/usr/share/doc/samhain/HOWTO-client+server-troubleshooting.html

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<p style="text-align: center; background: #ccc; border: 1px solid #2d5588;"><a 
   style="text-decoration: none;" 
   href="http://www.la-samhna.de/samhain/">samhain file integrity 
   scanner</a>&nbsp;|&nbsp;<a style="text-decoration: none;" 
   href="http://www.la-samhna.de/samhain/s_documentation.html">online 
   documentation</a></p>
<br><center>
<h1>Samhain client/server: What can go wrong, and how can you fix it ?</h1>
</center>
<br>
<hr>
<div class="warnblock">
<ul>
  <li>Almost all problems can only be diagnosed correctly by checking the 
      <b>server logs</b>.</li>
  <li>
    If the server does not write logs, <b>fix this first</b>. For debugging, 
    stop the server, then run it in the foreground with 
    <tt>yule -p info --foreground</tt>
    <ul>
      <li>
	By default, the server logs to the file 
	<tt>/var/log/yule/yule_log</tt>, and since the server drops 
	root privileges on startup, the directory <tt>/var/log/yule</tt>
	must be writable for the nonprivileged user the server runs 
	as (the first existing out of: yule, daemon, nobody).
      </li>
      <li>
	Logging to the logfile must be enabled in the
	<tt>/etc/yulerc</tt> config file (e.g. LogSeverity=mark, or 
	LogSeverity=info for enhanced verbosity).
      </li>
    </ul>
  </li>
</ul>
</div>
<p>
This document aims to explain how to diagnose and fix common problems that
may result from misunderstanding or misconfiguration when setting up 
a client/server samhain system. This document is divided in several sections
more or less corresponding to the different stages when a client
connects to a server. Each section starts with a brief explanation that
should provide a basic understanding of what is going on.
</p>
<p>
This document does not discuss <i>how</i> to setup a client/server (for
this, look into the manual and/or the HOWTO-client+server). 
</p>

<h2><a name="sect1">Table of Contents</a></h2>
<p>
<a href="#sect1">Connecting to the server</a><br>
<a href="#sect2">Authentication</a><br>
<a href="#sect3">Downloading config/database files</a><br>
<a href="#sect4">Other connection problems</a><br>
</p>

<h2><a name="sect1">Connecting to the server</a></h2>

<p>
Client/server connections are always initiated from the client. The port
is compiled in (there is a configure option to change the default).
The default port is 49777.
</p>

<h3>Problem #1</h3>
<p>
The client reports: <b>Connection refused</b>. The server reports nothing.
</p>
<p>
The server is down, listens on the wrong port, or network failure.
</p>

<h3>Problem #2</h3>
<p>
The client reports: <b>Connection error: Connection reset by peer</b>, and
later also <b>Session key negotiation failed</b>. The server reports:
<b>msg=&quot;Refused connection from ...&quot; subroutine=&quot;libwrap&quot;</b>.
</p>
<p>
The server is compiled with libwrap (TCP Wrapper) support, and the
client is either in <tt>/etc/hosts.deny</tt>, or you have set <i>yule: ALL</i>
in <tt>/etc/hosts.deny</tt>, and forgot to put the client in 
<tt>/etc/hosts.allow</tt>.
</p>
<p>
To fix: make proper entries in <tt>/etc/hosts.allow</tt> and/or 
<tt>/etc/hosts.deny</tt>. There is no need to restart/reload the server.
</p>


<h2><a name="sect2">Authentication</a></h2>
<p>
The client has a password that is used to authenticate to the server.
This password is located within the binary, and is set with the
<tt>samhain_setpwd</tt> helper application, as explained e.g. in the
manual or in the Client+Server HOWTO.
</p><p>
The server has a list of clients that are allowed to connect, and the
verifiers corresponding to the passwords of these clients.
</p>
<p>
Upon successful authentication, client and server will negotiate
a <b>session key</b> that is used for signing further messages
from the client.
</p>

<h3>Problem #1</h3>

<p>
If the password is wrong, the client will report 
<b>Session key negotiation failed</b>. The server will
report: <b>Invalid connection attempt: Session key mismatch</b>
</p>
<p>
To fix: make sure that the password has in fact been set, that you are
using the correct executable for the client (the one where the password is 
set), and that the entry in the server config file is the one generated
for this password (also look out for double entries for this client).
</p>

<h3>Problem #2</h3>

<p>
If the client name (as resolved on the server) is wrong, the client 
will report 
<b>Session key negotiation failed</b>. The server will
report: <b>Invalid connection attempt: Not in client list</b>,
<i>and</i> it will tell you in the same error message 
what name it has inferred for the connecting
client (example): <b>client=&quot;client.mydomain.com&quot;</b>.
</p>
<p> 
The fix depends on the nature of the problem. In principle, it should be
sufficient to change the name of the client in the config file entry, which
isn't really a solution if e.g. the server thinks the client is 'localhost'.
</p>
<p>
There are two different ways to determine the client name. 
Unfortunately, judging 
from customer feedback as well from common sense, both do not work very well
with a messed up local DNS (including /etc/hosts files) and/or
&uuml;berparanoid or misconfigured firewalls (in case of connections 
across one).
</p>
<ul>
  <li>
     <p>
     <i>First method: Determine client name on client, and 
     try to cross-check on server</i>
     <p>
     <p>
     This does not work for a number of people because
     <ol>
       <li>
	 the
	 <tt>/etc/hosts</tt> file on the client machine has errors 
	 (yes, there are plenty machines with a completely 
	 messed up <tt>/etc/hosts</tt> file),
       </li>
       <li>
	 the
	 server cannot resolve the client address because the local DNS is
	 misconfigured, or 
       </li>
       <li> 
	 the client machine has multiple network interfaces, and
	 the interface used is not the one the client name resolves to.
       </li>
     </ol>
     </p>

     <p>
       If the client uses the wrong interface on a multi-interface machine, 
       there is a config file option 
       <tt>SetBindAddress=</tt><i>IP address</i>
       that allows to choose the interface the client will use for
       outgoing connections.
     </p>
     <p>
       If you want to download the config file from the server, you
       should instead use the corresponding command line option
       <tt>--bind-address=</tt><i>IP address</i>
       to select the interface.
     </p>

     <p>
       If you encounter problems, you may (1) fix your 
       <tt>/etc/hosts</tt> file(s), (2) fix your local DNS, or
       (3) switch to the second method.
     </p>
     <p>
       Error messages related to name resolving/cross-checking can be 
       suppressed by setting a 
       very low severity (lower than the logging threshold), e.g.
     </p>
     <p>
       <tt>SeverityLookup=</tt><i>debug</i>
     </p>
     <p>
       in the <i>Misc</i> section of the server configuration,
       if you prefer running <i>unsafe</i> at any speed 
       instead of fixing the problem (you have been warned). Doing so will
       allow an attacker to pose as the client.
     </p>
  </li>
  <li>
     <p><i>Second method: Use address of connecting entity as 
     known to the communication layer</i></p>
     <p>
     This has been dropped as default 
     long ago because it may not always be the 
     address of the client machine. 
     To enable this method, use
     </p>
     <p>
     <tt>SetClientFromAccept=</tt><i>true</i>
     </p>
     <p>
     in the <i>Misc</i> section of the server configuration
     file. If the address cannot be resolved, or reverse lookup of the
     resolved name fails, <i>no</i> error message will be issued,
     but the numerical address will be used.
     </p>
  </li>
</ul>


<h2><a name="sect3">Downloading config/database files</a></h2>

<p>
The client does <i>not</i> tell the server the path to the requested
file - it just tells the <em>type</em> of the file, i.e. 
either a configuration file or a database file. It is entirely the
responsibility of the server to locate the correct file and send it.
</p>
<p>
The server has a <i>data directory</i>, which by default would be 
<tt>/var/lib/yule</tt>. Here the config/database files should be placed.
</p>
<p>
Configuration files: <tt>rc.</tt><i>client.mydomain.tld</i> or 
simply <tt>rc</tt> 
(this can be used as a catchall file).
</p>
<p>
Database files: <tt>file.</tt><i>client.mydomain.tld</i> or 
simply <tt>file</tt> 
(this can be used as a catchall file).
</p>

<h3>Problem #1</h3>

<p>
If the server cannot access the configuration (or database) file, either
because it does not exist or the server has no read permission, the
client will report <b>File download failed</b>. The server will
report: <b>File not accessible</b>, <i>and</i> it will tell you in the
same report the path where it would have expected the file (example):
<b>path=&quot;/var/lib/yule/rc.client.mydomain.com&quot;</b>
</p>
<p>
To fix: put the file in the correct location, make sure the permissions
are ok.
<ul>
  <li>
    Note that <em>the server drops root privileges at startup</em> and
    runs as an unprivileged user (the first existing out of: 
    yule, daemon, nobody).
  </li>
  <li>
    Also remember that to access a file, at least execute permission is required
    <em>for every directory in the path</em>.
  </li>
</ul>
</p>


<h2><a name="sect4">Other connection problems</a></h2>

<p>
The server has a table with client names and their session keys. If 
another client process accesses the server from the same host,
it will negotiate a fresh session key for that host. As a consequence,
the session key of the first client process will become <i>invalid</i>.
</p>
<p>
Also, the server keeps track of the status of a client. If a client 
process does not announce its termination to the server, the server
will not expect a <i>startup</i> message, and issue a warning for any
such message.
</p>

<h3>Problem #1</h3>

<p>
The client reports: <b>Invalid connection state</b>. The server reports:
<b>Invalid connection attempt: Signature mismatch</b>. This is a sign that
a client has tried to connect using an invalid session key. Most probably,
another instance of the client is/was started on the respective host.
</p>
<p>
To fix: if you need to have concurrent access to the server, 
suspend the first process with SIGUSR2 before starting the second. Use
SIGUSR2 again to wake up the first process. Give the process a second or two
to return into the main event loop and go into suspend mode. Do not just use
SIGSTOP/SIGCONT: it is important that the client tells the server that
it will go into suspend.
</p>

<h3>Problem #2</h3>

<p>
The server reports:
<b>Restart without prior exit</b> for a client.
This is a sign that
a client has re-started without informing the server about a previous
termination.
</p>
<p>
This would happen if the client was killed with SIGKILL, or if it terminated
within the routine to send a message to the server (the routine is 
not re-entrant). You may want to investigate messages logged via another
logging facility (e.g. the client's local logfile). Of course it <i>may</i>
also be a segfault, which would be reported via syslog.
</p>

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samhain 3.1.0-5ubuntu1 / usr / share / doc / samhain / HOWTO-client+server-troubleshooting.html
