linux-kernel - Re: [PATCH] Reserve N process to root

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Message-ID: <27658.1192045814@turing-police.cc.vt.edu>
Date:	Wed, 10 Oct 2007 15:50:14 -0400
From:	Valdis.Kletnieks@...edu
To:	Gustavo Chain <g@...f.cl>
Cc:	David Newall <david@...idnewall.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Reserve N process to root

On Wed, 10 Oct 2007 09:46:22 EDT, Gustavo Chain said:
> El Wed, 10 Oct 2007 15:14:06 +0930
> David Newall <david@...idnewall.com> escribió:
> > That was what I thought you had in mind; it protects from some kind
> > of fork bomb, right?  But it doesn't seem useful unless you guarantee 
> > having a process already running (with CAP_SYS_ADMIN) *before* the
> > bomb goes off.
> 
> Not really, because fork bomb will never reach maximum pid possible.
> And root will always have a "slot" to kill desired processes.

What David meant was that "root will always have a slot" doesn't *actually*
help unless you *also* have a way to actually *spawn* such a process.  In order
to do the ps, kill, and so on that you need to recover, you need to already
have either a root shell available, or a way to *get* a root shell that doesn't
rely on a non-root process (so /bin/su doesn't help here).

Many distros will leave a /sbin/mingetty running on tty1 through tty6, and
you *can* use those to get a root shell.  David's point is that without
something like that already in place, the patch doesn't help....

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