Re: code/module request: undo setuid

[Bruno Haible]

Sam Steingold wrote:
> > The general opinion, among security aware developers, already for 10
> > years, is that the amount of code which is executed with setuid root
> > permissions should be minimal.
> 
> this is all nice, but this does not answer my question.
> I agree that that it is not a good idea to run a large application
> setuid root

Fine.

> Please see the discussion here:
> https://sourceforge.net/forum/message.php?msg_id=5611456

The discussion is here:
  http://news.gmane.org/gmane.lisp.clisp.general/cutoff=12548
  http://article.gmane.org/gmane.lisp.clisp.general/12533
Please don't recommend URLs to https://sourceforge.net/forum/ any more -
I refuse to read discussions in an advertisement loaded environment.

In that discussion,
  - Fare says that he has some Lisp-based executables that are setuid root,
  - You insist on having an option that, given a Lisp-based executable,
    allows to get into a REP loop for that executable.

Taken together, it means that every setuid Lisp-based executable allows
every user to take control of the machine.

> All I can do is to revert setuid for a dangerous operation.

Is the REP loop above the "dangerous operation" you are talking about?

If so, the magic is

/* This is for executables that have the setgid bit set.  */
#if HAVE_SETREGID
  setregid (getgid (), getgid ());
#else
  setegid (getgid ());
#endif
/* This is for executables that have the setuid bit set.  */
#if HAVE_SETREUID
  setreuid (getuid (), getuid ());
#else
  seteuid (getuid ());
#endif

Bruno