From patchwork Thu Dec 17 17:26:25 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jesper Dangaard Brouer X-Patchwork-Id: 11980319 X-Patchwork-Delegate: bpf@iogearbox.net 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=-15.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham 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 AF56AC2BBCF for ; Thu, 17 Dec 2020 17:28:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8AB22239A4 for ; Thu, 17 Dec 2020 17:28:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729677AbgLQR2C (ORCPT ); Thu, 17 Dec 2020 12:28:02 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:35959 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729111AbgLQR2C (ORCPT ); Thu, 17 Dec 2020 12:28:02 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1608225995; 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=7RkBoMP87EGI+5/V3dgcPPlpmhk9OdwSH4A5eujpfic=; b=ieug2ZYQ0Mcgmvy1ozIQgsdaFJYZcjfTCMEt4/oQPtNWX5gR4VR4cABGvc/Q1PWxXd3D5K O0ImTJxOKzKvCzQrXd8KZ2vlFi9XvytMcV81znisJy4evmZ2Ri/A3PQgrUarN4/NeAiY4C YqZKnzOrXyHMWvLUj7j4SZ3yaPHLXYY= 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-324-AcnmwB8oMfOHmN9ScNJWfA-1; Thu, 17 Dec 2020 12:26:33 -0500 X-MC-Unique: AcnmwB8oMfOHmN9ScNJWfA-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id EB3068030AD; Thu, 17 Dec 2020 17:26:31 +0000 (UTC) Received: from firesoul.localdomain (unknown [10.40.208.19]) by smtp.corp.redhat.com (Postfix) with ESMTP id 87A541B18A; Thu, 17 Dec 2020 17:26:26 +0000 (UTC) Received: from [192.168.42.3] (localhost [IPv6:::1]) by firesoul.localdomain (Postfix) with ESMTP id 8BD5D32138454; Thu, 17 Dec 2020 18:26:25 +0100 (CET) Subject: [PATCH bpf-next V9 2/7] bpf: fix bpf_fib_lookup helper MTU check for SKB ctx From: Jesper Dangaard Brouer To: bpf@vger.kernel.org Cc: Jesper Dangaard Brouer , 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 Date: Thu, 17 Dec 2020 18:26:25 +0100 Message-ID: <160822598551.3481451.14159825721005377499.stgit@firesoul> In-Reply-To: <160822594178.3481451.1208057539613401103.stgit@firesoul> References: <160822594178.3481451.1208057539613401103.stgit@firesoul> User-Agent: StGit/0.19 MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org X-Patchwork-Delegate: bpf@iogearbox.net 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()). Fix this by using fib_params 'tot_len' for MTU check. If not provided (e.g. zero) then keep existing behaviour intact. Fixes: 4c79579b44b1 ("bpf: Change bpf_fib_lookup to return lookup status") Reported-by: Carlo Carraro Signed-off-by: Jesper Dangaard Brouer --- net/core/filter.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/net/core/filter.c b/net/core/filter.c index f8f198252ff2..95c6fdebd0db 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -5568,11 +5568,21 @@ BPF_CALL_4(bpf_skb_fib_lookup, struct sk_buff *, skb, #endif } - if (!rc) { + if (rc == BPF_FIB_LKUP_RET_SUCCESS) { struct net_device *dev; + u32 mtu; dev = dev_get_by_index_rcu(net, params->ifindex); - if (!is_skb_forwardable(dev, skb)) + mtu = READ_ONCE(dev->mtu); + + /* Using tot_len for (L3) MTU check if provided by user */ + if (params->tot_len && params->tot_len > mtu) + rc = BPF_FIB_LKUP_RET_FRAG_NEEDED; + + /* Notice at this TC cls_bpf level skb->len contains L2 size, + * but is_skb_forwardable takes that into account + */ + if (params->tot_len == 0 && !is_skb_forwardable(dev, skb)) rc = BPF_FIB_LKUP_RET_FRAG_NEEDED; }