PHPのセーフモードは共有サーバでのセキュリティの問題を解決するための
試みです。この問題をPHPのレベルで解決しようとするのはアーキテクチャ上
正しくありません。しかし、WebサーバやOSレベルでの代替策はあまり現実
てきではないため、多くのユーザ、特にISPではセーフモードが現在使用され ています。
表 22-1セキュリティとセーフモード設定ディレクティブ
名前 | デフォルト | 変更の可否 |
---|---|---|
safe_mode | "0" | PHP_INI_SYSTEM |
safe_mode_gid | "0" | PHP_INI_SYSTEM |
safe_mode_include_dir | NULL | PHP_INI_SYSTEM |
safe_mode_exec_dir | "" | PHP_INI_SYSTEM |
safe_mode_allowed_env_vars | PHP_ | PHP_INI_SYSTEM |
safe_mode_protected_env_vars | LD_LIBRARY_PATH | PHP_INI_SYSTEM |
open_basedir | NULL | PHP_INI_SYSTEM |
disable_functions | "" | PHP_INI_SYSTEM |
セーフモードの設定ディレクティブの簡単な説明を以下に示します。
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.
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).
注意 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. 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/"
注意 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
セーフモード
がonの場合、PHPは、 現在のスクリプトの所有者がファイル関数により処理されているファイル
の所有者に一致するかどうかを調べます。例えば、
-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:
disable_functions readfile,system |
Warning: readfile() has been disabled for security reasons in /docroot/script.php on line 2 |