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Correct port knocking action in the Events article 
Signed-off-by: Tom Eastep <teastep@shorewall.net>
2018-03-24 09:47:56 -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>Shorewall Events</title>
<authorgroup>
<author>
<firstname>Tom</firstname>
<surname>Eastep</surname>
</author>
</authorgroup>
<pubdate><?dbtimestamp format="Y/m/d"?></pubdate>
<copyright>
<year>2013</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>This article applies to Shorewall 4.5.19 and later and supersedes
<ulink url="PortKnocking.html">this article.</ulink></para>
</caution>
<section>
<title>Overview</title>
<para>Shorewall events were introduced in Shorewall 4.5.19 and provide a
high-level interface to the Netfilter<firstterm> recent match</firstterm>
capability. An event is actually a list of (IP address, timestamp) pairs,
and can be tested in a number of different ways:</para>
<itemizedlist>
<listitem>
<para>Has event E ever occurred for IP address A (is the IP address in
the list)?</para>
</listitem>
<listitem>
<para>Has event E occurred M or more times for IP address A?</para>
</listitem>
<listitem>
<para>Has Event E occurred in the last N seconds for IP Address A (is
there an entry for the address with a timestamp falling within the
last N seconds)?</para>
</listitem>
<listitem>
<para>Has Event E occurred M or more times in the last N seconds for
IP address A (are there M or more entries for the address with
timestamps falling within the last N seconds)?</para>
</listitem>
</itemizedlist>
<para>The event interface is implemented as three parameterized Shorewall
<ulink url="Actions.html">Actions</ulink>:</para>
<variablelist>
<varlistentry>
<term>SetEvent</term>
<listitem>
<para>This action initializes an event list for either the source or
destination IP address in the current packets. The list will contain
a single entry for the address that will have the current
timestamp.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>ResetEvent</term>
<listitem>
<para>This action removes all entries for either the source or
destination IP address from an event list.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>IfEvent</term>
<listitem>
<para>This action tests an event in one of the ways listed above,
and performs an action based on the result.</para>
</listitem>
</varlistentry>
</variablelist>
<para>Events are based on the Netfilter 'recent match' capability which is
required for their use.</para>
<para>The recent-match kernel component is xt_recent which has two options
that are of interest to Shorewall users:</para>
<variablelist>
<varlistentry>
<term>ip_list_tot</term>
<listitem>
<para>The number of addresses remembered per event. Default is
100.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>ip_pkt_list_tot</term>
<listitem>
<para>The number of packets (event occurrences) remembered per
address. Default is 20.</para>
</listitem>
</varlistentry>
</variablelist>
<para>These may be changed with the xt_recent module is loaded or on the
kernel bootloader runline.</para>
</section>
<section>
<title>Details</title>
<para>Because these are parameterized actions, optional parameters may be
omitted. Trailing omitted parameters may be omitted entirely while
embedded omitted parameters are represented by a hyphen ("-").</para>
<para>Each event is given a name. Event names:</para>
<itemizedlist>
<listitem>
<para>Must begin with a letter.</para>
</listitem>
<listitem>
<para>May be composed of letters, digits, hyphens ('-') or underscores
('_').</para>
</listitem>
<listitem>
<para>May be at most 29 characters in length.</para>
</listitem>
</itemizedlist>
<section id="SetEvent">
<title>SetEvent</title>
<para><emphasis role="bold">SetEvent</emphasis>(
<replaceable>event</replaceable>, [ <replaceable>action</replaceable> ],
[ <replaceable>src-dst</replaceable> ], [
<replaceable>disposition</replaceable> ] )</para>
<variablelist>
<varlistentry>
<term>event</term>
<listitem>
<para>Name of the event.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>action</term>
<listitem>
<para>An action to perform after the event is initialized. May be
any action that may appear in the ACTION column of <ulink
url="manpages/shorewall-rules.html">shorewall-rules</ulink> (5).
If no action is to be performed, use COUNT.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>src-dst</term>
<listitem>
<para>Specifies whether the source IP address (<emphasis
role="bold">src</emphasis>) or destination IP address (<emphasis
role="bold">dst</emphasis>) is to be added to the event. The
default is <emphasis role="bold">src</emphasis>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>disposition</term>
<listitem>
<para>If the <replaceable>action</replaceable> involves logging,
then this parameter specifies the disposition that will appear in
the log entry prefix. If no <replaceable>disposition</replaceable>
is given, the log prefix is determined normally. The default is
ACCEPT.</para>
</listitem>
</varlistentry>
</variablelist>
</section>
<section id="ResetEvent">
<title>ResetEvent</title>
<para><emphasis role="bold">ResetEvent</emphasis>(
<replaceable>event</replaceable>, [ <replaceable>action</replaceable> ],
[ <replaceable>src-dst</replaceable> ], [
<replaceable>disposition</replaceable> ] )</para>
<variablelist>
<varlistentry>
<term>event</term>
<listitem>
<para>Name of the event.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>action</term>
<listitem>
<para>An action to perform after the event is reset. May be any
action that may appear in the ACTION column of <ulink
url="manpages/shorewall-rules.html">shorewall-rules</ulink> (5).
If no action is to be performed, use COUNT. The default is
ACCEPT.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>src-dst</term>
<listitem>
<para>Specifies whether the source IP address (<emphasis
role="bold">src</emphasis>) or destination IP address (<emphasis
role="bold">dst</emphasis>) is to be removed from the event. The
default is <emphasis role="bold">src</emphasis>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>disposition</term>
<listitem>
<para>If the <replaceable>action</replaceable> involves logging,
then this parameter specifies the disposition that will appear in
the log entry prefix. If no <replaceable>disposition</replaceable>
is given, the log prefix is determined normally.</para>
</listitem>
</varlistentry>
</variablelist>
</section>
<section id="IfEvent">
<title>IfEvent</title>
<para><emphasis role="bold">IfEvent</emphasis>(
<replaceable>event</replaceable>, [ <replaceable>action</replaceable> ],
[ <replaceable>duration</replaceable> ], [
<replaceable>hitcount</replaceable> ], [
<replaceable>src-dst</replaceable>], [
<replaceable>command</replaceable>[:<replaceable>option</replaceable>]...,
[ <replaceable>disposition</replaceable> ] )</para>
<variablelist>
<varlistentry>
<term>event</term>
<listitem>
<para>Name of the event.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>action</term>
<listitem>
<para>An action to perform if the test succeeds. May be any action
that may appear in the ACTION column of <ulink
url="manpages/shorewall-rules.html">shorewall-rules</ulink> (5).
The default is ACCEPT.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>duration</term>
<listitem>
<para>Number of seconds over which the event is to be tested. If
not specified, the test is not constrained by time.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>hitcount</term>
<listitem>
<para>Specifies the minimum number of packets required for the
test to succeed. If not specified, 1 packet is assumed.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>src-dst</term>
<listitem>
<para>Specifies whether the source IP address (<emphasis
role="bold">src</emphasis>) or destination IP address (<emphasis
role="bold">dst</emphasis>) is to be tested. The default is
<emphasis role="bold">src</emphasis>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>command</term>
<listitem>
<para>May be one of the following:</para>
<variablelist>
<varlistentry>
<term>check</term>
<listitem>
<para>Simply test if the
<replaceable>duration</replaceable>/<replaceable>hitcount</replaceable>
test is satisfied. If so, the
<replaceable>action</replaceable> is performed.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>reset</term>
<listitem>
<para>Like <emphasis role="bold">check</emphasis>. If the
test succeeds, the <replaceable>event</replaceable> will be
reset before the <replaceable>action</replaceable> is taken.
Requires the <firstterm>Mark in filter table</firstterm>
capability in your kernel and iptables.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>update</term>
<listitem>
<para>Like <emphasis role="bold">check</emphasis>.
Regardless of whether the test succeeds, an entry with the
current time and for the <replaceable>src-dst</replaceable>
iP address will be added to the
<replaceable>event</replaceable>.</para>
</listitem>
</varlistentry>
</variablelist>
<para>The default is <emphasis
role="bold">check</emphasis>.</para>
<para><replaceable>option</replaceable> may be one of:</para>
<variablelist>
<varlistentry>
<term>reap</term>
<listitem>
<para>Regardless of whether the test succeeds, entries for
the <replaceable>src-dst</replaceable> IP address that are
older than <replaceable>duration</replaceable> seconds will
be deleted from the <replaceable>event</replaceable>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>ttl</term>
<listitem>
<para>Constrains the test to require that the packet TTL
match the ttl in the original packet that created the
entry.</para>
</listitem>
</varlistentry>
</variablelist>
</listitem>
</varlistentry>
<varlistentry>
<term>disposition</term>
<listitem>
<para>If the <replaceable>action</replaceable> involves logging,
then this parameter specifies the disposition that will appear in
the log entry prefix. If no <replaceable>disposition</replaceable>
is given, the log prefix is determined normally.</para>
</listitem>
</varlistentry>
</variablelist>
</section>
<section id="ShowEvents">
<title>'show event' and 'show events' Commands</title>
<para>The CLI programs (<filename>/sbin/shorewall</filename>,
<filename>/sbin/shorewall-lite</filename>, etc.) support <command>show
event</command> and <command>show events</command> commands.</para>
<para>The <command>show event</command> command shows the contents of
the events listed in the command while <emphasis role="bold">show
events</emphasis> lists the contents of all events.</para>
<programlisting>root@gateway:~# shorewall show events
Shorewall 4.5.19-Beta2 events at gateway - Sat Jul 13 07:17:59 PDT 2013
SSH
src=75.101.251.91 : 2225.808, 2225.592
src=218.87.16.135 : 2078.490
SSH_COUNTER
src=65.182.111.112 : 5755.790
src=113.162.155.243 : 4678.249
sticky001
src=172.20.1.146 : 5.733, 5.728, 5.623, 5.611, 5.606, 5.606, 5.589, 5.588, 5.565, 5.551, 5.543, 5.521, 5.377, 5.347, 5.347, 5.345, 5.258, 5.148, 5.048, 4.949
src=172.20.1.151 : 41.805, 41.800
sticky002
src=172.20.1.213 : 98.122, 98.105, 98.105, 98.105, 98.088, 98.088, 98.088, 98.088, 98.058, 98.058, 80.885, 53.528, 53.526, 53.526, 53.510, 53.383, 53.194, 53.138, 53.072, 3.119
src=172.20.1.146 : 4.914, 4.914, 4.898, 4.897, 4.897, 4.896, 4.896, 4.896, 4.882, 4.881, 4.875, 4.875, 4.875, 4.875, 4.875, 4.875, 4.875, 4.874, 4.874, 4.874
root@gateway:~# </programlisting>
<para>The SSH and SSH_COUNTER events are created using the following
Automatic Blacklisting example. The sticky001 and sticky002 events are
created by the SAME rule action.</para>
<para>Each line represents one event. The list of numbers following the
':' represent the number of seconds ago that a matching packet triggered
the event. The numbers are in chronological sequence, so In this event,
there were 20 packets from 172.20.1.146 that arrived between 5.733 and
4.949 seconds ago:</para>
<programlisting>sticky001
src=172.20.1.146 : <emphasis role="bold">5.733</emphasis>, 5.728, 5.623, 5.611, 5.606, 5.606, 5.589, 5.588, 5.565, 5.551, 5.543, 5.521, 5.377, 5.347, 5.347, 5.345, 5.258, 5.148, 5.048, <emphasis
role="bold">4.949</emphasis> </programlisting>
<para>Note that there may have been earlier packets that also matched,
but the system where this example was captured used the default value of
the <emphasis role="bold">ip_pkt_list_tot</emphasis> xt_recent option
(20).</para>
<para>The output of these commands is produced by processing the
contents of <filename>/proc/net/xt_recent/*</filename>. You can access
those files directly to see the raw data. The raw times are the uptime
in milliseconds. The %CURRENTTIME entry is created by the <command>show
event[s]</command> commands to obtain the current uptime.</para>
</section>
</section>
<section>
<title>Examples</title>
<section>
<title>Automatic Blacklisting</title>
<para>This example is for ssh, but it can be adapted for any
application.</para>
<para>The name SSH has been changed to SSHLIMIT so as not to override
the Shorewall macro of the same name.</para>
<para><filename>/etc/shorewall/actions</filename>:</para>
<programlisting>#ACTION OPTION DESCRIPTION
SSHLIMIT #Automatically blacklist hosts who exceed SSH connection limits
SSH_BLACKLIST #Helper for SSHLIMIT</programlisting>
<para><filename>/etc/shorewall/action.SSH_BLACKLIST</filename>:</para>
<programlisting>#
# Shorewall version 4 - SSH_BLACKLIST Action
#
?format 2
###############################################################################
#TARGET SOURCE DEST PROTO DPORT SPORT
#
# Log the Reject
#
LOG:warn:REJECT
#
# And set the SSH_COUNTER event for the SOURCE IP address
#
SetEvent(SSH_COUNTER,REJECT,src)</programlisting>
<para><filename>/etc/shorewall/action.SSH</filename>LIMIT:</para>
<programlisting>#
# Shorewall version 4 - SSHLIMIT Action
#
?format 2
###############################################################################
#TARGET SOURCE DEST PROTO DPORT SPORT
#
# Silently reject the client if blacklisted
#
IfEvent(SSH_COUNTER,REJECT,300,1)
#
# Blacklist if 5 attempts in the last minute
#
IfEvent(SSH,SSH_BLACKLIST,60,5,src,check:reap)
#
# Log and reject if the client has tried to connect
# in the last two seconds
#
IfEvent(SSH,REJECT:warn:,2,1,-,update,Added)
#
# Un-blacklist the client
#
ResetEvent(SSH_COUNTER,LOG:warn,-,Removed)
#
# Set the 'SSH' EVENT and accept the connection
#
SetEvent(SSH,ACCEPT,src)</programlisting>
<para><filename>etc/shorewall/rules</filename>:</para>
<programlisting>#ACTION SOURCE DEST PROTO DPORT
SSHLIMIT net $FW tcp 22 </programlisting>
<caution>
<para>The technique demonstrated in this example is not self-cleaning.
The SSH_COUNTER event can become full with blackisted addresses that
never attempt to connect again. When that happens and a new entry is
added via SetEvent, the least recently seen address in the table is
deleted.</para>
</caution>
</section>
<section id="AutoBL">
<title>Generalized Automatic Blacklisting</title>
<para>The above two actions are generalized in the AutoBL and AutoBLL
actions released in Shorewall 4.5.19. Only AutoBL is invoked directly
from your rules file; AutoBL invoked AutoBLL internally.</para>
<section>
<title>AutoBL</title>
<para><emphasis role="bold">AutoBL</emphasis>(
<replaceable>event</replaceable>, [
<replaceable>Interval</replaceable> ], [
<replaceable>hitcount</replaceable> ], [
<replaceable>successive</replaceable> ], [
<replaceable>blacklist-time</replaceable> ], [
<replaceable>disposition </replaceable>], [
<replaceable>log_level</replaceable> ] )</para>
<variablelist>
<varlistentry>
<term>event</term>
<listitem>
<para>Name of the event. The blacklisting event itself will be
<replaceable>event</replaceable>_BL (analogous to SSH_COUNTER
above).</para>
</listitem>
</varlistentry>
<varlistentry>
<term>interval</term>
<listitem>
<para>Interval, in seconds, over which hits are to be counted.
Default is 60 seconds.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>hitcount</term>
<listitem>
<para>Number of matching packets that will trigger automatic
blacklisting when they arrive in
<replaceable>interval</replaceable> seconds. Default is
5.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>successive</term>
<listitem>
<para>If a matching packet arrives within this many seconds of
the preceding one, it should be logged according to
<replaceable>log_level</replaceable> and handled according to
the <replaceable>disposition</replaceable>. If successive
packets are not to be considered, enter 0. Default is 2
seconds.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>blacklist-time</term>
<listitem>
<para>Time, in seconds, that the source IP address is to be
blacklisted. Default is 300 (5 minutes).</para>
</listitem>
</varlistentry>
<varlistentry>
<term>disposition</term>
<listitem>
<para>The disposition of blacklisted packets. Default is
DROP.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>log_level</term>
<listitem>
<para>Log level at which packets are to be logged. Default is
info.</para>
</listitem>
</varlistentry>
</variablelist>
<para>To duplicate the SSHLIMIT entry in
<filename>/etc/shorewall/rules</filename> shown above:</para>
<programlisting>#ACTION SOURCE DEST PROTO DPORT
AutoBL(SSH,-,-,-,REJECT,warn)\
net $FW tcp 22 </programlisting>
</section>
</section>
<section>
<title>Port Knocking</title>
<para>This example shows a different implementation of the one shown in
the <ulink url="PortKnocking.html">Port Knocking</ulink> article.</para>
<para>In this example:</para>
<orderedlist>
<listitem>
<para>Attempting to connect to port 1600 enables SSH access. Access
is enabled for 60 seconds.</para>
</listitem>
<listitem>
<para>Attempting to connect to port 1601 disables SSH access (note
that in the article linked above, attempting to connect to port 1599
also disables access. This is an port scan defence as explained in
the article).</para>
</listitem>
</orderedlist>
<para>To implement that approach:</para>
<para><filename>/etc/shorewall/actions</filename>:</para>
<programlisting>#ACTION OPTION DESCRIPTION
Knock #Port Knocking</programlisting>
<para><filename>/etc/shorewall/action.Knock</filename>:</para>
<programlisting>#
# Shorewall version 4 - Port-Knocking Action
#
?format 2
###############################################################################
#ACTION SOURCE DEST PROTO DPORT
IfEvent(SSH,ACCEPT:info,60,1,src,reset)\
- - tcp 22
SetEvent(SSH,ACCEPT) - - tcp 1600
ResetEvent(SSH,DROP:info) </programlisting>
<para><filename>etc/shorewall/rules</filename>:</para>
<programlisting>#ACTION SOURCE DEST PROTO DPORT
Knock net $FW tcp 22,1599-1601 </programlisting>
</section>
<section id="Stateful">
<title>Stateful Port Knocking (knock with a sequence of ports)</title>
<para><ulink url="http://www.wiesinger.com/">Gerhard Wiesinger</ulink>
has contributed a Perl module that allows you to define portknocking
sequences. Download <ulink
url="pub/shorewall/contrib/PortKnocking/KnockEnhanced.pm">the
module</ulink> and copy it into your site_perl directory.</para>
<para>Using Gerhard's module, a port-knocking rule is defined via a
'?PERL' statement. This example opens the SSH port from net-&gt;fw using
the knock sequence 52245, 15623, 19845:</para>
<programlisting>?BEGIN PERL
use KnockEnhanced;
KnockEnhanced 'net', '$FW', {name =&gt; 'SSH1', log_level =&gt; 3, proto =&gt; 'tcp', target =&gt; 'ssh', knocker =&gt; [52245,15623,19845]};
?END PERL</programlisting>
<para>A few notes on the parameters:</para>
<itemizedlist>
<listitem>
<para>The first parameter is the rule SOURCE</para>
</listitem>
<listitem>
<para>The second parameter is the rule DEST</para>
</listitem>
<listitem>
<para>The third parameter is a Perl hash reference that defines the
remaining parameters. Each parameter is specified via
<replaceable>param</replaceable> =&gt;
<replaceable>value</replaceable>.</para>
<itemizedlist>
<listitem>
<para><emphasis role="bold">proto</emphasis> is the protocol --
if not specified, the default is tcp</para>
</listitem>
<listitem>
<para><emphasis role="bold">seconds</emphasis> is the timeout
between successive events -- default is 60 seconds.</para>
</listitem>
<listitem>
<para><emphasis role="bold">original_dest</emphasis> is the rule
ORIGDEST</para>
</listitem>
<listitem>
<para><emphasis role="bold">target</emphasis> is the port(s)
that you are trying to open. May either be a single name or
number, or it may be a list of names and/or numbers separated by
commas and enclosed in square brackets ("[...]").</para>
</listitem>
<listitem>
<para><emphasis role="bold">name</emphasis> is a name used as
the base for event and chain names. If not supplied, the first
<emphasis role="bold">target</emphasis> is used, in which case
the first target must be a port name.</para>
</listitem>
<listitem>
<para><emphasis role="bold">log_level </emphasis>specifies
logging for the generated rules</para>
</listitem>
</itemizedlist>
<note>
<para>Port names and numbers may be optionally followed by a colon
(":") and a protocol name or number to override the specified
protocol.</para>
</note>
</listitem>
</itemizedlist>
<para>The module itself contains additional examples of its
usage.</para>
</section>
</section>
</article>
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