From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 39CA6C433E7 for ; Fri, 9 Oct 2020 18:56:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EBAE1222E8 for ; Fri, 9 Oct 2020 18:56:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388296AbgJISz7 (ORCPT ); Fri, 9 Oct 2020 14:55:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38444 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388184AbgJISz7 (ORCPT ); Fri, 9 Oct 2020 14:55:59 -0400 Received: from Chamillionaire.breakpoint.cc (Chamillionaire.breakpoint.cc [IPv6:2a0a:51c0:0:12e:520::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 325D7C0613D2; Fri, 9 Oct 2020 11:55:59 -0700 (PDT) Received: from fw by Chamillionaire.breakpoint.cc with local (Exim 4.92) (envelope-from ) id 1kQxYW-0000rj-1m; Fri, 09 Oct 2020 20:55:52 +0200 Date: Fri, 9 Oct 2020 20:55:52 +0200 From: Florian Westphal To: Jozsef Kadlecsik Cc: Florian Westphal , Francesco Ruggeri , open list , netdev , coreteam@netfilter.org, netfilter-devel@vger.kernel.org, Jakub Kicinski , David Miller , fw@strlen.org, Pablo Neira Ayuso Subject: Re: [PATCH nf v2] netfilter: conntrack: connection timeout after re-register Message-ID: <20201009185552.GF5723@breakpoint.cc> References: <20201007193252.7009D95C169C@us180.sjc.aristanetworks.com> <20201009110323.GC5723@breakpoint.cc> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Jozsef Kadlecsik wrote: > > The repro clears all rules, waits 4 seconds, then restores the ruleset. > > using iptables-restore < FOO; sleep 4; iptables-restore < FOO will not > > result in any unregister ops. > > > > We could make kernel defer unregister via some work queue but i don't > > see what this would help/accomplish (and its questionable of how long it > > should wait). > > Sorry, I can't put together the two paragraphs above: in the first you > wrote that no (hook) unregister-register happens and in the second one > that those could be derefed. Sorry, my reply is confusing indeed. Matches/targets that need conntrack increment a refcount. So, when all rules are flushed, refcount goes down to 0 and conntrack is disabled because the hooks get removed.. Just doing iptables-restore doesn't unregister as long as both the old and new rulesets need conntrack. The "delay unregister" remark was wrt. the "all rules were deleted" case, i.e. add a "grace period" rather than acting right away when conntrack use count did hit 0. > > We could disallow unregister, but that seems silly (forces reboot...). > > > > I think the patch is fine. > > The patch is fine, but why the packets are handled by conntrack (after the > first restore and during the 4s sleep? And then again after the second > restore?) as if all conntrack entries were removed? Conntrack entries are not removed, only the base hooks get unregistered. This is a problem for tcp window tracking. When re-register occurs, kernel is supposed to switch the existing entries to "loose" mode so window tracking won't flag packets as invalid, but apparently this isn't enough to handle keepalive case.