/*
* 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/in.h>
#include <linux/in6.h>
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <linux/pkt_cls.h>
#include <linux/swab.h>
#include <linux/tcp.h>
#include <linux/udp.h>
#include <stdbool.h>
#include <stdint.h>
#include "bpf_helpers.h"
#include "netdbpf/bpf_shared.h"
// bionic/libc/kernel/uapi/linux/udp.h:
// struct __kernel_udphdr {
// bionic/libc/kernel/tools/defaults.py:
// # We want to support both BSD and Linux member names in struct udphdr.
// "udphdr": "__kernel_udphdr",
// so instead it just doesn't work... ugh.
#define udphdr __kernel_udphdr
// From kernel:include/net/ip.h
#define IP_DF 0x4000 // Flag: "Don't Fragment"
// Android only supports little endian architectures
#define htons(x) (__builtin_constant_p(x) ? ___constant_swab16(x) : __builtin_bswap16(x))
#define htonl(x) (__builtin_constant_p(x) ? ___constant_swab32(x) : __builtin_bswap32(x))
#define ntohs(x) htons(x)
#define ntohl(x) htonl(x)
DEFINE_BPF_MAP(clat_ingress_map, HASH, ClatIngressKey, ClatIngressValue, 16)
static inline __always_inline int nat64(struct __sk_buff* skb, bool is_ethernet) {
const int l2_header_size = is_ethernet ? sizeof(struct ethhdr) : 0;
void* data = (void*)(long)skb->data;
const void* data_end = (void*)(long)skb->data_end;
const struct ethhdr* const eth = is_ethernet ? data : NULL; // used iff is_ethernet
const struct ipv6hdr* const ip6 = is_ethernet ? (void*)(eth + 1) : data;
const struct tcphdr* const tcp = (void*)(ip6 + 1);
const struct udphdr* const udp = (void*)(ip6 + 1);
// Must be meta-ethernet IPv6 frame
if (skb->protocol != 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 (is_ethernet && (eth->h_proto != 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 (ntohs(ip6->payload_len) > 0xFFFF - sizeof(struct iphdr)) return TC_ACT_OK;
switch (ip6->nexthdr) {
case IPPROTO_TCP: // If TCP, must have 20 byte minimal TCP header
if (tcp + 1 > (struct tcphdr*)data_end) return TC_ACT_OK;
break;
case IPPROTO_UDP: // If UDP, must have 8 byte minimal UDP header
if (udp + 1 > (struct udphdr*)data_end) return TC_ACT_OK;
break;
default: // do not know how to handle anything else
return TC_ACT_OK;
}
ClatIngressKey k = {
.iif = skb->ifindex,
.pfx96.in6_u.u6_addr32 =
{
ip6->saddr.in6_u.u6_addr32[0],
ip6->saddr.in6_u.u6_addr32[1],
ip6->saddr.in6_u.u6_addr32[2],
},
.local6 = ip6->daddr,
};
ClatIngressValue* v = bpf_clat_ingress_map_lookup_elem(&k);
if (!v) return TC_ACT_OK;
struct ethhdr eth2; // used iff is_ethernet
if (is_ethernet) {
eth2 = *eth; // Copy over the ethernet header (src/dst mac)
eth2.h_proto = 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 = htons(ntohs(ip6->payload_len) + sizeof(struct iphdr)), // u16
.id = 0, // u16
.frag_off = htons(IP_DF), // u16
.ttl = ip6->hop_limit, // u8
.protocol = ip6->nexthdr, // u8
.check = 0, // u16
.saddr = ip6->saddr.in6_u.u6_addr32[3], // u32
.daddr = v->local4.s_addr, // u32
};
// Calculate the IPv4 one's complement checksum of the IPv4 header.
__u32 sum = 0;
for (int i = 0; i < sizeof(ip) / sizeof(__u16); ++i) {
sum += ((__u16*)&ip)[i];
}
// Note that sum is guaranteed to be non-zero by virtue of ip.version == 4
sum = (sum & 0xFFFF) + (sum >> 16); // collapse u32 into range 1 .. 0x1FFFE
sum = (sum & 0xFFFF) + (sum >> 16); // collapse any potential carry into u16
ip.check = (__u16)~sum; // sum cannot be zero, so this is never 0xFFFF
// 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.
if (bpf_skb_change_proto(skb, htons(ETH_P_IP), 0)) return TC_ACT_SHOT;
// 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(struct iphdr) > data_end) return TC_ACT_SHOT;
if (is_ethernet) {
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;
} else {
// Copy over the new ipv4 header without an ethernet header.
*(struct iphdr*)data = ip;
}
// Redirect, possibly back to same interface, so tcpdump sees packet twice.
if (v->oif) return bpf_redirect(v->oif, BPF_F_INGRESS);
// Just let it through, tcpdump will not see IPv4 packet.
return TC_ACT_OK;
}
SEC("schedcls/ingress/clat_ether")
int sched_cls_ingress_clat_ether(struct __sk_buff* skb) {
return nat64(skb, true);
}
SEC("schedcls/ingress/clat_rawip")
int sched_cls_ingress_clat_rawip(struct __sk_buff* skb) {
return nat64(skb, false);
}
char _license[] SEC("license") = "Apache 2.0";