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    SubjectRe: Fork Bombing Patch
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    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@redhat.com> wrote:
    >> Krzysztof Halasa wrote:
    >> > Hi,
    >> >
    >> > "Anand Jahagirdar" <anandjigar@gmail.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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    --
    Simon Arlott
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