159 lines · c
1// SPDX-License-Identifier: GPL-2.02/* Copyright (c) 2017-18 David Ahern <dsahern@gmail.com>3 *4 * This program is free software; you can redistribute it and/or5 * modify it under the terms of version 2 of the GNU General Public6 * License as published by the Free Software Foundation.7 *8 * This program is distributed in the hope that it will be useful, but9 * WITHOUT ANY WARRANTY; without even the implied warranty of10 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU11 * General Public License for more details.12 */13#define KBUILD_MODNAME "foo"14#include <uapi/linux/bpf.h>15#include <linux/in.h>16#include <linux/if_ether.h>17#include <linux/if_packet.h>18#include <linux/if_vlan.h>19#include <linux/ip.h>20#include <linux/ipv6.h>21 22#include <bpf/bpf_helpers.h>23 24#define IPV6_FLOWINFO_MASK cpu_to_be32(0x0FFFFFFF)25 26struct {27 __uint(type, BPF_MAP_TYPE_DEVMAP);28 __uint(key_size, sizeof(int));29 __uint(value_size, sizeof(int));30 __uint(max_entries, 64);31} xdp_tx_ports SEC(".maps");32 33/* from include/net/ip.h */34static __always_inline int ip_decrease_ttl(struct iphdr *iph)35{36 u32 check = (__force u32)iph->check;37 38 check += (__force u32)htons(0x0100);39 iph->check = (__force __sum16)(check + (check >= 0xFFFF));40 return --iph->ttl;41}42 43static __always_inline int xdp_fwd_flags(struct xdp_md *ctx, u32 flags)44{45 void *data_end = (void *)(long)ctx->data_end;46 void *data = (void *)(long)ctx->data;47 struct bpf_fib_lookup fib_params;48 struct ethhdr *eth = data;49 struct ipv6hdr *ip6h;50 struct iphdr *iph;51 u16 h_proto;52 u64 nh_off;53 int rc;54 55 nh_off = sizeof(*eth);56 if (data + nh_off > data_end)57 return XDP_DROP;58 59 __builtin_memset(&fib_params, 0, sizeof(fib_params));60 61 h_proto = eth->h_proto;62 if (h_proto == htons(ETH_P_IP)) {63 iph = data + nh_off;64 65 if (iph + 1 > data_end)66 return XDP_DROP;67 68 if (iph->ttl <= 1)69 return XDP_PASS;70 71 fib_params.family = AF_INET;72 fib_params.tos = iph->tos;73 fib_params.l4_protocol = iph->protocol;74 fib_params.sport = 0;75 fib_params.dport = 0;76 fib_params.tot_len = ntohs(iph->tot_len);77 fib_params.ipv4_src = iph->saddr;78 fib_params.ipv4_dst = iph->daddr;79 } else if (h_proto == htons(ETH_P_IPV6)) {80 struct in6_addr *src = (struct in6_addr *) fib_params.ipv6_src;81 struct in6_addr *dst = (struct in6_addr *) fib_params.ipv6_dst;82 83 ip6h = data + nh_off;84 if (ip6h + 1 > data_end)85 return XDP_DROP;86 87 if (ip6h->hop_limit <= 1)88 return XDP_PASS;89 90 fib_params.family = AF_INET6;91 fib_params.flowinfo = *(__be32 *)ip6h & IPV6_FLOWINFO_MASK;92 fib_params.l4_protocol = ip6h->nexthdr;93 fib_params.sport = 0;94 fib_params.dport = 0;95 fib_params.tot_len = ntohs(ip6h->payload_len);96 *src = ip6h->saddr;97 *dst = ip6h->daddr;98 } else {99 return XDP_PASS;100 }101 102 fib_params.ifindex = ctx->ingress_ifindex;103 104 rc = bpf_fib_lookup(ctx, &fib_params, sizeof(fib_params), flags);105 /*106 * Some rc (return codes) from bpf_fib_lookup() are important,107 * to understand how this XDP-prog interacts with network stack.108 *109 * BPF_FIB_LKUP_RET_NO_NEIGH:110 * Even if route lookup was a success, then the MAC-addresses are also111 * needed. This is obtained from arp/neighbour table, but if table is112 * (still) empty then BPF_FIB_LKUP_RET_NO_NEIGH is returned. To avoid113 * doing ARP lookup directly from XDP, then send packet to normal114 * network stack via XDP_PASS and expect it will do ARP resolution.115 *116 * BPF_FIB_LKUP_RET_FWD_DISABLED:117 * The bpf_fib_lookup respect sysctl net.ipv{4,6}.conf.all.forwarding118 * setting, and will return BPF_FIB_LKUP_RET_FWD_DISABLED if not119 * enabled this on ingress device.120 */121 if (rc == BPF_FIB_LKUP_RET_SUCCESS) {122 /* Verify egress index has been configured as TX-port.123 * (Note: User can still have inserted an egress ifindex that124 * doesn't support XDP xmit, which will result in packet drops).125 *126 * Note: lookup in devmap supported since 0cdbb4b09a0.127 * If not supported will fail with:128 * cannot pass map_type 14 into func bpf_map_lookup_elem#1:129 */130 if (!bpf_map_lookup_elem(&xdp_tx_ports, &fib_params.ifindex))131 return XDP_PASS;132 133 if (h_proto == htons(ETH_P_IP))134 ip_decrease_ttl(iph);135 else if (h_proto == htons(ETH_P_IPV6))136 ip6h->hop_limit--;137 138 memcpy(eth->h_dest, fib_params.dmac, ETH_ALEN);139 memcpy(eth->h_source, fib_params.smac, ETH_ALEN);140 return bpf_redirect_map(&xdp_tx_ports, fib_params.ifindex, 0);141 }142 143 return XDP_PASS;144}145 146SEC("xdp_fwd")147int xdp_fwd_prog(struct xdp_md *ctx)148{149 return xdp_fwd_flags(ctx, 0);150}151 152SEC("xdp_fwd_direct")153int xdp_fwd_direct_prog(struct xdp_md *ctx)154{155 return xdp_fwd_flags(ctx, BPF_FIB_LOOKUP_DIRECT);156}157 158char _license[] SEC("license") = "GPL";159