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

      <listitem>
	<para>The capabilities of <acronym>MAC</acronym> security
	  policy modules as well as the difference between a labeled
	  and non-labeled policy.</para>
      </listitem>

      <listitem>
	<para>How to efficiently configure a system to use the
	  <acronym>MAC</acronym> framework.</para>
      </listitem>

      <listitem>
	<para>How to configure the different security policy modules
	  included with the <acronym>MAC</acronym> framework.</para>
      </listitem>

      <listitem>
	<para>How to implement a more secure environment using the
	  <acronym>MAC</acronym> framework.</para>
      </listitem>

      <listitem>
	<para>How to test the <acronym>MAC</acronym> configuration
	  to ensure the framework has been properly
	  implemented.</para>
      </listitem>
    </itemizedlist>

    <para>Before reading this chapter, you should:</para>

    <itemizedlist>
      <listitem>
	<para>Understand &unix; and &os; basics (<xref
	    linkend="basics"/>).</para>
      </listitem>

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

    <warning>
      <para>Improper <acronym>MAC</acronym> configuration may cause
	loss of system access, aggravation of users, or inability to
	access the features provided by
	<application>Xorg</application>.  More importantly,
	<acronym>MAC</acronym> should not be relied upon to completely
	secure a system.  The <acronym>MAC</acronym> framework only
	augments an existing security policy.  Without sound security
	practices and regular security checks, the system will never
	be completely secure.</para>

      <para>The examples contained within this chapter are for
	demonstration purposes and the example settings should
	<emphasis>not</emphasis> be implemented on a production
	system.  Implementing any security policy takes a good deal of
	understanding, proper design, and thorough testing.</para>
    </warning>

    <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>Beginning with &os;&nbsp;8.0, 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-implementing">
    <title>Nagios in a MAC Jail</title>

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

    <para>The following demonstration implements a secure
      environment using various <acronym>MAC</acronym> modules
      with properly configured policies.  This is only a test as
      implementing a policy and ignoring it could be disastrous in a
      production environment.</para>

    <para>Before beginning this process, <option>multilabel</option>
      must be set on each file system as not doing so will result in
      errors.  This example assumes that
      <package>net-mgmt/nagios-plugins</package>,
      <package>net-mgmt/nagios</package>, and
      <package>www/apache22</package> are all installed, configured,
      and working correctly.</para>

    <sect2>
      <title>Create an Insecure User Class</title>

      <para>Begin the procedure by adding the following user class
	to <filename>/etc/login.conf</filename>:</para>

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

      <para>Add the following line to the default user class:</para>

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

      <para>Next, issue the following command to rebuild the
	database:</para>

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

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

      <para>Add the following lines to
	<filename>/boot/loader.conf</filename>:</para>

      <programlisting>mac_biba_load="YES"
mac_seeotheruids_load="YES"</programlisting>
    </sect2>

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

      <para>Set the <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> 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 <systemitem class="username">nagios</systemitem>
	and <systemitem class="username">www</systemitem> users into
	the insecure class:</para>

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

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

      </sect2>

      <sect2>
	<title>Create the Contexts File</title>

	<para>A contexts file should now be created as
	  <filename>/etc/policy.contexts</filename>.</para>

	<programlisting># This is the default BIBA policy for this system.

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

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

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

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

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

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

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

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

# For apache
/usr/local/etc/apache           biba/10
/usr/local/etc/apache/*         biba/10</programlisting>

      <para>This policy enforces security by setting restrictions
	on the flow of information.  In this specific configuration,
	users, including <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 by the system by issuing the
	following command:</para>

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

      <note>
	<para>The above file system layout will differ depending
	  upon the environment and must be run on every file
	  system.</para>
      </note>

      <para><filename>/etc/mac.conf</filename> requires the following
	modifications in the main section:</para>

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

    <sect2>
      <title>Enable Networking</title>

      <para>Add the following line to
	<filename>/boot/loader.conf</filename>:</para>

      <programlisting>security.mac.biba.trust_all_interfaces=1</programlisting>

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

      <programlisting>maclabel biba/equal</programlisting>
    </sect2>

    <sect2>
      <title>Testing the Configuration</title>

      <indexterm>
	<primary>MAC Configuration Testing</primary>
      </indexterm>

      <para>Ensure that the web server and
	<application>Nagios</application> will not be started on
	system initialization and reboot.  Ensure the <systemitem
	  class="username">root</systemitem> user cannot access any of
	the files in the <application>Nagios</application>
	configuration directory.  If <systemitem
	  class="username">root</systemitem> can issue an &man.ls.1;
	command on <filename>/var/spool/nagios</filename>, something
	is wrong.  Otherwise a <quote>permission denied</quote> error
	should be returned.</para>

      <para>If all seems well, <application>Nagios</application>,
	<application>Apache</application>, and
	<application>Sendmail</application> can now be started:</para>

      <screen>&prompt.root; <userinput>cd /etc/mail &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.
	Use &man.sysctl.8; to disable the &man.mac.biba.4; security
	policy module enforcement and try starting everything again as
	usual.</para>

      <note>
	<para>The <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-userlocked">
    <title>User Lock Down</title>

    <para>This example considers a relatively small storage system
      with fewer than fifty users.  Users will have login
      capabilities, and be permitted to store data and access
      resources.</para>

    <para>For this scenario, the &man.mac.bsdextended.4; and
      &man.mac.seeotheruids.4; policy modules could co-exist and block
      access to system objects while hiding user processes.</para>

    <para>Begin by adding the following line to
      <filename>/boot/loader.conf</filename>:</para>

    <programlisting>mac_seeotheruids_load="YES"</programlisting>

    <para>The &man.mac.bsdextended.4; security policy module may be
      activated by adding this line to
      <filename>/etc/rc.conf</filename>:</para>

    <programlisting>ugidfw_enable="YES"</programlisting>

    <para>Default rules stored in
      <filename>/etc/rc.bsdextended</filename> will be loaded at
      system initialization.  However, the default entries may need
      modification.  Since this machine is expected only to service
      users, everything may be left commented out except the last
      two lines in order to force the loading of user owned system
      objects by default.</para>

    <para>Add the required users to this machine and reboot.  For
      testing purposes, try logging in as a different user across
      two consoles.  Run <command>ps aux</command> to see if processes
      of other users are visible.  Verify that running &man.ls.1; on
      another user's home directory fails.</para>

    <para>Do not try to test with the <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-troubleshoot">
    <title>Troubleshooting the MAC Framework</title>

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

    <para>This section discusses common configuration issues.</para>

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

	<para>The following steps may resolve this transient
	  error:</para>

	<procedure>
	  <step>
	    <para>Edit <filename>/etc/fstab</filename> and set the
	      root partition to <option>ro</option> for
	      read-only.</para>
	  </step>

	  <step>
	    <para>Reboot into single user mode.</para>
	  </step>

	  <step>
	    <para>Run <command>tunefs</command> <option>-l
		enable</option> on <filename>/</filename>.</para>
	  </step>

	  <step>
	    <para>Reboot the system.</para>
	  </step>

	  <step>
	    <para>Run <command>mount</command> <option>-urw</option>
	      <filename>/</filename> and change the
	      <option>ro</option> back to <option>rw</option> in
	      <filename>/etc/fstab</filename> and reboot the system
	      again.</para>
	  </step>

	  <step>
	    <para>Double-check the output from
	      <command>mount</command> to ensure that
	      <option>multilabel</option> has been properly set on the
	      root file system.</para>
	  </step>
	</procedure>
      </listitem>

      <listitem>
	<para>After establishing a secure environment with
	  <acronym>MAC</acronym>, I am no longer able to start
	  Xorg!</para>

	<para>This could be caused by the <acronym>MAC</acronym>
	  <literal>partition</literal> policy or by a mislabeling in
	  one of the <acronym>MAC</acronym> labeling policies.  To
	  debug, try the following:</para>

	<procedure>
	  <step>
	    <para>Check the error message; if the user is in the
	      <literal>insecure</literal> class, the
	      <literal>partition</literal> policy may be the culprit.
	      Try setting the user's class back to the
	      <literal>default</literal> class and rebuild the
	      database with <command>cap_mkdb</command>.  If this does
	      not alleviate the problem, go to step two.</para>
	  </step>

	  <step>
	    <para>Double-check the label policies.  Ensure that the
	      policies are set correctly for the user, the Xorg
	      application, and the <filename>/dev</filename>
	      entries.</para>
	  </step>

	  <step>
	    <para>If neither of these resolve the problem, send the
	      error message and a description of the environment to
	      the &a.questions; mailing list.</para>
	  </step>
	</procedure>
      </listitem>

      <listitem>
	<para>The error: <errorname>_secure_path: unable to stat
	    .login_conf</errorname> shows up.</para>

	<para>When a user attempts to switch from the <systemitem
	    class="username">root</systemitem> user to another user in
	  the system, the error message <errorname>_secure_path:
	    unable to stat .login_conf</errorname> appears.</para>

	<para>This message is usually shown when the user has a higher
	  label setting than that of the user they are attempting to
	  become.  For instance, <systemitem
	    class="username">joe</systemitem> has a default label of
	  <option>biba/low</option>.  The <systemitem
	    class="username">root</systemitem> user, who has a label
	  of <option>biba/high</option>, 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>

      <listitem>
	<para>The system no longer recognizes the <systemitem
	    class="username">root</systemitem> user.</para>

	<para>In normal or even single user mode, the <systemitem
	    class="username">root</systemitem> is not recognized,
	  <command>whoami</command> returns 0 (zero), and
	  <command>su</command> returns <errorname>who are
	    you?</errorname>.</para>

	<para>This can happen if a labeling policy has been disabled,
	  either by a &man.sysctl.8; or the policy module was
	  unloaded.  If the policy is disabled, the login capabilities
	  database needs to be reconfigured with
	  <option>label</option> removed.  Double check
	  <filename>login.conf</filename> to ensure that all
	  <option>label</option> options have been removed and rebuild
	  the database with <command>cap_mkdb</command>.</para>

	<para>This may also happen if a policy restricts access to
	  <filename>master.passwd</filename>.  This is usually caused
	  by an administrator altering the file under a label which
	  conflicts with the general policy being used by the system.
	  In these cases, the user information would be read by the
	  system and access would be blocked as the file has inherited
	  the new label.  Disable the policy using &man.sysctl.8; and
	  everything should return to normal.</para>
      </listitem>
    </itemizedlist>
  </sect1>
</chapter>