denying group of users from r/w/x files

[Chuck Anderson]

On Mon, Feb 09, 2009 at 10:59:53PM -0600, Ali Hamad wrote:
>    a)  create a rule for file that can not be accessed from known group  
> of users. i.e group A can not read/write/execute this file.  However,  
> the file permission is 666 and that file permission can not be changed.
>    b)  directory that has permission of 777. However, group A of users  
> can not write/read/execute  it.
>
> Any suggestion is highly appreciated.

How about using POSIX ACLs instead of SELinux?  Check out the getfacl 
and setfacl commands.