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