How do I make a shared web hosting setup with dynamic vhosts?

Question

We are building a sort of shared hosting web server setup, but everything is managed by a web application on ourdomain.com which has default apache user (www-data) to access everyone’s files.

Everybody has a user_name, and their web_root is [some_root_folder]/[user_name]

We are creating dynamic virtual hosts using

http://httpd.apache.org/docs/2.0/vhosts/mass.html#xtra-conf

as

[some_root_folder]/[user_name] user_name.ourdomain.com

we do

chown 770 user_name:www-data -R [some_root_folder]/[user_name]

We do not wish to create separate vhosts because that requires apache reload on each signup (i will ask your opinion on creating separate vhosts using mpm-itk on another entry).

Question

If user_michael executes:

<?php echo file_get_contents(‘../user_george/index.php’); ?> on user_michael.ourdomain.com/index.php

Michael is able to read George’s files because both directories belong to www-data user group (otherwise our web app can’t modify them)

So: How can www-data can modify both Michael's and George's files, but they can't modify each other's, given setup above?

Answer 1

When you run file_get_contents, the user which is reading the ../user_george/index.php file is the same as the web server (www-data) not the owner of the file.

PHP Safe Mode is a solution for this issue, but is deprecated. I'd recommend to check this series for solutions about Security in Shared Hosting.

Answer 2

Restarting Apache after each signup is probably not a problem. See graceful restart.

For your permission problem, if you only need php and don't want to run CGI you may want to look into PHP Safe Mode. It's deprecated, not the best way, but easy to use.
Another way is to use suPHP to run php script as user_name instead of apache users.