From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexey Dobriyan Subject: Re: [PATCH for 2.6.33] conntrack: restrict runtime hashsize modifications Date: Thu, 4 Feb 2010 21:47:44 +0200 Message-ID: <20100204194744.GA4185@x200> References: <20100203203929.GA6168@x200> <4B6AF36A.3050402@trash.net> <4B6AFE22.20304@trash.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: davem@davemloft.net, jonathan@jonmasters.org, eric.dumazet@gmail.com, netdev@vger.kernel.org, netfilter-devel@vger.kernel.org To: Patrick McHardy Return-path: Received: from mail-fx0-f220.google.com ([209.85.220.220]:54505 "EHLO mail-fx0-f220.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932592Ab0BDTru (ORCPT ); Thu, 4 Feb 2010 14:47:50 -0500 Content-Disposition: inline In-Reply-To: <4B6AFE22.20304@trash.net> Sender: netfilter-devel-owner@vger.kernel.org List-ID: On Thu, Feb 04, 2010 at 06:04:34PM +0100, Patrick McHardy wrote: > Patrick McHardy wrote: > > Alexey Dobriyan wrote: > >> Jon Masters correctly points out that conntrack hash sizes > >> (nf_conntrack_htable_size) are global (not per-netns) and > >> modifiable at runtime via /sys/module/nf_conntrack/hashsize . > >> > >> Steps to reproduce: > >> clone(CLONE_NEWNET) > >> [grow /sys/module/nf_conntrack/hashsize] > >> exit() > >> > >> At netns exit we are going to scan random memory for conntracks to be killed. > >> > >> Apparently there is a code which deals with hashtable resize for > >> init_net (and it was there befode netns conntrack code), so prohibit > >> hashsize modification if there is more than one netns exists. > >> > >> To change hashtable sizes, you need to reload module. > >> > >> Expectation hashtable size was simply glued to a variable with no code > >> to rehash expectations, so it was a bug to allow writing to it. > >> Make "expect_hashsize" readonly. > >> > >> This is temporarily until we figure out what to do. > > > > How about alternatively moving nf_conntrack_hsize into the > > per-namespace struct? It doesn't look more complicated or > > intrusive and would allow to still change the init_net > > hashsize. Also seems less hackish :) > > How about this (so far untested) patch? The htable_size is moved into > the per-namespace struct and initialized from the current (global) > value of nf_conntrack_htable_size. Changes through sysfs are still > permitted, but only affect the init namespace and newly created ones. No matter what we do, it's a hack! > Additionally I removed reinitializing the hash random value when > changing the hash size since that also requires to rehash in all > namespaces. I'm not fond of this, because we're not even closely going to allow changing hashtable size per-netns. As such having actual per-netns hashtable size just slows down everything.