From patchwork Fri Nov 20 16:18:16 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: 11921259 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=unavailable 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 365F1C56201 for ; Fri, 20 Nov 2020 16:18:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CE4F42408E for ; Fri, 20 Nov 2020 16:18:32 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="UB2qwK7Y" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729094AbgKTQS1 (ORCPT ); Fri, 20 Nov 2020 11:18:27 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:41516 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729129AbgKTQS0 (ORCPT ); Fri, 20 Nov 2020 11:18:26 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1605889105; 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=KVMZThUI3oPsd1omprnYCWaZp4TXk/i/DP0zyqt9kfw=; b=UB2qwK7YH9jP+TIHqJnJNo0dQeNX/PcC472kS2EMXRsU7wFfm0Q4W+JGZHIk7MPEnj5aQ0 DTGtJrWZH/ZZHnQbXfrO2xMQy/p3zBFHFhKsv5ZEqvW6oatMgASGbpj4abeDhWhw1Gi1ZR qIlkg7pgMdyRqjvNqDgnyBqwzElSvWA= 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-478-HK3PEeQvMyKDUucqyAAW8w-1; Fri, 20 Nov 2020 11:18:20 -0500 X-MC-Unique: HK3PEeQvMyKDUucqyAAW8w-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 8C1AB100A643; Fri, 20 Nov 2020 16:18:18 +0000 (UTC) Received: from firesoul.localdomain (unknown [10.40.208.7]) by smtp.corp.redhat.com (Postfix) with ESMTP id 1C3DE10016DB; Fri, 20 Nov 2020 16:18:18 +0000 (UTC) Received: from [192.168.42.3] (localhost [IPv6:::1]) by firesoul.localdomain (Postfix) with ESMTP id F32893213845D; Fri, 20 Nov 2020 17:18:16 +0100 (CET) Subject: [PATCH bpf-next V7 2/8] 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: Fri, 20 Nov 2020 17:18:16 +0100 Message-ID: <160588909693.2817268.17116187979657760922.stgit@firesoul> In-Reply-To: <160588903254.2817268.4861837335793475314.stgit@firesoul> References: <160588903254.2817268.4861837335793475314.stgit@firesoul> User-Agent: StGit/0.19 MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 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 1ee97fdeea64..84d77c425fbe 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -5565,11 +5565,21 @@ 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; }