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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 > - 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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