Mark writes:
> After the fork() you can do this to change the userid:
>
>         GETPRIVMODE();
>         setuid(new_uid);
>         GETUSERMODE();
>
> You should only do this after careful validation of the new_uid to make sure
> the PC isn't trying to gain access to unauthorized users.

I recommend encapsulating the above as follows:

   int my_setuid (uid_t new_uid)
      {
      GETPRIVMODE ();
      return setuid (new_uid);
      }

Note the lack of call to GETUSERMODE().  This means that if my_setuid is
called from an already privileged routine, my_setuid will not
incorrectly return in user mode.

Of course, you could also do:

    GETPRIVMODE ();    /* returns CCE if was in user mode */
    need_getusermode_call = (CCODE() == CCE);

    if (setuid (new_uid))
       ...oops, setuid failed...

    if (need_getusermode_call)
       GETUSERMODE ();

--
Stan Sieler                                          [log in to unmask]
                                     http://www.allegro.com/sieler.html