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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4ABDAC61DA4 for ; Sat, 4 Feb 2023 21:00:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231171AbjBDVAe (ORCPT ); Sat, 4 Feb 2023 16:00:34 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60306 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229448AbjBDVAb (ORCPT ); Sat, 4 Feb 2023 16:00:31 -0500 Received: from orbyte.nwl.cc (orbyte.nwl.cc [IPv6:2001:41d0:e:133a::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D8A5EFD for ; Sat, 4 Feb 2023 13:00:29 -0800 (PST) Received: from n0-1 by orbyte.nwl.cc with local (Exim 4.94.2) (envelope-from ) id 1pOPe5-0007wN-Ow; Sat, 04 Feb 2023 22:00:25 +0100 Date: Sat, 4 Feb 2023 22:00:25 +0100 From: Phil Sutter To: Pablo Neira Ayuso Cc: Florian Westphal , netfilter-devel@vger.kernel.org Subject: Re: [nf-next PATCH v2] netfilter: nf_tables: Introduce NFTA_RULE_ACTUAL_EXPR Message-ID: Mail-Followup-To: Phil Sutter , Pablo Neira Ayuso , Florian Westphal , netfilter-devel@vger.kernel.org References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: netfilter-devel@vger.kernel.org On Sat, Feb 04, 2023 at 10:41:37AM +0100, Pablo Neira Ayuso wrote: > On Fri, Feb 03, 2023 at 05:21:29PM +0100, Phil Sutter wrote: > [...] > > On Fri, Feb 03, 2023 at 04:32:01PM +0100, Pablo Neira Ayuso wrote: > [...] > > > I also wonder if this might cause problems with nftables and implicit > > > sets, they are bound to one single lookup expression that, when gone, > > > the set is released. Now you will have two expressions pointing to an > > > implicit set. Same thing with implicit chains. This might get tricky > > > with the transaction interface. > > > > While indeed two lookup expressions will refer to the same anonymous > > set, only one of those expressions will ever be in use. There's no way > > the kernel would switch between rule variants (or use both at the same > > time). > > OK, but control plane will reject two lookup expressions that refer to > the same anonymous set. Only if it sees the second expression: If NFTA_RULE_ACTUAL_EXPR is present, the kernel will copy the content of NFTA_RULE_EXPRESSIONS into a buffer pointed to by nft_rule::dump_expr. It does not inspect the content apart from nla_policy checking which merely ensures it's a nested array of elements conforming to nft_expr_policy (i.e., have a NAME and DATA attribute). The copied data is touched only by nf_tables_fill_rule_info() which copies it as-is into the skb. Later, nf_tables_rule_destroy() just frees the whole blob. So effectively the kernel doesn't know or care what expressions are contained in NFTA_RULE_EXPRESSIONS. > > > iptables is rather simple representation (no sets), but nftables is > > > more expressive. > > > > That's not true, at least ebtables' among match is implemented using > > sets. :) > > Then better have a look at this implicit set scenario I describe above > because I cannot see how this can work. Sure, I'll give it a try. Cheers, Phil