Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!snorkelwacker.mit.edu!bloom-picayune.mit.edu!athena.mit.edu!jik
From: jik@athena.mit.edu (Jonathan I. Kamens)
Newsgroups: comp.unix.misc
Subject: Re: Permission Question
Message-ID: <1991Mar11.000632.28526@athena.mit.edu>
Date: 11 Mar 91 00:06:32 GMT
References: <1991Mar9.212943.1961@casbah.acns.nwu.edu>
Sender: news@athena.mit.edu (News system)
Distribution: na
Organization: Massachusetts Institute of Technology
Lines: 30

In article <1991Mar9.212943.1961@casbah.acns.nwu.edu>, navarra@casbah.acns.nwu.edu (John Navarra) writes:
|>  I am not a member of staff but I wanted to see if I could do the following:
|> 
|>  cp /bin/sh /somedir/sh
|>  chmod g+s /sh
|>  ls -las | grep sh
|>  
|>  224 -rwx--x--x   1 navarra  staff     106496 Mar  9 13:18 sh
|> 
|>  AS you see I was not able to set this bit. I was wondering if you actually
|>  have to be a member of the group to set its bit? Is this true on all Unix
|>  systems?

  To allow a user to make a binary setgid to a group of which he is not a
member would be a gaping security hole, allowing any user to violate the
entire group security mechanism.  It should be clear why this is so; if I'm
not a member of a group but I can make a program setgid to that group, then I
can write a program to do anything I want that requires that group's access
rights, and then make it setgid to that group and run it.

  So yes, you actually have to be a member of a group to make something setgid
to that group.

  By the way, why the "na" distribution?

-- 
Jonathan Kamens			              USnail:
MIT Project Athena				11 Ashford Terrace
jik@Athena.MIT.EDU				Allston, MA  02134
Office: 617-253-8085			      Home: 617-782-0710