// SPDX-License-Identifier: GPL-2.0-only /* * This code is taken from the Android Open Source Project and the author * (Maciej Żenczykowski) has gave permission to relicense it under the * GPLv2. Therefore this program is free software; * You can redistribute it and/or modify it under the terms of the GNU * General Public License version 2 as published by the Free Software * Foundation * The original headers, including the original license headers, are * included below for completeness. * * Copyright (C) 2019 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ #include <linux/bpf.h> #include <linux/if.h> #include <linux/if_ether.h> #include <linux/if_packet.h> #include <linux/in.h> #include <linux/in6.h> #include <linux/ip.h> #include <linux/ipv6.h> #include <linux/pkt_cls.h> #include <linux/swab.h> #include <stdbool.h> #include <stdint.h> #include <linux/udp.h> #include <bpf/bpf_helpers.h> #include <bpf/bpf_endian.h> #define IP_DF 0x4000 // Flag: "Don't Fragment" SEC("schedcls/ingress6/nat_6") int sched_cls_ingress6_nat_6_prog(struct __sk_buff *skb) { const int l2_header_size = sizeof(struct ethhdr); void *data = (void *)(long)skb->data; const void *data_end = (void *)(long)skb->data_end; const struct ethhdr * const eth = data; // used iff is_ethernet const struct ipv6hdr * const ip6 = (void *)(eth + 1); // Require ethernet dst mac address to be our unicast address. if (skb->pkt_type != PACKET_HOST) return TC_ACT_OK; // Must be meta-ethernet IPv6 frame if (skb->protocol != bpf_htons(ETH_P_IPV6)) return TC_ACT_OK; // Must have (ethernet and) ipv6 header if (data + l2_header_size + sizeof(*ip6) > data_end) return TC_ACT_OK; // Ethertype - if present - must be IPv6 if (eth->h_proto != bpf_htons(ETH_P_IPV6)) return TC_ACT_OK; // IP version must be 6 if (ip6->version != 6) return TC_ACT_OK; // Maximum IPv6 payload length that can be translated to IPv4 if (bpf_ntohs(ip6->payload_len) > 0xFFFF - sizeof(struct iphdr)) return TC_ACT_OK; switch (ip6->nexthdr) { case IPPROTO_TCP: // For TCP & UDP the checksum neutrality of the chosen IPv6 case IPPROTO_UDP: // address means there is no need to update their checksums. case IPPROTO_GRE: // We do not need to bother looking at GRE/ESP headers, case IPPROTO_ESP: // since there is never a checksum to update. break; default: // do not know how to handle anything else return TC_ACT_OK; } struct ethhdr eth2; // used iff is_ethernet eth2 = *eth; // Copy over the ethernet header (src/dst mac) eth2.h_proto = bpf_htons(ETH_P_IP); // But replace the ethertype struct iphdr ip = { .version = 4, // u4 .ihl = sizeof(struct iphdr) / sizeof(__u32), // u4 .tos = (ip6->priority << 4) + (ip6->flow_lbl[0] >> 4), // u8 .tot_len = bpf_htons(bpf_ntohs(ip6->payload_len) + sizeof(struct iphdr)), // u16 .id = 0, // u16 .frag_off = bpf_htons(IP_DF), // u16 .ttl = ip6->hop_limit, // u8 .protocol = ip6->nexthdr, // u8 .check = 0, // u16 .saddr = 0x0201a8c0, // u32 .daddr = 0x0101a8c0, // u32 }; // Calculate the IPv4 one's complement checksum of the IPv4 header. __wsum sum4 = 0; for (int i = 0; i < sizeof(ip) / sizeof(__u16); ++i) sum4 += ((__u16 *)&ip)[i]; // Note that sum4 is guaranteed to be non-zero by virtue of ip.version == 4 sum4 = (sum4 & 0xFFFF) + (sum4 >> 16); // collapse u32 into range 1 .. 0x1FFFE sum4 = (sum4 & 0xFFFF) + (sum4 >> 16); // collapse any potential carry into u16 ip.check = (__u16)~sum4; // sum4 cannot be zero, so this is never 0xFFFF // Calculate the *negative* IPv6 16-bit one's complement checksum of the IPv6 header. __wsum sum6 = 0; // We'll end up with a non-zero sum due to ip6->version == 6 (which has '0' bits) for (int i = 0; i < sizeof(*ip6) / sizeof(__u16); ++i) sum6 += ~((__u16 *)ip6)[i]; // note the bitwise negation // Note that there is no L4 checksum update: we are relying on the checksum neutrality // of the ipv6 address chosen by netd's ClatdController. // Packet mutations begin - point of no return, but if this first modification fails // the packet is probably still pristine, so let clatd handle it. if (bpf_skb_change_proto(skb, bpf_htons(ETH_P_IP), 0)) return TC_ACT_OK; bpf_csum_update(skb, sum6); data = (void *)(long)skb->data; data_end = (void *)(long)skb->data_end; if (data + l2_header_size + sizeof(struct iphdr) > data_end) return TC_ACT_SHOT; struct ethhdr *new_eth = data; // Copy over the updated ethernet header *new_eth = eth2; // Copy over the new ipv4 header. *(struct iphdr *)(new_eth + 1) = ip; return bpf_redirect(skb->ifindex, BPF_F_INGRESS); } SEC("schedcls/egress4/snat4") int sched_cls_egress4_snat4_prog(struct __sk_buff *skb) { const int l2_header_size = sizeof(struct ethhdr); void *data = (void *)(long)skb->data; const void *data_end = (void *)(long)skb->data_end; const struct ethhdr *const eth = data; // used iff is_ethernet const struct iphdr *const ip4 = (void *)(eth + 1); // Must be meta-ethernet IPv4 frame if (skb->protocol != bpf_htons(ETH_P_IP)) return TC_ACT_OK; // Must have ipv4 header if (data + l2_header_size + sizeof(struct ipv6hdr) > data_end) return TC_ACT_OK; // Ethertype - if present - must be IPv4 if (eth->h_proto != bpf_htons(ETH_P_IP)) return TC_ACT_OK; // IP version must be 4 if (ip4->version != 4) return TC_ACT_OK; // We cannot handle IP options, just standard 20 byte == 5 dword minimal IPv4 header if (ip4->ihl != 5) return TC_ACT_OK; // Maximum IPv6 payload length that can be translated to IPv4 if (bpf_htons(ip4->tot_len) > 0xFFFF - sizeof(struct ipv6hdr)) return TC_ACT_OK; // Calculate the IPv4 one's complement checksum of the IPv4 header. __wsum sum4 = 0; for (int i = 0; i < sizeof(*ip4) / sizeof(__u16); ++i) sum4 += ((__u16 *)ip4)[i]; // Note that sum4 is guaranteed to be non-zero by virtue of ip4->version == 4 sum4 = (sum4 & 0xFFFF) + (sum4 >> 16); // collapse u32 into range 1 .. 0x1FFFE sum4 = (sum4 & 0xFFFF) + (sum4 >> 16); // collapse any potential carry into u16 // for a correct checksum we should get *a* zero, but sum4 must be positive, ie 0xFFFF if (sum4 != 0xFFFF) return TC_ACT_OK; // Minimum IPv4 total length is the size of the header if (bpf_ntohs(ip4->tot_len) < sizeof(*ip4)) return TC_ACT_OK; // We are incapable of dealing with IPv4 fragments if (ip4->frag_off & ~bpf_htons(IP_DF)) return TC_ACT_OK; switch (ip4->protocol) { case IPPROTO_TCP: // For TCP & UDP the checksum neutrality of the chosen IPv6 case IPPROTO_GRE: // address means there is no need to update their checksums. case IPPROTO_ESP: // We do not need to bother looking at GRE/ESP headers, break; // since there is never a checksum to update. case IPPROTO_UDP: // See above comment, but must also have UDP header... if (data + sizeof(*ip4) + sizeof(struct udphdr) > data_end) return TC_ACT_OK; const struct udphdr *uh = (const struct udphdr *)(ip4 + 1); // If IPv4/UDP checksum is 0 then fallback to clatd so it can calculate the // checksum. Otherwise the network or more likely the NAT64 gateway might // drop the packet because in most cases IPv6/UDP packets with a zero checksum // are invalid. See RFC 6935. TODO: calculate checksum via bpf_csum_diff() if (!uh->check) return TC_ACT_OK; break; default: // do not know how to handle anything else return TC_ACT_OK; } struct ethhdr eth2; // used iff is_ethernet eth2 = *eth; // Copy over the ethernet header (src/dst mac) eth2.h_proto = bpf_htons(ETH_P_IPV6); // But replace the ethertype struct ipv6hdr ip6 = { .version = 6, // __u8:4 .priority = ip4->tos >> 4, // __u8:4 .flow_lbl = {(ip4->tos & 0xF) << 4, 0, 0}, // __u8[3] .payload_len = bpf_htons(bpf_ntohs(ip4->tot_len) - 20), // __be16 .nexthdr = ip4->protocol, // __u8 .hop_limit = ip4->ttl, // __u8 }; ip6.saddr.in6_u.u6_addr32[0] = bpf_htonl(0x20010db8); ip6.saddr.in6_u.u6_addr32[1] = 0; ip6.saddr.in6_u.u6_addr32[2] = 0; ip6.saddr.in6_u.u6_addr32[3] = bpf_htonl(1); ip6.daddr.in6_u.u6_addr32[0] = bpf_htonl(0x20010db8); ip6.daddr.in6_u.u6_addr32[1] = 0; ip6.daddr.in6_u.u6_addr32[2] = 0; ip6.daddr.in6_u.u6_addr32[3] = bpf_htonl(2); // Calculate the IPv6 16-bit one's complement checksum of the IPv6 header. __wsum sum6 = 0; // We'll end up with a non-zero sum due to ip6.version == 6 for (int i = 0; i < sizeof(ip6) / sizeof(__u16); ++i) sum6 += ((__u16 *)&ip6)[i]; // Packet mutations begin - point of no return, but if this first modification fails // the packet is probably still pristine, so let clatd handle it. if (bpf_skb_change_proto(skb, bpf_htons(ETH_P_IPV6), 0)) return TC_ACT_OK; // This takes care of updating the skb->csum field for a CHECKSUM_COMPLETE packet. // In such a case, skb->csum is a 16-bit one's complement sum of the entire payload, // thus we need to subtract out the ipv4 header's sum, and add in the ipv6 header's sum. // However, we've already verified the ipv4 checksum is correct and thus 0. // Thus we only need to add the ipv6 header's sum. // // bpf_csum_update() always succeeds if the skb is CHECKSUM_COMPLETE and returns an error // (-ENOTSUPP) if it isn't. So we just ignore the return code (see above for more details). bpf_csum_update(skb, sum6); // bpf_skb_change_proto() invalidates all pointers - reload them. data = (void *)(long)skb->data; data_end = (void *)(long)skb->data_end; // I cannot think of any valid way for this error condition to trigger, however I do // believe the explicit check is required to keep the in kernel ebpf verifier happy. if (data + l2_header_size + sizeof(ip6) > data_end) return TC_ACT_SHOT; struct ethhdr *new_eth = data; // Copy over the updated ethernet header *new_eth = eth2; // Copy over the new ipv4 header. *(struct ipv6hdr *)(new_eth + 1) = ip6; return TC_ACT_OK; } char _license[] SEC("license") = ("GPL");
