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=-15.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 B0095C433DB for ; Sat, 23 Jan 2021 01:48:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 78742205F4 for ; Sat, 23 Jan 2021 01:48:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726501AbhAWBsN (ORCPT ); Fri, 22 Jan 2021 20:48:13 -0500 Received: from www62.your-server.de ([213.133.104.62]:33102 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726374AbhAWBsL (ORCPT ); Fri, 22 Jan 2021 20:48:11 -0500 Received: from sslproxy02.your-server.de ([78.47.166.47]) by www62.your-server.de with esmtpsa (TLSv1.3:TLS_AES_256_GCM_SHA384:256) (Exim 4.92.3) (envelope-from ) id 1l381R-0004qy-Iu; Sat, 23 Jan 2021 02:47:29 +0100 Received: from [85.7.101.30] (helo=pc-9.home) by sslproxy02.your-server.de with esmtpsa (TLSv1.3:TLS_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1l381R-000XKL-8p; Sat, 23 Jan 2021 02:47:29 +0100 Subject: Re: [PATCH bpf-next V12 2/7] bpf: fix bpf_fib_lookup helper MTU check for SKB ctx To: Jesper Dangaard Brouer , bpf@vger.kernel.org Cc: 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 References: <161098881526.108067.7603213364270807261.stgit@firesoul> <161098885996.108067.14467274374916086727.stgit@firesoul> From: Daniel Borkmann Message-ID: <06f94963-f16b-3339-abf2-6529b474a2f6@iogearbox.net> Date: Sat, 23 Jan 2021 02:47:28 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <161098885996.108067.14467274374916086727.stgit@firesoul> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Authenticated-Sender: daniel@iogearbox.net X-Virus-Scanned: Clear (ClamAV 0.102.4/26057/Fri Jan 22 13:30:31 2021) Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org 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/