chgrp resets the setuid and getgid bits

[Ben Stringer]

On Tue, 2006-07-25 at 21:18 +1000, Paul Dwerryhouse wrote:
> On Tue, Jul 25, 2006 at 07:44:14PM +1000, Ben Stringer wrote:
> > I observed this today on an RHEL4 system, and it applies to Fedora also.
> > I don't understand why this occurs - is it a security feature?
> 
> [snip]
> 
> > If anyone can shed light on this for me, I would appreciate it.
> 
> It's fairly standard for Unix systems; as far as I can remember,
> Solaris, Tru64, and every other Unix-like OS I've come across does this,
> too.

Thanks Paul. I tried it on a Solaris 8 system, and did not see the same
behaviour.

> 
> I can't think, off the top of my head, of a specific need for it to
> happen (since a user can't change the ownership or group of another
> user's file); it's probably done just to force an admin to confirm that
> they still want the file to be setuid/setgid when they alter it.

I suspected as much, but it seems a little arbitrary (why not also clear
these bits if the file changes size, for instance) and a little
undocumented.

Cheers, Ben