forked from extern/shorewall_code
824 lines
31 KiB
XML
824 lines
31 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
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"http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd">
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<article>
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<!--$Id$-->
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<articleinfo>
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<title>Actions</title>
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<authorgroup>
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<author>
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<firstname>Tom</firstname>
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<surname>Eastep</surname>
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</author>
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</authorgroup>
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<pubdate><?dbtimestamp format="Y/m/d"?></pubdate>
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<copyright>
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<year>2005</year>
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<year>2007</year>
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<year>2008</year>
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<year>2009</year>
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<year>2010</year>
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<holder>Thomas M. Eastep</holder>
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</copyright>
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<legalnotice>
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<para>Permission is granted to copy, distribute and/or modify this
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document under the terms of the GNU Free Documentation License, Version
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1.2 or any later version published by the Free Software Foundation; with
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no Invariant Sections, with no Front-Cover, and with no Back-Cover
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||
Texts. A copy of the license is included in the section entitled
|
||
<quote><ulink url="GnuCopyright.htm">GNU Free Documentation
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License</ulink></quote>.</para>
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||
</legalnotice>
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</articleinfo>
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||
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<caution>
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<para><emphasis role="bold">This article applies to Shorewall 4.3 and
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later. If you are running a version of Shorewall earlier than Shorewall
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4.3.5 then please see the documentation for that
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release.</emphasis></para>
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</caution>
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<section id="Intro">
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<title>What are Shorewall Actions?</title>
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<para>Shorewall actions allow a symbolic name to be associated with a
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series of one or more iptables rules. The symbolic name may appear in the
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ACTION column of an <filename><ulink
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url="manpages/shorewall-rules.html">/etc/shorewall/rules</ulink></filename>
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||
file entry, in which case the traffic matching that rules file entry will
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be passed to the series of iptables rules named by the action.</para>
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<para>Actions can be thought of as templates. When an action is invoked in
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an <filename>/etc/shorewall/rules</filename> entry, it may be qualified by
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a logging specification (log level and optionally a log tag). The presence
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of the log level/tag causes a modified series of rules to be generated in
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which each packet/rule match within the action causes a log message to be
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generated.</para>
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<para>For readers familiar with iptables, actions are the way in which you
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can create your own filter-table chains.</para>
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<para>There are three types of Shorewall actions:</para>
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<orderedlist>
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<listitem>
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<para>Built-in Actions. These actions are known by the Shorewall code
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itself. They are listed in the comments at the top of the file
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<filename>/usr/share/shorewall/actions.std</filename>.</para>
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</listitem>
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<listitem>
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<para>Standard Actions. These actions are released as part of
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Shorewall. They are listed in the file
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<filename>/usr/share/shorewall/actions.std</filename> and are defined
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in the corresponding action.* files in <filename
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class="directory">/usr/share/shorewall</filename>. Each
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<filename>action.*</filename> file has a comment at the beginning of
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the file that describes what the action does. As an example, here is
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the definition of the <firstterm>AllowSMB</firstterm> standard action
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from Shorewall version 2.2.</para>
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<programlisting>#
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# Shorewall 2.2 /usr/share/shorewall/action.AllowSMB
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#
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# Allow Microsoft SMB traffic. You need to invoke this action in
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# both directions.
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#
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######################################################################################
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#TARGET SOURCE DEST PROTO DEST SOURCE RATE USER/
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# PORT PORT(S) LIMIT GROUP
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ACCEPT - - udp 135,445
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ACCEPT - - udp 137:139
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ACCEPT - - udp 1024: 137
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ACCEPT - - tcp 135,139,445
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#LAST LINE -- ADD YOUR ENTRIES BEFORE THIS ONE -- DO NOT REMOVE</programlisting>
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<para>If you wish to modify one of the standard actions, do not modify
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the definition in <filename
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class="directory">/usr/share/shorewall</filename>. Rather, copy the
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file to <filename class="directory">/etc/shorewall</filename> (or
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somewhere else on your CONFIG_PATH) and modify the copy.</para>
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<para>Standard Actions have been largely replaced by <ulink
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url="Macros.html">macros</ulink> .</para>
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</listitem>
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<listitem>
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<para>User-defined Actions. These actions are created by end-users.
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They are listed in the file
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<filename>/etc/shorewall/actions</filename> and are defined in
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<filename>action.*</filename> files in <filename
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class="directory">/etc/shorewall</filename> or in another directory
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listed in your CONFIG_PATH (defined in <filename><ulink
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url="manpages/shorewall.conf.html">/etc/shorewall/shorewall.conf</ulink></filename>).</para>
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</listitem>
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</orderedlist>
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</section>
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<section id="Default">
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<title>Default Actions (Formerly Common Actions)</title>
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<para>Shorewall allows the association of a <firstterm>default
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action</firstterm> with policies. A separate default action may be
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associated with ACCEPT, DROP, REJECT, QUEUE and NFQUEUE policies. Default
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actions provide a way to invoke a set of common rules just before the
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policy is enforced. Default actions accomplish two goals:</para>
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<orderedlist>
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||
<listitem>
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<para>Relieve log congestion. Default actions typically include rules
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to silently drop or reject traffic that would otherwise be logged when
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the policy is enforced.</para>
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</listitem>
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<listitem>
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<para>Ensure correct operation. Default actions can also avoid common
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pitfalls like dropping connection requests on port TCP port 113. If
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these connections are dropped (rather than rejected) then you may
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encounter problems connecting to Internet services that utilize the
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AUTH protocol of client authentication<footnote>
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<para>AUTH is actually pretty silly on today's Internet but it's
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amazing how many servers still employ it.</para>
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</footnote>.</para>
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</listitem>
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</orderedlist>
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<para>Shorewall supports default actions for the ACCEPT, REJECT, DROP,
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QUEUE and NFQUEUE policies. These default actions are specified in the
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<filename>/etc/shorewall/shorewall.conf</filename> file using the
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ACCEPT_DEFAULT, REJECT_DEFAULT, DROP_DEFAULT, QUEUE_DEFAULT and
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NFQUEUE_DEFAULT options respectively. Policies whose default is set to a
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value of <quote>none</quote> have no default action.</para>
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<para>In addition, the default specified in
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<filename>/etc/shorewall/shorewall.conf</filename> may be overridden by
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specifying a different action in the POLICY column of <filename><ulink
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url="manpages/shorewall-policy.html">/etc/shorewall/policy</ulink></filename>.</para>
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<important>
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<para>Entries in the DROP and REJECT default actions <emphasis
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role="bold">ARE NOT THE CAUSE OF CONNECTION PROBLEMS</emphasis>.
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Remember — default actions are only invoked immediately before the
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packet is going to be dropped or rejected anyway!!!</para>
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</important>
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<para>Beginning with Shorewall 4.4.21, the standard Drop and Reject
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options are parameterized. Each has five parameters as follows:</para>
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<informaltable>
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<tgroup cols="4">
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<tbody>
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<row>
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<entry>ACTION</entry>
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<entry>PARAMETER</entry>
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<entry>VALUE</entry>
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<entry>DEFAULT</entry>
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</row>
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<row>
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<entry>Drop</entry>
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<entry>1</entry>
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<entry>Either '-' or 'audit'. 'audit' causes auditing by the
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builtin actions invoked by Drop</entry>
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<entry>-</entry>
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</row>
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<row>
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<entry>Drop</entry>
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<entry>2</entry>
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<entry>Determines what to do with Auth requests</entry>
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<entry>REJECT or A_REJECT depending on the setting of parameter
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1</entry>
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</row>
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<row>
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<entry>Drop</entry>
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<entry>3</entry>
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<entry>Determines what to do with SMB</entry>
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<entry>DROP or A_DROP depending on the setting of parameter
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1</entry>
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</row>
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<row>
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<entry>Reject</entry>
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<entry>1</entry>
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<entry>Either '-' or 'audit'. 'audit' causes auditing by the
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builtin actions invoked by Drop</entry>
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<entry>-</entry>
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</row>
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<row>
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<entry>Reject</entry>
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<entry>2</entry>
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<entry>Determines what to do with Auth requests</entry>
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<entry>REJECT or A_REJECT depending on the setting of parameter
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1</entry>
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</row>
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<row>
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<entry>Reject</entry>
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<entry>3</entry>
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<entry>Determines what to do with SMB</entry>
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<entry>REJECT or A_REJECT depending on the setting of parameter
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1</entry>
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</row>
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||
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<row>
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<entry>Both</entry>
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||
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<entry>4</entry>
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<entry>Determines what to do with accepted critical ICMP
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packets.</entry>
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||
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<entry>ACCEPT or A_ACCEPT depending on the setting of parameter
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1</entry>
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</row>
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<row>
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<entry>Both</entry>
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<entry>5</entry>
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<entry>Determines what to do with late-arriving DNS replies
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(source port 53) or UPnP (udp port 1900).</entry>
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<entry>DROP or A_DROP depending on the setting of parameter
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1.</entry>
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</row>
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</tbody>
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</tgroup>
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</informaltable>
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||
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<para>The parameters may be specified in either shorewall.conf (e.g.,
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DROP_DEFAULT=<emphasis role="bold">Drop(-,DROP)</emphasis> or in the
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POLICY column of <ulink
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url="manpages/shorewall-policy.html">shorewall-policy</ulink>(5) (e.g.,
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||
DROP:<emphasis role="bold">Drop(audit)</emphasis>:audit).</para>
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||
</section>
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||
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||
<section id="Defining">
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||
<title>Defining your own Actions</title>
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||
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||
<para>Before defining a new action, you should evaluate whether your goal
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||
can be best accomplished using an action or a
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||
<firstterm>macro</firstterm>. See <ulink url="Macros.html">this
|
||
article</ulink> for details.</para>
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||
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||
<para>To define a new action:</para>
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||
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||
<orderedlist>
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||
<listitem>
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||
<para>Add a line to <filename>/etc/shorewall/actions</filename> that
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||
names your new action. Action names must be valid shell variable names
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||
(must begin with a letter and be composed of letters, digits and
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underscore characters) as well as valid Netfilter chain names. If you
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||
intend to log from the action, the name must have a maximum of 11
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||
characters. It is recommended that the name you select for a new
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||
action begins with a capital letter; that way, the name won't conflict
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||
with a Shorewall-defined chain name.</para>
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||
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||
<para>Shorewall includes pre-defined actions for DROP and REJECT --
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see above.</para>
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||
</listitem>
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||
|
||
<listitem>
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||
<para>Once you have defined your new action name (ActionName), then
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||
copy <filename>/usr/share/shorewall/action.template</filename> to
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||
<filename>/etc/shorewall/action.ActionName</filename> (for example, if
|
||
your new action name is <quote>Foo</quote> then copy
|
||
<filename>/usr/share/shorewall/action.template</filename> to
|
||
<filename>/etc/shorewall/action.Foo</filename>).</para>
|
||
</listitem>
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||
|
||
<listitem>
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||
<para>Now modify the new file to define the new action.</para>
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||
</listitem>
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||
</orderedlist>
|
||
|
||
<section>
|
||
<title>Shorewall 4.4.16 and Later.</title>
|
||
|
||
<para>Beginning with Shorewall 4.4.16, the columns in action.template
|
||
are the same as those in shorewall-rules (5). The first non-commentary
|
||
line in the template must be</para>
|
||
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||
<programlisting>FORMAT 2</programlisting>
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||
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||
<para>When using Shorewall 4.4.16 or later, there are no restrictions
|
||
regarding which targets can be used within your action.</para>
|
||
|
||
<para>The SOURCE and DEST columns in the action file may not include
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||
zone names; those are given when the action is invoked.</para>
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||
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||
<para>Additionally, it is possible to pass parameters to an action, when
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it is invoked in the rules file or in another action.</para>
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||
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||
<para>Here's a trivial example:</para>
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||
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||
<para>/etc/shorewall/action.A:</para>
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||
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<programlisting>#TARGET SOURCE DEST PROTO DEST SOURCE ORIGINAL
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||
# PORT(S) PORT(S) DEST
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||
FORMAT 2
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||
$1 - - tcp 80 - 1.2.3.4</programlisting>
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||
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||
<para>/etc/shorewall/rules:</para>
|
||
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||
<programlisting>#TARGET SOURCE DEST PROTO DEST SOURCE ORIGINAL
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||
# PORT(S) PORT(S) DEST
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||
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||
A(REDIRECT) net fw</programlisting>
|
||
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||
<para>The above is equivalent to this rule:</para>
|
||
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||
<programlisting>#TARGET SOURCE DEST PROTO DEST SOURCE ORIGINAL
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||
# PORT(S) PORT(S) DEST
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||
REDIRECT net - tcp 80 - 1.2.3.4</programlisting>
|
||
|
||
<para>You can 'omit' parameters by using '-'.</para>
|
||
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||
<para>Example: ACTION(REDIRECT,-,info)</para>
|
||
|
||
<para>In the above example, $2 would expand to nothing.</para>
|
||
|
||
<para>If you want to make '-' a parameter value, use '--' (e.g.,
|
||
ACTION(REDIRECT,--.info)).</para>
|
||
|
||
<para>Beginning with Shorewall 4.4.21, you can specify the default
|
||
values of your FORMAT-2 actions:</para>
|
||
|
||
<programlisting>DEFAULTS <replaceable>def1</replaceable>,<replaceable>def2</replaceable>,...</programlisting>
|
||
|
||
<para>where <replaceable>def1</replaceable> is the default value for the
|
||
first parameter, <replaceable>def2</replaceable> is the default value
|
||
for the second parameter and so on. You can specify an empty default
|
||
using '-' (e.g. DEFAULTS DROP,-,audit).</para>
|
||
|
||
<para>The DEFAULTS directive also determines the maximum number of
|
||
parameters that an action may have. If more parameters are passed than
|
||
have default values, an error message is issued. </para>
|
||
</section>
|
||
|
||
<section>
|
||
<title>Shorewall 4.4.15 and Earlier.</title>
|
||
|
||
<para>Prior to 4.4.16, columns in the
|
||
<filename>action.template</filename> file were as follows:</para>
|
||
|
||
<itemizedlist>
|
||
<listitem>
|
||
<para>TARGET - Must be ACCEPT, DROP, REJECT, LOG, CONTINUE, QUEUE or
|
||
an <<emphasis>action</emphasis>> where
|
||
<<emphasis>action</emphasis>> is a previously-defined action
|
||
(that is, it must precede the action being defined in this file in
|
||
your <filename>/etc/shorewall/actions</filename> file). These
|
||
actions have the same meaning as they do in the
|
||
<filename>/etc/shorewall/rules</filename> file (CONTINUE terminates
|
||
processing of the current action and returns to the point where that
|
||
action was invoked). The TARGET may optionally be followed by a
|
||
colon (<quote>:</quote>) and a syslog log level (e.g, REJECT:info or
|
||
ACCEPT:debugging). This causes the packet to be logged at the
|
||
specified level. You may also specify ULOG (must be in upper case)
|
||
as a log level. This will log to the ULOG target for routing to a
|
||
separate log through use of ulogd (<ulink
|
||
url="http://www.netfilter.org/projects/ulogd/index.html">http://www.netfilter.org/projects/ulogd/index.html</ulink>).</para>
|
||
|
||
<para>You may also use a <ulink url="Macros.html">macro</ulink> in
|
||
your action provided that the macro's expansion only results in the
|
||
ACTIONs ACCEPT, DROP, REJECT, LOG, CONTINUE, or QUEUE. See
|
||
<filename>/usr/share/shorewall/action.Drop</filename> for an example
|
||
of an action that users macros extensively.</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>
|
||
</listitem>
|
||
|
||
<listitem>
|
||
<para>PROTO - Protocol - Must be <quote>tcp</quote>,
|
||
<quote>udp</quote>, <quote>icmp</quote>, a protocol 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 <<emphasis>low
|
||
port</emphasis>>:<<emphasis>high port</emphasis>>.</para>
|
||
|
||
<para>This column is ignored if PROTO = <quote>all</quote>, 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>
|
||
</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
|
||
any of the subsequent fields, then place <quote>-</quote> in this
|
||
column.</para>
|
||
</listitem>
|
||
|
||
<listitem>
|
||
<para>RATE LIMIT - You may rate-limit the rule by placing a value in
|
||
this column:</para>
|
||
|
||
<para><programlisting> <<emphasis>rate</emphasis>>/<<emphasis>interval</emphasis>>[:<<emphasis>burst</emphasis>>]</programlisting>where
|
||
<<emphasis>rate</emphasis>> is the number of connections per
|
||
<<emphasis>interval</emphasis>> (<quote>sec</quote> or
|
||
<quote>min</quote>) and <<emphasis>burst</emphasis>> is the
|
||
largest burst permitted. If no <<emphasis>burst</emphasis>> 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>[!]<<emphasis>user number</emphasis>>[:]</member>
|
||
|
||
<member>[!]<<emphasis>user name</emphasis>>[:]</member>
|
||
|
||
<member>[!]:<<emphasis>group number</emphasis>></member>
|
||
|
||
<member>[!]:<<emphasis>group name</emphasis>></member>
|
||
|
||
<member>[!]<<emphasis>user
|
||
number</emphasis>>:<<emphasis>group
|
||
number</emphasis>></member>
|
||
|
||
<member>[!]<<emphasis>user
|
||
name</emphasis>>:<<emphasis>group
|
||
number</emphasis>></member>
|
||
|
||
<member>[!]<<emphasis>user
|
||
inumber</emphasis>>:<<emphasis>group
|
||
name</emphasis>></member>
|
||
|
||
<member>[!]<<emphasis>user
|
||
name</emphasis>>:<<emphasis>group
|
||
name</emphasis>></member>
|
||
|
||
<member>[!]+<<emphasis>program name</emphasis>> (Note:
|
||
support for this form was removed from Netfilter in kernel version
|
||
2.6.14).</member>
|
||
</simplelist>
|
||
</listitem>
|
||
|
||
<listitem>
|
||
<para>MARK</para>
|
||
|
||
<para><simplelist>
|
||
<member>[!]<<emphasis>value</emphasis>>[/<<emphasis>mask</emphasis>>][:C]</member>
|
||
</simplelist></para>
|
||
|
||
<para>Defines a test on the existing packet or connection mark. The
|
||
rule will match only if the test returns true.</para>
|
||
|
||
<para>If you don’t want to define a test but need to specify
|
||
anything in the subsequent columns, place a <quote>-</quote> in this
|
||
field.<simplelist>
|
||
<member>! — Inverts the test (not equal)</member>
|
||
|
||
<member><<emphasis>value</emphasis>> — Value of the packet
|
||
or connection mark.</member>
|
||
|
||
<member><<emphasis>mask</emphasis>> —A mask to be applied
|
||
to the mark before testing.</member>
|
||
|
||
<member>:C — Designates a connection mark. If omitted, the
|
||
packet mark’s value is tested. This option is only supported by
|
||
Shorewall-perl</member>
|
||
</simplelist></para>
|
||
</listitem>
|
||
</itemizedlist>
|
||
|
||
<para>Omitted column entries should be entered using a dash
|
||
(<quote>-</quote>).</para>
|
||
|
||
<para>Example:</para>
|
||
|
||
<para><filename>/etc/shorewall/actions</filename>:</para>
|
||
|
||
<para><programlisting> #ACTION COMMENT (place '# ' below the 'C' in comment followed by
|
||
# v a comment describing the action)
|
||
LogAndAccept # LOG and ACCEPT a connection</programlisting><emphasis
|
||
role="bold">Note:</emphasis> If your
|
||
<filename>/etc/shorewall/actions</filename> file doesn't have an
|
||
indication where to place the comment, put the <quote>#</quote> in
|
||
column 21.</para>
|
||
|
||
<para><phrase><filename>/etc/shorewall/action.LogAndAccept</filename></phrase><programlisting> LOG:info
|
||
ACCEPT</programlisting></para>
|
||
|
||
<para>Placing a comment on the line causes the comment to appear in the
|
||
output of the <command>shorewall show actions</command> command.</para>
|
||
|
||
<para>To use your action, 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>
|
||
|
||
<section id="Logging">
|
||
<title>Actions and Logging</title>
|
||
|
||
<para>Specifying a log level in a rule that specifies a user-defined or
|
||
Shorewall-defined action will cause each rule in the action to be logged
|
||
with the specified level (and tag).</para>
|
||
|
||
<para>The extent to which logging of action rules occur is governed by the
|
||
following:</para>
|
||
|
||
<orderedlist>
|
||
<listitem>
|
||
<para>When you invoke an action and specify a log level, only those
|
||
rules in the action 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/action.foo</para>
|
||
|
||
<programlisting>#TARGET 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 invoke <quote>foo</quote> action will be as if
|
||
foo had been defined as:</para>
|
||
|
||
<programlisting>#TARGET SOURCE DEST PROTO DEST PORT(S)
|
||
ACCEPT:debug - - tcp 22
|
||
bar:info</programlisting>
|
||
</listitem>
|
||
|
||
<listitem>
|
||
<para>If you follow the log level with <quote>!</quote> then logging
|
||
will be set at that level for all rules recursively invoked by the
|
||
action.</para>
|
||
|
||
<para>Example:</para>
|
||
|
||
<para>/etc/shorewall/action.foo</para>
|
||
|
||
<programlisting>#TARGET 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! $FW net</programlisting>
|
||
|
||
<para>Logging in the invoke <quote>foo</quote> action will be as if
|
||
foo had been defined as:</para>
|
||
|
||
<programlisting>#TARGET SOURCE DEST PROTO DEST PORT(S)
|
||
ACCEPT:debug - - tcp 22
|
||
bar:debug</programlisting>
|
||
</listitem>
|
||
</orderedlist>
|
||
</section>
|
||
|
||
<section id="Extension">
|
||
<title>Creating an Action using an Extension Script</title>
|
||
|
||
<para>There may be cases where you wish to create a chain with rules that
|
||
can't be constructed using the tools defined in the
|
||
<filename>action.template</filename>. In that case, you can use an <ulink
|
||
url="shorewall_extension_scripts.htm">extension script</ulink>.<note>
|
||
<para>If you actually need an action to drop broadcast packets, use
|
||
the <command>dropBcast</command> standard action rather than create
|
||
one like this.</para>
|
||
</note></para>
|
||
|
||
<example id="Example">
|
||
<title>An action to drop all broadcast packets</title>
|
||
|
||
<para>If you define an action <quote>acton</quote> and you have an
|
||
<filename>/etc/shorewall/acton</filename> script, the rules compiler
|
||
sets lexical variables as follows:</para>
|
||
|
||
<itemizedlist>
|
||
<listitem>
|
||
<para><emphasis role="bold">$chainref</emphasis> is a reference to
|
||
the chain-table entry for the chain where your rules are to be
|
||
placed.</para>
|
||
</listitem>
|
||
|
||
<listitem>
|
||
<para><emphasis role="bold">$level</emphasis> is the log level. If
|
||
false, no logging was specified.</para>
|
||
</listitem>
|
||
|
||
<listitem>
|
||
<para><emphasis role="bold">$tag</emphasis> is the log tag.</para>
|
||
</listitem>
|
||
|
||
<listitem>
|
||
<para><emphasis role="bold">@params</emphasis> is the list of
|
||
parameter values (Shorewall 4.4.16 and later). 'Omitted' parameters
|
||
contain '-'.</para>
|
||
</listitem>
|
||
</itemizedlist>
|
||
|
||
<para>Example:</para>
|
||
|
||
<para>/etc/shorewall/actions<programlisting>DropBcasts</programlisting></para>
|
||
|
||
<para>/etc/shorewall/action.DropBcasts<programlisting># This file is empty</programlisting>/etc/shorewall/DropBcasts<programlisting>use Shorewall::Chains;
|
||
|
||
if ( $level ne '' ) {
|
||
log_rule_limit $level, $chainref, 'dropBcast' , 'DROP', '', $tag, 'add', ' -m addrtype --dst-type BROADCAST ';
|
||
log_rule_limit $level, $chainref, 'dropBcast' , 'DROP', '', $tag, 'add', ' -d 224.0.0.0/4 ';
|
||
}
|
||
|
||
add_rule $chainref, '-m addrtype --dst-type BROADCAST -j DROP';
|
||
add_rule $chainref, '-d 224.0.0.0/4 -j DROP';
|
||
|
||
1;</programlisting></para>
|
||
</example>
|
||
|
||
<para>For a richer example, see the next section.</para>
|
||
</section>
|
||
|
||
<section id="Limit">
|
||
<title>Limiting Per-IP Connection Rate using the Limit Action</title>
|
||
|
||
<para>Shorewall supports a <quote>Limit</quote> built-in action. Prior to
|
||
Shorewall 4.4.16, Limit is invoked with a comma-separated list in place of
|
||
a logging tag. Beginning in Shorewall 4.4.16, it may also be invoked with
|
||
a list of three parameters enclosed in parentheses. The list has three
|
||
elements:</para>
|
||
|
||
<orderedlist>
|
||
<listitem>
|
||
<para>The name of a <quote>recent</quote> list. You select the list
|
||
name which must conform to the rules for a valid chain name. Different
|
||
rules that specify the same list name will use the same set of
|
||
counters.</para>
|
||
</listitem>
|
||
|
||
<listitem>
|
||
<para>The number of connections permitted in a specified time
|
||
period.</para>
|
||
</listitem>
|
||
|
||
<listitem>
|
||
<para>The time period, expressed in seconds.</para>
|
||
</listitem>
|
||
</orderedlist>
|
||
|
||
<para>Connections that exceed the specified rate are dropped.</para>
|
||
|
||
<para>For example, to use a recent list name of <emphasis
|
||
role="bold">SSHA</emphasis>, and to limit SSH connections to 3 per minute,
|
||
use this entry in <filename>/etc/shorewall/rules</filename>:</para>
|
||
|
||
<programlisting>#ACTION SOURCE DEST PROTO DEST PORT(S)
|
||
Limit:none:SSHA,3,60 net $FW tcp 22</programlisting>
|
||
|
||
<para>Using Shorewall 4.4.16 or later, you can also invoke the action this
|
||
way:</para>
|
||
|
||
<programlisting>#ACTION SOURCE DEST PROTO DEST PORT(S)
|
||
Limit(SSHA,3,60):none net $FW tcp 22</programlisting>
|
||
|
||
<para>If you want dropped connections to be logged at the info level, use
|
||
this rule instead:</para>
|
||
|
||
<programlisting>#ACTION SOURCE DEST PROTO DEST PORT(S)
|
||
Limit:info:SSHA,3,60 net $FW tcp 22</programlisting>
|
||
|
||
<para>Shorewall 4.4.16 and later:<programlisting>#ACTION SOURCE DEST PROTO DEST PORT(S)
|
||
Limit(SSH,3,60):info net $FW tcp 22</programlisting></para>
|
||
|
||
<para>To summarize, you pass four pieces of information to the Limit
|
||
action:</para>
|
||
|
||
<itemizedlist>
|
||
<listitem>
|
||
<para>The log level. If you don't want to log, specify
|
||
<quote>none</quote>.</para>
|
||
</listitem>
|
||
|
||
<listitem>
|
||
<para>The name of the recent list that you want to use
|
||
(<quote>SSHA</quote> in this example).</para>
|
||
</listitem>
|
||
|
||
<listitem>
|
||
<para>The maximum number of connections to accept (3 in this
|
||
example).</para>
|
||
</listitem>
|
||
|
||
<listitem>
|
||
<para>The number of seconds over which you are willing to accept that
|
||
many connections (60 in this example).</para>
|
||
</listitem>
|
||
</itemizedlist>
|
||
|
||
<section id="LimitImp">
|
||
<title>How Limit is Implemented</title>
|
||
|
||
<para>For those who are curious, the Limit action in Shorewall 4.4.16 is
|
||
implemented as follows:</para>
|
||
|
||
<programlisting>use Shorewall::Chains;
|
||
|
||
@params = split( /,/, $tag ), $tag='' unless @params;
|
||
|
||
fatal_error 'Limit rules must include <list name>,<max connections>,<interval> as the log tag or params' unless @params == 3;
|
||
|
||
my $list = $params[0];
|
||
|
||
for ( @params[1,2] ) {
|
||
fatal_error 'Max connections and interval in Limit rules must be numeric (' . $_ . ')' unless /^\d+$/
|
||
}
|
||
|
||
my $count = $params[1] + 1;
|
||
|
||
add_rule $chainref, "-m recent --name $list --set";
|
||
|
||
if ( $level ) {
|
||
my $xchainref = new_chain 'filter' , "$chainref->{name}%";
|
||
log_rule_limit $level, $xchainref, $params[0], 'DROP', $tag, '', 'add', '';
|
||
add_rule $xchainref, '-j DROP';
|
||
add_rule $chainref, "-m recent --name $list --update --seconds $params[2] --hitcount $count -j $xchainref->{name}";
|
||
} else {
|
||
add_rule $chainref, "-m recent --update --name $list --seconds $params[2] --hitcount $count -j DROP";
|
||
}
|
||
|
||
add_rule $chainref, '-j ACCEPT';
|
||
|
||
1; </programlisting>
|
||
</section>
|
||
</section>
|
||
</article>
|