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=-2.3 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 4E67DC54FCB for ; Sun, 26 Apr 2020 21:57:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1FDB220700 for ; Sun, 26 Apr 2020 21:57:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726227AbgDZV5j (ORCPT ); Sun, 26 Apr 2020 17:57:39 -0400 Received: from correo.us.es ([193.147.175.20]:54762 "EHLO mail.us.es" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726184AbgDZV5i (ORCPT ); Sun, 26 Apr 2020 17:57:38 -0400 Received: from antivirus1-rhel7.int (unknown [192.168.2.11]) by mail.us.es (Postfix) with ESMTP id 22DD11022A2 for ; Sun, 26 Apr 2020 23:57:37 +0200 (CEST) Received: from antivirus1-rhel7.int (localhost [127.0.0.1]) by antivirus1-rhel7.int (Postfix) with ESMTP id 15DDDBAAA3 for ; Sun, 26 Apr 2020 23:57:37 +0200 (CEST) Received: by antivirus1-rhel7.int (Postfix, from userid 99) id 0AFC6BAAA1; Sun, 26 Apr 2020 23:57:37 +0200 (CEST) Received: from antivirus1-rhel7.int (localhost [127.0.0.1]) by antivirus1-rhel7.int (Postfix) with ESMTP id 1C1D3BAAA3; Sun, 26 Apr 2020 23:57:35 +0200 (CEST) Received: from 192.168.1.97 (192.168.1.97) by antivirus1-rhel7.int (F-Secure/fsigk_smtp/550/antivirus1-rhel7.int); Sun, 26 Apr 2020 23:57:35 +0200 (CEST) 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 F36BE42EF4E0; Sun, 26 Apr 2020 23:57:34 +0200 (CEST) Date: Sun, 26 Apr 2020 23:57:34 +0200 X-SMTPAUTHUS: auth mail.us.es From: Pablo Neira Ayuso To: Guillaume Nault Cc: Jozsef Kadlecsik , Florian Westphal , netfilter-devel@vger.kernel.org, netdev@vger.kernel.org Subject: Re: [PATCH net] netfilter: nat: never update the UDP checksum when it's 0 Message-ID: <20200426215734.GA7662@salvia> References: <335a95d93767f2b58ad89975e4a0b342ee00db91.1587429321.git.gnault@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <335a95d93767f2b58ad89975e4a0b342ee00db91.1587429321.git.gnault@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-Virus-Scanned: ClamAV using ClamSMTP Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Tue, Apr 21, 2020 at 02:42:19AM +0200, Guillaume Nault wrote: > If the UDP header of a local VXLAN endpoint is NAT-ed, and the VXLAN > device has disabled UDP checksums and enabled Tx checksum offloading, > then the skb passed to udp_manip_pkt() has hdr->check == 0 (outer > checksum disabled) and skb->ip_summed == CHECKSUM_PARTIAL (inner packet > checksum offloaded). > > Because of the ->ip_summed value, udp_manip_pkt() tries to update the > outer checksum with the new address and port, leading to an invalid > checksum sent on the wire, as the original null checksum obviously > didn't take the old address and port into account. > > So, we can't take ->ip_summed into account in udp_manip_pkt(), as it > might not refer to the checksum we're acting on. Instead, we can base > the decision to update the UDP checksum entirely on the value of > hdr->check, because it's null if and only if checksum is disabled: > > * A fully computed checksum can't be 0, since a 0 checksum is > represented by the CSUM_MANGLED_0 value instead. > > * A partial checksum can't be 0, since the pseudo-header always adds > at least one non-zero value (the UDP protocol type 0x11) and adding > more values to the sum can't make it wrap to 0 as the carry is then > added to the wrapped number. > > * A disabled checksum uses the special value 0. > > The problem seems to be there from day one, although it was probably > not visible before UDP tunnels were implemented. Applied, thanks.