shorewall_code/Shorewall-docs2/Macros.xml

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  <articleinfo>
    <title>Macros</title>

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

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

      <author>
        <firstname>Cristian</firstname>

        <surname>Rodríguez</surname>
      </author>
    </authorgroup>

    <pubdate>2005-11-02</pubdate>

    <copyright>
      <year>2005</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>

  <caution>
    <para><emphasis role="bold">This article applies to Shorewall 3.0 and
    later. If you are running a version of Shorewall earlier than Shorewall
    3.0.0 then please see the documentation for that
    release.</emphasis></para>
  </caution>

  <section>
    <title>Overview of Shorewall Macros?</title>

    <para>Shorewall macros allow a symbolic name to be associated with a
    series of one or more iptables rules. The symbolic name may appear in the
    ACTION column of an <filename><ulink
    url="Documentation.htm#Rules">/etc/shorewall/rules</ulink></filename> file
    entry and in the TARGET column of an action in which case, the traffic
    matching that rules file entry will be passed to the series of iptables
    rules named by the macro.</para>

    <para>Macros can be thought of as templates. When a macro is invoked in an
    <filename>/etc/shorewall/rules</filename> entry, it may be qualified by a
    logging specification (log level and optionally a log tag). The presence
    of the log level/tag causes a modified series of rules to be generated in
    which each packet/rule match within the macro causes a log message to be
    generated.</para>

    <para>There are two types of Shorewall macros:</para>

    <orderedlist>
      <listitem>
        <para>Standard Macros. These macros are released as part of Shorewall.
        They are defined in macros.* files in <filename
        class="directory">/usr/share/shorewall</filename>. Each
        <filename>macros.*</filename> file has a comment at the beginning of
        the file that describes what the macro does. As an example, here is
        the definition of the <firstterm>SMB</firstterm> standard
        macro.</para>

        <programlisting>#
# Shorewall 3.0 /usr/share/shorewall/macro.SMB
#
#       Handle Microsoft SMB traffic. You need to invoke this macro in
#       both directions.
#
######################################################################################
#TARGET  SOURCE         DEST            PROTO   DEST    SOURCE          RATE    USER/
#                                               PORT    PORT(S)         LIMIT   GROUP
PARAM    -              -               udp     135,445
PARAM    -              -               udp     137:139
PARAM    -              -               udp     1024:   137
PARAM    -              -               tcp     135,139,445
#LAST LINE -- ADD YOUR ENTRIES BEFORE THIS ONE -- DO NOT REMOVE</programlisting>

        <para>If you wish to modify one of the standard macros, do not modify
        the definition in /usr/share/shorewall. Rather, copy the file to
        <filename class="directory">/etc/shorewall</filename> (or somewhere
        else on your CONFIG_PATH) and modify the copy.</para>
      </listitem>

      <listitem>
        <para>User-defined Macros. These macros are created by end-users. They
        are defined in macros.* files in /etc/shorewall or in another
        directory listed in your CONFIG_PATH (defined in <ulink
        url="Documentation.htm#Conf">/etc/shorewall/shorewall.conf</ulink>).</para>
      </listitem>
    </orderedlist>

    <para>Most Standard Macros are <firstterm>parameterized</firstterm>. That
    means that you specify what you want to do (ACCEPT, DROP, REJECT, etc.)
    when you invoke the macro. The SMB macro shown above is parameterized
    (note PARAM in the TARGET column). When invoking a parameterized macro,
    you follow the name of the macro with a slash ("/") and the action that
    you want to substitute for PARAM.</para>

    <para>Example:</para>

    <blockquote>
      <para>/etc/shorewall/rules:</para>

      <programlisting>#ACTION      SOURCE        DEST         PROTO   DEST PORT(S)
SMB/ACCEPT   loc           fw         </programlisting>

      <para>The above is equivalent to coding the following series of
      rules:</para>

      <programlisting>#TARGET      SOURCE        DEST         PROTO   DEST PORT(s)
ACCEPT       loc           fw           udp     135,445
ACCEPT       loc           fw           udp     137:139
ACCEPT       loc           fw           udp     1024:   137
ACCEPT       loc           fw           tcp     135,139,445</programlisting>
    </blockquote>

    <para>Logging is covered in <link linkend="Logging">a following
    section</link>. The other columns are treated as follows:</para>

    <variablelist>
      <varlistentry>
        <term>SOURCE and DEST</term>

        <listitem>
          <para>If the rule in the macro file specifies a value and the
          invocation of the rule also specifies a value then the value in the
          invocation is appended to the value in the rule using ":" as a
          separator.</para>

          <para>Example:</para>

          <blockquote>
            <para>/etc/shorewall/macro.SMTP</para>

            <programlisting>#TARGET          SOURCE   DEST            PROTO    DEST PORT(S)
PARAM            -        loc             tcp      25</programlisting>

            <para>/etc/shorewall/rules</para>

            <programlisting>#ACTION          SOURCE   DEST            PROTO    DEST PORT(S)
SMTP/DNAT:info   net      192.168.1.5</programlisting>

            <para>This would be equivalent to coding the following directly in
            /etc/shorewall/rules</para>

            <programlisting>#ACTION          SOURCE   DEST            PROTO    DEST PORT(S)
DNAT:info        net      loc:192.168.1.5 tcp      25</programlisting>
          </blockquote>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>Remaining columns</term>

        <listitem>
          <para>Any value in the invocation replaces the value in the rule in
          the macro.</para>
        </listitem>
      </varlistentry>
    </variablelist>

    <para>One remaining restriction must be mentioned: macros that are invoked
    from actions cannot themselves invoke other actions.</para>
  </section>

  <section>
    <title>Defining your own Macros</title>

    <para>To define a new macro:</para>

    <orderedlist>
      <listitem>
        <para>Macro names must be valid shell variable names ((must begin with
        a letter and be composed of letters, digits and underscore characters)
        as well as valid Netfilter chain names.</para>
      </listitem>

      <listitem>
        <para>Copy /usr/share/shorewall/macro.template to
        <filename>/etc/shorewall/macro.MacroName</filename> (for example, if
        your new macro name is <quote>Foo</quote> then copy
        <filename>/usr/share/shorewall/macro.template</filename> to
        <filename>/etc/shorewall/macro.Foo</filename>).</para>
      </listitem>

      <listitem>
        <para>Now modify the new file to define the new macro.</para>
      </listitem>
    </orderedlist>

    <para>Columns in the macro.template file are as follows:</para>

    <itemizedlist>
      <listitem>
        <para>ACTION - ACCEPT, DROP, REJECT, DNAT, DNAT-, REDIRECT, CONTINUE,
        LOG, QUEUE, PARAM or an action name. Note that a macro may not invoke
        another macro.</para>

        <simplelist>
          <member>ACCEPT - allow the connection request</member>

          <member>ACCEPT+ - like ACCEPT but also excludes the connection from
          any subsequent DNAT[-] or REDIRECT[-] rules.</member>

          <member>NONAT - Excludes the connection from any subsequent DNAT[-]
          or REDIRECT[-] rules but doesn't generate a rule to accept the
          traffic.</member>

          <member>DROP - ignore the request</member>

          <member>REJECT - disallow the request and return an icmp unreachable
          or an RST packet.</member>

          <member>DNAT - Forward the request to another address (and
          optionally another port).</member>

          <member>DNAT- - Advanced users only. Like DNAT but only generates
          the DNAT iptables rule and not the companion ACCEPT rule.</member>

          <member>SAME - Similar to DNAT except that the port may not be
          remapped and when multiple server addresses are listed, all requests
          from a given remote system go to the same server.</member>

          <member>SAME- - Advanced users only. Like SAME but only generates
          the SAME iptables rule and not the companion ACCEPT rule.</member>

          <member>REDIRECT - Redirect the request to a local port on the
          firewall.</member>

          <member>REDIRECT- - Advanced users only. Like REDIRECT but only
          generates the REDIRECT iptables rule and not the companion ACCEPT
          rule.</member>

          <member>CONTINUE - (For experts only). Do not process any of the
          following rules for this (source zone,destination zone). If The
          source and/or destination If the address falls into a zone defined
          later in /etc/shorewall/zones, this connection request will be
          passed to the rules defined for that (those) zone(s).</member>

          <member>LOG - Simply log the packet and continue.</member>

          <member>QUEUE - Queue the packet to a user-space application such as
          ftwall (http://p2pwall.sf.net).</member>
        </simplelist>

        <para>The ACTION may optionally be followed by ":" and a syslog log
        level (e.g, REJECT:info or DNAT:debug). This causes the packet to be
        logged at the specified level.</para>
      </listitem>

      <listitem>
        <para>SOURCE - Source hosts to which the rule applies. A
        comma-separated list of subnets and/or hosts. Hosts may be specified
        by IP or MAC address; mac addresses must begin with <quote>~</quote>
        and must use <quote>-</quote> as a separator.</para>

        <para>Alternatively, clients may be specified by interface name. For
        example, eth1 specifies a client that communicates with the firewall
        system through eth1. This may be optionally followed by another colon
        (<quote>:</quote>) and an IP/MAC/subnet address as described above
        (e.g. eth1:192.168.1.5).</para>
      </listitem>

      <listitem>
        <para>DEST - Location of Server. Same as above with the exception that
        MAC addresses are not allowed.</para>

        <para>Unlike in the SOURCE column, you may specify a range of up to
        256 IP addresses using the syntax &lt;<emphasis>first
        ip</emphasis>&gt;-&lt;<emphasis>last ip</emphasis>&gt;.</para>
      </listitem>

      <listitem>
        <para>PROTO - Protocol - Must be <quote>tcp</quote>,
        <quote>udp</quote>, <quote>icmp</quote>, a number, or
        <quote>all</quote>.</para>
      </listitem>

      <listitem>
        <para>DEST PORT(S) - Destination Ports. A comma-separated list of Port
        names (from <filename>/etc/services</filename>), port numbers or port
        ranges; if the protocol is <quote>icmp</quote>, this column is
        interpreted as the destination icmp-type(s).</para>

        <para>A port range is expressed as &lt;<emphasis>low
        port</emphasis>&gt;:&lt;<emphasis>high port</emphasis>&gt;.</para>

        <para>This column is ignored if PROTOCOL = all but must be entered if
        any of the following fields are supplied. In that case, it is
        suggested that this field contain <quote>-</quote>.</para>

        <para>If your kernel contains multi-port match support, then only a
        single Netfilter rule will be generated if in this list and in the
        CLIENT PORT(S) list below:</para>

        <orderedlist>
          <listitem>
            <para>There are 15 or less ports listed.</para>
          </listitem>

          <listitem>
            <para>No port ranges are included.</para>
          </listitem>
        </orderedlist>

        <para>Otherwise, a separate rule will be generated for each
        port.</para>
      </listitem>

      <listitem>
        <para>SOURCE PORT(S) - Port(s) used by the client. If omitted, any
        source port is acceptable. Specified as a comma-separated list of port
        names, port numbers or port ranges.</para>

        <para>If you don't want to restrict client ports but need to specify
        an ADDRESS in the next column, then place "-" in this column.</para>

        <para>If your kernel contains multi-port match support, then only a
        single Netfilter rule will be generated if in this list and in the
        DEST PORT(S) list above:</para>

        <orderedlist>
          <listitem>
            <para>There are 15 or less ports listed.</para>
          </listitem>

          <listitem>
            <para>No port ranges are included.</para>
          </listitem>
        </orderedlist>

        <para>Otherwise, a separate rule will be generated for each
        port.</para>
      </listitem>

      <listitem>
        <para>RATE LIMIT - You may rate-limit the rule by placing a value in
        this column:</para>

        <para><programlisting>     &lt;<emphasis>rate</emphasis>&gt;/&lt;<emphasis>interval</emphasis>&gt;[:&lt;<emphasis>burst</emphasis>&gt;]</programlisting>where
        &lt;<emphasis>rate</emphasis>&gt; is the number of connections per
        &lt;<emphasis>interval</emphasis>&gt; (<quote>sec</quote> or
        <quote>min</quote>) and &lt;<emphasis>burst</emphasis>&gt; is the
        largest burst permitted. If no &lt;<emphasis>burst</emphasis>&gt; is
        given, a value of 5 is assumed. There may be no whitespace embedded in
        the specification.</para>

        <para><programlisting>     Example: 10/sec:20</programlisting></para>
      </listitem>

      <listitem>
        <para>USER/GROUP - For output rules (those with the firewall as their
        source), you may control connections based on the effective UID and/or
        GID of the process requesting the connection. This column can contain
        any of the following:</para>

        <simplelist>
          <member>[!]&lt;<emphasis>user number</emphasis>&gt;[:]</member>

          <member>[!]&lt;<emphasis>user name</emphasis>&gt;[:]</member>

          <member>[!]:&lt;<emphasis>group number</emphasis>&gt;</member>

          <member>[!]:&lt;<emphasis>group name</emphasis>&gt;</member>

          <member>[!]&lt;<emphasis>user
          number</emphasis>&gt;:&lt;<emphasis>group
          number</emphasis>&gt;</member>

          <member>[!]&lt;<emphasis>user
          name</emphasis>&gt;:&lt;<emphasis>group
          number</emphasis>&gt;</member>

          <member>[!]&lt;<emphasis>user
          inumber</emphasis>&gt;:&lt;<emphasis>group
          name</emphasis>&gt;</member>

          <member>[!]&lt;<emphasis>user
          name</emphasis>&gt;:&lt;<emphasis>group name</emphasis>&gt;</member>

          <member>[!]+&lt;<emphasis>program name</emphasis>&gt; (Note: support
          for this form was removed from Netfilter in kernel version
          2.6.14).</member>
        </simplelist>
      </listitem>
    </itemizedlist>

    <para>Omitted column entries should be entered using a dash ("-:).</para>

    <para>Example:</para>

    <para><phrase><filename>/etc/shorewall/macro.LogAndAccept</filename></phrase><programlisting>     LOG:info
     ACCEPT</programlisting></para>

    <para>To use your macro, in <filename>/etc/shorewall/rules</filename> you
    might do something like:</para>

    <programlisting>#ACTION      SOURCE      DEST        PROTO    DEST PORT(S)
LogAndAccept loc         $FW         tcp      22</programlisting>
  </section>

  <section id="Logging">
    <title>Macros and Logging</title>

    <para>Specifying a log level in a rule that invokes a user- or
    Shorewall-defined action will cause each rule in the macro to be logged
    with the specified level (and tag).</para>

    <para>The extent to which logging of macro rules occur is governed by the
    following:</para>

    <orderedlist>
      <listitem>
        <para>When you invoke a macro and specify a log level, only those
        rules in the macro that have no log level will be changed to log at
        the level specified at the action invocation.</para>

        <para>Example:</para>

        <para>/etc/shorewall/macro.foo</para>

        <programlisting>#ACTION      SOURCE     DEST     PROTO    DEST PORT(S)
ACCEPT       -          -        tcp      22
bar:info</programlisting>

        <para>/etc/shorewall/rules:</para>

        <programlisting>#ACTION      SOURCE     DEST     PROTO    DEST PORT(S)
foo:debug    $FW        net</programlisting>

        <para>Logging in the invoked 'foo' macro will be as if foo had been
        defined as:</para>

        <programlisting>#ACTION      SOURCE     DEST     PROTO    DEST PORT(S)
ACCEPT:debug -          -        tcp      22
bar:info</programlisting>
      </listitem>

      <listitem>
        <para>If you follow the log level with "!" then logging will be at
        that level for all rules recursively invoked by the macro.</para>

        <para>Example:</para>

        <para>/etc/shorewall/macro.foo</para>

        <programlisting>#ACTION      SOURCE     DEST     PROTO    DEST PORT(S)
ACCEPT       -          -        tcp      22
bar:info</programlisting>

        <para>/etc/shorewall/rules:</para>

        <programlisting>#ACTION      SOURCE     DEST     PROTO    DEST PORT(S)
foo:debug!   $FW        net</programlisting>

        <para>Logging in the invoked 'foo' macro will be as if foo had been
        defined as:</para>

        <programlisting>#ACTION      SOURCE     DEST     PROTO    DEST PORT(S)
ACCEPT:debug -          -        tcp      22
bar:debug</programlisting>
      </listitem>
    </orderedlist>
  </section>

  <section>
    <title>How do I know if I should create an Action or a Macro?</title>

    <para>While actions and macros perform similar functions, in any given
    case you will generally find that one is more appropriate than the
    other.</para>

    <orderedlist>
      <listitem>
        <para>You can not associate an Extension Script with a macro <ulink
        url="Actions.html#Extension">the way that you can with an
        Action</ulink>. So if you need access to iptables features not
        directly supported by Shorewall then you must use an action.</para>
      </listitem>

      <listitem>
        <para>Macros are expanded in-line while each action is it's own chain.
        So if there are a lot of rules involved in your new action/macro then
        it is generally better to use an action than a macro. Only the packets
        selected when you invoke the action are directed to the corresponding
        chain. On the other hand, if there are only one or two rules involved
        in what you want to do then a macro is more efficient.</para>
      </listitem>
    </orderedlist>
  </section>
</article>