Messages in this thread | | | Date | Mon, 11 May 2015 10:29:41 +0100 | From | Klaus Ethgen <> | Subject | Probably bug in netfilter hashlimit extension |
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Recently I tried to mitigate some slow attacks via netfilter rule utilizing hashlimit target. I used the following specification:
-A DETECT_INVALID -m hashlimit --hashlimit-upto 10/hour --hashlimit-mode srcip --hashlimit-name attack_invalid -j RETURN
Now I seen some strange stuff. The counter in /proc/net/ipt_hashlimit/attack_invalid only counts from 60 back to 0 and then the entry disappears. Than means that a rate of 10/hour will never ever be detected at all.
On that box I use kernel 3.16.0 from debian backport to oldstable Which seems to be somewhat equal to 3.16.7. So maybe that bug has beed find earlier or is even fixed upstream. I have no easy way to upgrade that kernel short term as the box is productive.
Shorter times like 30/hour with a slightly bigger burst (10 instead of the default 5) seems to work as expected but is not able to detect the attacks due to the slow rate.
Am I the only who seen that behaviour or is that a known limitation? I find no such notes anywhere that there is a limit here. (Although I would believe that there is a high limit somewhere. But then I would expect them to be returend with some errno when trying to set a to high value.)
Please keep me in Cc as I do not monitor this List that often.
Regards Klaus - -- Klaus Ethgen http://www.ethgen.ch/ pub 4096R/4E20AF1C 2011-05-16 Klaus Ethgen <Klaus@Ethgen.de> Fingerprint: 85D4 CA42 952C 949B 1753 62B3 79D0 B06F 4E20 AF1C -----BEGIN PGP SIGNATURE----- Version: GnuPG v1
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