Evaluate a command string for access control

Hi,
I need some help!

I will make this feature:
- given a directory name, a "client" can access only in this directory and all the subdirectory in it.

ES:
directory name: /home/tmp
The client can access to /home/tmp and all its subdirectory but not in /home or any other directory in the filesystem.

I will make this with C or LINUX shell commands.

NOTE: if the command is ls home/tmp/../../../tmp.txt the client can't access to this directory so a good evaluation of the command string given has to be performed.

I think to evaluate the string given to me expand the path (removing .. or . or symbolic link) and see if it match with the directory name given.

How can I do this? There are another method to do this?

Thanks for all.

Cant you just use chroot?

chroot - Wikipedia, the free encyclopedia

Thanks,
this can be a solution.

But I prefer a more flexible command for this reason:
- I can have a download and upload directory that aren't a subdirectory of a parent directory.

So, I can have access to /home/download and /home/upload directory for the command of upload and download of the client.

Thanks.

> The client can access to /home/tmp and all its subdirectory but not in /home or any other directory in the filesystem.
...
> So, I can have access to /home/download and /home/upload directory

OK, so do you or do you NOT allow roaming around in /home?

The more elaborate your "security" model becomes, the more likely someone is to spot a hole in it.

Quote:

---

OK, so do you or do you NOT allow roaming around in /home?

---

I can only access to /home/download and /home/upload and the subdirectory of these. I can't access to any other directory in the filesystem.

In idea is to expand the path received from the client resolving all links and other "tricks" for example:

string from client: /../../mnt/tmp
string to evaluate: /home/upload/../../mnt/tmp
evaluated string: /mnt/tmp
DENY ACCESS because this directory isn't in /home/upload.

I need a command that expand a given path resolving all link and . or .. for evaluate the final string.

Thanks.

You could probably use find or ls to resolve symlinks for you and remove . and .. to turn your path into a full path name. But if you do the checking yourself there's always a chance you'll get it wrong.

If you wanted to implement this at the operating-system level you could use access control lists. But be forewarned that it becomes *extremely* complicated very fast and you end up spending a lot of time on it. Plus it's very easy to make mistakes.

But if you really want to: Using ACLs with Fedora Core 2