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  • Committer: Teddy Hogeborn
  • Date: 2015-05-23 20:18:34 UTC
  • mto: This revision was merged to the branch mainline in revision 756.
  • Revision ID: teddy@recompile.se-20150523201834-e89ex4ito93yni8x
mandos: Use multiprocessing module to run checkers.

For a long time, the Mandos server has occasionally logged the message
"ERROR: Child process vanished".  This was never a fatal error, but it
has been annoying and slightly worrying, since a definite cause was
not found.  One potential cause could be the "multiprocessing" and
"subprocess" modules conflicting w.r.t. SIGCHLD.  To avoid this,
change the running of checkers from using subprocess.Popen
asynchronously to instead first create a multiprocessing.Process()
(which is asynchronous) calling a function, and have that function
then call subprocess.call() (which is synchronous).  In this way, the
only thing using any asynchronous subprocesses is the multiprocessing
module.

This makes it necessary to change one small thing in the D-Bus API,
since the subprocesses.call() function does not expose the raw wait(2)
status value.

DBUS-API (CheckerCompleted): Change the second value provided by this
                             D-Bus signal from the raw wait(2) status
                             to the actual terminating signal number.
mandos (subprocess_call_pipe): New function to be called by
                               multiprocessing.Process (starting a
                               separate process).
(Client.last_checker signal): New attribute for signal which
                              terminated last checker.  Like
                              last_checker_status, only not accessible
                              via D-Bus.
(Client.checker_callback): Take new "connection" argument and use it
                           to get returncode; set last_checker_signal.
                           Return False so gobject does not call this
                           callback again.
(Client.start_checker): Start checker using a multiprocessing.Process
                        instead of a subprocess.Popen.
(ClientDBus.checker_callback): Take new "connection" argument.        Call
                               Client.checker_callback early to have
                               it set last_checker_status and
                               last_checker_signal; use those.  Change
                               second value provided to D-Bus signal
                               CheckerCompleted to use
                               last_checker_signal if checker was
                               terminated by signal.
mandos-monitor: Update to reflect DBus API change.
(MandosClientWidget.checker_completed): Take "signal" instead of
                                        "condition" argument.  Use it
                                        accordingly.  Remove dead code
                                        (os.WCOREDUMP case).

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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
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<!ENTITY TIMESTAMP "2011-08-08">
 
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<!ENTITY TIMESTAMP "2015-03-08">
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<!ENTITY % common SYSTEM "common.ent">
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%common;
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]>
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        <firstname>Björn</firstname>
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        <surname>Påhlsson</surname>
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        <address>
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          <email>belorn@fukt.bsnet.se</email>
 
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          <email>belorn@recompile.se</email>
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        </address>
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      </author>
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      <author>
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        <firstname>Teddy</firstname>
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        <surname>Hogeborn</surname>
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        <address>
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          <email>teddy@fukt.bsnet.se</email>
 
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          <email>teddy@recompile.se</email>
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        </address>
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      </author>
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    </authorgroup>
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    <copyright>
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      <year>2011</year>
 
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      <year>2012</year>
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      <holder>Teddy Hogeborn</holder>
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      <holder>Björn Påhlsson</holder>
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    </copyright>
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      </para>
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    </refsect2>
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    <refsect2 id="sniff">
 
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      <title>How about sniffing the network traffic and decrypting it
 
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      later by physically grabbing the Mandos client and using its
 
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      key?</title>
 
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      <para>
 
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        We only use <acronym>PFS</acronym> (Perfect Forward Security)
 
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        key exchange algorithms in TLS, which protects against this.
 
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      </para>
 
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    </refsect2>
 
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    <refsect2 id="physgrab">
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      <title>Physically grabbing the Mandos server computer?</title>
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      <para>
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      </para>
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    </refsect2>
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    <refsect2 id="fakeping">
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      <title>Faking ping replies?</title>
 
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    <refsect2 id="fakecheck">
 
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      <title>Faking checker results?</title>
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      <para>
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        The default for the server is to use
 
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        If the Mandos client does not have an SSH server, the default
 
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        is for the Mandos server to use
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        <quote><literal>fping</literal></quote>, the replies to which
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        could be faked to eliminate the timeout.  But this could
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        easily be changed to any shell command, with any security
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        measures you like.  It could, for instance, be changed to an
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        SSH command with strict keychecking, which could not be faked.
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        Or IPsec could be used for the ping packets, making them
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        secure.
 
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        measures you like.  If the Mandos client
 
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        <emphasis>has</emphasis> an SSH server, the default
 
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        configuration (as generated by
 
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        <command>mandos-keygen</command> with the
 
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        <option>--password</option> option) is for the Mandos server
 
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        to use an <command>ssh-keyscan</command> command with strict
 
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        keychecking, which can not be faked.  Alternatively, IPsec
 
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        could be used for the ping packets, making them secure.
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      </para>
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    </refsect2>
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  </refsect1>
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    <variablelist>
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      <varlistentry>
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        <term>
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          <ulink url="http://www.fukt.bsnet.se/mandos">Mandos</ulink>
 
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          <ulink url="http://www.recompile.se/mandos">Mandos</ulink>
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        </term>
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        <listitem>
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          <para>