1 // SPDX-License-Identifier: GPL-2.0 2 /* Copyright (c) 2017-18 David Ahern <dsahern@gmail.com> 3 * 4 * This program is free software; you can redistribute it and/or 5 * modify it under the terms of version 2 of the GNU General Public 6 * License as published by the Free Software Foundation. 7 * 8 * This program is distributed in the hope that it will be useful, but 9 * WITHOUT ANY WARRANTY; without even the implied warranty of 10 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 11 * 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_helpers.h" 23 24 #define IPV6_FLOWINFO_MASK cpu_to_be32(0x0FFFFFFF) 25 26 /* For TX-traffic redirect requires net_device ifindex to be in this devmap */ 27 struct bpf_map_def SEC("maps") xdp_tx_ports = { 28 .type = BPF_MAP_TYPE_DEVMAP, 29 .key_size = sizeof(int), 30 .value_size = sizeof(int), 31 .max_entries = 64, 32 }; 33 34 /* from include/net/ip.h */ 35 static __always_inline int ip_decrease_ttl(struct iphdr *iph) 36 { 37 u32 check = (__force u32)iph->check; 38 39 check += (__force u32)htons(0x0100); 40 iph->check = (__force __sum16)(check + (check >= 0xFFFF)); 41 return --iph->ttl; 42 } 43 44 static __always_inline int xdp_fwd_flags(struct xdp_md *ctx, u32 flags) 45 { 46 void *data_end = (void *)(long)ctx->data_end; 47 void *data = (void *)(long)ctx->data; 48 struct bpf_fib_lookup fib_params; 49 struct ethhdr *eth = data; 50 struct ipv6hdr *ip6h; 51 struct iphdr *iph; 52 u16 h_proto; 53 u64 nh_off; 54 int rc; 55 56 nh_off = sizeof(*eth); 57 if (data + nh_off > data_end) 58 return XDP_DROP; 59 60 __builtin_memset(&fib_params, 0, sizeof(fib_params)); 61 62 h_proto = eth->h_proto; 63 if (h_proto == htons(ETH_P_IP)) { 64 iph = data + nh_off; 65 66 if (iph + 1 > data_end) 67 return XDP_DROP; 68 69 if (iph->ttl <= 1) 70 return XDP_PASS; 71 72 fib_params.family = AF_INET; 73 fib_params.tos = iph->tos; 74 fib_params.l4_protocol = iph->protocol; 75 fib_params.sport = 0; 76 fib_params.dport = 0; 77 fib_params.tot_len = ntohs(iph->tot_len); 78 fib_params.ipv4_src = iph->saddr; 79 fib_params.ipv4_dst = iph->daddr; 80 } else if (h_proto == htons(ETH_P_IPV6)) { 81 struct in6_addr *src = (struct in6_addr *) fib_params.ipv6_src; 82 struct in6_addr *dst = (struct in6_addr *) fib_params.ipv6_dst; 83 84 ip6h = data + nh_off; 85 if (ip6h + 1 > data_end) 86 return XDP_DROP; 87 88 if (ip6h->hop_limit <= 1) 89 return XDP_PASS; 90 91 fib_params.family = AF_INET6; 92 fib_params.flowinfo = *(__be32 *)ip6h & IPV6_FLOWINFO_MASK; 93 fib_params.l4_protocol = ip6h->nexthdr; 94 fib_params.sport = 0; 95 fib_params.dport = 0; 96 fib_params.tot_len = ntohs(ip6h->payload_len); 97 *src = ip6h->saddr; 98 *dst = ip6h->daddr; 99 } else { 100 return XDP_PASS; 101 } 102 103 fib_params.ifindex = ctx->ingress_ifindex; 104 105 rc = bpf_fib_lookup(ctx, &fib_params, sizeof(fib_params), flags); 106 /* 107 * Some rc (return codes) from bpf_fib_lookup() are important, 108 * to understand how this XDP-prog interacts with network stack. 109 * 110 * BPF_FIB_LKUP_RET_NO_NEIGH: 111 * Even if route lookup was a success, then the MAC-addresses are also 112 * needed. This is obtained from arp/neighbour table, but if table is 113 * (still) empty then BPF_FIB_LKUP_RET_NO_NEIGH is returned. To avoid 114 * doing ARP lookup directly from XDP, then send packet to normal 115 * network stack via XDP_PASS and expect it will do ARP resolution. 116 * 117 * BPF_FIB_LKUP_RET_FWD_DISABLED: 118 * The bpf_fib_lookup respect sysctl net.ipv{4,6}.conf.all.forwarding 119 * setting, and will return BPF_FIB_LKUP_RET_FWD_DISABLED if not 120 * enabled this on ingress device. 121 */ 122 if (rc == BPF_FIB_LKUP_RET_SUCCESS) { 123 /* Verify egress index has been configured as TX-port. 124 * (Note: User can still have inserted an egress ifindex that 125 * doesn't support XDP xmit, which will result in packet drops). 126 * 127 * Note: lookup in devmap supported since 0cdbb4b09a0. 128 * If not supported will fail with: 129 * cannot pass map_type 14 into func bpf_map_lookup_elem#1: 130 */ 131 if (!bpf_map_lookup_elem(&xdp_tx_ports, &fib_params.ifindex)) 132 return XDP_PASS; 133 134 if (h_proto == htons(ETH_P_IP)) 135 ip_decrease_ttl(iph); 136 else if (h_proto == htons(ETH_P_IPV6)) 137 ip6h->hop_limit--; 138 139 memcpy(eth->h_dest, fib_params.dmac, ETH_ALEN); 140 memcpy(eth->h_source, fib_params.smac, ETH_ALEN); 141 return bpf_redirect_map(&xdp_tx_ports, fib_params.ifindex, 0); 142 } 143 144 return XDP_PASS; 145 } 146 147 SEC("xdp_fwd") 148 int xdp_fwd_prog(struct xdp_md *ctx) 149 { 150 return xdp_fwd_flags(ctx, 0); 151 } 152 153 SEC("xdp_fwd_direct") 154 int xdp_fwd_direct_prog(struct xdp_md *ctx) 155 { 156 return xdp_fwd_flags(ctx, BPF_FIB_LOOKUP_DIRECT); 157 } 158 159 char _license[] SEC("license") = "GPL"; 160