Chmod Questions

[Fourjays]

I'm not really sure if this belongs in the PHP or Apache section - not sure which chmod falls under.

I'm making a CMS system, in PHP, that I plan to redistribute. Until now I've never had to think of programming for multiple situations, etc as I've just made things for my own servers where I know the exact settings.

This system is flat-file based, reading from and writing to XML files. The most sensitive data stored is the IP addresses of visitors (could use a different method which doesn't require the storage of this information). No passwords, system or otherwise. Apart from that the only data in the XML files are things like news articles, comments, etc.

I'm wondering how important Chmod/permissions are? The system only needs to be able to write to the files a little bit for the "user-side" (statistics, and comments). Now I could add the chmod function to my "savexml" function so that the files are made writable (0777) before hand, and set back to read-only (0644) afterwards, but in some cases (like my own host) this can't be done ("operation not permitted").

If the files were all left as 777 permanently, what damage could be done? What kind of security risk is there in doing this? Or is there a chmod value that will let the script read/write the files, but stop anyone from accessing it via other methods?

Any help is greatly appreciated.
Thanks.

[equalm]

chmod/permissions matter a great deal. world writable files open yourself up to the possibility of a rogue script rewriting one of your files to become a vicious php file which can do some bad things.

however, most people run PHP via Apache and it's nice that Apache runs a non-privileged user. If you're manipulating files, you have to make sure group or individual ownership is shared between the Apache process and the XML files.

Another thing to consider is that by forcing people to use 777 permissions for your CMS, you will already be eliminating a fair number of potential users from the get-go, as that that is a non-negotiable security decision to some.

And good luck to those folks who want to install it, but first have to convince their systems administrator to run it as 777!

.

[Fourjays]

Thanks for the reply. Just to clarify, I use my own functions for parsing my XML data, and not PHP's built-in expat functions. I fopen/fread all XML files.

Would a sensible approach be;
Have it automatically change permissions using chmod() if it is available. If it isn't, the user can set XML files that need writing to all the time, to 777 (or similar) and set ones that only need to be accessed by the admin to 644 until they need to edit them?

Any other ideas?

[edited by: Fourjays at 10:10 pm (utc) on Feb. 24, 2007]