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 struct { 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 */ 34 static __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 43 static __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 also 111 * needed. This is obtained from arp/neighbour table, but if table is 112 * (still) empty then BPF_FIB_LKUP_RET_NO_NEIGH is returned. To avoid 113 * doing ARP lookup directly from XDP, then send packet to normal 114 * 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.forwarding 118 * setting, and will return BPF_FIB_LKUP_RET_FWD_DISABLED if not 119 * 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 that 124 * 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 } 145 146 SEC("xdp_fwd") 147 int xdp_fwd_prog(struct xdp_md *ctx) 148 { 149 return xdp_fwd_flags(ctx, 0); 150 } 151 152 SEC("xdp_fwd_direct") 153 int xdp_fwd_direct_prog(struct xdp_md *ctx) 154 { 155 return xdp_fwd_flags(ctx, BPF_FIB_LOOKUP_DIRECT); 156 } 157 158 char _license[] SEC("license") = "GPL"; 159