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.
Here is a short explanation of the configuration
directives.
Whether to enable PHP's safe mode. Read the Security and chapter for
more information.
By default, Safe Mode does a UID compare check
when opening files. If you want to relax this to a
GID compare, then turn on safe_mode_gid. Whether to
use UID (FALSE) or
GID (TRUE)
checking upon file access.
UID/GID checks are bypassed when including
files from this directory and its subdirectories
(directory must also be in
include_path or full path must including).
As of PHP 4.2.0, this directive can take a
semi-colon separated path in a similar fashion to the
include_path directive, rather than just a single
directory.
The restriction specified is actually a prefix,
not a directory name. This means that
"safe_mode_include_dir = /dir/incl" also allows
access to "/dir/include" and "/dir/incls" if they
exist. When you want to restrict access to only the
specified directory, end with a slash. For example:
"safe_mode_include_dir = /dir/incl/"
If PHP is used in safe mode,
system() and the other functions executing system
programs refuse to start programs that are not in
this directory.
Setting certain environment variables may be a
potential security breach. This directive contains a
comma-delimited list of prefixes. In Safe Mode, the
user may only alter environment variables whose names
begin with the prefixes supplied here. By default,
users will only be able to set environment variables
that begin with PHP_ (e.g. PHP_FOO=BAR).
注: If this directive is empty, PHP will let the user modify ANY environment variable!
This directive contains a comma-delimited list
of environment variables that the end user won't be
able to change using
putenv(). These variables
will be protected even if safe_mode_allowed_env_vars
is set to allow to change them.
Limit the files that can be opened by PHP to the
specified directory-tree, including the file itself.
This directive is NOT affected by whether Safe
Mode is turned On or Off.
When a script tries to open a file with, for
example, fopen or gzopen, the location of the file is
checked. When the file is outside the specified
directory-tree, PHP will refuse to open it. All
symbolic links are resolved, so it's not possible to
avoid this restriction with a symlink.
The special value
. indicates that the directory in which the
script is stored will be used as base-directory.
Under Windows, separate the directories with a
semicolon. On all other systems, separate the
directories with a colon. As an Apache module,
open_basedir paths from parent directories are now
automatically inherited.
The restriction specified with open_basedir is
actually a prefix, not a directory name. This means
that "open_basedir = /dir/incl" also allows access to
"/dir/include" and "/dir/incls" if they exist. When
you want to restrict access to only the specified
directory, end with a slash. For example:
"open_basedir = /dir/incl/"
注: Support for multiple directories was added in 3.0.7.
The default is to allow all files to be
opened.
This directive allows you to disable certain
functions for security
reasons. It takes on a comma-dilimited list of
function names. disable_functions is not affected by
Safe
Mode.
This directive must be set in php.ini For example, you cannot set
this in httpd.conf.
See also:
register_globals, display_errors,
and
log_errors
When
safe_mode 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:
-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 |
?php readfile('/etc/passwd'); ? |
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 |
However, there may be environments where a strict UID check is not appropriate and a
relaxed GID check is sufficient.
This is supported by means of the
safe_mode_gid switch. Setting it to On performs the relaxed
GID checking, setting it to
Off (the default) performs
UID checking.
If instead of safe_mode, you
set an
open_basedir directory then all file operations will be
limited to files under the specified directory For example
(Apache httpd.conf example):
Directory /docroot php_admin_value open_basedir /docroot /Directory |
Warning: open_basedir restriction in effect. File is in wrong directory in /docroot/script.php on line 2 |
You can also disable individual functions. Note that
the disable_functions directive can not be used outside of
the php.ini file which means that
you cannot disable functions on a per-virtualhost or
per-directory basis in your httpd.conf file. If we add this
to our php.ini file:
Warning: readfile() has been disabled for security reasons in /docroot/script.php on line 2 |