and edit the configuration files without fear. The following command will permit the degradation of the security policy to a lower grade for a newly spawned shell:

# setpmac biba/10 csh

To block this from happening, force the user into a range via login.conf(5). If setpmac(8) attempts to run a command outside of the compartment's range, an error will be returned and the command will not be executed. In this case, setting root to biba/high(high-high).

Αυτό το κείμενο, και άλλα κείμενα, μπορεί να βρεθεί στο ftp://ftp.FreeBSD.org/pub/FreeBSD/doc/

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