background: #eeeeee;
border: dotted thin #999999;
margin-left: 36pt;
- padding: 10px;
+ padding: 10pt;
}
PRE.command EM, PRE.example EM {
}
BLOCKQUOTE {
- background: #cccccc;
+ background: #eeeeee;
border: solid thin #999999;
padding: 10pt;
}
font-size: 100%;
}
+H1.title {
+}
+
H2.title, H3.title {
border-bottom: solid 2pt #000000;
}
<body>
<div class='body'>
<!--
- "$Id: api-filter.header 8087 2008-10-27 21:37:05Z mike $"
+ "$Id: api-filter.header 8627 2009-05-13 21:39:17Z mike $"
Filter and backend programming header for the Common UNIX Printing System
(CUPS).
- Copyright 2008 by Apple Inc.
+ Copyright 2008-2009 by Apple Inc.
These coded instructions, statements, and computer programs are the
property of Apple Inc. and are protected by Federal copyright
file is missing or damaged, see the license at "http://www.cups.org/".
-->
+<h1 class='title'>Filter and Backend Programming</h1>
+
<div class='summary'><table summary='General Information'>
<thead>
<tr>
<ul class="subcontents">
<li><a href="#OVERVIEW">Overview</a><ul class="subcontents">
<li><a href="#SECURITY">Security Considerations</a></li>
+<li><a href="#PERMISSIONS">File Permissions</a></li>
<li><a href="#TEMPFILES">Temporary Files</a></li>
<li><a href="#COPIES">Copy Generation</a></li>
<li><a href="#EXITCODES">Exit Codes</a></li>
Filter and backend programming introduction for the Common UNIX Printing
System (CUPS).
- Copyright 2007-2008 by Apple Inc.
+ Copyright 2007-2009 by Apple Inc.
Copyright 1997-2006 by Easy Software Products, all rights reserved.
These coded instructions, statements, and computer programs are the
output. The backend is the last filter in the chain and writes to the
device.</p>
+<p>Filters are always run as a non-privileged user, typically "lp", with no
+connection to the user's desktop. Backends are run either as a non-privileged
+user or as root if the file permissions do not allow user or group execution.
+The <a href="#PERMISSIONS">file permissions</a> section talks about this in
+more detail.</p>
+
<h3><a name="SECURITY">Security Considerations</a></h3>
<p>It is always important to use security programming practices. Filters and
used by the filter since that can lead to an unauthorized disclosure of
information. <em>Always</em> treat input as suspect and validate it!</p>
-<p>If you are developing a backend that runs as root, make sure to check for
+<p>If you are developing a backend that runs as root , make sure to check for
potential buffer overflows, integer under/overflow conditions, and file
accesses since these can lead to privilege escalations. When writing files,
always validate the file path and <em>never</em> allow a user to determine
directory to write to.</p>
<p>In addition, some operating systems provide additional security mechanisms
-that further limit file system access, even for backends running as root. On
+that further limit file system access, even for backends running as root. On
Mac OS X, for example, no backend may write to a user's home directory.</p>
</blockquote>
+<h3><a name="PERMISSIONS">File Permissions</a></h3>
+
+<p>For security reasons, CUPS will only run filters and backends that are owned
+by root and do not have world write permissions. The recommended permissions for
+filters and backends are 0555 - read and execute but no write. Backends that
+must run as root should use permissions of 0500 - read and execute by root, no
+access for other users. Write permissions can be enabled for the root user
+only.</p>
+
+<p>To avoid a warning message, the directory containing your filter(s) must also
+be owned by root and have world write disabled - permissions of 0755 or 0555 are
+strongly encouraged.</p>
+
<h3><a name="TEMPFILES">Temporary Files</a></h3>
<p>Temporary files should be created in the directory specified by the
first.
</p>
-<h3 class="function"><span class="info"> CUPS 1.4 </span><a name="cupsBackendReport">cupsBackendReport</a></h3>
+<h3 class="function"><span class="info"> CUPS 1.4
/Mac OS X 10.6 </span><a name="cupsBackendReport">cupsBackendReport</a></h3>
<p class="description">Write a device line from a backend.</p>
<p class="code">
void cupsBackendReport (<br>
update the value to contain the number of data bytes in the buffer.
</p>
-<h3 class="function"><span class="info"> CUPS 1.4 </span><a name="cupsSideChannelSNMPGet">cupsSideChannelSNMPGet</a></h3>
+<h3 class="function"><span class="info"> CUPS 1.4
/Mac OS X 10.6 </span><a name="cupsSideChannelSNMPGet">cupsSideChannelSNMPGet</a></h3>
<p class="description">Query a SNMP OID's value.</p>
<p class="code">
<a href="#cups_sc_status_t">cups_sc_status_t</a> cupsSideChannelSNMPGet (<br>
the printer does not respond to the SNMP query.
</p>
-<h3 class="function"><span class="info"> CUPS 1.4 </span><a name="cupsSideChannelSNMPWalk">cupsSideChannelSNMPWalk</a></h3>
+<h3 class="function"><span class="info"> CUPS 1.4
/Mac OS X 10.6 </span><a name="cupsSideChannelSNMPWalk">cupsSideChannelSNMPWalk</a></h3>
<p class="description">Query multiple SNMP OID values.</p>
<p class="code">
<a href="#cups_sc_status_t">cups_sc_status_t</a> cupsSideChannelSNMPWalk (<br>
<dd class="description">Return the IEEE-1284 device ID</dd>
<dt>CUPS_SC_CMD_GET_STATE </dt>
<dd class="description">Return the device state</dd>
-<dt>CUPS_SC_CMD_SNMP_GET <span class="info"> CUPS 1.4 </span></dt>
+<dt>CUPS_SC_CMD_SNMP_GET <span class="info"> CUPS 1.4/Mac OS X 10.6 </span></dt>
<dd class="description">Query an SNMP OID </dd>
-<dt>CUPS_SC_CMD_SNMP_GET_NEXT <span class="info"> CUPS 1.4 </span></dt>
+<dt>CUPS_SC_CMD_SNMP_GET_NEXT <span class="info"> CUPS 1.4/Mac OS X 10.6 </span></dt>
<dd class="description">Query the next SNMP OID </dd>
<dt>CUPS_SC_CMD_SOFT_RESET </dt>
<dd class="description">Do a soft reset</dd>
projects / thirdparty / cups.git / blobdiff