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=-15.2 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,URIBL_BLOCKED, USER_AGENT_SANE_1 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 E507BC64E7B for ; Wed, 2 Dec 2020 22:24:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 85A6322201 for ; Wed, 2 Dec 2020 22:24:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727940AbgLBWYf (ORCPT ); Wed, 2 Dec 2020 17:24:35 -0500 Received: from www62.your-server.de ([213.133.104.62]:44946 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726987AbgLBWYf (ORCPT ); Wed, 2 Dec 2020 17:24:35 -0500 Received: from sslproxy01.your-server.de ([78.46.139.224]) by www62.your-server.de with esmtpsa (TLSv1.3:TLS_AES_256_GCM_SHA384:256) (Exim 4.92.3) (envelope-from ) id 1kkaXQ-0006sH-Ua; Wed, 02 Dec 2020 23:23:52 +0100 Received: from [85.7.101.30] (helo=pc-9.home) by sslproxy01.your-server.de with esmtpsa (TLSv1.3:TLS_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1kkaXQ-000Xh6-M4; Wed, 02 Dec 2020 23:23:52 +0100 Subject: Re: [PATCH bpf-next V8 3/8] bpf: bpf_fib_lookup return MTU value as output when looked up 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: <160650034591.2890576.1092952641487480652.stgit@firesoul> <160650039275.2890576.7191201185534571391.stgit@firesoul> From: Daniel Borkmann Message-ID: Date: Wed, 2 Dec 2020 23:23:51 +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: <160650039275.2890576.7191201185534571391.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 0.102.4/26006/Wed Dec 2 14:14:18 2020) Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 11/27/20 7:06 PM, Jesper Dangaard Brouer wrote: > The BPF-helpers for FIB lookup (bpf_xdp_fib_lookup and bpf_skb_fib_lookup) > can perform MTU check and return BPF_FIB_LKUP_RET_FRAG_NEEDED. The BPF-prog > don't know the MTU value that caused this rejection. > > If the BPF-prog wants to implement PMTU (Path MTU Discovery) (rfc1191) it > need to know this MTU value for the ICMP packet. > > Patch change lookup and result struct bpf_fib_lookup, to contain this MTU > value as output via a union with 'tot_len' as this is the value used for > the MTU lookup. > > V5: > - Fixed uninit value spotted by Dan Carpenter. > - Name struct output member mtu_result > > Reported-by: kernel test robot > Reported-by: Dan Carpenter > Signed-off-by: Jesper Dangaard Brouer > --- > include/uapi/linux/bpf.h | 11 +++++++++-- > net/core/filter.c | 22 +++++++++++++++------- > tools/include/uapi/linux/bpf.h | 11 +++++++++-- > 3 files changed, 33 insertions(+), 11 deletions(-) > > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h > index c3458ec1f30a..848398bd5a54 100644 > --- a/include/uapi/linux/bpf.h > +++ b/include/uapi/linux/bpf.h > @@ -2220,6 +2220,9 @@ union bpf_attr { > * * > 0 one of **BPF_FIB_LKUP_RET_** codes explaining why the > * packet is not forwarded or needs assist from full stack > * > + * If lookup fails with BPF_FIB_LKUP_RET_FRAG_NEEDED, then the MTU > + * was exceeded and output params->mtu_result contains the MTU. > + * > * long bpf_sock_hash_update(struct bpf_sock_ops *skops, struct bpf_map *map, void *key, u64 flags) > * Description > * Add an entry to, or update a sockhash *map* referencing sockets. > @@ -4961,9 +4964,13 @@ struct bpf_fib_lookup { > __be16 sport; > __be16 dport; > > - /* total length of packet from network header - used for MTU check */ > - __u16 tot_len; > + union { /* used for MTU check */ > + /* input to lookup */ > + __u16 tot_len; /* L3 length from network hdr (iph->tot_len) */ > > + /* output: MTU value */ > + __u16 mtu_result; > + }; > /* input: L3 device index for lookup > * output: device index from FIB lookup > */ > diff --git a/net/core/filter.c b/net/core/filter.c > index 84d77c425fbe..25b137ffdced 100644 > --- a/net/core/filter.c > +++ b/net/core/filter.c > @@ -5265,12 +5265,14 @@ static const struct bpf_func_proto bpf_skb_get_xfrm_state_proto = { > #if IS_ENABLED(CONFIG_INET) || IS_ENABLED(CONFIG_IPV6) > static int bpf_fib_set_fwd_params(struct bpf_fib_lookup *params, > const struct neighbour *neigh, > - const struct net_device *dev) > + const struct net_device *dev, u32 mtu) > { > memcpy(params->dmac, neigh->ha, ETH_ALEN); > memcpy(params->smac, dev->dev_addr, ETH_ALEN); > params->h_vlan_TCI = 0; > params->h_vlan_proto = 0; > + if (mtu) > + params->mtu_result = mtu; /* union with tot_len */ > > return 0; > } > @@ -5286,8 +5288,8 @@ static int bpf_ipv4_fib_lookup(struct net *net, struct bpf_fib_lookup *params, > struct net_device *dev; > struct fib_result res; > struct flowi4 fl4; > + u32 mtu = 0; > int err; > - u32 mtu; > > dev = dev_get_by_index_rcu(net, params->ifindex); > if (unlikely(!dev)) > @@ -5354,8 +5356,10 @@ static int bpf_ipv4_fib_lookup(struct net *net, struct bpf_fib_lookup *params, > > if (check_mtu) { > mtu = ip_mtu_from_fib_result(&res, params->ipv4_dst); > - if (params->tot_len > mtu) > + if (params->tot_len > mtu) { > + params->mtu_result = mtu; /* union with tot_len */ > return BPF_FIB_LKUP_RET_FRAG_NEEDED; > + } > } > > nhc = res.nhc; > @@ -5389,7 +5393,7 @@ static int bpf_ipv4_fib_lookup(struct net *net, struct bpf_fib_lookup *params, > if (!neigh) > return BPF_FIB_LKUP_RET_NO_NEIGH; > > - return bpf_fib_set_fwd_params(params, neigh, dev); > + return bpf_fib_set_fwd_params(params, neigh, dev, mtu); > } > #endif > > @@ -5406,7 +5410,7 @@ static int bpf_ipv6_fib_lookup(struct net *net, struct bpf_fib_lookup *params, > struct flowi6 fl6; > int strict = 0; > int oif, err; > - u32 mtu; > + u32 mtu = 0; > > /* link local addresses are never forwarded */ > if (rt6_need_strict(dst) || rt6_need_strict(src)) > @@ -5481,8 +5485,10 @@ static int bpf_ipv6_fib_lookup(struct net *net, struct bpf_fib_lookup *params, > > if (check_mtu) { > mtu = ipv6_stub->ip6_mtu_from_fib6(&res, dst, src); > - if (params->tot_len > mtu) > + if (params->tot_len > mtu) { > + params->mtu_result = mtu; /* union with tot_len */ > return BPF_FIB_LKUP_RET_FRAG_NEEDED; And with mentioned approach from [0] we also only ever need to set the above, but we don't need to drag it anywhere else via bpf_fib_set_fwd_params() with the extra zero check on mtu. So this should simplify this one as well. [0] https://lore.kernel.org/bpf/6f9cac4e-a231-ff8d-43a5-828995ca5ec7@iogearbox.net/ > + } > } > > if (res.nh->fib_nh_lws) > @@ -5502,7 +5508,7 @@ static int bpf_ipv6_fib_lookup(struct net *net, struct bpf_fib_lookup *params, > if (!neigh) > return BPF_FIB_LKUP_RET_NO_NEIGH; > > - return bpf_fib_set_fwd_params(params, neigh, dev); > + return bpf_fib_set_fwd_params(params, neigh, dev, mtu);