shorewall_code/docs/Shorewall-perl.xml

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  <articleinfo>
    <title>Shorewall-perl</title>

    <authorgroup>
      <author>
        <firstname>Tom</firstname>

        <surname>Eastep</surname>
      </author>
    </authorgroup>

    <pubdate><?dbtimestamp format="Y/m/d"?></pubdate>

    <copyright>
      <year>2007</year>

      <holder>Thomas M. Eastep</holder>
    </copyright>

    <legalnotice>
      <para>Permission is granted to copy, distribute and/or modify this
      document under the terms of the GNU Free Documentation License, Version
      1.2 or any later version published by the Free Software Foundation; with
      no Invariant Sections, with no Front-Cover, and with no Back-Cover
      Texts. A copy of the license is included in the section entitled
      <quote><ulink url="GnuCopyright.htm">GNU Free Documentation
      License</ulink></quote>.</para>
    </legalnotice>
  </articleinfo>

  <section>
    <title>Shorewall-perl - What is it?</title>

    <para>Shorewall-perl is a companion product to Shorewall. It requires
    Shorewall 3.4.2 or later.</para>

    <para>Shorewall-perl contains a re-implementation of the Shorewall
    compiler written in Perl. The advantages of using Shorewall-perl are over
    Shorewall-shell (the shell-based compiler included in earlier Shorewall
    3.x releases) are:</para>

    <itemizedlist>
      <listitem>
        <para>The Shorewall-perl compiler is much faster.</para>
      </listitem>

      <listitem>
        <para>The script generated by the compiler uses
        <command>iptables-restore</command> to instantiate the Netfilter
        configuration. So it runs much faster than the script generated by the
        Shorewall-shell compiler.</para>
      </listitem>

      <listitem>
        <para>The Shorewall-perl compiler does more thorough checking of the
        configuration than the Shorewall-shell compiler does.</para>
      </listitem>

      <listitem>
        <para>The error messages produced by the compiler are better, more
        consistent and always include the file name and line number where the
        error was detected.</para>
      </listitem>

      <listitem>
        <para>Going forward, the Shorewall-perl compiler will get all
        enhancements; the Shorewall-shell compiler will only get those
        enhancements that are easy to retrofit.</para>
      </listitem>
    </itemizedlist>
  </section>

  <section>
    <title>Shorewall-perl - The down side</title>

    <para>While there are advantages to using Shorewall-perl, there are also
    disadvantages:</para>

    <itemizedlist>
      <listitem>
        <para>There are a number of incompatibilities between the
        Shorewall-perl compiler and the earlier one.</para>

        <orderedlist>
          <listitem>
            <para>The Perl-based compiler requires the following capabilities
            in your kernel and iptables.</para>

            <itemizedlist>
              <listitem>
                <para>addrtype match (may be relaxed later)</para>
              </listitem>

              <listitem>
                <para>multiport match (will not be relaxed)</para>
              </listitem>
            </itemizedlist>

            <para>These capabilities are in current distributions.</para>
          </listitem>

          <listitem>
            <para>Now that Netfilter has features to deal reasonably with port
            lists, I see no reason to duplicate those features in Shorewall.
            The Shorewall-shell compiler goes to great pain (in some cases) to
            break very long port lists ( &gt; 15 where port ranges in lists
            count as two ports) into individual rules. In the new compiler,
            I'm avoiding the ugliness required to do that. The new compiler
            just generates an error if your list is too long. It will also
            produce an error if you insert a port range into a port list and
            you don't have extended multiport support.</para>
          </listitem>

          <listitem>
            <para>BRIDGING=Yes is not supported. The kernel code necessary to
            support this option was removed in Linux kernel 2.6.20.</para>
          </listitem>

          <listitem>
            <para>The BROADCAST column in the interfaces file is essentially
            unused; if you enter anything in this column but '-' or 'detect',
            you will receive a warning. This will be relaxed if and when the
            addrtype match requirement is relaxed.</para>
          </listitem>

          <listitem>
            <para>Because the compiler is now written in Perl, your
            compile-time extension scripts from earlier versions will no
            longer work. For now, if you want to use extension scripts, you
            will need to read the Perl code to see how the compiler operates
            internally. I will produce documentation before the first official
            release. Compile-time extension scripts are executed using the
            Perl 'do FILE' mechanism.</para>
          </listitem>

          <listitem>
            <para>The 'refresh' command is now synonymous with
            'restart'.</para>
          </listitem>

          <listitem>
            <para>Because the compiler is now written in Perl, your
            compile-time extension scripts from earlier versions will no
            longer work. Compile-time extension scripts are executed using the
            Perl 'eval `cat &lt;file&gt;`' mechanism. Be sure that each script
            returns a 'true' value; otherwise, the compiler will assume that
            the script failed and will abort the compilation.</para>

            <para>When a script is invoked, the $chainref scalar variable will
            hold a reference to a chain table entry.</para>

            <simplelist>
              <member>$chainref-&gt;{name} contains the name of the
              chain</member>

              <member>$chainref-&gt;{table} holds the table name</member>
            </simplelist>

            <para>To add a rule to the chain:</para>

            <simplelist>
              <member>add_rule $chainref, &lt;<replaceable>the
              rule</replaceable>&gt;</member>
            </simplelist>

            <para>Where</para>

            <simplelist>
              <member>&lt;<replaceable>the rule</replaceable>&gt; is a scalar
              argument holding the rule text. Do not include "-A
              &lt;<replaceable>chain name</replaceable>&gt;"</member>
            </simplelist>

            <para>Example:</para>

            <simplelist>
              <member>add_rule $chainref, '-j ACCEPT';</member>
            </simplelist>

            <para>To insert a rule into the chain:</para>

            <simplelist>
              <member>insert_rule $chainref,
              &lt;<replaceable>rulenum</replaceable>&gt;, &lt;<replaceable>the
              rule</replaceable>&gt;</member>
            </simplelist>

            <para>The log_rule_limit function works like it does in the shell
            compiler with two exceptions:</para>

            <itemizedlist>
              <listitem>
                <para>You pass the chain reference rather than the name of the
                chain.</para>
              </listitem>

              <listitem>
                <para>The commands are 'add' and 'insert' rather than '-A' and
                '-I'.</para>
              </listitem>

              <listitem>
                <para>There is only a single "pass as-is to iptables" argument
                (so you must quote that par</para>
              </listitem>
            </itemizedlist>

            <para>Example:</para>

            <programlisting>    log_rule_limit
              'info' , 
              $chainref , 
              $chainref-&gt;{name},
              'DROP' , 
              '',    #Limit
              '' ,   #Log tag
              'add';         </programlisting>
          </listitem>

          <listitem>
            <para>The <filename>/etc/shorewall/tos</filename> file now has
            zone-independent SOURCE and DEST columns as do all other files
            except the rules and policy files.</para>

            <para>The SOURCE column may be one of the following:</para>

            <simplelist>
              <member>[<command>all</command>:]&lt;<replaceable>address</replaceable>&gt;[,...]</member>

              <member>[<command>all</command>:]&lt;<replaceable>interface</replaceable>&gt;[:&lt;<replaceable>address</replaceable>&gt;[,...]]</member>

              <member><command>$FW</command>[:&lt;<replaceable>address</replaceable>&gt;[,...]]</member>
            </simplelist>

            <para>The DEST column may be one of the following:</para>

            <simplelist>
              <member>[<command>all</command>:]&lt;<replaceable>address</replaceable>&gt;[,...]</member>

              <member>[<command>all</command>:]&lt;<replaceable>interface</replaceable>&gt;[:&lt;<replaceable>address</replaceable>&gt;[,...]]</member>
            </simplelist>

            <para>This is a permanent change. The old zone-based rules have
            never worked right and this is a good time to replace them. I've
            tried to make the new syntax cover the most common cases without
            requiring change to existing files. In particular, it will handle
            the tos file released with Shorewall 1.4 and earlier.</para>
          </listitem>

          <listitem>
            <para>Currently, support for ipsets is untested. That will change
            with future pre-releases but one thing is certain -- Shorewall is
            now out of the ipset load/reload business. With scripts generated
            by the Perl-based Compiler, the Netfilter ruleset is never
            cleared. That means that there is no opportunity for Shorewall to
            load/reload your ipsets since that cannot be done while there are
            any current rules using ipsets.</para>

            <para>So:</para>

            <orderedlist numeration="upperroman">
              <listitem>
                <para>Your ipsets must be loaded before Shorewall starts. You
                are free to try to do that with the following code in
                <filename>/etc/shorewall/start</filename>:</para>

                <programlisting>if [ "$COMMAND" = start ]; then
    ipset -U :all: :all:
    ipset -F
    ipset -X
    ipset -R &lt; /etc/shorewall/ipsets
fi</programlisting>

                <para>The file <filename>/etc/shorewall/ipsets</filename> will
                normally be produced using the <command>ipset -S</command>
                command.</para>

                <para>The above will work most of the time but will fail in a
                <command>shorewall stop</command> - <command>shorewall
                start</command> sequence if you use ipsets in your
                routestopped file (see below).</para>
              </listitem>

              <listitem>
                <para>Your ipsets may not be reloaded until Shorewall is
                stopped or cleared.</para>
              </listitem>

              <listitem>
                <para>If you specify ipsets in your routestopped file then
                Shorewall must be cleared in order to reload your
                ipsets.</para>
              </listitem>
            </orderedlist>

            <para>As a consequence, scripts generated by the Perl-based
            compiler will ignore <filename>/etc/shorewall/ipsets</filename>
            and will issue a warning if you set SAVE_IPSETS=Yes in
            <filename>shorewall.conf</filename>.</para>
          </listitem>

          <listitem>
            <para>Because the configuration files (with the exception of
            <filename>/etc/shorewall/params</filename>) are now processed by
            the Shorewall-perl compiler rather than by the shell, only the
            basic forms of Shell expansion ($variable and ${variable}) are
            supported. The more exotic forms such as ${variable:=default} are
            not supported. Both variables defined in /etc/shorewall/params and
            environmental variables (exported by the shell) can be used in
            configuration files.</para>
          </listitem>

          <listitem>
            <para>USE_ACTIONS=No is not supported. That option is intended to
            minimize Shorewall's footprint in embedded applications. As a
            consequence, Default Macros are not supported.</para>
          </listitem>

          <listitem>
            <para>DELAYBLACKLISTLOAD=Yes is not supported. The entire ruleset
            is atomically loaded with one execution of
            <command>iptables-restore</command>.</para>
          </listitem>

          <listitem>
            <para>MAPOLDACTIONS=Yes is not supported. People should have
            converted to using macros by now.</para>
          </listitem>

          <listitem>
            <para>The pre Shorewall-3.0 format of the zones file is not
            supported; neither is the
            <filename>/etc/shorewall/ipsec</filename> file.</para>
          </listitem>
        </orderedlist>
      </listitem>
    </itemizedlist>
  </section>

  <section>
    <title>Shorewall-perl - Prerequisites</title>

    <para>In addition to Shorewall-3.4.2 or later, you need:</para>

    <itemizedlist>
      <listitem>
        <para>Perl (I use Perl 5.8.8 but other versions should work
        fine)</para>
      </listitem>

      <listitem>
        <para>Perl Cwd Module</para>
      </listitem>

      <listitem>
        <para>Perl File::Basename Module</para>
      </listitem>

      <listitem>
        <para>Perl File::Temp Module</para>
      </listitem>
    </itemizedlist>
  </section>

  <section>
    <title>Shorewall-perl - Installation</title>

    <caution>
      <para>Shorewall-perl is still part of the <ulink
      url="ReleaseModel.html">current development release</ulink>. Use it at
      your own risk.</para>
    </caution>

    <para>Either</para>

    <programlisting><command>tar -jxf shorewall-perl-3.9.1.tar.bz2</command>
<command>cd shorewall-perl-3.9.1</command>
<command>./install.sh</command></programlisting>

    <para>or</para>

    <programlisting><command>rpm -ivh shorewall-pl-3.9.1-1.noarch.rpm</command></programlisting>
  </section>

  <section>
    <title>Using Shorewall-perl</title>

    <para>By default, the Shorewall-shell compiler will be used.</para>

    <para>To use the Shorewall-perl compiler, add this to
    <filename>shorewall.conf</filename>:</para>

    <para>SHOREWALL_COMPILER=perl</para>

    <para>If you add this setting to
    <filename>/etc/shorewall/shorewall.conf</filename> then by default, the
    new compiler will be used on the system. If you add it to
    <filename>shorewall.conf</filename> in a separate directory (such as a
    Shorewall-lite export directory) then the new compiler will only be used
    when you compile from that directory.</para>

    <para>Regardless of the setting of SHOREWALL_COMPILER, there is one change
    in Shorewall operation that is triggered simply by installing
    Shorewall-perl. Your params file will be processed with the shell's '-a'
    option which causes any variables that you set or create in that file to
    be automatically exported. Since the params file is processed before
    <filename>shorewall.conf</filename>, using -a insures that the settings of
    your params variables are available to the new compiler should it's use be
    specified in <filename>shorewall.conf</filename>.</para>
  </section>
</article>