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SubjectRe: 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 <> wrote:
>> Krzysztof Halasa wrote:
>> > Hi,
>> >
>> > "Anand Jahagirdar" <> 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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Simon Arlott
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