From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael K. Edwards" Subject: Re: Extensible hashing and RCU Date: Tue, 20 Feb 2007 07:49:11 -0800 Message-ID: References: <200702191913.08125.dada1@cosmosbay.com> <20070220092523.GA6238@2ka.mipt.ru> <200702201104.16200.dada1@cosmosbay.com> <20070220.021209.39159087.davem@davemloft.net> <20070220151119.GA17326@2ka.mipt.ru> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: "David Miller" , dada1@cosmosbay.com, akepner@sgi.com, linux@horizon.com, netdev@vger.kernel.org, bcrl@kvack.org To: "Evgeniy Polyakov" Return-path: Received: from an-out-0708.google.com ([209.85.132.246]:15818 "EHLO an-out-0708.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965175AbXBTPto (ORCPT ); Tue, 20 Feb 2007 10:49:44 -0500 Received: by an-out-0708.google.com with SMTP id b33so382438ana for ; Tue, 20 Feb 2007 07:49:43 -0800 (PST) In-Reply-To: <20070220151119.GA17326@2ka.mipt.ru> Content-Disposition: inline Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On 2/20/07, Evgeniy Polyakov wrote: > Jenkins _does_ have them, I showed tests half a year ago and in this > thread too. Actually _any_ hash has them it is just a matter of time > to find one. I think you misunderstood me. If you are trying to DoS me from outside with a hash collision attack, you are trying to feed me packets that fall into the same hash bucket. The Jenkins hash does not have to be artifact-free, and does not have to be cryptographically strong. It just has to do a passable job of mixing a random salt into the tuple, so you don't know which string of packets to feed me in order to fill one (or a few) of my buckets. XORing salt into a folded tuple doesn't help; it just permutes the buckets. Cheers, - Michael