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From: lan_csse@netrix.nac.dec.com (CSSE LAN Test Account)
Newsgroups: comp.windows.x
Subject: Re: Xterm cannot write log files
Message-ID: <22173@shlump.nac.dec.com>
Date: 18 Apr 91 20:52:43 GMT
References: <9104100652.AA06486@lightning.McRCIM.McGill.EDU> <1991Apr10.222541.14268@ux1.cso.uiuc.edu>
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Organization: Digital Equipment
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In article <1991Apr10.222541.14268@ux1.cso.uiuc.edu> phil@ux1.cso.uiuc.edu (Phil Howard KA9WGN) writes:
>mouse@lightning.mcrcim.mcgill.EDU (der Mouse) writes:
>
>>> Is there any pressing reason for xterm to be suid root ?
>
>>Not unless you want utmp entries for your xterm windows.  (Unless you
>>make utmp world-writeable, which opens up other, fairly serious,
>>security holes, but that may be acceptable in trusting environments.)
>
>An alternate strategy that involves UNIX's "philosophy" of having extra
>processes:

There's an alternate Unix philosophy, that of using group permissions,
that just might do the job.  /etc/utmp is usually in the system group.
So why not make it group writable, and make xterm setgid-system?  This
seems like the way things really oughta be done, and you do away with
yet another spuriously-setuid-root program.

I think I'll try it on a few systems, and see what breaks...

...Nope, nothing broke.  I started up a bunch of windows to/from this
system, did an assortment of rlogins, and so on, verified that the new
windows corresponded to entries in /etc/utmp, and everything seems to
work fine.  When I type 
	ls -ldg /etc/utmp `which xterm`
the result is:
	-rw-rw-r--  1 root     system       1512 Apr 18 16:47 /etc/utmp
	-rwxr-sr-x  1 root     system     387072 Aug 31  1990 /usr/bin/X11/xterm
So I'd conclude that, unless I've missed something suble, setuid-root isn't 
necessary for xterm, and setgid-system suffices, if all the appropriate 
files are in the system group and are group writable.   It might help if
we could get a definitive list of just what files xterm wants to write.

Now if such a demo only worked so well for sendmail, which really *really*
shouldn't be setuid-root but almost always is...