Replace uid==0 tests with capability checks

[Scott Neugroschl]

> 
> What's still missing in OpenSSH is code which abstracts the idea of
the
> root user to the idea of a user with certain privileges.  At least
> Linux/Solaris/Cygwin/Windows allow to specify finer grained user
> rights,
> so that certain types of tasks are not necessarily run by the root
> user.
> In case of Cygwin/Windows there isn't even a root user, just users
with
> certain privileges.  Given that, the hardcoded checks for uid == 0
> don't
> make sense or rather, are too bulky in a couple of environments.  To
> reiterate an idea I'm proposing for quite some time now:
> 
>   Instead of checks as
> 
>     if (getuid() == 0)
>       do_foo_bar ();
>     else
>       EEEEK!
> 
>    openssh should have checks along the lines of
> 
>     if (uid_has_capability (getuid (), CAP_foo_bar))
>       do_foo_bar ();
>     else
>       EEEEK!
> 
> The function uid_has_capability() would be quite simple on systems
> which don't have fine-grained user rights:
> 
>     int
>     uid_has_capability (uid_t uid, int capability)
>     {
>       return uid == 0;
>     }
> 
> but could be much more elaborate on other platforms like Linux,
> Solaris,
> or Cygwin.  And, again, I'm willing to help with this stuff in terms
of
> coding.
> 

I'd love to see something like this.  I'm on an oddball system
(Tandem/HP NonStop),
where root isn't UID 0, and other stuff has ACL/permissions.