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shorewall_code/docs/Audit.xml
Tom Eastep 6f3497e353 Update Audit.xml with parameterized standard action info
Signed-off-by: Tom Eastep <teastep@shorewall.net>
2011-06-19 06:50:18 -07:00

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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
"http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd">
<article>
<!--$Id$-->
<articleinfo>
<title>AUDIT Target Support</title>
<authorgroup>
<author>
<firstname>Tom</firstname>
<surname>Eastep</surname>
</author>
</authorgroup>
<pubdate><?dbtimestamp format="Y/m/d"?></pubdate>
<copyright>
<year>2011</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>Background</title>
<para>In early 2011, Thomas Graf submitted a set of patches to the
Netfilter development list that implemented an AUDIT rule target. This is
from the initial submittal:</para>
<blockquote>
<para>This patch adds a new netfilter target which creates audit records
for packets traversing a certain chain. It can be used to record packets
which are rejected administraively as follows:</para>
<simplelist>
<member>-N AUDIT_DROP</member>
<member>-A AUDIT_DROP -j AUDIT --type DROP</member>
<member>-A AUDIT_DROP -j DROP</member>
</simplelist>
<para>A rule which would typically drop or reject a packet would then
invoke the new chain to record packets before dropping them.</para>
<simplelist>
<member>-j AUDIT_DROP</member>
</simplelist>
<para>The module is protocol independant and works for iptables,
ip6tables and ebtables.</para>
<itemizedlist>
<listitem>
<para>netfilter hook</para>
</listitem>
<listitem>
<para>packet length</para>
</listitem>
<listitem>
<para>incoming/outgoing interface</para>
</listitem>
<listitem>
<para>MAC src/dst/proto for ethernet packets</para>
</listitem>
<listitem>
<para>src/dst/protocol address for IPv4/IPv6</para>
</listitem>
<listitem>
<para>src/dst port for TCP/UDP/UDPLITE</para>
</listitem>
<listitem>
<para>icmp type/code</para>
</listitem>
</itemizedlist>
</blockquote>
<para>The audited packets are sent to a daemon (auditd) that write the
audit information to a log file.</para>
<para>In a related post by Eric Paris, the following additional
information was posted:</para>
<blockquote>
<para>AUDIT exists because a very large number of gov't customers (Not
just USA) have special requirements about how 'relevant' information is
gathered and stored. They require centralization and standardization and
require pretty formal documentation describing it's operation. The gov't
certification authority has recently added a requirement that they be
able to log 'illegal attempted network connections' via the approved
audit facility. Thus, this patch.</para>
</blockquote>
<para>The AUDIT target was included in Linux kernel 2.6.39.</para>
</section>
<section>
<title>Shorewall Support</title>
<para>Shorewall support for the AUDIT target was added in 4.4.20.</para>
<para>The support involves the following:</para>
<orderedlist numeration="loweralpha">
<listitem>
<para>A new "AUDIT Target" capability is added and is required for
auditing support. To use AUDIT support with a capabilities file, that
file must be generated using this or a later release.</para>
<para>Use 'shorewall show capabilities' after installing this release
to see if your kernel/iptables support the AUDIT target.</para>
</listitem>
<listitem>
<para>In /etc/shorewall/policy's POLICY column, the policy (and
default action, if any) may be followed by ':audit' to cause
application of the policy to be audited. Only ACCEPT, DROP and REJECT
policies may be audited.</para>
<para>Example:</para>
<programlisting>#SOURCE DEST POLICY LOG
# LEVEL
net fw DROP:audit</programlisting>
<para>It is allowed to also specify a log level on audited policies
resulting in both auditing and logging.</para>
</listitem>
<listitem>
<para>Three new builtin targets that may be used in the rules file, in
macros and in other actions.</para>
<itemizedlist>
<listitem>
<para>A_ACCEPT - Audits and accepts the connection request</para>
</listitem>
<listitem>
<para>A_DROP - Audits and drops the connection request</para>
</listitem>
<listitem>
<para>A_REJECT - Audits and rejects</para>
</listitem>
</itemizedlist>
<para>A log level may be supplied with these actions to provide both
auditing and logging.</para>
<para>Example:</para>
<programlisting>#ACTION SOURCE DEST PROTO
A_ACCEPT:info loc net ...</programlisting>
</listitem>
<listitem>
<para>The BLACKLIST_DISPOSITION, MACLIST_DISPOSITION,
SMURF_DISPOSITION and TCP_FLAGS_DISPOSITION options may be set as
follows:</para>
<informaltable>
<tgroup cols="2">
<tbody>
<row>
<entry>BLACKLIST_DISPOSITION</entry>
<entry>A_DROP or A_REJECT</entry>
</row>
<row>
<entry>MACLIST_DISPOSITION</entry>
<entry>A_DROP, A_REJECT unless MACLIST_TABLE=mangle</entry>
</row>
<row>
<entry>SMURF_DISPOSITION<footnote>
<para>This option was added in Shorewall 4.4.20</para>
</footnote></entry>
<entry>A_DROP</entry>
</row>
<row>
<entry>TCP_FLAGS_DISPOSITION</entry>
<entry>A_DROP or A_REJECT</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</listitem>
<listitem>
<para>An 'audit' option has been added to the /etc/shorewall/blacklist
file which causes the packets matching the entryto be audited. 'audit'
may not be specified together with 'accept'.</para>
</listitem>
<listitem>
<para>The builtin actions (dropBroadcast, rejNonSyn, etc.) now support
an 'audit' parameter which causes all ACCEPT, DROP and REJECTs
performed by the action to be audited.</para>
</listitem>
<listitem>
<para>There are audited versions of the standard <ulink
url="Actions.html#Default">Default Actions</ulink> (A_Drop and
A_Reject). These actions audit everything they do which is probably
more than you want; as a consequence, you probably will want to make
your own copies of these actions and modify them to only audit the
packets that you are interested in.</para>
</listitem>
<listitem>
<para>In Shorewall 4.4.21, the standard <ulink
url="Actions.html#Default">Default Actions</ulink> were parameterized,
accepting three parameters:</para>
<orderedlist>
<listitem>
<para>Pass 'audit' if you want all ACCEPTs, DROPs and REJECTs
audited. Pass '-' otherwise.</para>
</listitem>
<listitem>
<para>The action to be applied to Auth requests; the default
depends on the first parameter:</para>
<informaltable border="">
<tgroup cols="2">
<tbody>
<row>
<entry><emphasis role="bold">FIRST
PARAMETER</emphasis></entry>
<entry><emphasis role="bold">DEFAULT</emphasis></entry>
</row>
<row>
<entry>-</entry>
<entry>REJECT</entry>
</row>
<row>
<entry>audit</entry>
<entry>A_REJECT</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</listitem>
<listitem>
<para>The action to be applied to SMB traffic. The default depends
on the first parameter:</para>
<informaltable>
<tgroup cols="3">
<tbody>
<row>
<entry><emphasis role="bold">ACTION</emphasis></entry>
<entry><emphasis role="bold">FIRST
PARAMETER</emphasis></entry>
<entry><emphasis role="bold">DEFAULT</emphasis></entry>
</row>
<row>
<entry>Reject</entry>
<entry>-</entry>
<entry>REJECT</entry>
</row>
<row>
<entry>Drop</entry>
<entry>-</entry>
<entry>DROP</entry>
</row>
<row>
<entry>Reject</entry>
<entry>audit</entry>
<entry>A_REJECT</entry>
</row>
<row>
<entry>Drop</entry>
<entry>audit</entry>
<entry>A_DROP</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</listitem>
</orderedlist>
<para> The parameters can be passed in the POLICY column of the policy
file. </para>
<programlisting>SOURCE DEST POLICY
net all DROP:Drop(audit):audit #Same as DROP:A_DROP:audit
</programlisting>
<programlisting>SOURCE DEST POLICY
net all DROP:Drop(-,DROP) #DROP rather than REJECT Auth
</programlisting>
<para>The parameters can also be specified in shorewall.conf: </para>
<programlisting>DROP_DEFAULT=Drop(-,DROP) #DROP Auth rather than REJECT </programlisting>
</listitem>
</orderedlist>
</section>
</article>