[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-Id: <200710120837.23586.a1426z@gawab.com>
Date: Fri, 12 Oct 2007 08:37:23 +0300
From: Al Boldi <a1426z@...ab.com>
To: Kyle Moffett <mrmacman_g4@....com>
Cc: LKML Kernel <linux-kernel@...r.kernel.org>, g@...f.cl,
Valdis Kletnieks <Valdis.Kletnieks@...edu>
Subject: Re: [PATCH] Reserve N process to root
Kyle Moffett wrote:
> Please don't trim CC lists
>
> On Oct 11, 2007, at 17:02:37, Al Boldi wrote:
> > David Newall wrote:
> >> Valdis.Kletnieks@...edu wrote:
> >>> 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).
> >>
> >> That's right, although it's worse than that. You need to have a
> >> process with CAP_SYS_ADMIN. If root processes normally have that
> >> capability then the reserved slots may well disappear before you
> >> notice a problem. If root processes normally don't have it, then
> >> you need to guarantee that one is already running.
> >
> > I once posted a patch to handle this DoS, but, as usual, it wasn't
> > accepted. Go figure...
>
> This isn't really necessary any more with the new CFS scheduler. If
> you want to prevent excess memory usage then you limit memory usage,
> not process count, so just set the system max process count to
> something absurdly high and leave the user counts down at the maximum
> a user might run. Then as long as the sum of the user processes is
> less than the max number of processes (which you just set absurdly
> high or unlimited), you may still log in. With the per-user
> scheduling enabled CFS allows you to run an optimistically-real-time
> game as one user and several thousand busy-loops as another user and
> get almost picture perfect 50% CPU distribution between the users.
> To me that seems a much better DoS-prevention system than limits
> which don't scale based on how many people are requesting resources.
You have a point, and resource-controllers can probably control DoS a lot
better, but the they also incur more overhead. Think of this "lockout
prevention" patch as a near zero overhead safety valve.
Thanks!
--
Al
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists