Established method to enable suid scripts?

Chris Telting christopher-ml at
Fri May 13 09:28:38 UTC 2011

On 05/13/2011 00:32, Jonathan McKeown wrote:
> On Thursday 12 May 2011 17:26:49 Chris Telting wrote:
>> On 05/12/2011 07:57, Jonathan McKeown wrote:
>>> I'll say that again. It is inherently insecure to run an interpreted
>>> program set-uid, because the filename is opened twice and there's no
>>> guarantee that someone hasn't changed the contents of the file addressed
>>> by that name between the first and second open.
>>> It's one thing to tell people they need to be careful with suid because
>>> it has security implications. Deliberately introducing a well-known
>>> security hole into the system would in my view be dangerous and wrong.
>> That race condition bug was fixed in ancient times. Before Freebsd or
>> Linux ever existed I believe. It's a meme that just won't die.  People
>> accepted mediocrity in old commercial versions of Unix.  I personally am
>> unsatisfied by kludges.
> That seems somewhat unlikely given, as someone else pointed out upthread, that
> Perl still comes with a compile-time option SETUID_SCRIPTS_ARE_SECURE_NOW,
> suggesting that they often aren't. Yes, there are ways to avoid this race
> condition - the usual one is to pass a handle on the open file to the
> interpreter, rather than closing it and reopening it.
> This fix is not present in every Unix or Unix-like OS. In particular (although
> I'm happy to be corrected if I'm wrong) it's not present in FreeBSD, to the
> best of my knowledge. Whether there's a reason for that other than lack of
> developer time I don't know.
Indeed.  I think it's more of a case that since you can't count on it on 
other systems (especially closed source systems) to disable it for 
portability reasons although I would loved to be proved wrong.

Happy Friday.

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