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Message-ID: <33633.simon.1188386980@5ec7c279.invalid> Date: Wed, 29 Aug 2007 12:29:40 +0100 From: "Simon Arlott" <simon@...e.lp0.eu> To: "Anand Jahagirdar" <anandjigar@...il.com> Cc: "Chris Snook" <csnook@...hat.com>, "Krzysztof Halasa" <khc@...waw.pl>, linux-kernel@...r.kernel.org Subject: Re: Fork Bombing Patch On Wed, August 29, 2007 10:48, Anand Jahagirdar wrote: > 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. If ulimit "wont work" in some situations, how is it going to trigger this printk? (When doesn't it work?) > 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 >> > - > 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/ > -- Simon Arlott - 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/
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