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1// SPDX-License-Identifier: GPL-2.0-only2/*3 * This code is taken from the Android Open Source Project and the author4 * (Maciej Żenczykowski) has gave permission to relicense it under the5 * GPLv2. Therefore this program is free software;6 * You can redistribute it and/or modify it under the terms of the GNU7 * General Public License version 2 as published by the Free Software8 * Foundation9 10 * The original headers, including the original license headers, are11 * included below for completeness.12 *13 * Copyright (C) 2019 The Android Open Source Project14 *15 * Licensed under the Apache License, Version 2.0 (the "License");16 * you may not use this file except in compliance with the License.17 * You may obtain a copy of the License at18 *19 * http://www.apache.org/licenses/LICENSE-2.020 *21 * Unless required by applicable law or agreed to in writing, software22 * distributed under the License is distributed on an "AS IS" BASIS,23 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.24 * See the License for the specific language governing permissions and25 * limitations under the License.26 */27#include <linux/bpf.h>28#include <linux/if.h>29#include <linux/if_ether.h>30#include <linux/if_packet.h>31#include <linux/in.h>32#include <linux/in6.h>33#include <linux/ip.h>34#include <linux/ipv6.h>35#include <linux/pkt_cls.h>36#include <linux/swab.h>37#include <stdbool.h>38#include <stdint.h>39 40 41#include <linux/udp.h>42 43#include <bpf/bpf_helpers.h>44#include <bpf/bpf_endian.h>45 46#define IP_DF 0x4000 // Flag: "Don't Fragment"47 48SEC("schedcls/ingress6/nat_6")49int sched_cls_ingress6_nat_6_prog(struct __sk_buff *skb)50{51 const int l2_header_size = sizeof(struct ethhdr);52 void *data = (void *)(long)skb->data;53 const void *data_end = (void *)(long)skb->data_end;54 const struct ethhdr * const eth = data; // used iff is_ethernet55 const struct ipv6hdr * const ip6 = (void *)(eth + 1);56 57 // Require ethernet dst mac address to be our unicast address.58 if (skb->pkt_type != PACKET_HOST)59 return TC_ACT_OK;60 61 // Must be meta-ethernet IPv6 frame62 if (skb->protocol != bpf_htons(ETH_P_IPV6))63 return TC_ACT_OK;64 65 // Must have (ethernet and) ipv6 header66 if (data + l2_header_size + sizeof(*ip6) > data_end)67 return TC_ACT_OK;68 69 // Ethertype - if present - must be IPv670 if (eth->h_proto != bpf_htons(ETH_P_IPV6))71 return TC_ACT_OK;72 73 // IP version must be 674 if (ip6->version != 6)75 return TC_ACT_OK;76 // Maximum IPv6 payload length that can be translated to IPv477 if (bpf_ntohs(ip6->payload_len) > 0xFFFF - sizeof(struct iphdr))78 return TC_ACT_OK;79 switch (ip6->nexthdr) {80 case IPPROTO_TCP: // For TCP & UDP the checksum neutrality of the chosen IPv681 case IPPROTO_UDP: // address means there is no need to update their checksums.82 case IPPROTO_GRE: // We do not need to bother looking at GRE/ESP headers,83 case IPPROTO_ESP: // since there is never a checksum to update.84 break;85 default: // do not know how to handle anything else86 return TC_ACT_OK;87 }88 89 struct ethhdr eth2; // used iff is_ethernet90 91 eth2 = *eth; // Copy over the ethernet header (src/dst mac)92 eth2.h_proto = bpf_htons(ETH_P_IP); // But replace the ethertype93 94 struct iphdr ip = {95 .version = 4, // u496 .ihl = sizeof(struct iphdr) / sizeof(__u32), // u497 .tos = (ip6->priority << 4) + (ip6->flow_lbl[0] >> 4), // u898 .tot_len = bpf_htons(bpf_ntohs(ip6->payload_len) + sizeof(struct iphdr)), // u1699 .id = 0, // u16100 .frag_off = bpf_htons(IP_DF), // u16101 .ttl = ip6->hop_limit, // u8102 .protocol = ip6->nexthdr, // u8103 .check = 0, // u16104 .saddr = 0x0201a8c0, // u32105 .daddr = 0x0101a8c0, // u32106 };107 108 // Calculate the IPv4 one's complement checksum of the IPv4 header.109 __wsum sum4 = 0;110 111 for (int i = 0; i < sizeof(ip) / sizeof(__u16); ++i)112 sum4 += ((__u16 *)&ip)[i];113 114 // Note that sum4 is guaranteed to be non-zero by virtue of ip.version == 4115 sum4 = (sum4 & 0xFFFF) + (sum4 >> 16); // collapse u32 into range 1 .. 0x1FFFE116 sum4 = (sum4 & 0xFFFF) + (sum4 >> 16); // collapse any potential carry into u16117 ip.check = (__u16)~sum4; // sum4 cannot be zero, so this is never 0xFFFF118 119 // Calculate the *negative* IPv6 16-bit one's complement checksum of the IPv6 header.120 __wsum sum6 = 0;121 // We'll end up with a non-zero sum due to ip6->version == 6 (which has '0' bits)122 for (int i = 0; i < sizeof(*ip6) / sizeof(__u16); ++i)123 sum6 += ~((__u16 *)ip6)[i]; // note the bitwise negation124 125 // Note that there is no L4 checksum update: we are relying on the checksum neutrality126 // of the ipv6 address chosen by netd's ClatdController.127 128 // Packet mutations begin - point of no return, but if this first modification fails129 // the packet is probably still pristine, so let clatd handle it.130 if (bpf_skb_change_proto(skb, bpf_htons(ETH_P_IP), 0))131 return TC_ACT_OK;132 bpf_csum_update(skb, sum6);133 134 data = (void *)(long)skb->data;135 data_end = (void *)(long)skb->data_end;136 if (data + l2_header_size + sizeof(struct iphdr) > data_end)137 return TC_ACT_SHOT;138 139 struct ethhdr *new_eth = data;140 141 // Copy over the updated ethernet header142 *new_eth = eth2;143 144 // Copy over the new ipv4 header.145 *(struct iphdr *)(new_eth + 1) = ip;146 return bpf_redirect(skb->ifindex, BPF_F_INGRESS);147}148 149SEC("schedcls/egress4/snat4")150int sched_cls_egress4_snat4_prog(struct __sk_buff *skb)151{152 const int l2_header_size = sizeof(struct ethhdr);153 void *data = (void *)(long)skb->data;154 const void *data_end = (void *)(long)skb->data_end;155 const struct ethhdr *const eth = data; // used iff is_ethernet156 const struct iphdr *const ip4 = (void *)(eth + 1);157 158 // Must be meta-ethernet IPv4 frame159 if (skb->protocol != bpf_htons(ETH_P_IP))160 return TC_ACT_OK;161 162 // Must have ipv4 header163 if (data + l2_header_size + sizeof(struct ipv6hdr) > data_end)164 return TC_ACT_OK;165 166 // Ethertype - if present - must be IPv4167 if (eth->h_proto != bpf_htons(ETH_P_IP))168 return TC_ACT_OK;169 170 // IP version must be 4171 if (ip4->version != 4)172 return TC_ACT_OK;173 174 // We cannot handle IP options, just standard 20 byte == 5 dword minimal IPv4 header175 if (ip4->ihl != 5)176 return TC_ACT_OK;177 178 // Maximum IPv6 payload length that can be translated to IPv4179 if (bpf_htons(ip4->tot_len) > 0xFFFF - sizeof(struct ipv6hdr))180 return TC_ACT_OK;181 182 // Calculate the IPv4 one's complement checksum of the IPv4 header.183 __wsum sum4 = 0;184 185 for (int i = 0; i < sizeof(*ip4) / sizeof(__u16); ++i)186 sum4 += ((__u16 *)ip4)[i];187 188 // Note that sum4 is guaranteed to be non-zero by virtue of ip4->version == 4189 sum4 = (sum4 & 0xFFFF) + (sum4 >> 16); // collapse u32 into range 1 .. 0x1FFFE190 sum4 = (sum4 & 0xFFFF) + (sum4 >> 16); // collapse any potential carry into u16191 // for a correct checksum we should get *a* zero, but sum4 must be positive, ie 0xFFFF192 if (sum4 != 0xFFFF)193 return TC_ACT_OK;194 195 // Minimum IPv4 total length is the size of the header196 if (bpf_ntohs(ip4->tot_len) < sizeof(*ip4))197 return TC_ACT_OK;198 199 // We are incapable of dealing with IPv4 fragments200 if (ip4->frag_off & ~bpf_htons(IP_DF))201 return TC_ACT_OK;202 203 switch (ip4->protocol) {204 case IPPROTO_TCP: // For TCP & UDP the checksum neutrality of the chosen IPv6205 case IPPROTO_GRE: // address means there is no need to update their checksums.206 case IPPROTO_ESP: // We do not need to bother looking at GRE/ESP headers,207 break; // since there is never a checksum to update.208 209 case IPPROTO_UDP: // See above comment, but must also have UDP header...210 if (data + sizeof(*ip4) + sizeof(struct udphdr) > data_end)211 return TC_ACT_OK;212 const struct udphdr *uh = (const struct udphdr *)(ip4 + 1);213 // If IPv4/UDP checksum is 0 then fallback to clatd so it can calculate the214 // checksum. Otherwise the network or more likely the NAT64 gateway might215 // drop the packet because in most cases IPv6/UDP packets with a zero checksum216 // are invalid. See RFC 6935. TODO: calculate checksum via bpf_csum_diff()217 if (!uh->check)218 return TC_ACT_OK;219 break;220 221 default: // do not know how to handle anything else222 return TC_ACT_OK;223 }224 struct ethhdr eth2; // used iff is_ethernet225 226 eth2 = *eth; // Copy over the ethernet header (src/dst mac)227 eth2.h_proto = bpf_htons(ETH_P_IPV6); // But replace the ethertype228 229 struct ipv6hdr ip6 = {230 .version = 6, // __u8:4231 .priority = ip4->tos >> 4, // __u8:4232 .flow_lbl = {(ip4->tos & 0xF) << 4, 0, 0}, // __u8[3]233 .payload_len = bpf_htons(bpf_ntohs(ip4->tot_len) - 20), // __be16234 .nexthdr = ip4->protocol, // __u8235 .hop_limit = ip4->ttl, // __u8236 };237 ip6.saddr.in6_u.u6_addr32[0] = bpf_htonl(0x20010db8);238 ip6.saddr.in6_u.u6_addr32[1] = 0;239 ip6.saddr.in6_u.u6_addr32[2] = 0;240 ip6.saddr.in6_u.u6_addr32[3] = bpf_htonl(1);241 ip6.daddr.in6_u.u6_addr32[0] = bpf_htonl(0x20010db8);242 ip6.daddr.in6_u.u6_addr32[1] = 0;243 ip6.daddr.in6_u.u6_addr32[2] = 0;244 ip6.daddr.in6_u.u6_addr32[3] = bpf_htonl(2);245 246 // Calculate the IPv6 16-bit one's complement checksum of the IPv6 header.247 __wsum sum6 = 0;248 // We'll end up with a non-zero sum due to ip6.version == 6249 for (int i = 0; i < sizeof(ip6) / sizeof(__u16); ++i)250 sum6 += ((__u16 *)&ip6)[i];251 252 // Packet mutations begin - point of no return, but if this first modification fails253 // the packet is probably still pristine, so let clatd handle it.254 if (bpf_skb_change_proto(skb, bpf_htons(ETH_P_IPV6), 0))255 return TC_ACT_OK;256 257 // This takes care of updating the skb->csum field for a CHECKSUM_COMPLETE packet.258 // In such a case, skb->csum is a 16-bit one's complement sum of the entire payload,259 // thus we need to subtract out the ipv4 header's sum, and add in the ipv6 header's sum.260 // However, we've already verified the ipv4 checksum is correct and thus 0.261 // Thus we only need to add the ipv6 header's sum.262 //263 // bpf_csum_update() always succeeds if the skb is CHECKSUM_COMPLETE and returns an error264 // (-ENOTSUPP) if it isn't. So we just ignore the return code (see above for more details).265 bpf_csum_update(skb, sum6);266 267 // bpf_skb_change_proto() invalidates all pointers - reload them.268 data = (void *)(long)skb->data;269 data_end = (void *)(long)skb->data_end;270 271 // I cannot think of any valid way for this error condition to trigger, however I do272 // believe the explicit check is required to keep the in kernel ebpf verifier happy.273 if (data + l2_header_size + sizeof(ip6) > data_end)274 return TC_ACT_SHOT;275 276 struct ethhdr *new_eth = data;277 278 // Copy over the updated ethernet header279 *new_eth = eth2;280 // Copy over the new ipv4 header.281 *(struct ipv6hdr *)(new_eth + 1) = ip6;282 return TC_ACT_OK;283}284 285char _license[] SEC("license") = ("GPL");286