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<?xml version="1.0" encoding="iso-8859-1" standalone="no"?>
<!--
     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;&nbsp;5.X introduced new security extensions from the
      TrustedBSD project 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.  Mandatory Access Control allows
      new access control modules to be loaded, implementing new security
      policies.  Some provide protections of 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 comes from the fact that the enforcement of
      the controls is done by administrators and the system, and is
      not left up to the discretion of users as is done with
      discretionary access control (<acronym>DAC</acronym>, the standard
      file and System V <acronym>IPC</acronym> permissions on &os;).</para>

    <para>This chapter will focus on the
      Mandatory Access Control Framework (<acronym>MAC</acronym> Framework), and a set
      of pluggable security policy modules enabling various security
      mechanisms.</para>

    <para>After reading this chapter, you will know:</para>

    <itemizedlist>
      <listitem>
	<para>What <acronym>MAC</acronym> security policy modules are currently
          included in &os; and their associated mechanisms.</para>
      </listitem>

      <listitem>
	<para>What <acronym>MAC</acronym> security policy modules implement 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 and the examples
	  shown.</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>Be familiar with
	  the basics of kernel configuration/compilation
	  (<xref linkend="kernelconfig"/>).</para>
      </listitem>

      <listitem>
	<para>Have some familiarity with security and how it
	  pertains to &os; (<xref linkend="security"/>).</para>
      </listitem>
    </itemizedlist>

    <warning>
      <para>The improper use of the
	information contained herein may cause loss of system access,
	aggravation of users, or inability to access the features
	provided by X11.  More importantly, <acronym>MAC</acronym> should not
	be relied upon to completely secure a system.  The
	<acronym>MAC</acronym> framework only augments
	existing security policy; without sound security practices and
	regular security checks, the system will never be completely
	secure.</para>

      <para>It should also be noted that the examples contained
	within this chapter are just that, examples.  It is not
	recommended that these particular settings be rolled out
	on a production system.  Implementing the various security policy modules takes
	a good deal of thought and testing.  One who does not fully understand
	exactly how everything works may find him or herself going
	back through the entire system and reconfiguring many files
	or directories.</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 the &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, please review the 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.  This will hopefully clear up any confusion that
      may occur and avoid the abrupt introduction of new terms
      and information.</para>

    <itemizedlist>
      <listitem>
	<para><emphasis>compartment</emphasis>: A compartment is a
	  set of programs and data to be partitioned or separated,
	  where users are given explicit access to specific components
	  of a system.  Also, a compartment represents a grouping,
	  such as a work group, department, project, or topic.  Using
	  compartments, it is possible to implement a need-to-know
	  security policy.</para>
      </listitem>

      <listitem>
	<para><emphasis>high water mark</emphasis>: A high water mark
	  policy is one which 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 have a policy for this, but the definition
	  is included for completeness.</para>
      </listitem>

      <listitem>
	<para><emphasis>integrity</emphasis>: Integrity, as a key
	  concept, is 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 label is 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 for that specific
	  file and will only permit access by files, users, resources,
	  etc. with a similar security setting.  The meaning and
	  interpretation of label values depends on the policy configuration: while
	  some policies might treat a label as representing the
	  integrity or secrecy of an object, 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 water mark</emphasis>: A low water mark
	  policy is one which permits lowering of the 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>: The
	  <option>multilabel</option> property is a file system option
	  which can be set in single user mode using the
	  &man.tunefs.8; utility, during the boot operation
	  using the &man.fstab.5; file, or during the creation of
	  a new file system.  This option will permit 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 object or system
	  object is 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/moving device.  Basically, an object is a data container or
	  a system resource; access to an <emphasis>object</emphasis>
	  effectively means access to the 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 will
	  consider the term <emphasis>policy</emphasis> in this
	  context as a <emphasis>security policy</emphasis>; i.e.
	  a collection of rules which will control the flow of data
	  and information and define whom will have access to that
	  data and information.</para>
      </listitem>

      <listitem>
	<para><emphasis>sensitivity</emphasis>: Usually used when
	  discussing <acronym>MLS</acronym>.  A sensitivity level is
	  a term used to describe 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 single label is
	  when the entire file system uses one label to
	  enforce access control over the flow of data.  When a file
	  system has this set, which is any time when the
	  <option>multilabel</option> option is not set, all
	  files will conform to the same label setting.</para>
      </listitem>

      <listitem>
	<para><emphasis>subject</emphasis>: a subject is any
	  active entity that causes information to flow between
	  <emphasis>objects</emphasis>; e.g., a user, user process,
	  system process, etc.  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, block users from
      accessing certain ports and sockets, and more.  Perhaps
      the best use of the policy modules is to blend them together, by loading
      several security policy modules at a time for a multi-layered
      security environment.  In a multi-layered security environment,
      multiple policy modules are in effect to keep security in check.  This
      is different to a hardening policy, which typically hardens
      elements of a system that is used only for specific purposes.
      The only downside is administrative overhead in cases of
      multiple file system labels, setting network access control
      user by user, etc.</para>

    <para>These downsides are minimal when compared to the lasting
      effect of the framework; for instance, the ability to pick and choose
      which policies are required for a specific configuration 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>Thus a system utilizing <acronym>MAC</acronym> features
      should at least guarantee 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
      that total control of the <acronym>MAC</acronym> access
      rules are in the hands of the system administrator.</para>

    <para>It is the sole duty of the system administrator to
      carefully select the correct security policy modules.  Some environments
      may need to limit access control over the network; in these
      cases, the &man.mac.portacl.4;, &man.mac.ifoff.4; and even
      &man.mac.biba.4; policy modules might make good starting points.  In other
      cases, strict confidentiality of file system objects might
      be required.  Policy modules such as &man.mac.bsdextended.4;
      and &man.mac.mls.4; exist for this purpose.</para>

    <para>Policy decisions could be made based on network
      configuration.  Perhaps only certain users should be permitted
      access to facilities provided by &man.ssh.1; to access the
      network or the Internet.  The &man.mac.portacl.4; would be
      the policy module of choice for these situations.  But what should be
      done in the case of file systems?  Should all access to certain
      directories be severed from other groups or specific
      users?  Or should we limit user or utility access to specific
      files by setting certain objects as classified?</para>

    <para>In the file system case, access to objects might be
      considered confidential to some users, but not to others.
      For an example, a large development team might be broken
      off into smaller groups of individuals.  Developers in
      project A might not be permitted to access objects written
      by developers in project B.  Yet they might need to access
      objects created by developers in project C; that is quite a
      situation indeed.  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 areas without fear of information
      leakage.</para>

    <para>Thus, 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.  In many cases, the
      overall policy may need to be revised and reimplemented on
      the system.  Understanding the different security policy modules offered by
      the <acronym>MAC</acronym> framework will help administrators
      choose the best policies for their situations.</para>

    <para>The default &os; kernel does not include the option for
      the <acronym>MAC</acronym> framework; thus the following
      kernel option must be added before trying any of the examples or
      information in this chapter:</para>

    <programlisting>options	MAC</programlisting>

    <para>And the kernel will require a rebuild and a reinstall.</para>

    <caution>
      <para>While the various manual pages for <acronym>MAC</acronym>
	policy modules state that they may be built into the kernel,
	it is possible to lock the system out of
	the network and more.  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 while 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 user must be able to comprehend
      what it is, exactly, that is being done.  The attributes
      available on an object depend on the policy module loaded, and that
      policy modules interpret their attributes in different
      ways.  If improperly configured due to lack of comprehension, or
      the inability to understand the implications, the result will
      be the unexpected and perhaps, undesired, behavior of the
      system.</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 by itself contains all information necessary
      to make a decision; in other models, the labels may be processed
      as part of a larger rule set, etc.</para>

    <para>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.  These
      are the low, high, and equal labels.  Although they enforce
      access control in a different manner with each policy module, you
      can be sure that the low label will be the lowest setting,
      the equal label will set the subject or object to be disabled
      or unaffected, and the high label will enforce 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 will enforce 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.  For those cases, the
      <option>multilabel</option> option may be passed 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 say, classification only
      permitting access to that group or a higher group level.</para>

    <para>In most cases the administrator will only be setting up a
      single label to use throughout the file system.</para>

    <para><emphasis>Hey wait, this is similar to <acronym>DAC</acronym>!
      I thought <acronym>MAC</acronym> gave control strictly to the
      administrator.</emphasis>  That statement still holds true, 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 hierarchal/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 by use of the
	&man.setfmac.8; and &man.setpmac.8; utilities.
	The <command>setfmac</command> command is used to set
	<acronym>MAC</acronym> labels on system objects while the
	<command>setpmac</command> command is used to set the labels
	on system subjects.  Observe:</para>

      <screen>&prompt.root; <userinput>setfmac biba/high test</userinput></screen>

      <para>If no errors occurred with the command above, a prompt
	will be returned.  The only time these commands are not
	quiescent is when an error occurred; similarly to the
	&man.chmod.1; and &man.chown.8; commands.  In some cases this
	error may be a <errorname>Permission denied</errorname> and
	is usually obtained 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	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>As we see above, <command>setpmac</command>
	can be used to override the policy module's settings by assigning
	a different label to the invoked process.  The
	<command>getpmac</command> utility is usually used with currently
	running processes, such as <application>sendmail</application>:
	although it takes a process ID in place of
	a command the logic is extremely similar.  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, what follows is a brief description of
	  what these labels provide:</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 will block 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 instate a different information flow directive.  Reading
	  the proper manual pages will further explain 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>; thus
	    the following:</para>

	  <programlisting>biba/10:2+3+6(5:2+3-20:2+3+4+5+6)</programlisting>

	  <para>May be interpreted as:</para>

	  <para><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;
	    indeed, they offered for more advanced
	    configurations.</para>

	  <para>When applied to system objects, they will only have a
	    current grade/compartments as opposed to system subjects
	    as they 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 referred to 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, you
	    have rights to a set of compartments,
	    <quote>need to know</quote>, 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 themselves are required to have labels so that
	  their files and processes may properly interact with the
	  security policy defined on the system.  This is
	  configured through the <filename>login.conf</filename> file
	  by use of 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>The <literal>label</literal> option is used to set the
	  user class default label which will be enforced by
	  <acronym>MAC</acronym>.  Users will never be permitted to
	  modify this value, thus it can be considered not optional
	  in the user case.  In a real configuration, however, the
	  administrator will never wish to enable every policy module.
	  It is recommended that the rest of this chapter be reviewed
	  before any of this configuration is implemented.</para>

	<note>
	  <para>Users may change their label after the initial login;
	    however, this change is subject constraints of the policy.
	    The example above tells the Biba policy that a process's
	    minimum integrity is 5, its maximum is 15, but the default
	    effective label is 10.  The process will run at 10 until
	    it chooses to change label, perhaps due to the user using
	    the setpmac command, which will be constrained by Biba to
	    the range set at login.</para>
	</note>

	<para>In all cases, after a change to
	  <filename>login.conf</filename>, the login class capability
	  database must be rebuilt using <command>cap_mkdb</command>
	  and this will be reflected throughout every forthcoming
	  example or discussion.</para>

	<para>It is useful to note that many sites may have a
	  particularly 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 also be set on network interfaces to help
	  control the flow of data across the network.  In all cases
	  they function in the same way the 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>The <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; otherwise an error will be 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 from <command>sysctl</command>, the policy manual
	  pages, or even the information found later in this chapter
	  for those tunables.</para>
      </sect3>
    </sect2>

    <sect2>
      <title>Singlelabel or Multilabel?</title>
<!-- Stopped here with my edits -->
      <para>By default the system will use the
	<option>singlelabel</option> option.  But what does this
	mean to the administrator?  There are several differences
	which, in their own right, offer pros and cons to the
	flexibility in the systems security model.</para>

      <para>The <option>singlelabel</option> only permits for one
	label, for instance <literal>biba/high</literal> to be used
	for each subject or object.  It provides for lower
	administration overhead but decreases the flexibility of
	policies which support labeling.  Many administrators may
	want to use the <option>multilabel</option> option in
	their security policy.</para>

      <para>The <option>multilabel</option> option will permit each
	subject or object to have its own independent
	<acronym>MAC</acronym> label in
	place of the standard <option>singlelabel</option> option
	which will allow only one label throughout the partition.
	The <option>multilabel</option> and <option>single</option>
	label options are only required for the policies which
	implement the labeling feature, including the Biba, Lomac,
	<acronym>MLS</acronym> and <acronym>SEBSD</acronym>
	policies.</para>

      <para>In many cases, the <option>multilabel</option> may not need
	to be set at all.  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.
	    Here the file system would not require the
	    <option>multilabel</option> 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 Biba policy and how it works
	    will be discussed later, so if the previous comment was
	    difficult to interpret just continue reading and return.
	    The server could use a separate partition set at
	    <literal>biba/low</literal> for most if not all of its
	    runtime state.  Much is lacking from this example, for
	    instance the restrictions on data, configuration and user
	    settings; however, this is just a quick example to prove the
	    aforementioned point.</para>
	</listitem>
      </itemizedlist>

      <para>If any of the non-labeling policies are to be used,
	then the <option>multilabel</option> option would never
	be required.  These include the <literal>seeotheruids</literal>,
	<literal>portacl</literal> and <literal>partition</literal>
	policies.</para>

      <para>It should also be noted that using
	<option>multilabel</option> with a partition and establishing
	a security model based on <option>multilabel</option>
	functionality could open the doors for higher administrative
	overhead as everything in the file system would have 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:</para>

      <screen>&prompt.root; <userinput>tunefs -l enable /</userinput></screen>

      <para>This is not a requirement for the swap file
	system.</para>

      <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
      always a good idea.  During the planning stages, an administrator
      should in general look at the <quote>big picture</quote>, trying
      to keep in view at least the following:</para>

    <itemizedlist>
      <listitem>
	<para>The implementation requirements;</para>
      </listitem>

      <listitem>
	<para>The implementation goals;</para>
      </listitem>
    </itemizedlist>

    <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>What sorts of 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>It is always possible to reconfigure and change the
      system resources and security settings, it is quite often very inconvenient to
      search through the system and fix existing files and user
      accounts.  Planning helps to ensure a trouble-free and efficient
      trusted system implementation.  A trial run of the trusted system,
      including the configuration, is often vital and definitely
      beneficial <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 may have explicit needs and
      requirements.  Establishing an in depth and complete security
      profile will decrease the need of changes once the system
      goes live.  As such, the future sections will cover the
      different modules available to administrators; describe their
      use and configuration; and in some cases provide insight on
      what situations they would be most suitable for.  For instance,
      a web server might roll out the &man.mac.biba.4; and
      &man.mac.bsdextended.4; policies.  In other cases, a machine
      with very few local users, the &man.mac.partition.4; might
      be a good choice.</para>
  </sect1>

  <sect1 id="mac-modules">
    <title>Module Configuration</title>

    <para>Every module included with the <acronym>MAC</acronym>
      framework may be either compiled into the kernel as noted above
      or loaded as a run-time kernel module.
      The recommended method is to add the module name to the
      <filename>/boot/loader.conf</filename> file so that it will load
      during the initial boot operation.</para>

    <para>The following sections will discuss the various
      <acronym>MAC</acronym> modules and cover their features.
      Implementing them into a specific environment will also
      be a consideration of this chapter.  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 would enforce 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 seeotheruids Module</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 <literal>security.bsd.see_other_uids</literal> and
      <literal>security.bsd.see_other_gids</literal>
      <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><literal>security.mac.seeotheruids.enabled</literal>
	  will enable the module's features and use the default
	  settings.  These default settings will deny users the
	  ability to view processes and sockets owned by other
	  users.</para>
      </listitem>

      <listitem>
	<para>
	  <literal>security.mac.seeotheruids.specificgid_enabled</literal>
	  will allow a certain group to be exempt from this policy.
	  To exempt specific groups from this policy, use the
	  <literal>security.mac.seeotheruids.specificgid=<replaceable>XXX</replaceable></literal>
	  <command>sysctl</command> tunable.  In the above example,
	  the <replaceable>XXX</replaceable> should be replaced with the
	  numeric group ID to be exempted.</para>
      </listitem>

      <listitem>
	<para>
	  <literal>security.mac.seeotheruids.primarygroup_enabled</literal>
	  is used to exempt specific primary groups from this policy.
	  When using this tunable, the
	  <literal>security.mac.seeotheruids.specificgid_enabled</literal>
	  may not be set.</para>
      </listitem>
    </itemizedlist>
  </sect1>

  <sect1 id="mac-bsdextended">
    <title>The MAC bsdextended Module</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,
      security.mac.bsdextended.firstmatch_enabled.  Similar to
      other firewall modules in &os;, a file containing 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 a utility, &man.ugidfw.8;,
      that has a syntax similar to that of &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; 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>As expected, there are no rules defined.  This means that
	everything is still completely accessible.  To create a rule
	which will block all access by users but leave
	<username>root</username> unaffected, simply 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>.  A more patriotic list of rules
	might be:</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>This will block any and all access, including directory
	listings, to <username><replaceable>user2</replaceable></username>'s home
	directory from the username <username>user1</username>.</para>

      <para>In place of <username>user1</username>, the
	<option>not uid <replaceable>user2</replaceable></option> could
	be passed.  This will enforce the same access restrictions
	above for all users in place of just one user.</para>

      <note>
	<para>The <username>root</username> user will be unaffected
	    by these changes.</para>
      </note>

      <para>This should provide a general idea of how the
	&man.mac.bsdextended.4; module may be used to help fortify
	a file system.  For more information, see the
	&man.mac.bsdextended.4; and the &man.ugidfw.8; manual
	pages.</para>
    </sect2>
  </sect1>

  <sect1 id="mac-ifoff">
    <title>The MAC ifoff Module</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 the initial system boot.  It does not require
      any labels to be set up on the system, nor does it have a
      dependency on other <acronym>MAC</acronym> modules.</para>

    <para>Most of the control is done through the
      <command>sysctl</command> tunables listed below.</para>

    <itemizedlist>
      <listitem>
	<para><literal>security.mac.ifoff.lo_enabled</literal> will
	  enable/disable all traffic on the loopback (&man.lo.4;)
	  interface.</para>
      </listitem>

      <listitem>
	<para><literal>security.mac.ifoff.bpfrecv_enabled</literal> will
	  enable/disable all traffic on the Berkeley Packet Filter
	  interface (&man.bpf.4;)</para>
      </listitem>

      <listitem>
	<para><literal>security.mac.ifoff.other_enabled</literal> will
	  enable/disable 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 portacl Module</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.  In
      essence &man.mac.portacl.4; makes it possible to allow
      non-<username>root</username> users to bind to specified
      privileged ports, i.e., ports below 1024.</para>

    <para>Once loaded, this module will enable the
      <acronym>MAC</acronym> policy on all sockets.  The following
      tunables are available:</para>

    <itemizedlist>
      <listitem>
	<para><literal>security.mac.portacl.enabled</literal> will
	  enable/disable the policy completely.</para>
      </listitem>

      <listitem>
	<para><literal>security.mac.portacl.port_high</literal> will set
	  the highest port number that &man.mac.portacl.4;
	  will enable protection for.</para>
      </listitem>

      <listitem>
	<para><literal>security.mac.portacl.suser_exempt</literal> will,
	  when set to a non-zero value, exempt the
	  <username>root</username> user from this policy.</para>
      </listitem>

      <listitem>
	<para><literal>security.mac.portacl.rules</literal> will
	  specify the actual mac_portacl policy; see below.</para>
      </listitem>
    </itemizedlist>

    <para>The actual <literal>mac_portacl</literal> policy, as
      specified in the <literal>security.mac.portacl.rules</literal>
      sysctl, 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 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>

    <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, on &unix;-like systems, ports below 1024
      can only be used by/bound to privileged processes,
      i.e., those run as <username>root</username>.  For
      &man.mac.portacl.4; to allow non-privileged processes to bind
      to ports below 1024 this standard &unix; restriction has to be
      disabled.  This can be accomplished by setting the &man.sysctl.8;
      variables <literal>net.inet.ip.portrange.reservedlow</literal> and
      <literal>net.inet.ip.portrange.reservedhigh</literal>
      to zero.</para>

    <para>See the examples below or review the &man.mac.portacl.4;
      manual page for further information.</para>

    <sect2>
      <title>Examples</title>

      <para>The following examples should illuminate the above
	discussion a little better:</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>First we set &man.mac.portacl.4; to cover the standard
	privileged ports and disable the normal &unix; bind
	restrictions.</para>

      <screen>&prompt.root; <userinput>sysctl security.mac.portacl.suser_exempt=1</userinput></screen>

      <para>The <username>root</username> user should not be crippled
	by this policy, thus set the
	<literal>security.mac.portacl.suser_exempt</literal> to a
	non-zero value.  The &man.mac.portacl.4; module
	has now been set up to behave the same way &unix;-like systems
	behave by default.</para>

      <screen>&prompt.root; <userinput>sysctl security.mac.portacl.rules=uid:80:tcp:80</userinput></screen>

      <para>Allow the user with <acronym>UID</acronym> 80 (normally
	the <username>www</username> user) to bind to port 80.
	This can be used to allow 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:1001:tcp:110,uid:1001:tcp:995</userinput></screen>

      <para>Permit 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 will permit this user to start a server that accepts
	connections on ports 110 and 995.</para>
    </sect2>
  </sect1>

  <sect1 id="mac-partition">
    <title>The MAC partition Module</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.  Think of it as a special
      type of &man.jail.8;, though that is hardly a worthy
      comparison.</para>

    <para>This is one module that should be added to the
      &man.loader.conf.5; file so that it loads
      and enables the policy during the boot process.</para>

    <para>Most configuration for this policy is done using
      the &man.setpmac.8; utility which will be explained below.
      The following <command>sysctl</command> tunable is
      available for this policy:</para>

    <itemizedlist>
      <listitem>
	<para><literal>security.mac.partition.enabled</literal> will
	  enable 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 above will not be permitted
      to access the <command>top</command> 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 will add the <command>top</command> command to the
      label set on users in the <literal>insecure</literal> class.
      Note that 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 show you the partition label
	and the process list:</para>

      <screen>&prompt.root; <userinput>ps Zax</userinput></screen>

      <para>This next command will allow the viewing of 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 each subject or objects
      label, along with compartments.  Since these clearance or
      sensibility levels can reach numbers greater than six 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 already 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.  In addition, this label will
	  prevent 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 for:</para>

    <itemizedlist>
      <listitem>
	<para>A hierarchical security level with a set of non
	  hierarchical categories;</para>
      </listitem>

      <listitem>
	<para>Fixed rules: no read up, no write down (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 (preventing inappropriate disclosure
	  of data);</para>
      </listitem>

      <listitem>
	<para>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><literal>security.mac.mls.enabled</literal> is used to
	  enable/disable the <acronym>MLS</acronym> policy.</para>
      </listitem>

      <listitem>
	<para><literal>security.mac.mls.ptys_equal</literal> will label
	  all &man.pty.4; devices as <literal>mls/equal</literal> during
	  creation.</para>
      </listitem>

      <listitem>
	<para><literal>security.mac.mls.revocation_enabled</literal> is
	  used to revoke access to objects after their label changes
	  to a label of a lower grade.</para>
      </listitem>

      <listitem>
	<para><literal>security.mac.mls.max_compartments</literal> is
	  used to set the maximum number of compartment levels with
	  objects; basically the maximum compartment number allowed
	  on a system.</para>
      </listitem>
    </itemizedlist>

    <para>To manipulate the <acronym>MLS</acronym> labels, the
      &man.setfmac.8; command has been provided.  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>This is a summary of the <acronym>MLS</acronym>
      policy's features.  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 into the <command>setfmac</command> command.  This
      method will be explained after all policies are covered.</para>

    <sect2>
      <title>Planning Mandatory Sensitivity</title>

      <para>With the Multi-Level Security Policy Module, an
	administrator plans for controlling the flow of sensitive
	information.  By default, with its block read up block write
	down nature, the system defaults everything to a low state.
	Everything is accessible and an administrator
	slowly changes this during the configuration stage; augmenting
	the confidentiality of the information.</para>

      <para>Beyond the three basic label options above, 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 familiarized with words, for
	instance classifications such as
	<literal>Confidential</literal>, <literal>Secret</literal>,
	and <literal>Top Secret</literal>.  Some administrators might
	just create different groups based on project levels.
	Regardless of classification method, a well thought out plan
	must exist before implementing such a restrictive policy.</para>

      <para>Some example situations for this security policy module
	could be an e-commerce web server, a file server holding critical
	company information, and financial institution environments.
	The most unlikely place would be a personal workstation with
	only two or three users.</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 works much like that of the
      <acronym>MLS</acronym> policy with the exception that the rules
      for information flow
      are slightly reversed.  This is said to prevent the downward
      flow of sensitive information whereas the <acronym>MLS</acronym>
      policy prevents the upward flow of sensitive information; thus,
      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
      hierarchal grades, and non-hierarchal components.  As an object's
      or subject's 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 for:</para>

    <itemizedlist>
      <listitem>
	<para>Hierarchical integrity level with a set of non
	  hierarchical integrity categories;</para>
      </listitem>

      <listitem>
	<para>Fixed rules: no write up, no read down (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 (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><literal>security.mac.biba.enabled</literal> may be used
	  to enable/disable enforcement of the Biba policy on the
	  target machine.</para>
      </listitem>

      <listitem>
	<para><literal>security.mac.biba.ptys_equal</literal> may be
	  used to disable the Biba policy on &man.pty.4;
	  devices.</para>
      </listitem>

      <listitem>
	<para><literal>security.mac.biba.revocation_enabled</literal>
	  will force 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
      the <command>setfmac</command> and <command>getfmac</command>
      commands:</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, 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
	and in some cases even 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 or
	users may see and invoke while assuring that the programs and
	files are free from threats and trusted by the system for that
	user, or group of users.</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 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 as
	described above, 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.  While other users would be grouped into other
	categories such as testers, designers, or just ordinary
	users and would only be permitted read access.</para>

      <para>With its natural security control, a lower integrity subject
	is unable to write to a higher integrity subject; 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, development and test machine, and 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, not to be confused with the older &man.lomac.4;
      implementation, 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 of <literal>[auxgrade]</literal>.
      When assigning a lomac policy with an auxiliary grade, it
      should look a little bit like: <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.  This is the
      <literal>[auxgrade]</literal> option discussed above, thus 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;
	the <command>setfmac</command> and <command>setpmac</command>
	utilities may be 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>Notice the auxiliary grade here is <literal>low</literal>,
	this 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 will implement a secure
      environment using various <acronym>MAC</acronym> 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.</para>

    <para>Before beginning this process, the
      <literal>multilabel</literal> 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
      <filename role="package">net-mngt/nagios-plugins</filename>,
      <filename role="package">net-mngt/nagios</filename>, and
      <filename role="package">www/apache22</filename> ports 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 the <filename>/etc/login.conf</filename> file:</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>And adding the following line to the default user
	class:</para>

      <programlisting>:label=biba/high:</programlisting>

      <para>Once this is completed, the following command must be
	issued to rebuild the database:</para>

      <screen>&prompt.root; <userinput>cap_mkdb /etc/login.conf</userinput></screen>
    </sect2>

    <sect2>
      <title>Boot Configuration</title>

      <para>Do not reboot yet, just add the following lines to
	<filename>/boot/loader.conf</filename> so the required
	modules will load during system initialization:</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 &gt;= 1001) &amp;&amp; ($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; the following example
	file should be placed in
	<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 will enforce security by setting restrictions
	on the flow of information.  In this specific configuration,
	users, <username>root</username> and others, 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 may now be read into our 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 may be different depending
	  on environment; however, it must be run on every single file
	  system.</para>
      </note>

      <para>The <filename>/etc/mac.conf</filename> file 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>, then 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 in a way
	fitting of the security policy.  The following commands will
	make this happen:</para>

      <screen>&prompt.root; <userinput>cd /etc/mail &amp;&amp; make stop &amp;&amp; \
setpmac biba/equal make start &amp;&amp; setpmac biba/10\(10-10\) apachectl start &amp;&amp; \
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 or error messages.  Use
	the &man.sysctl.8; utility to disable the &man.mac.biba.4;
	security policy module enforcement and try starting everything
	again, like normal.</para>

      <note>
	<para>The <username>root</username> 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:</para>

	<screen>&prompt.root; <userinput>setpmac biba/10 csh</userinput></screen>

	<para>To block this from happening, force the user into a range
	  via &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, setting 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, fewer than fifty
      users, storage system.  Users would have login capabilities, and
      be permitted to not only store data but access resources as
      well.</para>

    <para>For this scenario, the &man.mac.bsdextended.4; mixed with
      &man.mac.seeotheruids.4; could co-exist and block access not
      only to system objects, but to hide user processes as
      well.</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 through the use of the following rc.conf
      variable:</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.  These will 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 the <command>ps aux</command> command to see if
      processes of other users are visible.  Try to run &man.ls.1; on
      another users home directory, it should fail.</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, simply unload the security policy module and reload
	it again using the &man.kldunload.8; and &man.kldload.8;
	utilities.</para>
    </note>
  </sect1>

  <sect1 id="mac-troubleshoot">
    <title>Troubleshooting the MAC Framework</title>

    <indexterm>
      <primary>MAC Troubleshooting</primary>
    </indexterm>

    <para>During the development stage, a few users reported problems
      with normal configuration.  Some of these problems
      are listed below:</para>

    <sect2>
      <title>The <option>multilabel</option> option cannot be enabled on
	<filename>/</filename></title>

      <para>The <option>multilabel</option> flag does not stay
	enabled on my root (<filename>/</filename>) partition!</para>


      <para>It seems that one out of every fifty users has this
	problem, indeed, we had this problem during our initial
	configuration.  Further observation of this so called
	<quote>bug</quote> has lead me to believe that it is a
	result of either incorrect documentation or misinterpretation
	of the documentation.  Regardless of why it happened, the
	following steps may be taken to resolve it:</para>

      <procedure>
	<step>
	  <para>Edit <filename>/etc/fstab</filename> and set the root
	    partition at <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 into normal mode.</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 the
	  <command>mount</command> to ensure that
	  <option>multilabel</option> has been properly set on the
	  root file system.</para>
	</step>
     </procedure>
    </sect2>

    <sect2>
      <title>X11 Server Will Not Start After <acronym>MAC</acronym></title>

      <para>After establishing a secure environment with
	<acronym>MAC</acronym>, I am no longer able to start
	X!</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 the <command>cap_mkdb</command> 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 in question, the
	    X11 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 your environment to
	    the TrustedBSD discussion lists located at the
	    <ulink url="http://www.TrustedBSD.org">TrustedBSD</ulink>
	    website or to the &a.questions;
	    mailing list.</para>
	</step>
      </procedure>
    </sect2>

    <sect2>
      <title>Error: &man..secure.path.3; cannot stat <filename>.login_conf</filename></title>

      <para>When I attempt to switch from the <username>root</username> user
	to another user in the system, the error message
	<errorname>_secure_path: unable to state .login_conf</errorname> appears.</para>

      <para>This message is usually shown when the user has a higher
	label setting then that of the user whom they are attempting to
	become.  For instance a user on the system,
	<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
	regardless if <username>root</username> has used the
	<command>su</command> command to become <username>joe</username>,
	or not.  In this scenario, the Biba integrity model will not
	permit <username>root</username> to view objects set at a lower
	integrity level.</para>
    </sect2>

    <sect2>
      <title>The <username>root</username> username is broken!</title>

      <para>In normal or even single user mode, the
	<username>root</username> is not recognized.  The
	<command>whoami</command> command returns 0 (zero) and
	<command>su</command> returns <errorname>who are you?</errorname>.
	What could be going on?</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 being disabled or has been temporarily
	disabled, then the login capabilities database needs to be
	reconfigured with the <option>label</option> option being
	removed.  Double check the <filename>login.conf</filename>
	file to ensure that all <option>label</option> options have
	been removed and rebuild the database with the
	<command>cap_mkdb</command> command.</para>

      <para>This may also happen if a policy restricts access to the
	<filename>master.passwd</filename> file or database.  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 via a
	&man.sysctl.8; and everything should return to normal.</para>
    </sect2>
  </sect1>
</chapter>