<?xml version="1.0" encoding="iso-8859-1"?>
<!--
The FreeBSD Documentation Project
$FreeBSD$
-->
<chapter id="mac">
<chapterinfo>
<authorgroup>
<author>
<firstname>Tom</firstname>
<surname>Rhodes</surname>
<contrib>Written by </contrib>
</author>
</authorgroup>
</chapterinfo>
<title>Mandatory Access Control</title>
<sect1 id="mac-synopsis">
<title>Synopsis</title>
<indexterm><primary>MAC</primary></indexterm>
<indexterm>
<primary>Mandatory Access Control</primary>
<see>MAC</see>
</indexterm>
<para>&os; 5.X introduced new security extensions from the
<ulink url="http://www.trustedbsd.org">TrustedBSD
Project</ulink> based on the &posix;.1e draft. Two of the
most significant new security mechanisms are file system Access
Control Lists (<acronym>ACL</acronym>s) and Mandatory Access
Control (<acronym>MAC</acronym>) facilities. MAC allows new
access control modules to be loaded, implementing new security
policies. Some modules provide protections for a narrow subset
of the system, hardening a particular service. Others provide
comprehensive labeled security across all subjects and objects.
The mandatory part of the definition indicates that enforcement
of controls is performed by administrators and the operating
system. This is in contrast to the default security mechanism
of Discretionary Access Control (<acronym>DAC</acronym> where
enforcement is left to the discretion of users.</para>
<para>This chapter focuses on the <acronym>MAC</acronym> framework
and the set of pluggable security policy modules &os; provides
for enabling various security mechanisms.</para>
<para>After reading this chapter, you will know:</para>
<itemizedlist>
<listitem>
<para>Which <acronym>MAC</acronym> security policy modules
are included in &os; and their associated mechanisms.</para>
</listitem>
<listitem>
<para>The capabilities of <acronym>MAC</acronym> security
policy modules as well as the difference between a labeled
and non-labeled policy.</para>
</listitem>
<listitem>
<para>How to efficiently configure a system to use the
<acronym>MAC</acronym> framework.</para>
</listitem>
<listitem>
<para>How to configure the different security policy modules
included with the <acronym>MAC</acronym> framework.</para>
</listitem>
<listitem>
<para>How to implement a more secure environment using the
<acronym>MAC</acronym> framework.</para>
</listitem>
<listitem>
<para>How to test the <acronym>MAC</acronym> configuration
to ensure the framework has been properly
implemented.</para>
</listitem>
</itemizedlist>
<para>Before reading this chapter, you should:</para>
<itemizedlist>
<listitem>
<para>Understand &unix; and &os; basics
(<xref linkend="basics"/>).</para>
</listitem>
<listitem>
<para>Have some familiarity with security and how it
pertains to &os; (<xref linkend="security"/>).</para>
</listitem>
</itemizedlist>
<warning>
<para>Improper <acronym>MAC</acronym> configuration may cause
loss of system access, aggravation of users, or inability to
access the features provided by
<application>Xorg</application>. More importantly,
<acronym>MAC</acronym> should not be relied upon to completely
secure a system. The <acronym>MAC</acronym> framework only
augments an existing security policy. Without sound security
practices and regular security checks, the system will never
be completely secure.</para>
<para>The examples contained within this chapter are for
demonstration purposes and the example settings should
<emphasis>not</emphasis> be implemented on a production
system. Implementing any security policy takes a good deal of
understanding, proper design, and thorough testing.</para>
</warning>
<sect2>
<title>What Will Not Be Covered</title>
<para>This chapter covers a broad range of security issues
relating to the <acronym>MAC</acronym> framework. The
development of new <acronym>MAC</acronym> security policy
modules will not be covered. A number of security policy
modules included with the <acronym>MAC</acronym> framework
have specific characteristics which are provided for both
testing and new module development. These include
&man.mac.test.4;, &man.mac.stub.4; and &man.mac.none.4;.
For more information on these security policy modules and
the various mechanisms they provide, refer to their manual
pages.</para>
</sect2>
</sect1>
<sect1 id="mac-inline-glossary">
<title>Key Terms in This Chapter</title>
<para>Before reading this chapter, a few key terms must be
explained:</para>
<itemizedlist>
<listitem>
<para><emphasis>compartment</emphasis>: a set of programs and
data to be partitioned or separated, where users are given
explicit access to specific component of a system. A
compartment represents a grouping, such as a work group,
department, project, or topic. Compartments make it
possible to implement a need-to-know-basis security
policy.</para>
</listitem>
<listitem>
<para><emphasis>high-watermark</emphasis>: this type of
policy permits the raising of security levels for the
purpose of accessing higher level information. In most
cases, the original level is restored after the process
is complete. Currently, the &os; <acronym>MAC</acronym>
framework does not include this type of policy.</para>
</listitem>
<listitem>
<para><emphasis>integrity</emphasis>: the level of trust which
can be placed on data. As the integrity of the data is
elevated, so does the ability to trust that data.</para>
</listitem>
<listitem>
<para><emphasis>label</emphasis>: a security attribute which
can be applied to files, directories, or other items in the
system. It could be considered a confidentiality stamp.
When a label is placed on a file, it describes the security
properties of that file and will only permit access by
files, users, and resources with a similar security setting.
The meaning and interpretation of label values depends on
the policy configuration. Some policies treat a label as
representing the integrity or secrecy of an object while
other policies might use labels to hold rules for
access.</para>
</listitem>
<listitem>
<para><emphasis>level</emphasis>: the increased or decreased
setting of a security attribute. As the level increases,
its security is considered to elevate as well.</para>
</listitem>
<listitem>
<para><emphasis>low-watermark</emphasis>: this type of
policy permits lowering security levels for the purpose of
accessing information which is less secure. In most cases,
the original security level of the user is restored after
the process is complete. The only security policy module in
&os; to use this is &man.mac.lomac.4;.</para>
</listitem>
<listitem>
<para><emphasis>multilabel</emphasis>: this property is a file
system option which can be set in single user mode using
&man.tunefs.8;, during boot using &man.fstab.5;, or during
the creation of a new file system. This option permits
an administrator to apply different <acronym>MAC</acronym>
labels on different objects. This option only applies to
security policy modules which support labeling.</para>
</listitem>
<listitem>
<para><emphasis>object</emphasis>: an entity through which
information flows under the direction of a
<emphasis>subject</emphasis>. This includes directories,
files, fields, screens, keyboards, memory, magnetic storage,
printers or any other data storage or moving device. An
object is a data container or a system resource. Access to
an <emphasis>object</emphasis> effectively means access to
its data.</para>
</listitem>
<listitem>
<para><emphasis>policy</emphasis>: a collection of rules
which defines how objectives are to be achieved. A
<emphasis>policy</emphasis> usually documents how certain
items are to be handled. This chapter considers the term
<emphasis>policy</emphasis> to be a <emphasis>security
policy</emphasis>, or a collection of rules which controls
the flow of data and information and defines who has access
to that data and information.</para>
</listitem>
<listitem>
<para><emphasis>sensitivity</emphasis>: usually used when
discussing Multilevel Security <acronym>MLS</acronym>. A
sensitivity level describes how important or secret the data
should be. As the sensitivity level increases, so does the
importance of the secrecy, or confidentiality, of the
data.</para>
</listitem>
<listitem>
<para><emphasis>single label</emphasis>: a policy where the
entire file system uses one label to enforce access control
over the flow of data. Whenever <option>multilabel</option>
is not set, all files will conform to the same label
setting.</para>
</listitem>
<listitem>
<para><emphasis>subject</emphasis>: any active entity that
causes information to flow between
<emphasis>objects</emphasis> such as a user, user process,
or system process. On &os;, this is almost always a
thread acting in a process on behalf of a user.</para>
</listitem>
</itemizedlist>
</sect1>
<sect1 id="mac-initial">
<title>Explanation of MAC</title>
<para>With all of these new terms in mind, consider how the
<acronym>MAC</acronym> framework augments the security of
the system as a whole. The various security policy modules
provided by the <acronym>MAC</acronym> framework could be used
to protect the network and file systems or to block users from
accessing certain ports and sockets. Perhaps the best use of
the policy modules is to load several security policy modules at
a time in order to provide a <acronym>MLS</acronym> environment.
This approach differs from a hardening policy, which typically
hardens elements of a system which are used only for specific
purposes. The downside to <acronym>MLS</acronym> is increased
administrative overhead.</para>
<para>The overhead is minimal when compared to the lasting effect
of a framework which provides the ability to pick and choose
which policies are required for a specific configuration and
which keeps performance overhead down. The reduction of support
for unneeded policies can increase the overall performance of
the system as well as offer flexibility of choice. A good
implementation would consider the overall security requirements
and effectively implement the various security policy modules
offered by the framework.</para>
<para>A system utilizing <acronym>MAC</acronym> guarantees that a
user will not be permitted to change security attributes at
will. All user utilities, programs, and scripts must work
within the constraints of the access rules provided by the
selected security policy modules and total control of the
<acronym>MAC</acronym> access rules are in the hands of the
system administrator.</para>
<para>It is the duty of the system administrator to
carefully select the correct security policy modules. For an
environment that needs to limit access control over the network,
the &man.mac.portacl.4;, &man.mac.ifoff.4;, and &man.mac.biba.4;
policy modules make good starting points. For an environment
where strict confidentiality of file system objects is required,
consider the &man.mac.bsdextended.4; and &man.mac.mls.4; policy
modules.</para>
<para>Policy decisions could be made based on network
configuration. If only certain users should be permitted
access to &man.ssh.1;, the &man.mac.portacl.4; policy module is
a good choice. In the case of file systems, access to objects
might be considered confidential to some users, but not to
others. As an example, a large development team might be
broken off into smaller projects where developers in project A
might not be permitted to access objects written by developers
in project B. Yet both projects might need to access objects
created by developers in project C. Using the different
security policy modules provided by the <acronym>MAC</acronym>
framework, users could be divided into these groups and then
given access to the appropriate objects.</para>
<para>Each security policy module has a unique way of dealing with
the overall security of a system. Module selection should be
based on a well thought out security policy which may require
revision and reimplementation. Understanding the different
security policy modules offered by the <acronym>MAC</acronym>
framework will help administrators choose the best policies
for their situations.</para>
<caution>
<para>Implementing <acronym>MAC</acronym> is much like
implementing a firewall, care must be taken to prevent being
completely locked out of the system. The ability to revert
back to a previous configuration should be considered and the
implementation of <acronym>MAC</acronym> remotely should be
done with extreme caution.</para>
</caution>
</sect1>
<sect1 id="mac-understandlabel">
<title>Understanding MAC Labels</title>
<para>A <acronym>MAC</acronym> label is a security attribute
which may be applied to subjects and objects throughout
the system.</para>
<para>When setting a label, the administrator must be able to
comprehend what exactly is being done and understand any
implications in order to prevent unexpected or undesired
behavior of the system. The attributes available on an object
depend on the loaded policy module as policy modules interpret
their attributes in different ways.</para>
<para>The security label on an object is used as a part of a
security access control decision by a policy. With some
policies, the label contains all of the information necessary
to make a decision. In other policies, the labels may be
processed as part of a larger rule set. For instance, setting
the label of <literal>biba/low</literal> on a file will
represent a label maintained by the Biba security policy module,
with a value of <quote>low</quote>.</para>
<para>A few policy modules which support the labeling feature
in &os; offer three specific predefined labels: low, high, and
equal. Such policy modules enforce access control in a
different manner with each policy module, where the low label is
the lowest setting, the equal label sets the subject or object
to be disabled or unaffected, and the high label enforces the
highest setting available in the Biba and <acronym>MLS</acronym>
policy modules.</para>
<para>Within single label file system environments, only one
label may be used on objects. This label enforces one set of
access permissions across the entire system and in many
environments may be all that is required. There are a few
cases where multiple labels may be set on objects or subjects
in the file system by passing <option>multilabel</option> to
&man.tunefs.8;.</para>
<para>In the case of Biba and <acronym>MLS</acronym>, a numeric
label may be set to indicate the precise level of hierarchical
control. This numeric level is used to partition or sort
information into different groups of classification only
permitting access to that group or a higher group level.</para>
<para>In most cases, the administrator will set up a single label
to use throughout the file system. This is similar to
<acronym>DAC</acronym> to some extent as
<username>root</username> is the one in control and who
configures the policies so that users are placed in the
appropriate categories/access levels. Alas, many policy modules
can restrict the <username>root</username> user as well. Basic
control over objects will then be released to the group, but
<username>root</username> may revoke or modify the settings
at any time. This is the hierarchical/clearance model covered
by policies such as Biba and <acronym>MLS</acronym>.</para>
<sect2>
<title>Label Configuration</title>
<para>Virtually all aspects of label policy module configuration
will be performed using the base system utilities. These
commands provide a simple interface for object or subject
configuration or the manipulation and verification of
the configuration.</para>
<para>All configuration may be done using &man.setfmac.8; and
&man.setpmac.8;. <command>setfmac</command> is used to set
<acronym>MAC</acronym> labels on system objects while
<command>setpmac</command> is used to set the labels on system
subjects. Observe:</para>
<screen>&prompt.root; <userinput>setfmac biba/high test</userinput></screen>
<para>If the configuration is successful, the prompt will be
returned without error. A common error is
<errorname>Permission denied</errorname> which usually occurs
when the label is being set or modified on an object which is
restricted.<footnote><para>Other conditions may produce different
failures. For instance, the file may not be owned by the
user attempting to relabel the object, the object may not
exist, or the object may be read only. A mandatory policy
will not allow the process to relabel the file, maybe
because of a property of the file, a property of the
process, or a property of the proposed new label value. For
example, a user running at low integrity tries to change the
label of a high integrity file. Or perhaps a user running
at low integrity tries to change the label of a low
integrity file to a high integrity label.</para></footnote> The
system administrator may use the following commands to
overcome this:</para>
<screen>&prompt.root; <userinput>setfmac biba/high test</userinput>
<errorname>Permission denied</errorname>
&prompt.root; <userinput>setpmac biba/low setfmac biba/high test</userinput>
&prompt.root; <userinput>getfmac test</userinput>
test: biba/high</screen>
<para><command>setpmac</command> can be used to override the
policy module's settings by assigning a different label to the
invoked process. <command>getpmac</command> is usually used
with currently running processes, such as
<application>sendmail</application>. It takes a process ID in
place of a command. If users attempt to manipulate a file not
in their access, subject to the rules of the loaded policy
modules, the <errorname>Operation not permitted</errorname>
error will be displayed by the
<function>mac_set_link</function> function.</para>
<sect3>
<title>Common Label Types</title>
<para>For the &man.mac.biba.4;, &man.mac.mls.4; and
&man.mac.lomac.4; policy modules, the ability to assign
simple labels is provided. These take the form of high,
equal, and low, where:</para>
<itemizedlist>
<listitem>
<para>The <literal>low</literal> label is considered the
lowest label setting an object or subject may have.
Setting this on objects or subjects blocks their access
to objects or subjects marked high.</para>
</listitem>
<listitem>
<para>The <literal>equal</literal> label should only be
placed on objects considered to be exempt from the
policy.</para>
</listitem>
<listitem>
<para>The <literal>high</literal> label grants an object
or subject the highest possible setting.</para>
</listitem>
</itemizedlist>
<para>With respect to each policy module, each of those
settings will establish a different information flow
directive. Refer to the manual pages of the module to
determine the traits of these generic label
configurations.</para>
<sect4>
<title>Advanced Label Configuration</title>
<para>Numeric grade labels are used for
<literal>comparison:compartment+compartment</literal>.
For example:</para>
<programlisting>biba/10:2+3+6(5:2+3-20:2+3+4+5+6)</programlisting>
<para>may be interpreted as <quote>Biba Policy
Label</quote>/<quote>Grade
10</quote>:<quote>Compartments 2, 3 and 6</quote>:
(<quote>grade 5 ...</quote>)</para>
<para>In this example, the first grade would be considered
the <quote>effective grade</quote> with
<quote>effective compartments</quote>, the second grade
is the low grade, and the last one is the high grade.
In most configurations, these settings will not be used
as they are advanced configurations.</para>
<para>System objects only have a current grade/compartment.
System subjects reflect the range of available rights in
the system, and network interfaces, where they are used
for access control.</para>
<para>The grade and compartments in a subject and object
pair are used to construct a relationship known as
<quote>dominance</quote>, in which a subject dominates an
object, the object dominates the subject, neither
dominates the other, or both dominate each other. The
<quote>both dominate</quote> case occurs when the two
labels are equal. Due to the information flow nature of
Biba, a user has rights to a set of compartments that
might correspond to projects, but objects also have a set
of compartments. Users may have to subset their rights
using <command>su</command> or <command>setpmac</command>
in order to access objects in a compartment from which
they are not restricted.</para>
</sect4>
</sect3>
<sect3>
<title>Users and Label Settings</title>
<para>Users are required to have labels so that their files
and processes properly interact with the security policy
defined on the system. This is configured in
<filename>login.conf</filename> using login classes. Every
policy module that uses labels will implement the user class
setting.</para>
<para>An example entry containing every policy module setting
is displayed below:</para>
<programlisting>default:\
: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=partition/13,mls/5,biba/10(5-15),lomac/10[2]:</programlisting>
<para>To set the
user class default label which will be enforced by
<acronym>MAC</acronym>, use <option>label</option>. Users
are never permitted to modify this value. In a real
configuration, however, the administrator would never enable
every policy module. It is recommended that the rest of
this chapter be reviewed before any configuration is
implemented.</para>
<note>
<para>Users may change their label after they login, subject
to the constraints of the policy. The example above tells
the Biba policy that a process's minimum integrity is 5,
its maximum is 15, and the default effective label is 10.
The process will run at 10 until it chooses to change
label, perhaps due to the user using &man.setpmac.8;,
which will be constrained by Biba to the configured
range.</para>
</note>
<para>After any change to
<filename>login.conf</filename>, the login class capability
database must be rebuilt using
<command>cap_mkdb</command>.</para>
<para>Many sites have a large number of users requiring
several different user classes. In depth planning is
required as this may get extremely difficult to
manage.</para>
</sect3>
<sect3>
<title>Network Interfaces and Label Settings</title>
<para>Labels may be set on network interfaces to help
control the flow of data across the network. Policies
using network interface labels function in the same way that
policies function with respect to objects. Users at high
settings in <literal>biba</literal>, for example, will not
be permitted to access network interfaces with a label of
low.</para>
<para><option>maclabel</option> may be passed to
<command>ifconfig</command> when setting the
<acronym>MAC</acronym> label on network interfaces. For
example:</para>
<screen>&prompt.root; <userinput>ifconfig bge0 maclabel biba/equal</userinput></screen>
<para>will set the <acronym>MAC</acronym> label of
<literal>biba/equal</literal> on the &man.bge.4; interface.
When using a setting similar to
<literal>biba/high(low-high)</literal>, the entire label
should be quoted to prevent an error from being
returned.</para>
<para>Each policy module which supports labeling has a tunable
which may be used to disable the <acronym>MAC</acronym>
label on network interfaces. Setting the label to
<option>equal</option> will have a similar effect. Review
the output of <command>sysctl</command>, the policy manual
pages, and the information in this chapter for more
information on those tunables.</para>
</sect3>
</sect2>
<sect2>
<title>Singlelabel or Multilabel?</title>
<para>By default, the system will use
<option>singlelabel</option>. For the administrator, there
are several differences which offer pros and cons to the
flexibility in the system's security model.</para>
<para>A security policy which uses <option>singlelabel</option>
only permits one label, such as <literal>biba/high</literal>,
to be used for each subject or object. This provides lower
administration overhead, but decreases the flexibility of
policies which support labeling.</para>
<para><option>multilabel</option> permits each subject or object
to have its own independent <acronym>MAC</acronym> label.
The decision to use <option>multilabel</option> or
<option>singlelabel</option> is only required for the policies
which implement the labeling feature, including the Biba,
Lomac, and <acronym>MLS</acronym> policies.</para>
<para>In many cases, <option>multilabel</option> may not be
needed. Consider the following situation and security
model:</para>
<itemizedlist>
<listitem>
<para>&os; web-server using the <acronym>MAC</acronym>
framework and a mix of the various policies.</para>
</listitem>
<listitem>
<para>This machine only requires one label,
<literal>biba/high</literal>, for everything in the
system. This file system would not require
<option>multilabel</option> as a single label will always
be in effect.</para>
</listitem>
<listitem>
<para>But, this machine will be a web server and should
have the web server run at <literal>biba/low</literal>
to prevent write up capabilities. The server could
use a separate partition set at
<literal>biba/low</literal> for most if not all
of its runtime state.</para>
</listitem>
</itemizedlist>
<para>If any of the non-labeling policies are to be used,
<option>multilabel</option> would not be required. These
include the <literal>seeotheruids</literal>,
<literal>portacl</literal> and <literal>partition</literal>
policies.</para>
<para>Using <option>multilabel</option> with a partition and
establishing a security model based on
<option>multilabel</option> functionality could increase
administrative overhead as everything in the file system has a
label. This includes directories, files, and even device
nodes.</para>
<para>The following command will set <option>multilabel</option>
on the file systems to have multiple labels. This may only be
done in single user mode and is not a requirement for the swap
file system:</para>
<screen>&prompt.root; <userinput>tunefs -l enable /</userinput></screen>
<note>
<para>Some users have experienced problems with setting the
<option>multilabel</option> flag on the root partition.
If this is the case, please review the
<xref linkend="mac-troubleshoot"/> of this chapter.</para>
</note>
</sect2>
</sect1>
<sect1 id="mac-planning">
<title>Planning the Security Configuration</title>
<para>Whenever a new technology is implemented, a planning phase
is recommended. During the planning stages, an administrator
should consider the implementation requirements and the
implementation goals.</para>
<para>For <acronym>MAC</acronym> installations, these
include:</para>
<itemizedlist>
<listitem>
<para>How to classify information and resources available on
the target systems.</para>
</listitem>
<listitem>
<para>Which information or resources to restrict access to
along with the type of restrictions that should be
applied.</para>
</listitem>
<listitem>
<para>Which <acronym>MAC</acronym> module or modules will be
required to achieve this goal.</para>
</listitem>
</itemizedlist>
<para>Good planning helps to ensure a trouble-free and efficient
trusted system implementation. A trial run of the trusted
system and its configuration should occur
<emphasis>before</emphasis> a <acronym>MAC</acronym>
implementation is used on production systems. The idea of
just letting loose on a system with <acronym>MAC</acronym> is
like setting up for failure.</para>
<para>Different environments have different needs and
requirements. Establishing an in depth and complete security
profile will decrease the need of changes once the system
goes live. The rest of this chapter covers the available
modules, describes their use and configuration, and in some
cases, provides insight on applicable situations. For instance,
a web server might use the &man.mac.biba.4; and
&man.mac.bsdextended.4; policies. In the case of a machine
with few local users, &man.mac.partition.4; might be a good
choice.</para>
</sect1>
<sect1 id="mac-modules">
<title>Module Configuration</title>
<para>Beginning with &os; 8.0, the default &os; kernel
includes <literal>options MAC</literal>. This means that
every module included with the <acronym>MAC</acronym>
framework may be loaded as a run-time kernel module. The
recommended method is to add the module name to
<filename>/boot/loader.conf</filename> so that it will load
during boot. Each module also provides a kernel option
for those administrators who choose to compile their own
custom kernel.</para>
<para>Some modules support the use of labeling, which is
controlling access by enforcing a label such as <quote>this is
allowed and this is not</quote>. A label configuration file may
control how files may be accessed, network communication can be
exchanged, and more. The previous section showed how the
<option>multilabel</option> flag could be set on file systems to
enable per-file or per-partition access control.</para>
<para>A single label configuration enforces only one label
across the system, that is why the <command>tunefs</command>
option is called <option>multilabel</option>.</para>
</sect1>
<sect1 id="mac-seeotheruids">
<title>The MAC See Other UIDs Policy</title>
<indexterm>
<primary>MAC See Other UIDs Policy</primary>
</indexterm>
<para>Module name: <filename>mac_seeotheruids.ko</filename></para>
<para>Kernel configuration line:
<literal>options MAC_SEEOTHERUIDS</literal></para>
<para>Boot option:
<literal>mac_seeotheruids_load="YES"</literal></para>
<para>The &man.mac.seeotheruids.4; module mimics and extends
the <varname>security.bsd.see_other_uids</varname> and
<varname>security.bsd.see_other_gids</varname>
<command>sysctl</command> tunables. This option does
not require any labels to be set before configuration and
can operate transparently with the other modules.</para>
<para>After loading the module, the following
<command>sysctl</command> tunables may be used to control
the features:</para>
<itemizedlist>
<listitem>
<para><varname>security.mac.seeotheruids.enabled</varname>
enables the module and uses the default settings which deny
users the ability to view processes and sockets owned by
other users.</para>
</listitem>
<listitem>
<para>
<varname>security.mac.seeotheruids.specificgid_enabled</varname>
allows certain groups to be exempt from this policy. To
exempt specific groups from this policy, use the
<varname>security.mac.seeotheruids.specificgid=<replaceable>XXX</replaceable></varname>
<command>sysctl</command> tunable. Replace
<replaceable>XXX</replaceable> with the numeric group ID to
be exempted.</para>
</listitem>
<listitem>
<para>
<varname>security.mac.seeotheruids.primarygroup_enabled</varname>
is used to exempt specific primary groups from this policy.
When using this tunable,
<varname>security.mac.seeotheruids.specificgid_enabled</varname>
may not be set.</para>
</listitem>
</itemizedlist>
</sect1>
<sect1 id="mac-bsdextended">
<title>The MAC BSD Extended Policy</title>
<indexterm>
<primary>MAC</primary>
<secondary>File System Firewall Policy</secondary>
</indexterm>
<para>Module name: <filename>mac_bsdextended.ko</filename></para>
<para>Kernel configuration line:
<literal>options MAC_BSDEXTENDED</literal></para>
<para>Boot option:
<literal>mac_bsdextended_load="YES"</literal></para>
<para>The &man.mac.bsdextended.4; module enforces the file system
firewall. This module's policy provides an extension to the
standard file system permissions model, permitting an
administrator to create a firewall-like ruleset to protect
files, utilities, and directories in the file system hierarchy.
When access to a file system object is attempted, the list of
rules is iterated until either a matching rule is located or
the end is reached. This behavior may be changed by the use
of a &man.sysctl.8; parameter,
<varname>security.mac.bsdextended.firstmatch_enabled</varname>.
Similar to other firewall modules in &os;, a file containing
the access control rules can be created and read by the system
at boot time using an &man.rc.conf.5; variable.</para>
<para>The rule list may be entered using &man.ugidfw.8; which has
a syntax similar to &man.ipfw.8;. More tools can be written by
using the functions in the &man.libugidfw.3; library.</para>
<para>Extreme caution should be taken when working with this
module as incorrect use could block access to certain parts of
the file system.</para>
<sect2>
<title>Examples</title>
<para>After the &man.mac.bsdextended.4; module has been loaded,
the following command may be used to list the current rule
configuration:</para>
<screen>&prompt.root; <userinput>ugidfw list</userinput>
0 slots, 0 rules</screen>
<para>By default, no rules are defined and everything is
completely accessible. To create a rule which will block all
access by users but leave <username>root</username>
unaffected, run the following command:</para>
<screen>&prompt.root; <userinput>ugidfw add subject not uid root new object not uid root mode n</userinput></screen>
<para>This is a very bad idea as it will block all users from
issuing even the most simple commands, such as
<command>ls</command>. The next example will block
<username>user1</username> any and all access, including
directory listings, to
<username><replaceable>user2</replaceable></username>'s home
directory:</para>
<screen>&prompt.root; <userinput>ugidfw set 2 subject uid <replaceable>user1</replaceable> object uid <replaceable>user2</replaceable> mode n</userinput>
&prompt.root; <userinput>ugidfw set 3 subject uid <replaceable>user1</replaceable> object gid <replaceable>user2</replaceable> mode n</userinput></screen>
<para>Instead of <username>user1</username>,
<option>not uid <replaceable>user2</replaceable></option>
could be used. This enforces the same access restrictions for
all users instead of just one user.</para>
<note>
<para>The <username>root</username> user is unaffected by
these changes.</para>
</note>
<para>For more information, refer to &man.mac.bsdextended.4; and
&man.ugidfw.8;</para>
</sect2>
</sect1>
<sect1 id="mac-ifoff">
<title>The MAC Interface Silencing Policy</title>
<indexterm>
<primary>MAC Interface Silencing Policy</primary>
</indexterm>
<para>Module name: <filename>mac_ifoff.ko</filename></para>
<para>Kernel configuration line:
<literal>options MAC_IFOFF</literal></para>
<para>Boot option:
<literal>mac_ifoff_load="YES"</literal></para>
<para>The &man.mac.ifoff.4; module exists solely to disable
network interfaces on the fly and keep network interfaces from
being brought up during system boot. It does not require any
labels to be set up on the system, nor does it depend on other
<acronym>MAC</acronym> modules.</para>
<para>Most of this module's control is performed through the
<command>sysctl</command> tunables listed below.</para>
<itemizedlist>
<listitem>
<para><varname>security.mac.ifoff.lo_enabled</varname>
enables or disables all traffic on the loopback (&man.lo.4;)
interface.</para>
</listitem>
<listitem>
<para><varname>security.mac.ifoff.bpfrecv_enabled</varname>
enables or disables all traffic on the Berkeley Packet
Filter interface (&man.bpf.4;)</para>
</listitem>
<listitem>
<para><varname>security.mac.ifoff.other_enabled</varname>
enables or disables traffic on all other interfaces.</para>
</listitem>
</itemizedlist>
<para>One of the most common uses of &man.mac.ifoff.4; is network
monitoring in an environment where network traffic should not
be permitted during the boot sequence. Another suggested use
would be to write a script which uses
<filename role="package">security/aide</filename> to
automatically block network traffic if it finds new or altered
files in protected directories.</para>
</sect1>
<sect1 id="mac-portacl">
<title>The MAC Port Access Control List Policy</title>
<indexterm>
<primary>MAC Port Access Control List Policy</primary>
</indexterm>
<para>Module name: <filename>mac_portacl.ko</filename></para>
<para>Kernel configuration line:
<literal>MAC_PORTACL</literal></para>
<para>Boot option:
<literal>mac_portacl_load="YES"</literal></para>
<para>The &man.mac.portacl.4; module is used to limit binding to
local <acronym>TCP</acronym> and <acronym>UDP</acronym> ports
using a variety of <command>sysctl</command> variables.
&man.mac.portacl.4; makes it possible to allow
non-<username>root</username> users to bind to specified
privileged ports below 1024.</para>
<para>Once loaded, this module enables the
<acronym>MAC</acronym> policy on all sockets. The following
tunables are available:</para>
<itemizedlist>
<listitem>
<para><varname>security.mac.portacl.enabled</varname>
enables or disables the policy completely.</para>
</listitem>
<listitem>
<para><varname>security.mac.portacl.port_high</varname>
sets the highest port number that &man.mac.portacl.4;
protects.</para>
</listitem>
<listitem>
<para><varname>security.mac.portacl.suser_exempt</varname>,
when set to a non-zero value, exempts the
<username>root</username> user from this policy.</para>
</listitem>
<listitem>
<para><varname>security.mac.portacl.rules</varname>
specifies the mac_portacl policy, which is a text string of
the form: <literal>rule[,rule,...]</literal> with as many
rules as needed. Each rule is of the form:
<literal>idtype:id:protocol:port</literal>. The
<parameter>idtype</parameter> parameter can be
<literal>uid</literal> or <literal>gid</literal> and is used
to interpret the <parameter>id</parameter> parameter as
either a user id or group id, respectively. The
<parameter>protocol</parameter> parameter is used to
determine if the rule should apply to <acronym>TCP</acronym>
or <acronym>UDP</acronym> by setting the parameter to
<literal>tcp</literal> or <literal>udp</literal>. The final
<parameter>port</parameter> parameter is the port number to
allow the specified user or group to bind to.</para>
</listitem>
</itemizedlist>
<note>
<para>Since the ruleset is interpreted directly by the kernel,
only numeric values can be used for the user ID, group ID,
and port parameters. Names cannot be used for users,
groups, or services.</para>
</note>
<para>By default, ports below 1024 can only be used by or bound
to privileged processes, which run as
<username>root</username>. For &man.mac.portacl.4; to allow
non-privileged processes to bind to ports below 1024, this
restriction has to be disabled by setting the &man.sysctl.8;
variables
<varname>net.inet.ip.portrange.reservedlow</varname> and
<varname>net.inet.ip.portrange.reservedhigh</varname> to
zero:</para>
<screen>&prompt.root; <userinput>sysctl security.mac.portacl.port_high=1023</userinput>
&prompt.root; <userinput>sysctl net.inet.ip.portrange.reservedlow=0
net.inet.ip.portrange.reservedhigh=0</userinput></screen>
<para>See the examples below or refer to &man.mac.portacl.4; for
further information.</para>
<sect2>
<title>Examples</title>
<para>Since the <username>root</username> user should not be
crippled by this policy, this example starts by setting the
<varname>security.mac.portacl.suser_exempt</varname> to a
non-zero value.</para>
<screen>&prompt.root; <userinput>sysctl security.mac.portacl.suser_exempt=1</userinput></screen>
<para>Next, allow the user with <acronym>UID</acronym> 80
to bind to port 80. This allows the <username>www</username>
user to run a web server without ever having
<username>root</username> privilege.</para>
<screen>&prompt.root; <userinput>sysctl security.mac.portacl.rules=uid:80:tcp:80</userinput></screen>
<para>The next example permits the user with the
<acronym>UID</acronym> of 1001 to bind to the
<acronym>TCP</acronym> ports 110 (<quote>pop3</quote>) and 995
(<quote>pop3s</quote>). This permits this user to start a
server that accepts connections on ports 110 and 995.</para>
<screen>&prompt.root; <userinput>sysctl security.mac.portacl.rules=uid:1001:tcp:110,uid:1001:tcp:995</userinput></screen>
</sect2>
</sect1>
<sect1 id="mac-partition">
<title>The MAC Partition Policy</title>
<indexterm>
<primary>MAC Process Partition Policy</primary>
</indexterm>
<para>Module name: <filename>mac_partition.ko</filename></para>
<para>Kernel configuration line:
<literal>options MAC_PARTITION</literal></para>
<para>Boot option:
<literal>mac_partition_load="YES"</literal></para>
<para>The &man.mac.partition.4; policy will drop processes into
specific <quote>partitions</quote> based on their
<acronym>MAC</acronym> label. This module should be added to
&man.loader.conf.5; so that it loads and enables the policy
at system boot.</para>
<para>Most configuration for this policy is done using
&man.setpmac.8;. One <command>sysctl</command> tunable is
available for this policy:</para>
<itemizedlist>
<listitem>
<para><varname>security.mac.partition.enabled</varname>
enables the enforcement of <acronym>MAC</acronym> process
partitions.</para>
</listitem>
</itemizedlist>
<para>When this policy is enabled, users will only be permitted
to see their processes, and any others within their partition,
but will not be permitted to work with utilities outside the
scope of this partition. For instance, a user in the
<literal>insecure</literal> class will not be permitted to
access <command>top</command> as well as many other commands
that must spawn a process.</para>
<para>To set or drop utilities into a partition label, use the
<command>setpmac</command> utility:</para>
<screen>&prompt.root; <userinput>setpmac partition/13 top</userinput></screen>
<para>This example adds <command>top</command> to the label set on
users in the <literal>insecure</literal> class. All processes
spawned by users in the <literal>insecure</literal> class will
stay in the <literal>partition/13</literal> label.</para>
<sect2>
<title>Examples</title>
<para>The following command will display the partition label
and the process list:</para>
<screen>&prompt.root; <userinput>ps Zax</userinput></screen>
<para>This command will display another user's process partition
label and that user's currently running processes:</para>
<screen>&prompt.root; <userinput>ps -ZU trhodes</userinput></screen>
<note>
<para>Users can see processes in <username>root</username>'s
label unless the &man.mac.seeotheruids.4; policy is
loaded.</para>
</note>
<para>A really crafty implementation could have all of the
services disabled in <filename>/etc/rc.conf</filename> and
started by a script that starts them with the proper
labeling set.</para>
<note>
<para>The following policies support integer settings
in place of the three default labels offered. These
options, including their limitations, are further explained
in the module manual pages.</para>
</note>
</sect2>
</sect1>
<sect1 id="mac-mls">
<title>The MAC Multi-Level Security Module</title>
<indexterm>
<primary>MAC Multi-Level Security Policy</primary>
</indexterm>
<para>Module name: <filename>mac_mls.ko</filename></para>
<para>Kernel configuration line:
<literal>options MAC_MLS</literal></para>
<para>Boot option: <literal>mac_mls_load="YES"</literal></para>
<para>The &man.mac.mls.4; policy controls access between subjects
and objects in the system by enforcing a strict information
flow policy.</para>
<para>In <acronym>MLS</acronym> environments, a
<quote>clearance</quote> level is set in the label of each
subject or object, along with compartments. Since these
clearance or sensibility levels can reach numbers greater than
several thousand; it would be a daunting task for any system
administrator to thoroughly configure each subject or object.
Thankfully, three <quote>instant</quote> labels are included in
this policy.</para>
<para>These labels are <literal>mls/low</literal>,
<literal>mls/equal</literal> and <literal>mls/high</literal>.
Since these labels are described in depth in the manual page,
they will only get a brief description here:</para>
<itemizedlist>
<listitem>
<para>The <literal>mls/low</literal> label contains a low
configuration which permits it to be dominated by all other
objects. Anything labeled with <literal>mls/low</literal>
will have a low clearance level and not be permitted to
access information of a higher level. This label also
prevents objects of a higher clearance level from writing or
passing information on to them.</para>
</listitem>
<listitem>
<para>The <literal>mls/equal</literal> label should be
placed on objects considered to be exempt from the
policy.</para>
</listitem>
<listitem>
<para>The <literal>mls/high</literal> label is the highest
level of clearance possible. Objects assigned this label
will hold dominance over all other objects in the system;
however, they will not permit the leaking of information
to objects of a lower class.</para>
</listitem>
</itemizedlist>
<para><acronym>MLS</acronym> provides:</para>
<itemizedlist>
<listitem>
<para>A hierarchical security level with a set of non
hierarchical categories.</para>
</listitem>
<listitem>
<para>Fixed rules of <literal>no read up, no write
down</literal>. This means that a subject can have read
access to objects on its own level or below, but not above.
Similarly, a subject can have write access to objects on its
own level or above but not beneath.</para>
</listitem>
<listitem>
<para>Secrecy, or the prevention of inappropriate disclosure
of data.</para>
</listitem>
<listitem>
<para>A basis for the design of systems that concurrently
handle data at multiple sensitivity levels without leaking
information between secret and confidential.</para>
</listitem>
</itemizedlist>
<para>The following <command>sysctl</command> tunables are
available for the configuration of special services and
interfaces:</para>
<itemizedlist>
<listitem>
<para><varname>security.mac.mls.enabled</varname> is used to
enable or disable the <acronym>MLS</acronym> policy.</para>
</listitem>
<listitem>
<para><varname>security.mac.mls.ptys_equal</varname>
labels all &man.pty.4; devices as
<literal>mls/equal</literal> during creation.</para>
</listitem>
<listitem>
<para><varname>security.mac.mls.revocation_enabled</varname>
revokes access to objects after their label changes to a
label of a lower grade.</para>
</listitem>
<listitem>
<para><varname>security.mac.mls.max_compartments</varname>
sets the maximum number of compartment levels allowed on a
system.</para>
</listitem>
</itemizedlist>
<para>To manipulate the <acronym>MLS</acronym> labels, use
&man.setfmac.8;. To assign a label to an object, issue the
following command:</para>
<screen>&prompt.root; <userinput>setfmac mls/5 test</userinput></screen>
<para>To get the <acronym>MLS</acronym> label for the file
<filename>test</filename>, issue the following command:</para>
<screen>&prompt.root; <userinput>getfmac test</userinput></screen>
<para>Another approach is to create a master policy file in
<filename class="directory">/etc/</filename> which specifies the
<acronym>MLS</acronym> policy information and to feed that file
to <command>setfmac</command>. This method will be explained
after all policies are covered.</para>
<sect2>
<title>Planning Mandatory Sensitivity</title>
<para>When using the MLS policy module, an administrator plans
to control the flow of sensitive information. The default
<literal>block read up block write down</literal> sets
everything to a low state. Everything is accessible and an
administrator slowly augments the confidentiality of the
information during the configuration stage;.</para>
<para>Beyond the three basic label options, an administrator may
group users and groups as required to block the information
flow between them. It might be easier to look at the
information in clearance levels using descriptive words, such
as classifications of <literal>Confidential</literal>,
<literal>Secret</literal>, and <literal>Top Secret</literal>.
Some administrators instead create different groups based on
project levels. Regardless of the classification method, a
well thought out plan must exist before implementing such a
restrictive policy.</para>
<para>Some example situations for the MLS policy module
include an e-commerce web server, a file server holding
critical company information, and financial institution
environments.</para>
</sect2>
</sect1>
<sect1 id="mac-biba">
<title>The MAC Biba Module</title>
<indexterm>
<primary>MAC Biba Integrity Policy</primary>
</indexterm>
<para>Module name: <filename>mac_biba.ko</filename></para>
<para>Kernel configuration line: <literal>options
MAC_BIBA</literal></para>
<para>Boot option: <literal>mac_biba_load="YES"</literal></para>
<para>The &man.mac.biba.4; module loads the <acronym>MAC</acronym>
Biba policy. This policy is similar to the
<acronym>MLS</acronym> policy with the exception that the rules
for information flow are slightly reversed. This is to prevent
the downward flow of sensitive information whereas the
<acronym>MLS</acronym> policy prevents the upward flow of
sensitive information. Much of this section can apply to both
policies.</para>
<para>In Biba environments, an <quote>integrity</quote> label is
set on each subject or object. These labels are made up of
hierarchical grades and non-hierarchical components. As an
grade ascends, so does its integrity.</para>
<para>Supported labels are <literal>biba/low</literal>,
<literal>biba/equal</literal>, and <literal>biba/high</literal>;
as explained below:</para>
<itemizedlist>
<listitem>
<para>The <literal>biba/low</literal> label is considered the
lowest integrity an object or subject may have. Setting
this on objects or subjects will block their write access
to objects or subjects marked high. They still have read
access though.</para>
</listitem>
<listitem>
<para>The <literal>biba/equal</literal> label should only be
placed on objects considered to be exempt from the
policy.</para>
</listitem>
<listitem>
<para>The <literal>biba/high</literal> label will permit
writing to objects set at a lower label, but not
permit reading that object. It is recommended that this
label be placed on objects that affect the integrity of
the entire system.</para>
</listitem>
</itemizedlist>
<para>Biba provides:</para>
<itemizedlist>
<listitem>
<para>Hierarchical integrity level with a set of non
hierarchical integrity categories.</para>
</listitem>
<listitem>
<para>Fixed rules are <literal>no write up, no read
down</literal>, the opposite of
<acronym>MLS</acronym>. A subject can have write access
to objects on its own level or below, but not above.
Similarly, a subject can have read access to objects on
its own level or above, but not below.</para>
</listitem>
<listitem>
<para>Integrity by preventing inappropriate modification of
data.</para>
</listitem>
<listitem>
<para>Integrity levels instead of MLS sensitivity
levels.</para>
</listitem>
</itemizedlist>
<para>The following <command>sysctl</command> tunables can
be used to manipulate the Biba policy:</para>
<itemizedlist>
<listitem>
<para><varname>security.mac.biba.enabled</varname> is used
to enable or disable enforcement of the Biba policy on the
target machine.</para>
</listitem>
<listitem>
<para><varname>security.mac.biba.ptys_equal</varname> is
used to disable the Biba policy on &man.pty.4;
devices.</para>
</listitem>
<listitem>
<para><varname>security.mac.biba.revocation_enabled</varname>
forces the revocation of access to objects if the label
is changed to dominate the subject.</para>
</listitem>
</itemizedlist>
<para>To access the Biba policy setting on system objects, use
<command>setfmac</command> and
<command>getfmac</command>:</para>
<screen>&prompt.root; <userinput>setfmac biba/low test</userinput>
&prompt.root; <userinput>getfmac test</userinput>
test: biba/low</screen>
<sect2>
<title>Planning Mandatory Integrity</title>
<para>Integrity, which is different from sensitivity, guarantees
that the information will never be manipulated by untrusted
parties. This includes information passed between subjects,
objects, and both. It ensures that users will only be able to
modify or access information they explicitly need to.</para>
<para>The &man.mac.biba.4; security policy module permits an
administrator to address which files and programs a user may
see and invoke while assuring that the programs and files are
free from threats and trusted by the system for that
user.</para>
<para>During the initial planning phase, an administrator must
be prepared to partition users into grades, levels, and areas.
Users will be blocked access not only to data but to programs
and utilities both before and after they start. The system
will default to a high label once this policy module is
enabled, and it is up to the administrator to configure the
different grades and levels for users. Instead of using
clearance levels, a good planning method could include topics.
For instance, only allow developers modification access to the
source code repository, source code compiler, and other
development utilities. Other users would be grouped into
other categories such as testers, designers, or end users and
would only be permitted read access.</para>
<para>A lower integrity subject is unable to write to a higher
integrity subject and a higher integrity subject cannot
observe or read a lower integrity object. Setting a label at
the lowest possible grade could make it inaccessible to
subjects. Some prospective environments for this security
policy module would include a constrained web server, a
development and test machine, and a source code repository. A
less useful implementation would be a personal workstation, a
machine used as a router, or a network firewall.</para>
</sect2>
</sect1>
<sect1 id="mac-lomac">
<title>The MAC LOMAC Module</title>
<indexterm>
<primary>MAC LOMAC</primary>
</indexterm>
<para>Module name: <filename>mac_lomac.ko</filename></para>
<para>Kernel configuration line: <literal>options
MAC_LOMAC</literal></para>
<para>Boot option: <literal>mac_lomac_load="YES"</literal></para>
<para>Unlike the <acronym>MAC</acronym> Biba policy, the
&man.mac.lomac.4; policy permits access to lower integrity
objects only after decreasing the integrity level to not disrupt
any integrity rules.</para>
<para>The <acronym>MAC</acronym> version of the Low-watermark
integrity policy works almost identically to Biba, but with the
exception of using floating labels to support subject demotion
via an auxiliary grade compartment. This secondary compartment
takes the form <literal>[auxgrade]</literal>. When assigning
a LOMAC policy with an auxiliary grade, use the syntax
<literal>lomac/10[2]</literal> where the number two (2) is the
auxiliary grade.</para>
<para>The <acronym>MAC</acronym> LOMAC policy relies on the
ubiquitous labeling of all system objects with integrity labels,
permitting subjects to read from low integrity objects and then
downgrading the label on the subject to prevent future writes to
high integrity objects using <literal>[auxgrade]</literal>. The
policy may provide for greater compatibility and require less
initial configuration than Biba.</para>
<sect2>
<title>Examples</title>
<para>Like the Biba and <acronym>MLS</acronym> policies,
<command>setfmac</command> and <command>setpmac</command>
are used to place labels on system objects:</para>
<screen>&prompt.root; <userinput>setfmac /usr/home/trhodes lomac/high[low]</userinput>
&prompt.root; <userinput>getfmac /usr/home/trhodes</userinput> lomac/high[low]</screen>
<para>The auxiliary grade <literal>low</literal> is a feature
provided only by the <acronym>MAC</acronym> LOMAC
policy.</para>
</sect2>
</sect1>
<sect1 id="mac-implementing">
<title>Nagios in a MAC Jail</title>
<indexterm>
<primary>Nagios in a MAC Jail</primary>
</indexterm>
<para>The following demonstration implements a secure
environment using various <acronym>MAC</acronym> modules
with properly configured policies. This is only a test as
implementing a policy and ignoring it could be disastrous in a
production environment.</para>
<para>Before beginning this process, <option>multilabel</option>
must be set on each file system as not doing so will result in
errors. This example assumes that <filename
role="package">net-mngt/nagios-plugins</filename>,
<filename role="package">net-mngt/nagios</filename>, and
<filename role="package">www/apache22</filename> are all
installed, configured, and working correctly.</para>
<sect2>
<title>Create an Insecure User Class</title>
<para>Begin the procedure by adding the following user class
to <filename>/etc/login.conf</filename>:</para>
<programlisting>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):</programlisting>
<para>Add the following line to the default user class:</para>
<programlisting>:label=biba/high:</programlisting>
<para>Next, issue the following command to rebuild the
database:</para>
<screen>&prompt.root; <userinput>cap_mkdb /etc/login.conf</userinput></screen>
</sect2>
<sect2>
<title>Boot Configuration</title>
<para>Add the following lines to
<filename>/boot/loader.conf</filename>:</para>
<programlisting>mac_biba_load="YES"
mac_seeotheruids_load="YES"</programlisting>
</sect2>
<sect2>
<title>Configure Users</title>
<para>Set the <username>root</username> user to the default
class using:</para>
<screen>&prompt.root; <userinput>pw usermod root -L default</userinput></screen>
<para>All user accounts that are not <username>root</username>
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 &man.vi.1;. The following
<command>sh</command> script should do the trick:</para>
<screen>&prompt.root; <userinput>for x in `awk -F: '($3 >= 1001) && ($3 != 65534) { print $1 }' \</userinput>
<userinput>/etc/passwd`; do pw usermod $x -L default; done;</userinput></screen>
<para>Drop the <username>nagios</username> and
<username>www</username> users into the insecure class:</para>
<screen>&prompt.root; <userinput>pw usermod nagios -L insecure</userinput></screen>
<screen>&prompt.root; <userinput>pw usermod www -L insecure</userinput></screen>
</sect2>
<sect2>
<title>Create the Contexts File</title>
<para>A contexts file should now be created as
<filename>/etc/policy.contexts</filename>.</para>
<programlisting># 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</programlisting>
<para>This policy enforces security by setting restrictions
on the flow of information. In this specific configuration,
users, including <username>root</username>, should never be
allowed to access <application>Nagios</application>.
Configuration files and processes that are a part of
<application>Nagios</application> will be completely self
contained or jailed.</para>
<para>This file will be read by the system by issuing the
following command:</para>
<screen>&prompt.root; <userinput>setfsmac -ef /etc/policy.contexts /</userinput>
&prompt.root; <userinput>setfsmac -ef /etc/policy.contexts /</userinput></screen>
<note>
<para>The above file system layout will differ depending
upon the environment and must be run on every file
system.</para>
</note>
<para><filename>/etc/mac.conf</filename> requires the following
modifications in the main section:</para>
<programlisting>default_labels file ?biba
default_labels ifnet ?biba
default_labels process ?biba
default_labels socket ?biba</programlisting>
</sect2>
<sect2>
<title>Enable Networking</title>
<para>Add the following line to
<filename>/boot/loader.conf</filename>:</para>
<programlisting>security.mac.biba.trust_all_interfaces=1</programlisting>
<para>And the following to the network card configuration stored
in <filename>rc.conf</filename>. If the primary Internet
configuration is done via <acronym>DHCP</acronym>, this may
need to be configured manually after every system boot:</para>
<programlisting>maclabel biba/equal</programlisting>
</sect2>
<sect2>
<title>Testing the Configuration</title>
<indexterm>
<primary>MAC Configuration Testing</primary>
</indexterm>
<para>Ensure that the web server and
<application>Nagios</application> will not be started on
system initialization and reboot. Ensure the
<username>root</username> user cannot access any of the files
in the <application>Nagios</application> configuration
directory. If <username>root</username> can issue an
&man.ls.1; command on <filename>/var/spool/nagios</filename>,
something is wrong. Otherwise a <quote>permission
denied</quote> error should be returned.</para>
<para>If all seems well, <application>Nagios</application>,
<application>Apache</application>, and
<application>Sendmail</application> can now be started:</para>
<screen>&prompt.root; <userinput>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</userinput></screen>
<para>Double check to ensure that everything is working
properly. If not, check the log files for error messages.
Use &man.sysctl.8; to disable the &man.mac.biba.4; security
policy module enforcement and try starting everything again as
usual.</para>
<note>
<para>The <username>root</username> user can still change the
security enforcement and edit its configuration files. The
following command will permit the degradation of the
security policy to a lower grade for a newly spawned
shell:</para>
<screen>&prompt.root; <userinput>setpmac biba/10 csh</userinput></screen>
<para>To block this from happening, force the user into a
range using &man.login.conf.5;. If &man.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, set root to
<literal>biba/high(high-high)</literal>.</para>
</note>
</sect2>
</sect1>
<sect1 id="mac-userlocked">
<title>User Lock Down</title>
<para>This example considers a relatively small storage system
with fewer than fifty users. Users will have login
capabilities, and be permitted to store data and access
resources.</para>
<para>For this scenario, the &man.mac.bsdextended.4; and
&man.mac.seeotheruids.4; policy modules could co-exist and block
access to system objects while hiding user processes.</para>
<para>Begin by adding the following line to
<filename>/boot/loader.conf</filename>:</para>
<programlisting>mac_seeotheruids_load="YES"</programlisting>
<para>The &man.mac.bsdextended.4; security policy module may be
activated by adding this line to
<filename>/etc/rc.conf</filename>:</para>
<programlisting>ugidfw_enable="YES"</programlisting>
<para>Default rules stored in
<filename>/etc/rc.bsdextended</filename> will be loaded at
system initialization. However, the default entries may need
modification. Since this machine is expected only to service
users, everything may be left commented out except the last
two lines in order to force the loading of user owned system
objects by default.</para>
<para>Add the required users to this machine and reboot. For
testing purposes, try logging in as a different user across
two consoles. Run <command>ps aux</command> to see if processes
of other users are visible. Verify that running &man.ls.1; on
another user's home directory fails.</para>
<para>Do not try to test with the <username>root</username> user
unless the specific <command>sysctl</command>s have been
modified to block super user access.</para>
<note>
<para>When a new user is added, their &man.mac.bsdextended.4;
rule will not be in the ruleset list. To update the ruleset
quickly, unload the security policy module and reload it again
using &man.kldunload.8; and &man.kldload.8;.</para>
</note>
</sect1>
<sect1 id="mac-troubleshoot">
<title>Troubleshooting the MAC Framework</title>
<indexterm>
<primary>MAC Troubleshooting</primary>
</indexterm>
<para>This section discusses common configuration issues.</para>
<itemizedlist>
<listitem>
<para>The <option>multilabel</option> flag does not stay
enabled on my root (<filename>/</filename>) partition!</para>
<para>The following steps may resolve this transient
error:</para>
<procedure>
<step>
<para>Edit <filename>/etc/fstab</filename> and set the root
partition to <option>ro</option> for read-only.</para>
</step>
<step>
<para>Reboot into single user mode.</para>
</step>
<step>
<para>Run <command>tunefs</command> <option>-l
enable</option>
on <filename>/</filename>.</para>
</step>
<step>
<para>Reboot the system.</para>
</step>
<step>
<para>Run <command>mount</command> <option>-urw</option>
<filename>/</filename> and change the <option>ro</option>
back to <option>rw</option> in
<filename>/etc/fstab</filename> and reboot the system
again.</para>
</step>
<step>
<para>Double-check the output from
<command>mount</command> to ensure that
<option>multilabel</option> has been properly set on the
root file system.</para>
</step>
</procedure>
</listitem>
<listitem>
<para>After establishing a secure environment with
<acronym>MAC</acronym>, I am no longer able to start
Xorg!</para>
<para>This could be caused by the <acronym>MAC</acronym>
<literal>partition</literal> policy or by a mislabeling in
one of the <acronym>MAC</acronym> labeling policies. To
debug, try the following:</para>
<procedure>
<step>
<para>Check the error message; if the user is in the
<literal>insecure</literal> class, the
<literal>partition</literal> policy may be the culprit.
Try setting the user's class back to the
<literal>default</literal> class and rebuild the database
with <command>cap_mkdb</command>. If this does not
alleviate the problem, go to step two.</para>
</step>
<step>
<para>Double-check the label policies. Ensure that the
policies are set correctly for the user, the Xorg
application, and the <filename
class="directory">/dev</filename> entries.</para>
</step>
<step>
<para>If neither of these resolve the problem, send the
error message and a description of the environment to
the &a.questions; mailing list.</para>
</step>
</procedure>
</listitem>
<listitem>
<para>The error: <errorname>_secure_path: unable to stat
.login_conf</errorname> shows up.</para>
<para>When a user attempts to switch from the
<username>root</username> user to another user in the system,
the error message <errorname>_secure_path: unable to stat
.login_conf</errorname> appears.</para>
<para>This message is usually shown when the user has a higher
label setting than that of the user they are attempting to
become. For instance, <username>joe</username> has a default
label of <option>biba/low</option>. The
<username>root</username> user, who has a label of
<option>biba/high</option>, cannot view
<username>joe</username>'s home directory. This will happen
whether or not <username>root</username> has used
<command>su</command> to become <username>joe</username> as
the Biba integrity model will not permit
<username>root</username> to view objects set at a lower
integrity level.</para>
</listitem>
<listitem>
<para>The system no longer recognizes the
<username>root</username> user.</para>
<para>In normal or even single user mode, the
<username>root</username> is not recognized,
<command>whoami</command> returns 0 (zero), and
<command>su</command> returns <errorname>who are
you?</errorname>.</para>
<para>This can happen if a labeling policy has been disabled,
either by a &man.sysctl.8; or the policy module was unloaded.
If the policy is disabled, the login capabilities database
needs to be reconfigured with <option>label</option> removed.
Double check <filename>login.conf</filename> to ensure that
all <option>label</option> options have been removed and
rebuild the database with <command>cap_mkdb</command>.</para>
<para>This may also happen if a policy restricts access to
<filename>master.passwd</filename>. This is usually caused by
an administrator altering the file under a label which
conflicts with the general policy being used by the system.
In these cases, the user information would be read by the
system and access would be blocked as the file has inherited
the new label. Disable the policy using &man.sysctl.8; and
everything should return to normal.</para>
</listitem>
</itemizedlist>
</sect1>
</chapter>