From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: arp_hash Date: Sun, 22 Mar 2015 19:50:03 -0400 (EDT) Message-ID: <20150322.195003.654000183854114521.davem@davemloft.net> References: <20150322215612.GA8274@gondor.apana.org.au> <20150322.185850.927485035002538859.davem@davemloft.net> <20150322230848.GA8989@gondor.apana.org.au> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: eric.dumazet@gmail.com, netdev@vger.kernel.org, roland@purestorage.com To: herbert@gondor.apana.org.au Return-path: Received: from shards.monkeyblade.net ([149.20.54.216]:49941 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752190AbbCVXuH (ORCPT ); Sun, 22 Mar 2015 19:50:07 -0400 In-Reply-To: <20150322230848.GA8989@gondor.apana.org.au> Sender: netdev-owner@vger.kernel.org List-ID: From: Herbert Xu Date: Mon, 23 Mar 2015 10:08:48 +1100 > On Sun, Mar 22, 2015 at 06:58:50PM -0400, David Miller wrote: >> >> But I do not agree with the idea that it is in any way possible to >> stop someone with root access on the physical network from crudding up >> our ARP hash tables. > > But you don't need root access to exploit the neighbour hash > table. You just need a sufficiently large (e.g., /16) route > to a network and anybody on the system can then generate traffic > to it. > > Granted these days hardly anybody on IPv4 would have such a route > but if you do then the hash table makes you exposed. > > And for IPv6 everybody is potentially exposed. BTW I asked for feedback when I posted the patches which created this situation, and the multiply with the random input was believed to have sufficient entropy and not create a situation any worse, asymptotically, than what we had beforehand. Perhaps the ipv6 case can be improved, by using a u32 random input for each u32 of the address being hashed.