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authorDru Lavigne <dru@FreeBSD.org>2014-03-28 15:55:53 +0000
committerDru Lavigne <dru@FreeBSD.org>2014-03-28 15:55:53 +0000
commit94d3851b1fb4828c65524995fb55325ca393e3c2 (patch)
treef973ea95492436ea9a938ab555b0a07c0777872a /en_US.ISO8859-1/books/handbook/mac
parent16e8132f179e9b979b95db6de7ba81765d4b924e (diff)
downloaddoc-94d3851b1fb4828c65524995fb55325ca393e3c2.tar.gz
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Editorial review of Available MAC Policies.
Sponsored by: iXsystems
Notes
Notes: svn path=/head/; revision=44374
Diffstat (limited to 'en_US.ISO8859-1/books/handbook/mac')
-rw-r--r--en_US.ISO8859-1/books/handbook/mac/chapter.xml404
1 files changed, 150 insertions, 254 deletions
diff --git a/en_US.ISO8859-1/books/handbook/mac/chapter.xml b/en_US.ISO8859-1/books/handbook/mac/chapter.xml
index e173f475ac..8851e2f08e 100644
--- a/en_US.ISO8859-1/books/handbook/mac/chapter.xml
+++ b/en_US.ISO8859-1/books/handbook/mac/chapter.xml
@@ -552,13 +552,10 @@ test: biba/high</screen>
<sect1 xml:id="mac-planning">
<title>Planning the Security Configuration</title>
- <para>Whenever a new technology is implemented, a planning phase
+ <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 the
- implementation goals.</para>
-
- <para>For <acronym>MAC</acronym> installations, these
- include:</para>
+ should consider the implementation requirements and
+ goals, such as:</para>
<itemizedlist>
<listitem>
@@ -573,29 +570,19 @@ test: biba/high</screen>
</listitem>
<listitem>
- <para>Which <acronym>MAC</acronym> module or modules will be
+ <para>Which <acronym>MAC</acronym> modules will be
required to achieve this goal.</para>
</listitem>
</itemizedlist>
- <para>Good planning helps to ensure a trouble-free and efficient
- trusted system implementation. A trial run of the trusted
+ <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. The idea of
- just letting loose on a system with <acronym>MAC</acronym> is
- like setting up for failure.</para>
-
- <para>Different environments have different needs and
- requirements. Establishing an in depth and complete security
+ 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. The rest of this chapter covers the available
- modules, describes their use and configuration, and in some
- cases, provides insight on applicable situations. For instance,
- a web server might use the &man.mac.biba.4; and
- &man.mac.bsdextended.4; policies. In the case of a machine
- with few local users, &man.mac.partition.4; might be a good
- choice.</para>
+ goes live.</para>
<para>Consider how the
<acronym>MAC</acronym> framework augments the security of
@@ -624,8 +611,8 @@ test: biba/high</screen>
user will not be permitted to change security attributes at
will. All user utilities, programs, and scripts must work
within the constraints of the access rules provided by the
- selected security policy modules and total control of the
- <acronym>MAC</acronym> access rules are in the hands of the
+ 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
@@ -659,47 +646,37 @@ test: biba/high</screen>
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, care must be taken to prevent being
+ 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> remotely should be
+ implementation of <acronym>MAC</acronym> over a remote connection should be
done with extreme caution.</para>
</caution>
</sect1>
- <sect1 xml:id="mac-modules">
- <title>Module Configuration</title>
+ <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 may be loaded as a run-time kernel module. The
- recommended method is to add the module name to
+ 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>Some modules support the use of labeling, which is
- controlling access by enforcing a label such as <quote>this is
- allowed and this is not</quote>. A label configuration file may
- control how files may be accessed, network communication can be
- exchanged, and more. The previous section showed how the
- <option>multilabel</option> flag could be set on file systems to
- enable per-file or per-partition access control.</para>
-
- <para>A single label configuration enforces only one label
- across the system, that is why the <command>tunefs</command>
- option is called <option>multilabel</option>.</para>
- </sect1>
-
- <sect1 xml:id="mac-policies">
- <title>Available MAC Policies</title>
-
<para>&os; includes a group of policies that will cover most
- security requirements. Each policy is discussed below.</para>
+ 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>
@@ -716,21 +693,21 @@ test: biba/high</screen>
<para>Boot option:
<literal>mac_seeotheruids_load="YES"</literal></para>
- <para>The &man.mac.seeotheruids.4; module mimics and extends
+ <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 the other modules.</para>
+ operate transparently with other modules.</para>
<para>After loading the module, the following
- <command>sysctl</command> tunables may be used to control the
+ <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 uses the default settings which
+ enables the module and implements the default settings which
deny users the ability to view processes and sockets owned
by other users.</para>
</listitem>
@@ -738,10 +715,10 @@ test: biba/high</screen>
<listitem>
<para>
<varname>security.mac.seeotheruids.specificgid_enabled</varname>
- allows certain groups to be exempt from this policy. To
- exempt specific groups from this policy, use the
+ 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. Replace
+ <command>sysctl</command> tunable, replacing
<replaceable>XXX</replaceable> with the numeric group ID
to be exempted.</para>
</listitem>
@@ -773,15 +750,15 @@ test: biba/high</screen>
<para>Boot option:
<literal>mac_bsdextended_load="YES"</literal></para>
- <para>The &man.mac.bsdextended.4; module enforces the file
- system firewall. This module's policy provides an extension
+ <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
- by the use of a &man.sysctl.8; parameter,
+ 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
@@ -792,13 +769,6 @@ test: biba/high</screen>
written by using the functions in the &man.libugidfw.3;
library.</para>
- <para>Extreme caution should be taken when working with this
- module as incorrect use could block access to certain parts of
- the file system.</para>
-
- <sect3>
- <title>Examples</title>
-
<para>After the &man.mac.bsdextended.4; module has been
loaded, the following command may be used to list the
current rule configuration:</para>
@@ -807,17 +777,15 @@ test: biba/high</screen>
0 slots, 0 rules</screen>
<para>By default, no rules are defined and everything is
- completely accessible. To create a rule which will block
- all access by users but leave <systemitem
- class="username">root</systemitem> unaffected, run the
- following command:</para>
+ 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>This is a very bad idea as it will block all users from
- issuing even the most simple commands, such as
- <command>ls</command>. The next example will block
- <systemitem class="username">user1</systemitem> any and all
+ <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>
@@ -828,17 +796,15 @@ test: biba/high</screen>
<para>Instead of <systemitem
class="username">user1</systemitem>, <option>not
uid <replaceable>user2</replaceable></option> could be
- used. This enforces the same access restrictions for all
- users instead of just one user.</para>
+ 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>The <systemitem class="username">root</systemitem>
- user is unaffected by these changes.</para>
- </note>
-
- <para>For more information, refer to &man.mac.bsdextended.4;
- and &man.ugidfw.8;</para>
- </sect3>
+ <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">
@@ -855,26 +821,26 @@ test: biba/high</screen>
<para>Boot option:
<literal>mac_ifoff_load="YES"</literal></para>
- <para>The &man.mac.ifoff.4; module exists solely to disable
- network interfaces on the fly and keep network interfaces from
- being brought up during system boot. It does not require any
- labels to be set up on the system, nor does it depend on other
+ <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 the
- <command>sysctl</command> tunables listed below.</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>
+ 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>
+ Filter interface, &man.bpf.4;.</para>
</listitem>
<listitem>
@@ -887,7 +853,7 @@ test: biba/high</screen>
<para>One of the most common uses of &man.mac.ifoff.4; is
network monitoring in an environment where network traffic
should not be permitted during the boot sequence. Another
- suggested use would be to write a script which uses
+ 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>
@@ -908,9 +874,8 @@ test: biba/high</screen>
<literal>mac_portacl_load="YES"</literal></para>
<para>The &man.mac.portacl.4; module is used to limit binding to
- local <acronym>TCP</acronym> and <acronym>UDP</acronym> ports
- using a variety of <command>sysctl</command> variables.
- &man.mac.portacl.4; makes it possible to allow non-<systemitem
+ 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>
@@ -939,76 +904,54 @@ test: biba/high</screen>
<listitem>
<para><varname>security.mac.portacl.rules</varname>
- specifies the mac_portacl policy, which is a text string
- of the form: <literal>rule[,rule,...]</literal> with as
- many rules as needed. Each rule is of the form:
+ 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> parameter can be
- <literal>uid</literal> or <literal>gid</literal> and is
- used to interpret the <parameter>id</parameter> parameter
- as either a user id or group id, respectively. The
- <parameter>protocol</parameter> parameter is used to
- determine if the rule should apply to
- <acronym>TCP</acronym> or <acronym>UDP</acronym> by
- setting the parameter to <literal>tcp</literal> or
- <literal>udp</literal>. The final
+ <parameter>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.</para>
+ 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>
- <note>
- <para>Since the ruleset is interpreted directly by the kernel,
- only numeric values can be used for the user ID, group ID,
- and port parameters. Names cannot be used for users,
- groups, or services.</para>
- </note>
-
- <para>By default, ports below 1024 can only be used by or bound
- to privileged processes, which run as <systemitem
+ <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,
- this restriction has to be disabled by setting the
- &man.sysctl.8; variables
- <varname>net.inet.ip.portrange.reservedlow</varname> and
- <varname>net.inet.ip.portrange.reservedhigh</varname> to
- zero:</para>
+ 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
-net.inet.ip.portrange.reservedhigh=0</userinput></screen>
+&prompt.root; <userinput>sysctl net.inet.ip.portrange.reservedlow=0</userinput>
+&prompt.root; <userinput>sysctl net.inet.ip.portrange.reservedhigh=0</userinput></screen>
- <para>See the examples below or refer to &man.mac.portacl.4; for
- further information.</para>
-
- <sect3>
- <title>Examples</title>
-
- <para>Since the <systemitem class="username">root</systemitem>
- user should not be crippled by this policy, this example
- starts by setting the
+ <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>Next, allow the user with <acronym>UID</acronym> 80
- to bind to port 80. This allows the <systemitem
- class="username">www</systemitem> user to run a web server
- without ever having <systemitem
- class="username">root</systemitem> privilege.</para>
+ <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>The next example permits the user with the
- <acronym>UID</acronym> of 1001 to bind to the
- <acronym>TCP</acronym> ports 110 (<quote>pop3</quote>) and
- 995 (<quote>pop3s</quote>). This permits this user to start
- a server that accepts connections on ports 110 and
- 995.</para>
+ <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>
- </sect3>
</sect2>
<sect2 xml:id="mac-partition">
@@ -1025,13 +968,9 @@ net.inet.ip.portrange.reservedhigh=0</userinput></screen>
<para>Boot option:
<literal>mac_partition_load="YES"</literal></para>
- <para>The &man.mac.partition.4; policy will drop processes into
+ <para>The &man.mac.partition.4; policy drops processes into
specific <quote>partitions</quote> based on their
- <acronym>MAC</acronym> label. This module should be added to
- &man.loader.conf.5; so that it loads and enables the policy
- at system boot.</para>
-
- <para>Most configuration for this policy is done using
+ <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>
@@ -1051,26 +990,20 @@ net.inet.ip.portrange.reservedhigh=0</userinput></screen>
access <command>top</command> as well as many other commands
that must spawn a process.</para>
- <para>To set or drop utilities into a partition label, use the
- <command>setpmac</command> utility:</para>
-
- <screen>&prompt.root; <userinput>setpmac partition/13 top</userinput></screen>
-
<para>This example adds <command>top</command> to the label set
on users in the <literal>insecure</literal> class. All
processes spawned by users in the <literal>insecure</literal>
class will stay in the <literal>partition/13</literal>
label.</para>
- <sect3>
- <title>Examples</title>
+ <screen>&prompt.root; <userinput>setpmac partition/13 top</userinput></screen>
- <para>The following command will display the partition label
+ <para>This command displays the partition label
and the process list:</para>
<screen>&prompt.root; <userinput>ps Zax</userinput></screen>
- <para>This command will display another user's process
+ <para>This command displays another user's process
partition label and that user's currently running
processes:</para>
@@ -1081,19 +1014,6 @@ net.inet.ip.portrange.reservedhigh=0</userinput></screen>
class="username">root</systemitem>'s label unless the
&man.mac.seeotheruids.4; policy is loaded.</para>
</note>
-
- <para>A really crafty implementation could have all of the
- services disabled in <filename>/etc/rc.conf</filename> and
- started by a script that starts them with the proper
- labeling set.</para>
-
- <note>
- <para>The following policies support integer settings
- in place of the three default labels offered. These
- options, including their limitations, are further
- explained in the module manual pages.</para>
- </note>
- </sect3>
</sect2>
<sect2 xml:id="mac-mls">
@@ -1116,37 +1036,32 @@ net.inet.ip.portrange.reservedhigh=0</userinput></screen>
<para>In <acronym>MLS</acronym> environments, a
<quote>clearance</quote> level is set in the label of each
subject or object, along with compartments. Since these
- clearance or sensibility levels can reach numbers greater than
- several thousand; it would be a daunting task for any system
- administrator to thoroughly configure each subject or object.
- Thankfully, three <quote>instant</quote> labels are included
- in this policy.</para>
-
- <para>These labels are <literal>mls/low</literal>,
- <literal>mls/equal</literal> and <literal>mls/high</literal>.
- Since these labels are described in depth in the manual page,
- they will only get a brief description here:</para>
+ 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>The <literal>mls/low</literal> label contains a low
- configuration which permits it to be dominated by all
- other objects. Anything labeled with
+ <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 on to
- them.</para>
+ clearance level from writing or passing information to a
+ lower level.</para>
</listitem>
<listitem>
- <para>The <literal>mls/equal</literal> label should be
- placed on objects considered to be exempt from the
+ <para><literal>mls/equal</literal> should be
+ placed on objects which should be exempt from the
policy.</para>
</listitem>
<listitem>
- <para>The <literal>mls/high</literal> label is the highest
+ <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
@@ -1158,8 +1073,8 @@ net.inet.ip.portrange.reservedhigh=0</userinput></screen>
<itemizedlist>
<listitem>
- <para>A hierarchical security level with a set of non
- hierarchical categories.</para>
+ <para>A hierarchical security level with a set of
+ non-hierarchical categories.</para>
</listitem>
<listitem>
@@ -1167,7 +1082,7 @@ net.inet.ip.portrange.reservedhigh=0</userinput></screen>
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>
+ objects on its own level or above, but not beneath.</para>
</listitem>
<listitem>
@@ -1183,8 +1098,7 @@ net.inet.ip.portrange.reservedhigh=0</userinput></screen>
</itemizedlist>
<para>The following <command>sysctl</command> tunables are
- available for the configuration of special services and
- interfaces:</para>
+ available:</para>
<itemizedlist>
<listitem>
@@ -1212,32 +1126,27 @@ net.inet.ip.portrange.reservedhigh=0</userinput></screen>
</listitem>
</itemizedlist>
- <para>To manipulate the <acronym>MLS</acronym> labels, use
- &man.setfmac.8;. To assign a label to an object, issue the
- following command:</para>
+ <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>, issue the following command:</para>
+ <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>. This method will be
- explained after all policies are covered.</para>
-
- <sect3>
- <title>Planning Mandatory Sensitivity</title>
+ file to <command>setfmac</command>.</para>
- <para>When using the MLS policy module, an administrator plans
+ <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 during the configuration stage;.</para>
+ information.</para>
<para>Beyond the three basic label options, an administrator
may group users and groups as required to block the
@@ -1248,14 +1157,13 @@ net.inet.ip.portrange.reservedhigh=0</userinput></screen>
and <literal>Top Secret</literal>. Some administrators
instead create different groups based on project levels.
Regardless of the classification method, a well thought out
- plan must exist before implementing such a restrictive
+ plan must exist before implementing a restrictive
policy.</para>
- <para>Some example situations for the MLS policy module
+ <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>
- </sect3>
</sect2>
<sect2 xml:id="mac-biba">
@@ -1277,36 +1185,35 @@ net.inet.ip.portrange.reservedhigh=0</userinput></screen>
rules for information flow are slightly reversed. This is to
prevent the downward flow of sensitive information whereas the
<acronym>MLS</acronym> policy prevents the upward flow of
- sensitive information. Much of this section can apply to both
- policies.</para>
+ 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 an
+ 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>; as explained below:</para>
+ <literal>biba/high</literal>, where:</para>
<itemizedlist>
<listitem>
- <para>The <literal>biba/low</literal> label is considered
+ <para><literal>biba/low</literal> is considered
the lowest integrity an object or subject may have.
- Setting this on objects or subjects will block their write
- access to objects or subjects marked high. They still
- have read access though.</para>
+ 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>The <literal>biba/equal</literal> label should only be
+ <para><literal>biba/equal</literal> should only be
placed on objects considered to be exempt from the
policy.</para>
</listitem>
<listitem>
- <para>The <literal>biba/high</literal> label will permit
- writing to objects set at a lower label, but not permit
+ <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>
@@ -1317,8 +1224,8 @@ net.inet.ip.portrange.reservedhigh=0</userinput></screen>
<itemizedlist>
<listitem>
- <para>Hierarchical integrity level with a set of non
- hierarchical integrity categories.</para>
+ <para>Hierarchical integrity levels with a set of
+ non-hierarchical integrity categories.</para>
</listitem>
<listitem>
@@ -1336,12 +1243,12 @@ net.inet.ip.portrange.reservedhigh=0</userinput></screen>
</listitem>
<listitem>
- <para>Integrity levels instead of MLS sensitivity
+ <para>Integrity levels instead of <acronym>MLS</acronym> sensitivity
levels.</para>
</listitem>
</itemizedlist>
- <para>The following <command>sysctl</command> tunables can be
+ <para>The following tunables can be
used to manipulate the Biba policy:</para>
<itemizedlist>
@@ -1372,26 +1279,20 @@ net.inet.ip.portrange.reservedhigh=0</userinput></screen>
&prompt.root; <userinput>getfmac test</userinput>
test: biba/low</screen>
- <sect3>
- <title>Planning Mandatory Integrity</title>
-
- <para>Integrity, which is different from sensitivity,
- guarantees that the information will never be manipulated by
+ <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, objects, and both. It ensures that users will
- only be able to modify or access information they explicitly
- need to.</para>
-
- <para>The &man.mac.biba.4; security policy module permits an
- administrator to address which files and programs a user may
+ 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 free from threats and trusted by the system for that
+ 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. Users will be blocked access not only to data but to
- programs and utilities both before and after they start.
+ 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.
@@ -1405,7 +1306,7 @@ test: biba/low</screen>
<para>A lower integrity subject is unable to write to a higher
integrity subject and a higher integrity subject cannot
- observe or read a lower integrity object. Setting a label
+ 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
@@ -1413,11 +1314,10 @@ test: biba/low</screen>
A less useful implementation would be a personal
workstation, a machine used as a router, or a network
firewall.</para>
- </sect3>
</sect2>
<sect2 xml:id="mac-lomac">
- <title>The MAC LOMAC Module</title>
+ <title>The MAC Low-watermark Module</title>
<indexterm>
<primary>MAC LOMAC</primary>
@@ -1435,38 +1335,34 @@ test: biba/low</screen>
objects only after decreasing the integrity level to not
disrupt any integrity rules.</para>
- <para>The <acronym>MAC</acronym> version of the Low-watermark
- integrity policy works almost identically to Biba, but with
+ <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 LOMAC policy with an auxiliary grade, use the
- syntax <literal>lomac/10[2]</literal> where the number two
- (2) is the auxiliary grade.</para>
+ 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>The <acronym>MAC</acronym> LOMAC policy relies on the
+ <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 for
+ <literal>[auxgrade]</literal>. The policy may provide
greater compatibility and require less initial configuration
than Biba.</para>
- <sect3>
- <title>Examples</title>
-
<para>Like the Biba and <acronym>MLS</acronym> policies,
<command>setfmac</command> and <command>setpmac</command>
are used to place labels on system objects:</para>
<screen>&prompt.root; <userinput>setfmac /usr/home/trhodes lomac/high[low]</userinput>
-&prompt.root; <userinput>getfmac /usr/home/trhodes</userinput> lomac/high[low]</screen>
+&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> LOMAC
+ provided only by the <acronym>MAC</acronym> <acronym>LOMAC</acronym>
policy.</para>
- </sect3>
</sect2>
</sect1>