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=-16.0 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, URIBL_BLOCKED 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 C9DEEC433E9 for ; Tue, 26 Jan 2021 05:38:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9767422ADF for ; Tue, 26 Jan 2021 05:38:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728821AbhAZFhu (ORCPT ); Tue, 26 Jan 2021 00:37:50 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:46647 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728949AbhAYQAY (ORCPT ); Mon, 25 Jan 2021 11:00:24 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1611590334; 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=FjO7IzXQfUSbflOYOdqxjoPa6fZg3R1AGbOy1QaC80k=; b=hQJwr5Z7qUY+YVCb4sWOlt4wnLq2dE1yuJbowO74CetMQ5NJWt+C7o58DQfoOopKneFWHl eGqmi5/mrdqHsrTxP6XDkL7r+8X11tPH2Io3V9Q58l1zjaVk1kGEzKZJsD3R8T3W8eAPU4 /O2ZHTbOQlhrHLB0lIbZMBKiCtkAQpE= 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-582-p90vs-uoMuqicxcFY4TL4Q-1; Mon, 25 Jan 2021 10:58:50 -0500 X-MC-Unique: p90vs-uoMuqicxcFY4TL4Q-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 04996104F958; Mon, 25 Jan 2021 15:58:48 +0000 (UTC) Received: from carbon (unknown [10.36.110.4]) by smtp.corp.redhat.com (Postfix) with ESMTP id E30601045D22; Mon, 25 Jan 2021 15:58:35 +0000 (UTC) Date: Mon, 25 Jan 2021 16:58:34 +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, brouer@redhat.com Subject: Re: [PATCH bpf-next V12 2/7] bpf: fix bpf_fib_lookup helper MTU check for SKB ctx Message-ID: <20210125165834.558f7fe1@carbon> In-Reply-To: <06f94963-f16b-3339-abf2-6529b474a2f6@iogearbox.net> References: <161098881526.108067.7603213364270807261.stgit@firesoul> <161098885996.108067.14467274374916086727.stgit@firesoul> <06f94963-f16b-3339-abf2-6529b474a2f6@iogearbox.net> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Sat, 23 Jan 2021 02:47:28 +0100 Daniel Borkmann wrote: > On 1/18/21 5:54 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. > > > > V10: > > - Use same method as XDP for 'tot_len' MTU check > > > > 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 | 13 ++++++++++--- > > 1 file changed, 10 insertions(+), 3 deletions(-) > > > > diff --git a/net/core/filter.c b/net/core/filter.c > > index 5beadd659091..d5e6f395cf64 100644 > > --- a/net/core/filter.c > > +++ b/net/core/filter.c > > @@ -5569,6 +5569,7 @@ BPF_CALL_4(bpf_skb_fib_lookup, struct sk_buff *, skb, > > { > > struct net *net = dev_net(skb->dev); > > int rc = -EAFNOSUPPORT; > > + bool check_mtu = false; > > > > if (plen < sizeof(*params)) > > return -EINVAL; > > @@ -5576,22 +5577,28 @@ BPF_CALL_4(bpf_skb_fib_lookup, struct sk_buff *, skb, > > if (flags & ~(BPF_FIB_LOOKUP_DIRECT | BPF_FIB_LOOKUP_OUTPUT)) > > return -EINVAL; > > > > + if (params->tot_len) > > + check_mtu = true; > > + > > switch (params->family) { > > #if IS_ENABLED(CONFIG_INET) > > case AF_INET: > > - rc = bpf_ipv4_fib_lookup(net, params, flags, false); > > + rc = bpf_ipv4_fib_lookup(net, params, flags, check_mtu); > > break; > > #endif > > #if IS_ENABLED(CONFIG_IPV6) > > case AF_INET6: > > - rc = bpf_ipv6_fib_lookup(net, params, flags, false); > > + rc = bpf_ipv6_fib_lookup(net, params, flags, check_mtu); > > break; > > #endif > > } > > > > - if (!rc) { > > + if (rc == BPF_FIB_LKUP_RET_SUCCESS && !check_mtu) { > > struct net_device *dev; > > > > + /* When tot_len isn't provided by user, > > + * check skb against net_device MTU > > + */ > > dev = dev_get_by_index_rcu(net, params->ifindex); > > if (!is_skb_forwardable(dev, skb)) > > rc = BPF_FIB_LKUP_RET_FRAG_NEEDED; > > Btw, looking at some of the old feedback, looks like [0] got missed somehow. Would > be nice if we could simplify this rather ugly bit with refetching dev for tc. > > [0] https://lore.kernel.org/bpf/f959017b-5d3c-5cdb-a016-c467a3c9a2fc@iogearbox.net/ > https://lore.kernel.org/bpf/f8ff26f0-b1b6-6dd1-738d-4c592a8efdb0@gmail.com/ I have tried to incorporate the ideas from [0]. If you notice this code path is only called in-case params->tot_len is zero (!check_mtu). Then if params->tot_len does contain something, then the check_mtu code path of bpf_ipv4_fib_lookup() and bpf_ipv6_fib_lookup(). I agree, that it is ugly refetching dev. I'll look at moving the lookup dev_get_by_index_rcu() call one level-up, as both bpf_ipv4_fib_lookup() and bpf_ipv6_fib_lookup() does this call. (I cannot move the check into the functions due skb is not avail in XDP case) -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer