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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,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 B0991C432C0 for ; Wed, 20 Nov 2019 11:45:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 93AD922304 for ; Wed, 20 Nov 2019 11:45:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728542AbfKTLpt (ORCPT ); Wed, 20 Nov 2019 06:45:49 -0500 Received: from orbyte.nwl.cc ([151.80.46.58]:38534 "EHLO orbyte.nwl.cc" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728287AbfKTLps (ORCPT ); Wed, 20 Nov 2019 06:45:48 -0500 Received: from n0-1 by orbyte.nwl.cc with local (Exim 4.91) (envelope-from ) id 1iXOQc-0007ke-C1; Wed, 20 Nov 2019 12:45:46 +0100 Date: Wed, 20 Nov 2019 12:45:46 +0100 From: Phil Sutter To: Pablo Neira Ayuso Cc: Ander Juaristi , netfilter-devel@vger.kernel.org Subject: Re: [nft PATCH] tests/py: Set a fixed timezone in nft-test.py Message-ID: <20191120114546.GJ8016@orbyte.nwl.cc> Mail-Followup-To: Phil Sutter , Pablo Neira Ayuso , Ander Juaristi , netfilter-devel@vger.kernel.org References: <20191116213218.14698-1-phil@nwl.cc> <20191118183459.qkqztuc5pn4fezzn@salvia> <20191119221236.jfedafspmixjnivw@salvia> <20191119222023.GH8016@orbyte.nwl.cc> <20191119223318.n7zgdsfmetltwobo@salvia> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20191119223318.n7zgdsfmetltwobo@salvia> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: netfilter-devel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netfilter-devel@vger.kernel.org Hi Pablo, On Tue, Nov 19, 2019 at 11:33:18PM +0100, Pablo Neira Ayuso wrote: > On Tue, Nov 19, 2019 at 11:20:23PM +0100, Phil Sutter wrote: > > Hi, > > > > On Tue, Nov 19, 2019 at 11:12:36PM +0100, Pablo Neira Ayuso wrote: > > > On Tue, Nov 19, 2019 at 12:06:23PM +0100, Ander Juaristi wrote: > > > > El 2019-11-18 19:34, Pablo Neira Ayuso escribió: > > > > > Hi Phil, > > > > > > > > > > On Sat, Nov 16, 2019 at 10:32:18PM +0100, Phil Sutter wrote: > > > > > > Payload generated for 'meta time' matches depends on host's timezone > > > > > > and > > > > > > DST setting. To produce constant output, set a fixed timezone in > > > > > > nft-test.py. Choose UTC-2 since most payloads are correct then, adjust > > > > > > the remaining two tests. > > > > > > > > > > This means that the ruleset listing for the user changes when daylight > > > > > saving occurs, right? Just like it happened to our tests. > > > > > > > > It shouldn't, as the date is converted to a timestamp that doesn't take DST > > > > into account (using timegm(3), which is Linux-specific). > > > > > > > > The problem is that payloads are hard-coded in the tests. > > > > > > > > Correct me if I'm missing something. > > > > > > I see, so it's just the _snprintf() function in the library. I > > > remember we found another problem with these on big endian, it would > > > be probably to move them to libnftables at some point. > > > > > > Acked-by: Pablo Neira Ayuso > > > > Ah, now that I reread your question, I finally got it. And you're right: > > If DST occurs, time values will change. This is clear from looking at > > hour_type_print(): Whatever the kernel returned gets cur_tm->tm_gmtoff > > added to it. Here, this is either 3600 or 7200 depending on whether DST > > is active or not. > > > > The other alternative would be to make kernel DST-aware, I don't think > > that's the case. > > Hm, so the ruleset listing changes after DST. Yes, but only because payload (and hence kernel data) remains the same. > If the user specifies the time according to the userspace timezone, > then ruleset listing should not change? > > I'm still trying to understand if this is a real problem. IMHO, it's a controversy of whether we want to make the time match respect DST changes or not: It should, because when I restrict internet access to my kids after 8pm, I don't want to touch my firewall's ruleset twice a year. It needs not, because upon the next reboot things are correct again, anyway. It should not because otherwise once a year there are two spooky hours in which things run twice that should never ever run more than once per night. Apart from that, description of --kerneltz in iptables-extensions(8) speaks for itself. So long story short, it is always a problem no matter how it is solved. :( Cheers, Phil