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=-6.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 D4CB0C433E0 for ; Mon, 8 Feb 2021 16:29:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7C29464D87 for ; Mon, 8 Feb 2021 16:29:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234376AbhBHQ3D (ORCPT ); Mon, 8 Feb 2021 11:29:03 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:48719 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234162AbhBHQ2u (ORCPT ); Mon, 8 Feb 2021 11:28:50 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1612801644; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=K9lNJnNNY1Fz7QWSI+VzlyuLnjOEnPi/oNdJ+JCAbmg=; b=Io/fozKcSDRnWpLhN9sjVOMbh33JzDnnyGOQNPEUnlKFo4CIic4+SenO0DMZXsaDXTCofH NwOaGsE38fpJH9Ok6t/sEszF5i7uxwURDnrwIG5BHPicTtKLqIoTk3aAucjnezoK98noWe +Wmx3elA8oYmyxkdS6iRy++VQWtMMH8= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-140-SQ-Af8sWOo6gFa4yt4oVwQ-1; Mon, 08 Feb 2021 11:27:20 -0500 X-MC-Unique: SQ-Af8sWOo6gFa4yt4oVwQ-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id EFABF79EC0; Mon, 8 Feb 2021 16:27:17 +0000 (UTC) Received: from carbon (unknown [10.36.110.45]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2D3F76085D; Mon, 8 Feb 2021 16:27:10 +0000 (UTC) Date: Mon, 8 Feb 2021 17:27:09 +0100 From: Jesper Dangaard Brouer To: Daniel Borkmann Cc: bpf@vger.kernel.org, netdev@vger.kernel.org, Daniel Borkmann , Alexei Starovoitov , maze@google.com, lmb@cloudflare.com, shaun@tigera.io, Lorenzo Bianconi , marek@cloudflare.com, John Fastabend , Jakub Kicinski , eyal.birger@gmail.com, colrack@gmail.com, David Ahern , brouer@redhat.com Subject: Re: [PATCH bpf-next V15 2/7] bpf: fix bpf_fib_lookup helper MTU check for SKB ctx Message-ID: <20210208172709.15415a46@carbon> In-Reply-To: <547131a3-5125-d419-8e61-0fc675d663a8@iogearbox.net> References: <161228314075.576669.15427172810948915572.stgit@firesoul> <161228321177.576669.11521750082473556168.stgit@firesoul> <20210208145713.4ee3e9ba@carbon> <20210208162056.44b0236e@carbon> <547131a3-5125-d419-8e61-0fc675d663a8@iogearbox.net> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Mon, 8 Feb 2021 16:41:24 +0100 Daniel Borkmann wrote: > On 2/8/21 4:20 PM, Jesper Dangaard Brouer wrote: > > On Mon, 8 Feb 2021 14:57:13 +0100 > > Jesper Dangaard Brouer wrote: > >> On Fri, 5 Feb 2021 01:06:35 +0100 > >> Daniel Borkmann wrote: > >>> On 2/2/21 5:26 PM, Jesper Dangaard Brouer wrote: > >>>> BPF end-user on Cilium slack-channel (Carlo Carraro) wants to use > >>>> bpf_fib_lookup for doing MTU-check, but *prior* to extending packet size, > >>>> by adjusting fib_params 'tot_len' with the packet length plus the expected > >>>> encap size. (Just like the bpf_check_mtu helper supports). He discovered > >>>> that for SKB ctx the param->tot_len was not used, instead skb->len was used > >>>> (via MTU check in is_skb_forwardable() that checks against netdev MTU). > >>>> > >>>> Fix this by using fib_params 'tot_len' for MTU check. If not provided (e.g. > >>>> zero) then keep existing TC behaviour intact. Notice that 'tot_len' for MTU > >>>> check is done like XDP code-path, which checks against FIB-dst MTU. > [...] > >>>> - if (!rc) { > >>>> - struct net_device *dev; > >>>> - > >>>> - dev = dev_get_by_index_rcu(net, params->ifindex); > >>>> + if (rc == BPF_FIB_LKUP_RET_SUCCESS && !check_mtu) { > >>>> + /* When tot_len isn't provided by user, > >>>> + * check skb against net_device MTU > >>>> + */ > >>>> if (!is_skb_forwardable(dev, skb)) > >>>> rc = BPF_FIB_LKUP_RET_FRAG_NEEDED; > >>> > >>> ... so using old cached dev from above will result in wrong MTU check & > >>> subsequent passing of wrong params->mtu_result = dev->mtu this way. > >> > >> Yes, you are right, params->ifindex have a chance to change in the calls. > >> So, our attempt to save an ifindex lookup (dev_get_by_index_rcu) is not > >> correct. > >> > >>> So one > >>> way to fix is that we would need to pass &dev to bpf_ipv{4,6}_fib_lookup(). > >> > >> Ok, I will try to code it up, and see how ugly it looks, but I'm no > >> longer sure that it is worth saving this ifindex lookup, as it will > >> only happen if BPF-prog didn't specify params->tot_len. > > > > I guess we can still do this as an "optimization", but the dev/ifindex > > will very likely be another at this point. > > I would say for sake of progress, lets ship your series w/o this optimization so > it can land, and we revisit this later on independent from here. I would really really like to make progress for this patchset. I unfortunately finished coding this up (and tested with selftests) before I noticed this request (without optimizations). I guess, I can revert my recent work by pulling in V12 of the patch. I'll do it tomorrow, as I want to have time to run my tests before re-sending patchset. > Actually DavidA back then acked the old poc patch I posted, so maybe > that's worth a revisit as well but needs more testing first. Yes, we can always revisit this as an optimization. -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer