shorewall_code/docs/Audit.xml

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  <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
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>