shorewall_code/docs/Shorewall-perl.xml
2007-07-27 04:25:56 +00:00

599 lines
22 KiB
XML

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<article>
<!--$Id: template.xml 4194 2006-07-07 01:04:16Z judas_iscariote $-->
<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 id="What">
<title>Shorewall-perl - What is it?</title>
<para>Shorewall-perl is a companion product to Shorewall.</para>
<para>Shorewall-perl contains a re-implementation of the Shorewall
compiler written in Perl. The advantages of using Shorewall-perl 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 id="DownSide">
<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 (Restriction relaxed in Shorewall-perl
4.0.1)</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. <ulink
url="bridge-Shorewall-perl.html">Alternative bridge
support</ulink> is provided by Shorewall-perl.</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>The 'refresh' command is now similar to restart with the
exceptios that:</para>
<itemizedlist>
<listitem>
<para>The command fails if Shorewall is not running.</para>
</listitem>
<listitem>
<para>A directory name cannot be specified in the
command.</para>
</listitem>
<listitem>
<para>The refresh command does not alter the Netfilter
configuration except for the static blacklist.</para>
</listitem>
</itemizedlist>
</listitem>
<listitem>
<para>With the shell-based compiler, extension scripts were copied
into the compiled script and executed at run-time. In many cases,
this approach doesn't work with Shorewall Perl because (almost)
the entire ruleset is built by the compiler. As a result,
Shorewall-perl runs many extension scripts at compile-time rather
than at run-time. Because the compiler is written in Perl, your
extension scripts from earlier versions will no longer
work.</para>
<para>The following table summarizes when the various extension
scripts are run:<informaltable frame="all">
<tgroup cols="3">
<tbody>
<row>
<entry><emphasis
role="bold">Compile-time</emphasis></entry>
<entry><emphasis role="bold">Run-time</emphasis></entry>
<entry><emphasis
role="bold">Eliminated</emphasis></entry>
</row>
<row>
<entry>initdone</entry>
<entry>clear</entry>
<entry>continue</entry>
</row>
<row>
<entry>maclog</entry>
<entry>initdone</entry>
<entry></entry>
</row>
<row>
<entry>Per-chain (including those associated with
actions)</entry>
<entry>start</entry>
<entry></entry>
</row>
<row>
<entry></entry>
<entry>started</entry>
<entry></entry>
</row>
<row>
<entry></entry>
<entry>stop</entry>
<entry></entry>
</row>
<row>
<entry></entry>
<entry>stopped</entry>
<entry></entry>
</row>
<row>
<entry></entry>
<entry>tcclear</entry>
<entry></entry>
</row>
</tbody>
</tgroup>
</informaltable></para>
<para>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 <emphasis
role="bold">$chainref</emphasis> scalar variable will hold a
reference to a chain table entry.</para>
<simplelist>
<member><emphasis role="bold">$chainref-&gt;{name}</emphasis>
contains the name of the chain</member>
<member><emphasis role="bold">$chainref-&gt;{table}</emphasis>
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 part</para>
</listitem>
</itemizedlist>
<para>Example:</para>
<programlisting> log_rule_limit
'info' ,
$chainref ,
$chainref-&gt;{name},
'DROP' ,
'', #Limit
'' , #Log tag
'add'
'-p tcp '; </programlisting>
<para>Here is an example of an actual initdone script used with
Shorewall 3.4:<programlisting>run_iptables -t mangle -I PREROUTING -p esp -j MARK --set-mark 0x50
run_iptables -t filter -I INPUT -p udp --dport 1701 -m mark --mark 0x50 -j ACCEPT
run_iptables -t filter -I OUTPUT -p udp --sport 1701 -j ACCEPT
</programlisting></para>
<para>Here is the corresponding script used with
Shorewall-perl:<programlisting>use Shorewall::Chains;
insert_rule $mangle_table-&gt;{PREROUTING}, 1, "-p esp -j MARK --set-mark 0x50";
insert_rule $filter_table-&gt;{INPUT}, 1, "-p udp --dport 1701 -m mark --mark 0x50 -j ACCEPT";
insert_rule $filter_table-&gt;{OUTPUT}, 1, "-p udp --sport 1701 -j ACCEPT";
1;</programlisting></para>
<para>The initdone script is unique because the $chainref variable
is not set before the script is called. The above script
illustrates how the $mangle_table, $filter_table, and $nat_table
references can be used to add or insert rules in arbitrary
chains.</para>
</listitem>
<listitem>
<para>The <filename>/etc/shorewall/tos</filename> file now has
zone-independent SOURCE and DEST columns as do all other files
except the rules and policy files.</para>
<para>The SOURCE column may be one of the following:</para>
<simplelist>
<member>[<command>all</command>:]&lt;<replaceable>address</replaceable>&gt;[,...]</member>
<member>[<command>all</command>:]&lt;<replaceable>interface</replaceable>&gt;[:&lt;<replaceable>address</replaceable>&gt;[,...]]</member>
<member><command>$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>Shorewall-perl insists that ipset names begin with a letter
and be composed of alphanumeric characters and underscores (_).
When used in a Shorewall configuration file, the name must be
preceded by a plus sign (+) as with the shell-based
compiler.</para>
<para>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>
<listitem>
<para>BLACKLISTNEWONLY=No is not permitted with FASTACCEPT=Yes.
This combination doesn't work in previous versions of Shorewall so
the Perl-based compiler simply rejects it.</para>
</listitem>
<listitem>
<para>Shorewall-perl has a single rule generator that is used for
all rule-oriented files. So it is important that the syntax is
consistent between files.</para>
<para>With shorewall-shell, there is a special syntax in the
SOURCE column of /etc/shorewall/masq to designate "all traffic
entering the firewall on this interface except...".</para>
<para>Example:<programlisting>#INTERFACE SOURCE ADDRESSES
eth0 eth1!192.168.4.9 ...</programlisting>Shorewall-perl
uses syntax that is consistent with the rest of
Shorewall:<programlisting>#INTERFACE SOURCE ADDRESSES
eth0 eth1:!192.168.4.9 ...</programlisting></para>
</listitem>
<listitem>
<para>The 'allowoutUPnP' built-in action is no longer supported.
In kernel 2.6.14, the Netfilter team have removed support for '-m
owner --owner-cmd' which that action depended on.</para>
</listitem>
<listitem>
<para>The PKTTYPE option is ignored by Shorewall-perl.
Shorewall-perl 4.0.0 requires Address type match. Shorewall-perl
versions 4.0.1 and later will use Address type match if it is
available; otherwise, they will behave as if PKTTYPE=No had been
specified.</para>
</listitem>
<listitem>
<para> Shorewall-perl detects dead policy file entries that result
when an entry is masked by an earlier more general entry.</para>
<para>Example:</para>
<programlisting>#SOURCE DEST POLICY LOG LEVEL
all all REJECT info
loc net ACCEPT</programlisting>
</listitem>
</orderedlist>
</listitem>
<listitem>
<para>Shorewall-perl is dependent on Perl (see the next section) which
has a large disk footprint. This makes Shorewall-perl less desirable
in an embedded environment.</para>
</listitem>
</itemizedlist>
</section>
<section id="Prerequisites">
<title>Shorewall-perl - Prerequisites</title>
<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>
<listitem>
<para>Perl Getopts::Long Module</para>
</listitem>
<listitem>
<para>Perl Carp Module</para>
</listitem>
</itemizedlist>
</section>
<section id="Install">
<title>Shorewall-perl - Installation</title>
<para>Either</para>
<programlisting><command>tar -jxf shorewall-perl-4.0.x.tar.bz2</command>
<command>cd shorewall-perl-4.0.x</command>
<command>./install.sh</command></programlisting>
<para>or</para>
<programlisting><command>rpm -ivh shorewall-perl-4.0.x.noarch.rpm</command></programlisting>
</section>
<section id="Using">
<title>Using Shorewall-perl</title>
<para>If you only install one compiler, then that compiler will be
used.</para>
<para>If you install both compilers, then the compiler actually used
depends on the SHOREWALL_COMPILER setting in
<filename>shorewall.conf</filename>. The value of this option can be
either 'perl' or 'shell'.</para>
<para>If you add 'SHOREWALL_COMPILER=perl' 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>If you only install one compiler, it is suggested that you do not
set SHOREWALL_COMPILER.</para>
<para>You may also select the compiler to use on the command line using
the 'C option:<simplelist>
<member>'-C shell' means use the shell compiler</member>
<member>'-C perl' means use the perl compiler</member>
</simplelist>The -C option overrides the setting in
shorewall.conf.</para>
<para>Example:<programlisting><command>shorewall restart -C perl</command></programlisting></para>
<para>When the Shorewall-perl compiler has been selected, the
<filename>params</filename> file is processed twice, the second time using
the <option>-a</option> option which causes all variables set within the
file to be exported automatically by the shell. The Shorewall-perl
compiler uses the current environmental variables to perform variable
expansion within the other Shorewall configuration files.</para>
</section>
</article>