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<?xml version="1.0" encoding="iso-8859-1"?>
<!-- $Revision: 1.1 $ -->
<chapter id="features.safe-mode">
<title>Safe Mode</title>
<para>
The PHP safe mode is an attempt to solve the shared-server security
problem. It is architecturally incorrect to try to solve this
problem at the PHP level, but since the alternatives at the web
server and OS levels aren't very realistic, many people,
especially ISP's, use safe mode for now.
</para>
<para>
The configuration directives that control safe mode are:
<programlisting role="ini">
<![CDATA[
safe_mode = Off
open_basedir =
safe_mode_exec_dir =
safe_mode_allowed_env_vars = PHP_
safe_mode_protected_env_vars = LD_LIBRARY_PATH
disable_functions =
]]>
</programlisting>
</para>
<para>
When <link linkend="ini.safe-mode">safe_mode</link> is on, PHP checks to see
if the owner of the current script matches the owner of the file to be
operated on by a file function. For example:
<programlisting role="ls">
<![CDATA[
-rw-rw-r-- 1 rasmus rasmus 33 Jul 1 19:20 script.php
-rw-r--r-- 1 root root 1116 May 26 18:01 /etc/passwd
]]>
</programlisting>
Running this script.php
<programlisting role="php">
<![CDATA[
<?php
readfile('/etc/passwd');
?>
]]>
</programlisting>
results in this error when safe mode is enabled:
<screen>
<![CDATA[
Warning: SAFE MODE Restriction in effect. The script whose uid is 500 is not
allowed to access /etc/passwd owned by uid 0 in /docroot/script.php on line 2
]]>
</screen>
</para>
<para>
If instead of <link linkend="ini.safe-mode">safe_mode</link>, you set an
<link linkend="ini.open-basedir">open_basedir</link> directory then all
file operations will be limited to files under the specified directory
For example (Apache httpd.conf example):
<programlisting role="ini">
<![CDATA[
<Directory /docroot>
php_admin_value open_basedir /docroot
</Directory>
]]>
</programlisting>
If you run the same script.php with this
<link linkend="ini.open-basedir">open_basedir</link> setting
then this is the result:
<screen>
<![CDATA[
Warning: open_basedir restriction in effect. File is in wrong directory in
/docroot/script.php on line 2
]]>
</screen>
</para>
<para>
You can also disable individual functions. If we add this to our php.ini
file:
<programlisting role="ini">
<![CDATA[
disable_functions readfile,system
]]>
</programlisting>
Then we get this output:
<screen>
<![CDATA[
Warning: readfile() has been disabled for security reasons in
/docroot/script.php on line 2
]]>
</screen>
</para>
<sect1 id="features.safe-mode.functions">
<title>Functions restricted/disabled by safe mode</title>
<para>
This is a still probably incomplete and possibly incorrect listing
of the functions limited by
<link linkend="features.safe-mode">safe mode</link>.
<!-- TODO: add ¬e.sm.*; to the functions mentioned here.
That entity should link to this section -->
<table>
<title>Safe mode limited functions</title>
<tgroup cols="2">
<thead>
<row>
<entry>Function</entry>
<entry>Limitations</entry>
</row>
</thead>
<tbody>
<row>
<entry><function>dbmopen</function></entry>
<entry>&sm.uidcheck;</entry>
</row>
<row>
<entry><function>dbase_open</function></entry>
<entry>&sm.uidcheck;</entry>
</row>
<row>
<entry><function>filepro</function></entry>
<entry>&sm.uidcheck;</entry>
</row>
<row>
<entry><function>filepro_rowcount</function></entry>
<entry>&sm.uidcheck;</entry>
</row>
<row>
<entry><function>filepro_retrieve</function></entry>
<entry>&sm.uidcheck;</entry>
</row>
<row>
<entry><function>ifx_*</function></entry>
<entry>sql_safe_mode restrictions, (!= safe mode)</entry>
<!-- TODO: more info on sql-safe-mode -->
</row>
<row>
<entry><function>ingres_*</function></entry>
<entry>sql_safe_mode restrictions, (!= safe mode)</entry>
<!-- TODO: more info on sql-safe-mode -->
</row>
<row>
<entry><function>mysql_*</function></entry>
<entry>sql_safe_mode restrictions, (!= safe mode)</entry>
<!-- TODO: more info on sql-safe-mode -->
</row>
<row>
<entry><function>pg_loimport</function></entry>
<entry>&sm.uidcheck;</entry>
<!-- source TODO: there is no PHP-warning for that safe-mode-restriction -->
</row>
<row>
<entry><function>posix_mkfifo</function></entry>
<entry>&sm.uidcheck.dir;</entry>
</row>
<row>
<entry><function>putenv</function></entry>
<entry>Obeys the safe_mode_protected_env_vars and
safe_mode_allowed_env_vars ini-directives. See also the documentation
on <function>putenv</function></entry>
<!-- TODO: document those directives in chapters/config.xml -->
</row>
<row>
<entry><function>move_uploaded_file</function></entry>
<entry>&sm.uidcheck; <!-- TODO: check this --></entry>
</row>
<!-- TODO: from here on, add warning to the function itself -->
<row>
<entry><function>chdir</function></entry>
<entry>&sm.uidcheck.dir;</entry>
</row>
<row>
<entry><function>dl</function></entry>
<entry>&sm.disabled;</entry>
</row>
<row>
<entry><link linkend="language.operators.execution">backtick operator</link></entry>
<entry>&sm.disabled;</entry>
</row>
<row>
<entry><function>shell_exec</function> (functional equivalent
of backticks)</entry>
<entry>&sm.disabled;</entry>
</row>
<row>
<entry><function>exec</function></entry>
<entry>You can only execute executables within the <link
linkend="ini.safe-mode-exec-dir">safe_mode_exec_dir</link>.
For practical reasons it's currently not allowed to have
<literal>..</literal> components in the path to the executable.</entry>
</row>
<row>
<entry><function>system</function></entry>
<entry>You can only execute executables within the <link
linkend="ini.safe-mode-exec-dir">safe_mode_exec_dir</link>.
For practical reasons it's currently not allowed to have
<literal>..</literal> components in the path to the executable.</entry>
</row>
<row>
<entry><function>passthru</function></entry>
<entry>You can only execute executables within the <link
linkend="ini.safe-mode-exec-dir">safe_mode_exec_dir</link>.
For practical reasons it's currently not allowed to have
<literal>..</literal> components in the path to the executable.</entry>
</row>
<row>
<entry><function>popen</function></entry>
<entry>You can only execute executables within the <link
linkend="ini.safe-mode-exec-dir">safe_mode_exec_dir</link>.
For practical reasons it's currently not allowed to have
<literal>..</literal> components in the path to the executable.</entry>
<!-- TODO: not sure. popen uses a completely different implementation
Don't know why, don't know whether it's behaving the same -->
</row>
<row>
<entry><function>mkdir</function></entry>
<entry>&sm.uidcheck.dir;</entry>
</row>
<row>
<entry><function>rmdir</function></entry>
<entry>&sm.uidcheck;</entry>
</row>
<row>
<entry><function>rename</function></entry>
<entry>&sm.uidcheck; &sm.uidcheck.dir;<!-- on the old name only, it seems. Is rename preventing moving files? --></entry>
</row>
<row>
<entry><function>unlink</function></entry>
<entry>&sm.uidcheck; &sm.uidcheck.dir;</entry>
</row>
<row>
<entry><function>copy</function></entry>
<entry>&sm.uidcheck; &sm.uidcheck.dir; (on
<parameter>source</parameter> and
<parameter>target</parameter>) </entry>
</row>
<row>
<entry><function>chgrp</function></entry>
<entry>&sm.uidcheck;</entry>
</row>
<row>
<entry><function>chown</function></entry>
<entry>&sm.uidcheck;</entry>
</row>
<row>
<entry><function>chmod</function></entry>
<entry>&sm.uidcheck; In addition, you cannot
set the SUID, SGID and sticky bits</entry>
</row>
<row>
<entry><function>touch</function></entry>
<entry>&sm.uidcheck; &sm.uidcheck.dir;</entry>
</row>
<row>
<entry><function>symlink</function></entry>
<entry>&sm.uidcheck; &sm.uidcheck.dir; (note: only the target is
checked)</entry>
</row>
<row>
<entry><function>link</function></entry>
<entry>&sm.uidcheck; &sm.uidcheck.dir; (note: only the target is
checked)</entry>
</row>
<row>
<entry><function>getallheaders</function></entry>
<entry>In safe mode, headers beginning with 'authorization'
(case-insensitive)
will not be returned. Warning: this is broken with the aol-server
implementation of <function>getallheaders</function>!</entry>
</row>
<row>
<entry>Any function that uses
<filename>php4/main/fopen_wrappers.c</filename>
</entry>
<entry>??</entry>
</row>
</tbody>
</tgroup>
</table>
</para>
</sect1>
</chapter>
<!-- Keep this comment at the end of the file
Local variables:
mode: sgml
sgml-omittag:t
sgml-shorttag:t
sgml-minimize-attributes:nil
sgml-always-quote-attributes:t
sgml-indent-step:1
sgml-indent-data:t
indent-tabs-mode:nil
sgml-parent-document:nil
sgml-default-dtd-file:"../../manual.ced"
sgml-exposed-tags:nil
sgml-local-catalogs:nil
sgml-local-ecat-files:nil
End:
vim600: syn=xml fen fdm=syntax fdl=2 si
vim: et tw=78 syn=sgml
vi: ts=1 sw=1
-->
|
