Date: Thu, 24 Sep 1998 09:50:05 -0400 (EDT) From: Robert Watson <robert@cyrus.watson.org> To: Brian Tao <taob@risc.org> Cc: FREEBSD-CURRENT <freebsd-current@FreeBSD.ORG> Subject: Re: Limit 'ps' to show only user's processes Message-ID: <Pine.BSF.3.96.980924094715.27219B-100000@fledge.watson.org> In-Reply-To: <Pine.GSO.3.96.980924094103.16314b-100000@tor-dev1.nbc.netcom.ca>
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On Thu, 24 Sep 1998, Brian Tao wrote:
> On Fri, 18 Sep 1998, Robert Watson wrote:
> >
> > I don't think there is any way to hide the existence of other
> > processes -- a process that performs:
> >
> > int i, lasti;
> > while (1) {
> > i = fork();
> > if (!i) {
> > exit(0);
> > }
> > if (i != lasti + 1) {
> >
> > ....
>
> On a slightly different track, using randomized pid's would limit
> the usefulness of such a scan, although with a fast enough fork(), you
> could still map the entire pid space and find the "holes".
I suppose a 'personal' pid space could be used -- that is, your pid space
corresponds to your uid in some way (perhaps bump pid to 64-bit and use a
32-bit uid as the first half). However, I have the feeling that this
exceeds what is feasible to protect with a time-sharing system. Without
real-time behavior (and even with), processes can observe the amount of
time context-switches take when they are preemptive, and the availability
of ports to bind, etc, do determine things about other running processes.
Similarly, they can observe the availability of flock exclusive locking on
key files, the presence of temporary and lock files, and so on. Modifying
ps command line arguments is about a degree of privacy; taking it much
further would probably require seriously rethinking the process model we
use.
Robert N Watson
Carnegie Mellon University http://www.cmu.edu/
TIS Labs at Network Associates, Inc. http://www.tis.com/
SafePort Network Services http://www.safeport.com/
robert@fledge.watson.org http://www.watson.org/~robert/
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