Programming PHP

Restrict Filesystem Access to a Specific Directory
If your application must operate on the filesystem, you can set the open_basedir
option to further secure the application by restricting access to a specific directory.If
open_basedir is set in php.ini, PHP limits filesystem and I/O functions so that they
can operate only within that directory or any of its subdirectories. For example:
open_basedir = /some/path
With this configuration in effect, the following function calls succeed:
unlink("/some/path/unwanted.exe");
include("/some/path/less/travelled.inc");
But these generate runtime errors:
$fp = fopen ("/some/other/file.exe", "r");
$dp = opendir("/some/path/../other/file.exe");
Of course, one web server can run many applications, and each application typically
stores files in its own directory.You can configure open_basedir on a per-virtual host
basis in your httpd.conf file like this:
ServerName domainA.com
DocumentRoot /web/sites/domainA
php_admin_value open_basedir /web/sites/domainA
Similarly, you can configure it per directory or per URL in httpd.conf:
# by directory
php_admin_value open_basedir /home/httpd/html/app1
# by URL
php_admin_value open_basedir /home/httpd/html/app2
The open_basedir directory can be set only in the httpd.conf file, not in .htaccess files,
and you must use php_admin_value to set it.
File Uploads
File uploads combine the two dangers we’ve seen so far: user-modifiable data and
the filesystem.While PHP 4 itself is secure in how it handles uploaded files, there are
several potential traps for unwary programmers.
Distrust Browser-Supplied Filenames
Be careful using the filename sent by the browser.If possible, do not use this as the
name of the file on your filesystem.It’s easy to make the browser send a file identified
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