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From: windemut@lisboa.ks.uiuc.edu (Andreas Windemuth)
Newsgroups: comp.sys.next
Subject: Re: Preserving file ownerships on OD?
Keywords: file ownerships, removable media, optical disk, security
Message-ID: <1991Jun27.020017.602@ux1.cso.uiuc.edu>
Date: 27 Jun 91 02:00:17 GMT
References: <11043@idunno.Princeton.EDU>
Sender: usenet@ux1.cso.uiuc.edu (News)
Organization: University of Illinois at Urbana
Lines: 52

In article <11043@idunno.Princeton.EDU> sksircar@shade.princeton.edu (Subrata  
Sircar) writes:
> Wait.  Are you people saying that if I log in to the Next, and insert a  
backup
> optical disk (made by root) that all of the files on that disk are now owned
> by me?  Even if the mountable media has root-owned files?
> 
> If so, that's not just stupid, that's criminal.  What's to prevent anyone 
> from doing ANYTHING they want to a mountable medium, for example a source  
disk
> mounted over a network?
> 

Well, I think this is a grave misunderstanding of the issue. 
It has to be assumed, given the fact that you can carry the 
medium around, put it into a magnet or into a specially designed 
computer with an optical disk drive, the person in posession
of the disk can do ANYTHING he or she likes to do to it anyway.
The way to prevent that is to keep the disk out of unauthorized hands.

That which has to be protected is not the disk (which can be easily
protected by storing it in a safe), but the system that the disk 
is mounted on (assuming anyone can put his/her disk in, 
i.e. the system is not equipped with a padlock on the drive). 
If the ownerships were not correctly set to the user 
physically inserting the disk, anyone could fabricate data 
with arbitrary userid, including root. 

It has been correctly pointed out that this is a serious security problem 
in the case of suid programs, but it is in general a violation
of the principle that it should not be possible to make one's own
data appear to originate from somebody else (try chown on your files).
Not to speak of the case where the users owning files on the disk
don't even exist on the system the disk is inserted in.

Thus, the way it is done now is neither stupid nor criminal, 
it is exactly how it should be.
If you really want to mount a disk with other user's ownerships on it,
you have to be superuser. You are then responsible for the integrity of
the data on the medium. If I am not mistaken, this is indeed possible
by mounting the optical drive like any other hard disk and inserting the
disk itself on request.  
 
--
		Andreas Windemuth

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