Path: utzoo!utgpu!watserv1!watmath!att!linac!pacific.mps.ohio-state.edu!zaphod.mps.ohio-state.edu!wuarchive!uunet!mcsun!ukc!yorkohm!nigelm
From: nigelm@ohm.york.ac.uk (Nigel Metheringham)
Newsgroups: news.software.b
Subject: Re: "fascist" option (or posting security)
Message-ID: <1991May1.124919.8706@ohm.york.ac.uk>
Date: 1 May 91 12:49:19 GMT
References: <1991Apr26.070028.705000@zeus.calpoly.edu> <17196@celit.fps.com>
Organization: Electronics Department, University of York, UK
Lines: 50

[Reposted, because the idiot who set up nn set the default
distribution to campus - shame that me and that idiot share a
brain!]

I haven't looked at this very hard yet, but think it may be a
reasonable way of getting fascism in C-News.  If not I'm sure
someone will point out the problems fast enough.

Basic premises:-
  + Posting is done with inews.
  + Inews calls relaynews after mangling the headers.
  + relaynews is also called by the incoming batch processors
    (from a cron job running UID news).
  + relaynews currently runs setuid news to allow it to write the
    news articles themselves.  
  + relaynews can be called directly, bypassing anything you put
    into inews, making inews a bad place to do this...
  + relaynews only needs to be setuid for local posting - ie
    anything going through inews - everything else calls it 
    with the correct uid.


So, why can't we knock the setuid bits off relaynews, and then add a
small setuid (news) program (maybe called injectnews), which is the
one called by inews.

relaynews would still work for processing batches etc, but could not
be called by normal users to bypass the protections...

injectnews checks the current UID against a stop list (or for the
really fascist, against a valid posters list).  If it accepted
someone then it could be passed on to relaynews (which would be run
from injectnews, and inherit the setuid status), otherwise it could
drop the article or maybe the distribution header could be
rewritten.  For my own use, it would need to look at and possibly
limit the distribution header.

Since posting new news tends not to be the most common operation of
the news system this should not hit performance badly.

So, comments please, before I get my trusty C compiler out....
(Actually it sounds like a job for Perl to me...)

        Nigel.

-- 
# Nigel Metheringham         #  EMail: nigelm@ohm.york.ac.uk #
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