linux-kernel - Re: Fork Bombing Patch

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Message-ID: <25ae38200708290248w2cdd152fpbdaa1b123de0b7ef@mail.gmail.com>
Date:	Wed, 29 Aug 2007 15:18:20 +0530
From:	"Anand Jahagirdar" <anandjigar@...il.com>
To:	"Chris Snook" <csnook@...hat.com>
Cc:	"Krzysztof Halasa" <khc@...waw.pl>, linux-kernel@...r.kernel.org
Subject: Re: Fork Bombing Patch

Hi
                printk_ratelimit function takes care of flooding the
syslog. due to printk_ratelimit function syslog will not be flooded
anymore. as soon as administrator gets this message, he can take
action against that user (may be block user's access on server). i
think the my fork patch is very useful and helps administrator lot.
                i would also like to mention that in some of the cases
ulimit solution wont work. in that case fork bombing takes the machine
and server needs a reboot. i am sure in that situation this printk
statement helps administrator to know what has happened.

Anand

On 8/24/07, Chris Snook <csnook@...hat.com> wrote:
> Krzysztof Halasa wrote:
> > Hi,
> >
> > "Anand Jahagirdar" <anandjigar@...il.com> writes:
> >
> >>    I am forwarding one more improved patch which i have modified as
> >> per your suggestions. Insted of KERN_INFO i have used KERN_NOTICE and
> >> i have added one more if block to check hard limit. how good it is?
> >
> > Not very, still lacks "#ifdef CONFIG_something" and the required
> > Kconfig change (or other runtime thing defaulting to "no printk").
>
> Wrapping a single printk that's unrelated to debugging in an #ifdef
> CONFIG_* or a sysctl strikes me as abuse of those configuration
> facilities.  Where would we draw the line for other patches wanting to
> do similar things?
>
> I realized that even checking the hard limit it insufficient, because
> that can be lowered (but not raised) by unprivileged processes.  If we
> can't do this unconditionally (and we can't, because the log pollution
> would be intolerable for many people) then we shouldn't do it at all.
>
> Anand -- I appreciate the effort, but I think you should reconsider
> precisely what problem you're trying to solve here.  This approach can't
> tell the difference between legitimate self-regulation of resource
> utilization and a real attack.  Worse, in the event of a real attack, it
> could be used to make it more difficult for the administrator to notice
> something much more serious than a forkbomb.
>
> I suspect that userspace might be a better place to solve this problem.
>  You could run your monitoring app with elevated or even realtime
> priority to ensure it will still function, and you have much more
> freedom in making the reporting configurable.  You can also look at much
> more data than we could ever allow in fork.c, and possibly detect
> attacks that this patch would miss if a clever attacker stayed just
> below the limit.
>
>        -- Chris
>
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