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<title>ProFTPD module mod_proxy_protocol</title>
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<h2><b>ProFTPD module <code>mod_proxy_protocol</code></b></h2>
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<p>
The purpose of the <code>mod_proxy_protocol</code> module is to handle
protocols which are used by proxies, <i>e.g.</i> <code>haproxy</code>, for
conveying information about the real origin/client to the backend server.
Protocols like HTTP often have their own mechanism for doing so, via headers
such as "X-Forwarded-For". Unfortunately, FTP does <b>not</b> have such a
mechanism, nor does SSH.
<p>
However, there <em>are</em> protocols which an provide this information without
impacting FTP. HAproxy's <a href="http://haproxy.1wt.eu/download/1.5/doc/proxy-protocol.txt"><code>PROXY</code></a> protocol is one such mechanism. The
<code>mod_proxy_protocol</code> module uses these mechanisms to change the
information about the "remote" client so that it is the real client, not the
proxy, whose IP address/port are logged and used for <i>e.g.</i> network ACLs.
<p>
This module is contained in the <code>mod_proxy_protocol.c</code> file for
ProFTPD 1.3.<i>x</i>, and is not compiled by default. Installation
instructions are discussed <a href="#Installation">here</a>; detailed
notes on best practices for using this module are <a href="#Usage">here</a>.
<p>
The most current version of <code>mod_proxy_protocol</code> can be found at:
<pre>
<a href="https://github.com/Castaglia/proftpd-mod_proxy_protocol.git">https://github.com/Castaglia/proftpd-mod_proxy_protocol.git</a>
</pre>
<h2>Author</h2>
<p>
Please contact TJ Saunders <tj <i>at</i> castaglia.org> with any
questions, concerns, or suggestions regarding this module.
<h2>Directives</h2>
<ul>
<li><a href="#ProxyProtocolEngine">ProxyProtocolEngine</a>
<li><a href="#ProxyProtocolTimeout">ProxyProtocolTimeout</a>
<li><a href="#ProxyProtocolVersion">ProxyProtocolVersion</a>
</ul>
<p>
<hr>
<h2><a name="ProxyProtocolEngine">ProxyProtocolEngine</a></h2>
<strong>Syntax:</strong> ProxyProtocolEngine <em>on|off</em><br>
<strong>Default:</strong> None<br>
<strong>Context:</strong> server config, <code><VirtualHost></code>, <code><Global></code><br>
<strong>Module:</strong> mod_proxy_protocol<br>
<strong>Compatibility:</strong> 1.3.5rc4 and later
<p>
The <code>ProxyProtocolEngine</code> directive enables the expectation
and handling of protocols which provide information on proxied connections;
support for these protocols is provided by <code>mod_proxy_protocol</code>.
<p>
<hr>
<h2><a name="ProxyProtocolTimeout">ProxyProtocolTimeout</a></h2>
<strong>Syntax:</strong> ProxyProtocolTimeout <em>seconds</em><br>
<strong>Default:</strong> 3sec<br>
<strong>Context:</strong> server config, <code><VirtualHost></code>, <code><Global></code><br>
<strong>Module:</strong> mod_proxy_protocol<br>
<strong>Compatibility:</strong> 1.3.5rc4 and later
<p>
The <code>ProxyProtocolTimeout</code> directive is used to configure the
amount of time, in seconds, that <code>mod_proxy_protocol</code> will wait to
receive the full expected proxy information. If the full information is
not received within the given number of seconds, the connection to the client
is closed.
<p>
<hr>
<h2><a name="ProxyProtocolVersion">ProxyProtocolVersion</a></h2>
<strong>Syntax:</strong> ProxyProtocolVersion <em>protocolVersion</em><br>
<strong>Default:</strong> haproxyV1<br>
<strong>Context:</strong> server config, <code><VirtualHost></code>, <code><Global></code><br>
<strong>Module:</strong> mod_proxy_protocol<br>
<strong>Compatibility:</strong> 1.3.5rc4 and later
<p>
The <code>ProxyProtocolVersion</code> directive is used to configure the
protocol that <code>mod_proxy_protocol</code> expects to handle. The
currently supported values are:
<ul>
<li><code>haproxyV1</code>
<li><code>haproxyV2</code>
</ul>
<p>
<hr>
<h2><a name="Usage">Usage</a></h2>
<p>
<b>Example Configuration</b><br>
<pre>
<IfModule mod_proxy_protocol.c>
ProxyProtocolEngine on
ProxyProtocolTimeout 3sec
# Necessary to allow data transfers
AllowForeignAddress on
</IfModule>
</pre>
<p>
<b>Module Load Order</b><br>
In order for <code>mod_proxy_protocol</code> to work its magic, it <b>must</b>
the first module in line to handle the bytes coming in from the client.
If some other module (such as <code>mod_sftp</code> or <code>mod_tls</code>)
tries to handle the incoming bytes first, Bad Things will happen, since those
modules will expect different protocols than the <code>PROXY</code> protocol.
<p>
For <code>mod_proxy_protocol</code> to be the first module called, it must
the <b>last</b> module loaded. To do this as a static module, you would
use something like this when building proftpd:
<pre>
# ./configure --with-modules=...:mod_proxy_protocol
</pre>
ensuring that <code>mod_proxy_protocol</code> is the <b>last</b> module in
your <code>--with-modules</code> list.
<p>
As a shared module, configuring <code>mod_proxy_protocol</code> to be the
last module loaded is much easier. Your configuration will have a list
of <code>LoadModule</code> directives; the last of which would be:
<pre>
LoadModule mod_proxy_protocol.c
</pre>
<p>
<b>Trusting Senders of Proxy Data</b><br>
Use of these proxy protocols means changes in audit trails and/or client
access permissions (<i>e.g.</i> different <code>mod_wrap2</code> and/or
<code>mod_geoip</code> rules will apply). Unscrupulous senders may try to
actively lie to your server about the original client using these protocols.
Thus you <b>must</b> trust the upstream machines <b>before</b> enabling the
<code>mod_proxy_protocol</code> module.
<p>
Put another way: do <b>not</b> use the <code>mod_proxy_protocol</code> module
if your server handles connections from the open Internet. Doing so means
that any machine can use the proxy protocol to hide their activities, or
make it look like the connection is coming from someone else. <b>Only accept
proxy information from trusted sources.</b>
<p>
<b>Why <code>AllowForeignAddress</code> Is Needed</b><br>
One of the consequences of allowing <code>mod_proxy_protocol</code> to change
the remote IP address is that security checks performed on data transfers
will cause problems. For active data transfers (<i>i.e.</i> for clients
which send the <code>PORT</code> or <code>EPRT</code> commands),
<code>proftpd</code> requires that the IP address sent in the command matches
the IP address of the client which sends the command. Otherwise, a message
like the following is logged:
<pre>
Refused PORT 127,0,0,1,218,225 (address mismatch)
</pre>
and the command is rejected.
<p>
Similarly for passive data transfers (<i>i.e.</i> for clients which send the
<code>PASV</code> or <code>EPSV</code> commands), <code>proftpd</code> requires
that the remote IP address of the client which connects to the data transfer
address <b>must</b> match the remote IP address of the client on the control
connection. If the addresses do no match, then the following is logged:
<pre>
SECURITY VIOLATION: Passive connection from 127.0.0.1 rejected.
</pre>
and the control connection is closed.
<p>
These security measures are done to prevent abuses of FTP data transfers
such as the <a href="http://www.proftpd.org/docs/howto/FXP.html">FTP bounce</a>
attack. However, the very fact that <code>mod_proxy_protocol</code> changes
the remote IP address means that to allow data transfers when using this module,
you need to use:
<pre>
AllowForeignAddress on
</pre>
in the same virtual host section in which the <code>ProxyProtocolEngine</code>
directive appears.
<p>
<hr>
<h2><a name="Installation">Installation</a></h2>
To install <code>mod_proxy_protocol</code>, copy the
<code>mod_proxy_protocol.c</code> file into:
<pre>
<i>proftpd-dir</i>/contrib/
</pre>
after unpacking the latest proftpd-1.3.<i>x</i> source code. For including
<code>mod_proxy_protocol</code> as a staticly linked module:
<pre>
$ ./configure --with-modules=...:mod_proxy_protocol
</pre>
To build <code>mod_proxy_protocol</code> as a DSO module:
<pre>
$ ./configure --enable-dso --with-shared=...:mod_proxy_protocol
</pre>
Then follow the usual steps:
<pre>
$ make
$ make install
</pre>
<p>
For those with an existing ProFTPD installation, you can use the
<code>prxs</code> tool to add <code>mod_proxy_protocol</code>, as a DSO module,
to your existing server:
<pre>
$ prxs -c -i -d mod_proxy_protocol.c
</pre>
<p>
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<font size=2><b><i>
© Copyright 2013-2017 TJ Saunders<br>
All Rights Reserved<br>
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