How do shared hosts protect different sites?

Question

I host all my websites from a single Linode VPN, and am about to sell some limited space of my Linode to a friend to host their new blog (it's going to be a simple wordpress blog). It'll simply be another entry in Apache, and then a dedicated folder to that website which will contain all the Wordpress files. My issue (I'm thinking ahead - I haven't actually sold him the stuff yet) is with security. If someone manages to somehow hack his Wordpress blog (He might have a weak password or there could be another flaw (I'm going to try and make it pretty watertight though - I have full server control over his site, he doesn't have SSH access or anything)), will my main site be comprimised?

What is the easiest way to prevent or make an effort to prevent any of the files in his website directory or anyone that gains access there, getting access to any of my other folders or files?

Answer 1

With the setup you've proposed there, yes. The only solution here is something like suPHP. If his website runs as the same user as your website, there is nothing that you can do to protect yourself. You need to set his website up as a different user, and ensure permissions on all the files are tight (0700 ideally).

Answer 2

Assuming you are running PHP, you can try to isolate your friend's website in either of these ways:

1. (easier, but less secure and convenient) Set safe_mode and open_basedir for your friend. In this case, the files in his directory wouldn't have access to anything else on the web server. Though, as written on PHP website, relying on safe_mode is discouraged and this feature is deprecated in PHP 5.3.0 .

2. (difficult for the first time, but more secure and convenient later) Make PHP execute scripts in your friend's directory under a separate user. How to achieve that depends on your current PHP and Apache configuration. If you are using mod_php, then you may look at suPHP (http://www.suphp.org/), which is an also an Apache module. If you have PHP as CGI or FastCGI, you may try to set up suEXEC (https://httpd.apache.org/docs/2.2/suexec.html).