![Jesper Dangaard Brouer](/assets/img/avatar_default.png)
Make it clear that this XDP program depend on the network stack to do the ARP resolution. This is connected with the BPF_FIB_LKUP_RET_NO_NEIGH return code from bpf_fib_lookup(). Another common mistake (seen via XDP-tutorial) is that users don't realize that sysctl net.ipv{4,6}.conf.all.forwarding setting is honored by bpf_fib_lookup. Reported-by: Anton Protopopov <a.s.protopopov@gmail.com> Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com> Reviewed-by: David Ahern <dsahern@gmail.com> Acked-by: Yonghong Song <yhs@fb.com> Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
160 lines
4.6 KiB
C
160 lines
4.6 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/* Copyright (c) 2017-18 David Ahern <dsahern@gmail.com>
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of version 2 of the GNU General Public
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* License as published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*/
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#define KBUILD_MODNAME "foo"
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#include <uapi/linux/bpf.h>
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#include <linux/in.h>
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#include <linux/if_ether.h>
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#include <linux/if_packet.h>
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#include <linux/if_vlan.h>
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#include <linux/ip.h>
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#include <linux/ipv6.h>
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#include "bpf_helpers.h"
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#define IPV6_FLOWINFO_MASK cpu_to_be32(0x0FFFFFFF)
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/* For TX-traffic redirect requires net_device ifindex to be in this devmap */
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struct bpf_map_def SEC("maps") xdp_tx_ports = {
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.type = BPF_MAP_TYPE_DEVMAP,
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.key_size = sizeof(int),
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.value_size = sizeof(int),
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.max_entries = 64,
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};
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/* from include/net/ip.h */
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static __always_inline int ip_decrease_ttl(struct iphdr *iph)
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{
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u32 check = (__force u32)iph->check;
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check += (__force u32)htons(0x0100);
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iph->check = (__force __sum16)(check + (check >= 0xFFFF));
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return --iph->ttl;
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}
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static __always_inline int xdp_fwd_flags(struct xdp_md *ctx, u32 flags)
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{
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void *data_end = (void *)(long)ctx->data_end;
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void *data = (void *)(long)ctx->data;
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struct bpf_fib_lookup fib_params;
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struct ethhdr *eth = data;
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struct ipv6hdr *ip6h;
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struct iphdr *iph;
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u16 h_proto;
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u64 nh_off;
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int rc;
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nh_off = sizeof(*eth);
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if (data + nh_off > data_end)
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return XDP_DROP;
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__builtin_memset(&fib_params, 0, sizeof(fib_params));
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h_proto = eth->h_proto;
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if (h_proto == htons(ETH_P_IP)) {
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iph = data + nh_off;
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if (iph + 1 > data_end)
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return XDP_DROP;
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if (iph->ttl <= 1)
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return XDP_PASS;
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fib_params.family = AF_INET;
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fib_params.tos = iph->tos;
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fib_params.l4_protocol = iph->protocol;
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fib_params.sport = 0;
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fib_params.dport = 0;
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fib_params.tot_len = ntohs(iph->tot_len);
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fib_params.ipv4_src = iph->saddr;
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fib_params.ipv4_dst = iph->daddr;
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} else if (h_proto == htons(ETH_P_IPV6)) {
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struct in6_addr *src = (struct in6_addr *) fib_params.ipv6_src;
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struct in6_addr *dst = (struct in6_addr *) fib_params.ipv6_dst;
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ip6h = data + nh_off;
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if (ip6h + 1 > data_end)
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return XDP_DROP;
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if (ip6h->hop_limit <= 1)
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return XDP_PASS;
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fib_params.family = AF_INET6;
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fib_params.flowinfo = *(__be32 *)ip6h & IPV6_FLOWINFO_MASK;
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fib_params.l4_protocol = ip6h->nexthdr;
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fib_params.sport = 0;
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fib_params.dport = 0;
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fib_params.tot_len = ntohs(ip6h->payload_len);
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*src = ip6h->saddr;
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*dst = ip6h->daddr;
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} else {
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return XDP_PASS;
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}
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fib_params.ifindex = ctx->ingress_ifindex;
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rc = bpf_fib_lookup(ctx, &fib_params, sizeof(fib_params), flags);
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/*
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* Some rc (return codes) from bpf_fib_lookup() are important,
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* to understand how this XDP-prog interacts with network stack.
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*
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* BPF_FIB_LKUP_RET_NO_NEIGH:
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* Even if route lookup was a success, then the MAC-addresses are also
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* needed. This is obtained from arp/neighbour table, but if table is
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* (still) empty then BPF_FIB_LKUP_RET_NO_NEIGH is returned. To avoid
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* doing ARP lookup directly from XDP, then send packet to normal
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* network stack via XDP_PASS and expect it will do ARP resolution.
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*
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* BPF_FIB_LKUP_RET_FWD_DISABLED:
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* The bpf_fib_lookup respect sysctl net.ipv{4,6}.conf.all.forwarding
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* setting, and will return BPF_FIB_LKUP_RET_FWD_DISABLED if not
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* enabled this on ingress device.
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*/
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if (rc == BPF_FIB_LKUP_RET_SUCCESS) {
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/* Verify egress index has been configured as TX-port.
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* (Note: User can still have inserted an egress ifindex that
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* doesn't support XDP xmit, which will result in packet drops).
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*
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* Note: lookup in devmap supported since 0cdbb4b09a0.
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* If not supported will fail with:
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* cannot pass map_type 14 into func bpf_map_lookup_elem#1:
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*/
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if (!bpf_map_lookup_elem(&xdp_tx_ports, &fib_params.ifindex))
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return XDP_PASS;
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if (h_proto == htons(ETH_P_IP))
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ip_decrease_ttl(iph);
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else if (h_proto == htons(ETH_P_IPV6))
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ip6h->hop_limit--;
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memcpy(eth->h_dest, fib_params.dmac, ETH_ALEN);
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memcpy(eth->h_source, fib_params.smac, ETH_ALEN);
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return bpf_redirect_map(&xdp_tx_ports, fib_params.ifindex, 0);
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}
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return XDP_PASS;
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}
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SEC("xdp_fwd")
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int xdp_fwd_prog(struct xdp_md *ctx)
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{
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return xdp_fwd_flags(ctx, 0);
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}
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SEC("xdp_fwd_direct")
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int xdp_fwd_direct_prog(struct xdp_md *ctx)
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{
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return xdp_fwd_flags(ctx, BPF_FIB_LOOKUP_DIRECT);
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}
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char _license[] SEC("license") = "GPL";
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