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=-1.4 required=3.0 tests=BAYES_00,FORGED_MUA_MOZILLA, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS 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 1EA36C433DB for ; Tue, 9 Mar 2021 10:28:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DFF6E6527B for ; Tue, 9 Mar 2021 10:28:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230142AbhCIK17 (ORCPT ); Tue, 9 Mar 2021 05:27:59 -0500 Received: from correo.us.es ([193.147.175.20]:34284 "EHLO mail.us.es" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229878AbhCIK1p (ORCPT ); Tue, 9 Mar 2021 05:27:45 -0500 Received: from antivirus1-rhel7.int (unknown [192.168.2.11]) by mail.us.es (Postfix) with ESMTP id E1630F2583 for ; Tue, 9 Mar 2021 11:27:43 +0100 (CET) Received: from antivirus1-rhel7.int (localhost [127.0.0.1]) by antivirus1-rhel7.int (Postfix) with ESMTP id D1F7ADA704 for ; Tue, 9 Mar 2021 11:27:43 +0100 (CET) Received: by antivirus1-rhel7.int (Postfix, from userid 99) id C752CDA793; Tue, 9 Mar 2021 11:27:43 +0100 (CET) Received: from antivirus1-rhel7.int (localhost [127.0.0.1]) by antivirus1-rhel7.int (Postfix) with ESMTP id 739E6DA78A; Tue, 9 Mar 2021 11:27:41 +0100 (CET) Received: from 192.168.1.97 (192.168.1.97) by antivirus1-rhel7.int (F-Secure/fsigk_smtp/550/antivirus1-rhel7.int); Tue, 09 Mar 2021 11:27:41 +0100 (CET) X-Virus-Status: clean(F-Secure/fsigk_smtp/550/antivirus1-rhel7.int) Received: from us.es (unknown [90.77.255.23]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) (Authenticated sender: 1984lsi) by entrada.int (Postfix) with ESMTPSA id 5311442DC6E2; Tue, 9 Mar 2021 11:27:41 +0100 (CET) Date: Tue, 9 Mar 2021 11:27:40 +0100 X-SMTPAUTHUS: auth mail.us.es From: Pablo Neira Ayuso To: Marc =?utf-8?Q?Aur=C3=A8le?= La France Cc: netfilter-devel@vger.kernel.org Subject: Re: [PATCH nf] netfilter REJECT: Fix destination MAC in RST packets Message-ID: <20210309102740.GA30899@salvia> References: <20210308102510.GA23497@salvia> <20210309013621.GA27206@salvia> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mozilla/5.0 X-Virus-Scanned: ClamAV using ClamSMTP Precedence: bulk List-ID: X-Mailing-List: netfilter-devel@vger.kernel.org On Mon, Mar 08, 2021 at 09:25:28PM -0700, Marc Aurèle La France wrote: > On Tue, 9 Mar 2021, Pablo Neira Ayuso wrote: > > On Mon, Mar 08, 2021 at 09:21:20AM -0700, Marc Aurèle La France wrote: > > > On Mon, 8 Mar 2021, Pablo Neira Ayuso wrote: > > > > On Sun, Mar 07, 2021 at 06:16:34PM -0700, Marc Aurèle La France wrote: > > > > > > In the non-bridge case, the REJECT target code assumes the REJECTed > > > > > packets were originally emitted by the local host, but that's not > > > > > necessarily true when the local host is the default route of a subnet > > > > > it is on, resulting in RST packets being sent out with an incorrect > > > > > destination MAC. Address this by refactoring the handling of bridged > > > > > packets which deals with a similar issue. Modulo patch fuzz, the > > > > > following applies to v5 and later kernels. > > > > > The code this patch updates is related to BRIDGE_NETFILTER. Your patch > > > > description refers to the non-bridge case. What are you trying to > > > > achieve? > > > > Via DHCP, my subnet's default route is a Linux system so that it can monitor > > > all outbound traffic. By doing so, for example, I have determined that my > > > Android phone connects to Facebook despite the fact that I have no such app > > > installed. I want to know, and control, what other behind-the-scenes > > > (under-handed) traffic devices on my subnet generate. > > > > > dev_queue_xmit() path should not be exercised from the prerouting > > > > chain, packets generated from the IP later must follow the > > > > ip_local_out() path. > > > > Well, I can tell you dev_queue_xmit() does in fact work in prerouting > > > chains, as it must for the bridging case. The only potential problem I've > > > found so far is that the RST packet doesn't go through any netfilter hooks. > > > That's the issue, Netfilter rejects code from the IP layer, so the > > packets follows the ip_local_out() path. > > ... which sets an incorrect destination MAC. Also, in this case, netfilter > doesn't reject any such thing. It doesn't even "see" the RST packet > dev_queue_xmit() sends out. That's OK as there is no further need to > process such a packet. dev_queue_xmit() skips the policy in the local out path for the generated RST packet. If you want to plain reject using dev_queue_xmit() then you have to use the ingress hook. > At least, the device whose connection request is being denied > doesn't hang anymore... The neighbour cache selects the destination MAC from the destination IP address of the RST packet. Your patch also refers to non-bridge scenario (no br_netfilter in place). Could you describe what you're trying to achieve in plain layman terms?