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<?xml version="1.0" encoding="iso-8859-1"?>
<!--
     The FreeBSD Documentation Project
     $FreeBSD$
-->
<chapter xmlns="http://docbook.org/ns/docbook"
  xmlns:xlink="http://www.w3.org/1999/xlink" version="5.0"
  xml:id="mac">
  <info>
    <title>Mandatory Access Control</title>

    <authorgroup>
      <author><personname><firstname>Tom</firstname><surname>Rhodes</surname></personname><contrib>Written
	by </contrib></author>
    </authorgroup>
  </info>

  <sect1 xml:id="mac-synopsis">
    <title>Synopsis</title>

    <indexterm><primary>MAC</primary></indexterm>
    <indexterm>
      <primary>Mandatory Access Control</primary>
      <see>MAC</see>
    </indexterm>

    <para>&os; supports security extensions  based on the
      &posix;.1e draft.  These security mechanisms include file system
      Access Control Lists (<xref linkend="fs-acl"/>) and Mandatory
      Access Control (<acronym>MAC</acronym>).  <acronym>MAC</acronym>
      allows access control modules to be loaded in order to implement
      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>The terminology associated with the
	  <acronym>MAC</acronym> framework.</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>The considerations to take into account before
	  configuring a system to use the
	  <acronym>MAC</acronym> framework.</para>
      </listitem>
      <listitem>
	<para>Which <acronym>MAC</acronym> security policy modules
	  are included in &os; and how to configure them.</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>

    <para>While 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.  Refer to &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.</para>
  </sect1>

  <sect1 xml:id="mac-inline-glossary">
    <title>Key Terms</title>

    <para>The following key terms are used when referring to the
      <acronym>MAC</acronym> framework:</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>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>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>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>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>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>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 object effectively means access to its data.</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>

      <listitem>
	<para><emphasis>policy</emphasis>: a collection of rules
	  which defines how objectives are to be achieved.  A policy
	  usually documents how certain items are to be handled.  This
	  chapter considers a policy to be 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>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>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>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>
    </itemizedlist>
  </sect1>

  <sect1 xml: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.  When setting a label, the administrator must
      understand its 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.</para>

    <para>There are two types of label policies: single label and
      multi label.  By default, the system will use single label.  The
      administrator should be aware of the pros and cons of each in
      order to implement policies which meet the requirements of the
      system's security model.</para>

    <para>A single label security policy only permits one label to be
      used for every subject or object.  Since a single label policy
      enforces one set of access permissions across the entire system,
      it provides lower administration overhead, but decreases the
      flexibility of policies which support labeling.  However, in
      many environments, a single label policy may be all that is
      required.</para>

    <para>A single label policy is somewhat similar to
      <acronym>DAC</acronym> as <systemitem
	class="username">root</systemitem> configures the policies so
      that users are placed in the appropriate categories and access
      levels.  A notable difference is that many policy modules can
      also restrict <systemitem class="username">root</systemitem>.
      Basic control over objects will then be released to the group,
      but <systemitem class="username">root</systemitem> may revoke or
      modify the settings at any time.</para>

    <para>When appropriate, a multi label policy can be set on a
      <acronym>UFS</acronym> file system by passing
      <option>multilabel</option> to &man.tunefs.8;.  A multi label
      policy permits each subject or object to have its own
      independent <acronym>MAC</acronym> label.  The decision to use a
      multi label or single label policy is only required for policies
      which implement the labeling feature, such as
      <literal>biba</literal>, <literal>lomac</literal>, and
      <literal>mls</literal>.  Some policies, such as
      <literal>seeotheruids</literal>, <literal>portacl</literal> and
      <literal>partition</literal>, do not use labels at all.</para>

    <para>Using a multi label policy on a partition and establishing a
      multi label security model can increase administrative overhead
      as everything in that 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 specified <acronym>UFS</acronym> file system.  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 <xref
	  linkend="mac-troubleshoot"/>.</para>
    </note>

    <para>Since the multi label policy is set on a per-file system
      basis, a multi label policy may not be needed if the file system
      layout is well designed.  Consider an example security
      <acronym>MAC</acronym> model for a &os; web server.  This
      machine uses the single label, <literal>biba/high</literal>, for
      everything in the default file systems.  If the web server needs
      to run at <literal>biba/low</literal> to prevent write up
      capabilities, it could be installed to a separate
      <acronym>UFS</acronym> <filename>/usr/local</filename> file
      system set at <literal>biba/low</literal>.</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
	<command>setfmac</command>, which is used to set
	<acronym>MAC</acronym> labels on system objects, and
	<command>setpmac</command>, which is used to set the labels on
	system subjects.  For example, to set the
	<literal>biba</literal> <acronym>MAC</acronym> label to
	<literal>high</literal> on <filename>test</filename>:</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 a restricted
	object.  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, if a user running at
	low integrity tries to change the label of a high integrity
	file, or a user running at low integrity tries to change the
	label of a low integrity file to a high integrity label, these
	operations will fail.</para>

      <para>The system administrator may use
	<command>setpmac</command> to override the policy module's
	settings by assigning a different label to the invoked
	process:</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>For currently running processes, such as
	<application>sendmail</application>,
	<command>getpmac</command> is usually used instead.  This
	command takes a process ID (<acronym>PID</acronym>) in place
	of a command name.  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.</para>
    </sect2>

    <sect2>
      <title>Predefined Labels</title>

      <para>A few &os; policy modules which support the labeling
	feature offer three predefined labels: <literal>low</literal>,
	<literal>equal</literal>, and <literal>high</literal>,
	where:</para>

      <itemizedlist>
	<listitem>
	  <para><literal>low</literal> 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><literal>equal</literal> sets the subject or object to
	    be disabled or unaffected and should only be placed on
	    objects considered to be exempt from the policy.</para>
	</listitem>

	<listitem>
	  <para><literal>high</literal> grants an object or subject
	    the highest setting available in the Biba and
	    <acronym>MLS</acronym> policy modules.</para>
	</listitem>
      </itemizedlist>

      <para>Such policy modules include &man.mac.biba.4;,
	&man.mac.mls.4; and &man.mac.lomac.4;.  Each of the predefined
	labels establishes a different information flow directive.
	Refer to the manual page of the module to determine the traits
	of the generic label configurations.</para>
    </sect2>

    <sect2>
      <title>Numeric Labels</title>

      <para>The Biba and <acronym>MLS</acronym> policy modules support
	a numeric label which 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.  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/Grade
	  10:Compartments 2, 3 and 6: (grade 5 ...</quote>)</para>

      <para>In this example, the first grade would be considered the
	effective grade with effective compartments, the second grade
	is the low grade, and the last one is the high grade.  In most
	configurations, such fine-grained settings are not needed as
	they are considered to be advanced configurations.</para>

      <para>System objects only have a current grade and 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
	<firstterm>dominance</firstterm>, 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>
    </sect2>

    <sect2>
      <title>User Labels</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>/etc/login.conf</filename> using login classes.
	Every policy module that uses labels will implement the user
	class setting.</para>

      <para>To set the user class default label which will be enforced
	by <acronym>MAC</acronym>, add a <option>label</option> entry.
	An example <option>label</option> entry containing every
	policy module is displayed below.  Note that in a real
	configuration, 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>

      <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>While users can not modify the default value, they 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
	<literal>5</literal>, its maximum is <literal>15</literal>,
	and the default effective label is <literal>10</literal>.  The
	process will run at <literal>10</literal> until it chooses to
	change label, perhaps due to the user using
	<command>setpmac</command>, which will be constrained by Biba
	to the configured range.</para>

      <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 can become difficult to manage.</para>
    </sect2>

    <sect2>
      <title>Network Interface Labels</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
	Biba, for example, will not be permitted to access network
	interfaces with a label of <literal>low</literal>.</para>

      <para>When setting the <acronym>MAC</acronym> label on network
	interfaces, <option>maclabel</option> may be passed to
	<command>ifconfig</command>:</para>

      <screen>&prompt.root; <userinput>ifconfig bge0 maclabel biba/equal</userinput></screen>

      <para>This example will set the <acronym>MAC</acronym> label of
	<literal>biba/equal</literal> on the <literal>bge0</literal>
	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 the rest of this chapter for
	more information on those tunables.</para>
    </sect2>
  </sect1>

  <sect1 xml:id="mac-planning">
    <title>Planning the Security Configuration</title>

    <para>Before implementing any <acronym>MAC</acronym> policies, a
      planning phase is recommended.  During the planning stages, an
      administrator should consider the implementation requirements
      and goals, such as:</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> modules will be required to
	  achieve this goal.</para>
      </listitem>
    </itemizedlist>

    <para>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.  Since different environments have different needs and
      requirements, establishing a complete security profile will
      decrease the need of changes once the system goes live.</para>

    <para>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 control of the
      <acronym>MAC</acronym> access rules is 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>

    <para>  The rest of this chapter covers the available modules,
      describes their use and configuration, and in some cases,
      provides insight on applicable situations.</para>

    <caution>
      <para>Implementing <acronym>MAC</acronym> is much like
	implementing a firewall since 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> over a remote
	connection should be done with extreme caution.</para>
    </caution>
  </sect1>

  <sect1 xml:id="mac-policies">
    <title>Available MAC Policies</title>

    <para>The default &os; kernel
      includes <literal>options MAC</literal>.  This means that every
      module included with the <acronym>MAC</acronym> framework can be
      loaded with <command>kldload</command> as a run-time kernel
      module.  After testing the module, 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>&os; includes a group of policies that will cover most
      security requirements.  Each policy is summarized below.  The
      last three policies support integer settings in place of the
      three default labels.</para>

    <sect2 xml: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 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 other modules.</para>

      <para>After loading the module, the following
	<command>sysctl</command> tunables may be used to control its
	features:</para>

      <itemizedlist>
	<listitem>
	  <para><varname>security.mac.seeotheruids.enabled</varname>
	    enables the module and implements 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 specified groups to be exempt from this policy.  To
	    exempt specific groups, use the
	    <varname>security.mac.seeotheruids.specificgid=<replaceable>XXX</replaceable></varname>
	    <command>sysctl</command> tunable, replacing
	    <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>
    </sect2>

    <sect2 xml: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 a file system
	firewall.  It 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 using
	<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>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 blocks all
	access by users but leaves <systemitem
	  class="username">root</systemitem> unaffected:</para>

      <screen>&prompt.root; <userinput>ugidfw add subject not uid root new object not uid root mode n</userinput></screen>

      <para>While this rule is simple to implement, it is a very bad
	idea as it blocks all users from issuing any commands.  A
	more realistic example blocks <systemitem
	  class="username">user1</systemitem> all access, including
	directory listings, to <systemitem
	  class="username"><replaceable>user2</replaceable></systemitem>'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 <systemitem
	  class="username">user1</systemitem>, <option>not
	  uid <replaceable>user2</replaceable></option> could be used
	in order to enforce the same access restrictions for all
	users.  However, the <systemitem
	  class="username">root</systemitem> user is unaffected by
	these rules.</para>

      <note>
	<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>
      </note>
    </sect2>

    <sect2 xml: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 is used to disable network
	interfaces on the fly and to keep network interfaces from
	being brought up during system boot.  It does not use labels
	and does not depend on any other
	<acronym>MAC</acronym> modules.</para>

      <para>Most of this module's control is performed through these
	<command>sysctl</command> tunables:</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
	use would be to write a script which uses an application such
	as <package>security/aide</package> to automatically block
	network traffic if it finds new or altered files in protected
	directories.</para>
    </sect2>

    <sect2 xml: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,
	making it possible to allow non-<systemitem
	  class="username">root</systemitem> 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 <systemitem
	      class="username">root</systemitem> user from this
	    policy.</para>
	</listitem>

	<listitem>
	  <para><varname>security.mac.portacl.rules</varname>
	    specifies the policy as a text string of the form
	    <literal>rule[,rule,...]</literal>, with as many rules as
	    needed, and where each rule is of the form
	    <literal>idtype:id:protocol:port</literal>.  The
	    <parameter>idtype</parameter> is either
	    <literal>uid</literal> or <literal>gid</literal>.  The
	    <parameter>protocol</parameter> parameter can be
	    <literal>tcp</literal> or <literal>udp</literal>.  The
	    <parameter>port</parameter> parameter is the port number
	    to allow the specified user or group to bind to.  Only
	    numeric values can be used for the user ID, group ID,
	    and port parameters.</para>
	</listitem>
      </itemizedlist>

      <para>By default, ports below 1024 can only be used by
	privileged processes which run as <systemitem
	  class="username">root</systemitem>.  For &man.mac.portacl.4;
	to allow non-privileged processes to bind to ports below 1024,
	set the following tunables as
	follows:</para>

      <screen>&prompt.root; <userinput>sysctl security.mac.portacl.port_high=1023</userinput>
&prompt.root; <userinput>sysctl net.inet.ip.portrange.reservedlow=0</userinput>
&prompt.root; <userinput>sysctl net.inet.ip.portrange.reservedhigh=0</userinput></screen>

      <para>To prevent the <systemitem
	  class="username">root</systemitem> user from being affected
	by this policy, set
	<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>To allow the <systemitem class="username">www</systemitem>
	user with <acronym>UID</acronym> 80 to bind to port 80
	without ever needing <systemitem
	  class="username">root</systemitem> privilege:</para>

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

      <para>This next example permits the user with the
	<acronym>UID</acronym> of 1001 to bind to
	<acronym>TCP</acronym> ports 110 (POP3) and 995
	(POP3s):</para>

      <screen>&prompt.root; <userinput>sysctl security.mac.portacl.rules=uid:1001:tcp:110,uid:1001:tcp:995</userinput></screen>
    </sect2>

    <sect2 xml: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 drops processes into
	specific <quote>partitions</quote> based on their
	<acronym>MAC</acronym> label.  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>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>

      <screen>&prompt.root; <userinput>setpmac partition/13 top</userinput></screen>

      <para>This command displays the partition label and the process
	list:</para>

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

      <para>This command displays 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 <systemitem
	    class="username">root</systemitem>'s label unless the
	  &man.mac.seeotheruids.4; policy is loaded.</para>
      </note>
    </sect2>

    <sect2 xml: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 levels can reach numbers greater than several
	thousand, it would be a daunting task to thoroughly configure
	every subject or object.  To ease this administrative
	overhead, three labels are included in this policy:
	<literal>mls/low</literal>, <literal>mls/equal</literal>, and
	<literal>mls/high</literal>, where:</para>

      <itemizedlist>
	<listitem>
	  <para>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 to a lower level.</para>
	</listitem>

	<listitem>
	  <para><literal>mls/equal</literal> should be placed on
	    objects which should be exempt from the policy.</para>
	</listitem>

	<listitem>
	  <para><literal>mls/high</literal> 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:</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 <acronym>MLS</acronym> labels, use
	&man.setfmac.8;.  To assign a label to an object:</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>:</para>

      <screen>&prompt.root; <userinput>getfmac test</userinput></screen>

      <para>Another approach is to create a master policy file in
	<filename>/etc/</filename> which specifies the
	<acronym>MLS</acronym> policy information and to feed that
	file to <command>setfmac</command>.</para>

      <para>When using the <acronym>MLS</acronym> 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.</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 a
	restrictive policy.</para>

      <para>Some example situations for the <acronym>MLS</acronym>
	policy module include an e-commerce web server, a file server
	holding critical company information, and financial
	institution environments.</para>
    </sect2>

    <sect2 xml: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.</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 a
	grade ascends, so does its integrity.</para>

      <para>Supported labels are <literal>biba/low</literal>,
	<literal>biba/equal</literal>, and
	<literal>biba/high</literal>, where:</para>

      <itemizedlist>
	<listitem>
	  <para><literal>biba/low</literal> is considered the lowest
	    integrity an object or subject may have.  Setting this on
	    objects or subjects blocks their write access to objects
	    or subjects marked as <literal>biba/high</literal>, but
	    will not prevent read access.</para>
	</listitem>

	<listitem>
	  <para><literal>biba/equal</literal> should only be placed on
	    objects considered to be exempt from the policy.</para>
	</listitem>

	<listitem>
	  <para><literal>biba/high</literal> permits writing to
	    objects set at a lower label, but does 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 levels 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 <acronym>MLS</acronym>
	    sensitivity levels.</para>
	</listitem>
      </itemizedlist>

      <para>The following 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>

      <para>Integrity, which is different from sensitivity, is used to
	guarantee that information is not manipulated by untrusted
	parties.  This includes information passed between subjects
	and objects.  It ensures that users will only be able to
	modify or access information they have been given explicit
	access to.  The &man.mac.biba.4; security policy module
	permits an administrator to configure which files and programs
	a user may see and invoke while assuring that the programs and
	files are 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.
	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 list
	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>

    <sect2 xml:id="mac-lomac">
      <title>The MAC Low-watermark 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 Low-watermark integrity policy works almost
	identically to Biba, 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 policy with
	an auxiliary grade, use the syntax
	<literal>lomac/10[2]</literal>, where
	<literal>2</literal> is the auxiliary grade.</para>

      <para>This 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 greater compatibility and require less initial
	configuration than Biba.</para>

      <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 lomac/high[low]</userinput></screen>

      <para>The auxiliary grade <literal>low</literal> is a feature
	provided only by the <acronym>MAC</acronym>
	<acronym>LOMAC</acronym> policy.</para>
    </sect2>
  </sect1>

  <sect1 xml: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 are 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 <systemitem
	class="username">root</systemitem> 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 xml:id="mac-implementing">
    <title>Nagios in a MAC Jail</title>

    <indexterm>
      <primary>Nagios in a MAC Jail</primary>
    </indexterm>

    <para>This section demonstrates the steps that are needed to
      implement the <application>Nagios</application> network
      monitoring system in a <acronym>MAC</acronym> environment.  This
      is meant as an example which still requires the administrator to
      test that the implemented policy meets the security requirements
      of the network before using in a production environment.</para>

    <para>This example requires <option>multilabel</option> to be set
      on each file system.  It also assumes that
      <package>net-mgmt/nagios-plugins</package>,
      <package>net-mgmt/nagios</package>, and
      <package>www/apache22</package> are all installed, configured,
      and working correctly before attempting the integration into the
      <acronym>MAC</acronym> framework.</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>Then, add the following line to the default user class
	section:</para>

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

      <para>Save the edits and issue the following command to rebuild
	the database:</para>

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

    <sect2>
      <title>Configure Users</title>

      <para>Set the <systemitem class="username">root</systemitem>
	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 <systemitem
	  class="username">root</systemitem> will now require a login
	class.  The login class is required, otherwise users will be
	refused access to common commands.  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>Next, drop the <systemitem
	  class="username">nagios</systemitem> and <systemitem
	  class="username">www</systemitem> accounts into the insecure
	class:</para>

      <screen>&prompt.root; <userinput>pw usermod nagios -L insecure</userinput>
&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

/dev/(/.*)?			biba/equal

/var				biba/equal
/var/spool(/.*)?		biba/equal

/var/log(/.*)?			biba/equal

/tmp(/.*)?			biba/equal
/var/tmp(/.*)?			biba/equal

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

# For Nagios:
/usr/local/etc/nagios(/.*)?	biba/10

/var/spool/nagios(/.*)?		biba/10

# For apache
/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 <systemitem
	  class="username">root</systemitem>, 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 after running
	<command>setfsmac</command> on every file system.  This
	example sets the policy on the root file system:</para>

      <screen>&prompt.root; <userinput>setfsmac -ef /etc/policy.contexts /</userinput></screen>

      <para>Next, add these edits to the main section of
	<filename>/etc/mac.conf</filename>:</para>

      <programlisting>default_labels file ?biba
default_labels ifnet ?biba
default_labels process ?biba
default_labels socket ?biba</programlisting>
    </sect2>

    <sect2>
      <title>Loader Configuration</title>

      <para>To finish the configuration, add the following lines to
	<filename>/boot/loader.conf</filename>:</para>

      <programlisting>mac_biba_load="YES"
mac_seeotheruids_load="YES"
security.mac.biba.trust_all_interfaces=1</programlisting>

      <para>And the following line to the network card configuration
	stored in <filename>/etc/rc.conf</filename>.  If the primary
	network 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>First, ensure that the web server and
	<application>Nagios</application> will not be started on
	system initialization and reboot.  Ensure that <systemitem
	  class="username">root</systemitem> cannot access any of the
	files in the <application>Nagios</application> configuration
	directory.  If <systemitem class="username">root</systemitem>
	can list the contents of
	<filename>/var/spool/nagios</filename>, something is wrong.
	Instead, 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 &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 for error messages.  If
	needed, use &man.sysctl.8; to disable the &man.mac.biba.4;
	security policy module and try starting everything again as
	usual.</para>

      <note>
	<para>The <systemitem class="username">root</systemitem> 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 xml:id="mac-troubleshoot">
    <title>Troubleshooting the MAC Framework</title>

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

    <para>This section discusses common configuration errors and how
      to resolve them.</para>

    <variablelist>
      <varlistentry>
	<term>The <option>multilabel</option> flag does not stay
	  enabled on the root (<filename>/</filename>)
	  partition:</term>

	<listitem>
	  <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>
      </varlistentry>

      <varlistentry>
	<term>After establishing a secure environment with
	  <acronym>MAC</acronym>, <application>Xorg</application> no
	  longer starts:</term>
	<listitem>
	  <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 that the label policies are set
		correctly for the user,
		<application>Xorg</application>, and the
		<filename>/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;.</para>
	    </step>
	  </procedure>
	</listitem>
      </varlistentry>

      <varlistentry>
	<term>The <errorname>_secure_path: unable to stat
	    .login_conf</errorname> error appears:</term>
	<listitem>
	  <para>This error can appear when a user attempts to switch
	    from the <systemitem class="username">root</systemitem>
	    user to another user in the system.  This message
	    usually occurs when the user has a higher label setting
	    than that of the user they are attempting to become.
	    For instance, if <systemitem
	      class="username">joe</systemitem> has a default label
	    of <option>biba/low</option> and <systemitem
	      class="username">root</systemitem> has a label of
	    <option>biba/high</option>, <systemitem
	      class="username">root</systemitem> cannot view
	    <systemitem class="username">joe</systemitem>'s home
	    directory.  This will happen whether or not <systemitem
		class="username">root</systemitem> has used
	    <command>su</command> to become <systemitem
		class="username">joe</systemitem> as the Biba
	    integrity model will not permit <systemitem
		class="username">root</systemitem> to view objects set
	    at a lower integrity level.</para>
	</listitem>
      </varlistentry>

      <varlistentry>
	<term>The system no longer recognizes <systemitem
	    class="username">root</systemitem>:</term>
	<listitem>
	  <para>When this occurs, <command>whoami</command> returns
	    <literal>0</literal> and <command>su</command> returns
	    <errorname>who are you?</errorname>.</para>

	  <para>This can happen if a labeling policy has been
	    disabled by &man.sysctl.8; or the policy module was
	    unloaded.  If the policy is disabled, the login
	    capabilities database needs to be reconfigured.  Double
	    check <filename>/etc/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>
      </varlistentry>
    </variablelist>
  </sect1>
</chapter>