mirror of https://github.com/BOINC/boinc.git
255 lines
10 KiB
PHP
255 lines
10 KiB
PHP
<?php
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require_once("docutil.php");
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page_head("Sandbox design");
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echo "
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This document describes a proposed modification to the Unix
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(including Linux and Mac OS X) versions of BOINC.
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The goal of this change is to 'sandbox' BOINC applications,
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i.e. to limit the amount of damage that a malicious
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or malfunctioning application can cause.
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<p>
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In our design, BOINC applications run under a specially-created account
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having a minimal set of privileges.
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Previously, the applications typically ran as the user who installed BOINC,
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and had the full privileges of that account.
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";
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function prot($user, $group, $perm) {
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return "
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<br>
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user: $user
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<br>
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group: $group
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<br>
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protection: $perm";
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}
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$pp06640775 = prot('boinc_project', 'boinc_project', '0664 or 0775');
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$mp2500 = prot('boinc_master', 'boinc_project', '0500+setgid');
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$rm4050 = prot('root', 'boinc_master', '0050+setuid');
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$rm4055 = prot('root', 'boinc_master', '0055+setuid');
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$mm0550 = prot('boinc_master', 'boinc_master', '0550');
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$mm0440 = prot('boinc_master', 'boinc_master', '0440');
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$mm0660 = prot('boinc_master', 'boinc_master', '0660');
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$mm0775 = prot('boinc_master', 'boinc_master', '0775');
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$mm0664 = prot('boinc_master', 'boinc_master', '0664');
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$mp0775 = prot('boinc_master', 'boinc_project', '0775');
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$mp06640775 = prot('boinc_master', 'boinc_project', '0664 or 0775');
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$mm2555 = prot('boinc_master', 'boinc_master', '0555+setgid');
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$mm6555 = prot('boinc_master', 'boinc_master', '0555+setuid+setgid');
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$ua0555 = prot('(installing user)', 'admin', '0555');
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$colors = array('ddddff', 'ccccff', 'bbbbff');
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function show_dir($level, $name, $prot, $contents) {
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global $colors;
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$color = $colors[$level];
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$x = "
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<table bgcolor=$color cellpadding=6 cellspacing=0 border=1 width=100%>
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<tr>
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<td valign=top><b>$name</b> <font size=-1>$prot</font></td><td valign=top>
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";
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for ($i=0; $i<sizeof($contents); $i++) {
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if ($i) $x .= '<br>';
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$c = $contents[$i];
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$x .= $c;
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}
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$x .= "
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</td></tr>
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</table>
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";
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return $x;
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}
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function show_file($name, $prot) {
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return "
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$name <font size=-1>$prot</font><br>
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";
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}
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echo "
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<p>
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Our design uses two users and two groups,
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both specially created for use by BOINC.
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These users and groups are created by the installation process.
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<ul>
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<li>Group: <b>boinc_master</b>
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<li>Group: <b>boinc_project</b>
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<li>User: <b>boinc_master</b>
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<ul>
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<li>Primary group: <b>boinc_master</b>
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<li>Supplementary groups: none
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</ul>
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<li>User: <b>boinc_project</b>
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<ul>
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<li>Primary group: <b>boinc_project</b>
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<li>Supplementary groups: none
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</ul>
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</ul>
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On Mac OS X, <b>boinc_project</b> and <b>boinc_master</b>
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are added to the Supplementary Groups Lists of those other users
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who are members of group <b>admin</b>.
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This gives admin users full access to all BOINC and project files.
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<p>
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The following diagram shows user, group and permissions
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for the BOINC file and directory tree:
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<p>
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";
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echo
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show_dir(0, 'BOINC data', $mm0775, array(
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show_dir(1, 'projects', $mm0775, array(
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show_dir(2, 'setiathome.berkeley.edu', $mp0775, array(
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show_file('files created by BOINC Client', $mp06640775),
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show_file('files created by project apps', $pp06640775)
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))
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)),
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show_dir(1, 'slots', $mm0775, array(
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show_dir(2, '0', $mp0775, array(
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show_file('files created by BOINC Client', $mp06640775),
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show_file('files created by project apps', $pp06640775)
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))
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)),
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show_dir(1, 'switcher (directory)', $mm0550, array(
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show_file('switcher (executable)', $rm4050),
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show_file('setprojectgrp (executable)', $mp2500)
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)),
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show_dir(1, 'locale', $mm0550, array(
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show_dir(2, 'de', $mm0550, array(
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show_file('BOINC Manager.mo', $mm0440),
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show_file('wxstd.mo', $mm0440)
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))
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)),
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show_file('account_*.xml', $mm0664),
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show_file('acct_mgr_login.xml', $mm0664),
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show_file('client_state.xml', $mm0664),
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show_file('gui_rpc_auth.cfg', $mm0660),
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show_file('sched_reply*', $mm0664),
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show_file('sched_request*', $mm0664)
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));
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echo "<br><br>";
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echo
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show_dir(0, 'BOINC executables', $ua0555, array(
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show_file('BOINC Manager', $mm2555),
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show_file('BOINC Client', $mm6555),
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show_dir(1, 'screensaver (directory)', $ua0555, array(
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show_file('gfx_switcher (executable)', $rm4055)
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)),
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));
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echo "
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<p>Implementation notes:
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<ul>
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<li>BOINC Client runs setuid and setgid to <b>boinc_master:boinc_master</b>.
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<li>BOINC Client uses the helper application <i>setprojectgrp</i> to
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set project and slot files and directories to group <b>boinc_project</b>.
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<li>BOINC Client does not directly execute project applications.
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It runs the helper application <i>switcher</i>,
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passing the request in the argument list.
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<i>switcher</i> runs setuid <b>root</b> and immediately changes its real and
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effective user ID and group ID to <b>boinc_project</b>,
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so all project applications inherit user and group <b>boinc_project</b>.
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This blocks project applications from accessing unauthorized files.
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<li>In most cases, it is best to avoid running setuid <b>root</b> because
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it can present a security risk. In this case, however, this is necessary to
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<i>reduce</i> the risk because only the superuser can change the <i>real</i>
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user and group of a process. This prevents a malicious or malfunctioning
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application from reverting to the user and group who launched BOINC, since any
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process can change its user and group back to the <i>real</i> user and
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group IDs.
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<li>BOINC's use of setuid <b>root</b> for the <i>switcher</i> application is
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safe because:
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<ul>
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<li>The <i>switcher</i> application is inside the <i>switcher</i> directory.
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This directory is accessible only by user and group <b>boinc_master</b>,
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so that project applications cannot modify the <i>switcher</i>
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application's permissions or code. This also prevents unauthorized users
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from using <i>switcher</i> to damage or manipulate project files.
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<li>The <i>switcher</i> application is readable and executable only by
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group <b>boinc_master</b>; all other access is forbidden.
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<li>When it is run, the <i>switcher</i> application immediately changes
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its real and effective user ID and group ID to <b>boinc_project</b>, disabling
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its superuser privileges.
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</ul>
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<li>BOINC Manager runs setgid to group <b>boinc_master</b>.
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It can access all files in group <b>boinc_master</b>.
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It runs as the user who launched it,
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which is necessary for a number of GUI features to work correctly.
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Although this means that BOINC Manager cannot modify files
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created by project applications, there is no need for it to do so.
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<li>Starting with BOINC version 6.0, project science applications use a
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separate companion application to display graphics. These graphics
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applications are launched by the BOINC Manager when the user clicks on
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the <i>Show Graphics</i> button. Running the graphics application
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with the BOINC Manager's user and group would be a security risk, so
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BOINC Manager uses the <i>switcher</i> application to launch them as
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user and group <b>boinc_project</b>.
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<li>The screensaver also can run the graphics applications. The Macintosh
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screensaver is launched by the operating system, so it runs as the
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currently logged in user and group. Since running the science projects' graphics applications
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with this user and group would be a security risk, the screensaver has
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its own embedded helper application <i>gfx_switcher</i> which it uses to
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launch the graphics applications.
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Like the <i>switcher</i> application, <i>gfx_switcher</i> runs setuid
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<b>root</b> and immediately changes its real and effective user ID and
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group ID to <b>boinc_project</b>
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<li>The BOINC screensaver's use of setuid <b>root</b> for the
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<i>gfx_switcher</i> application is safe because:
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<ul>
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<li>When it is run, the <i>gfx_switcher</i> application immediately changes
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its real and effective user ID and group ID to <b>boinc_project</b>, disabling
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its superuser privileges.
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<li>The <i>gfx_switcher</i> application has very limited functionality. It
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accepts only two commands as its first argument:.
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<ul>
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<li><i>launch_gfx</i>: the second argument is the slot number. It looks for
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a soft-link named <b>graphics_app</b> in the specified slot directory and launches
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the referenced graphics application.
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<li><i>kill_gfx</i>: the second argument is the process ID. It kills the
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application with the process ID; since it is running as user and group
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<b>boinc_project</b>, it can affect only processes belonging to that user.
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</ul>
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</ul>
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<li>BOINC Manager and BOINC Client set their umasks to 002,
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which is inherited by all child applications.
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The default permissions for all files and directories they create prevent
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modification outside the user and group.
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Because files are world-readable, BOINC Client can read files written by projects.
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Third-party add-ons can also read BOINC data files.
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<li>Non-admin users cannot directly modify BOINC or project files.
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They can modify these files only by running the BOINC Manager and Client.
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<li>Users with admin access are members of groups <b>boinc_master</b>
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and <b>boinc_project</b> so that they do have
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direct access to all BOINC and project files
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to simplify maintenance and administration.
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<li>The RPC password file <i>gui_rpc_auth.cfg</i>
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is accessible only by user and group <b>boinc_master</b>.
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In other words, only BOINC Manager, BOINC Client and
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authorized administrative users can read or modify it,
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limiting access to most BOINC RPC functions.
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<li>BOINC Manager restricts certain functions to authorized users:
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Attach to Project, Detach from Project, Reset Project, Abort Task,
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Abort Transfer, Update Account Manager.
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If an unauthorized user requests these functions,
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the Manager requires password authentication.
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<li>On Macintosh computers, the actual directory structures
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of the BOINC Manager application bundle and the screensaver bundle are
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more complex than implied by the box <i>BOINC executables</i> in the
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BOINC tree diagram shown above.
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<li>Some Macintosh system administrators may wish to limit which users
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can perform BOINC Manager functions (Activity Menu, etc.).
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This can be done by moving BOINC Manager out of the
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<b>/Applications</b> directory into a directory with restricted access.
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</ul>
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</p>
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";
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page_tail();
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?>
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