/*
* Copyright 2011 Daniel Drown
*
* 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.
*
* translate.c - CLAT functions / partial implementation of rfc6145
*/
#include <string.h>
#include "netutils/checksum.h"
#include "clatd.h"
#include "common.h"
#include "config.h"
#include "debug.h"
#include "icmp.h"
#include "logging.h"
#include "translate.h"
#include "tun.h"
/* function: packet_checksum
* calculates the checksum over all the packet components starting from pos
* checksum - checksum of packet components before pos
* packet - packet to calculate the checksum of
* pos - position to start counting from
* returns - the completed 16-bit checksum, ready to write into a checksum header field
*/
uint16_t packet_checksum(uint32_t checksum, clat_packet packet, clat_packet_index pos) {
int i;
for (i = pos; i < CLAT_POS_MAX; i++) {
if (packet[i].iov_len > 0) {
checksum = ip_checksum_add(checksum, packet[i].iov_base, packet[i].iov_len);
}
}
return ip_checksum_finish(checksum);
}
/* function: packet_length
* returns the total length of all the packet components after pos
* packet - packet to calculate the length of
* pos - position to start counting after
* returns: the total length of the packet components after pos
*/
uint16_t packet_length(clat_packet packet, clat_packet_index pos) {
size_t len = 0;
int i;
for (i = pos + 1; i < CLAT_POS_MAX; i++) {
len += packet[i].iov_len;
}
return len;
}
/* function: is_in_plat_subnet
* returns true iff the given IPv6 address is in the plat subnet.
* addr - IPv6 address
*/
int is_in_plat_subnet(const struct in6_addr *addr6) {
// Assumes a /96 plat subnet.
return (addr6 != NULL) && (memcmp(addr6, &Global_Clatd_Config.plat_subnet, 12) == 0);
}
/* function: ipv6_addr_to_ipv4_addr
* return the corresponding ipv4 address for the given ipv6 address
* addr6 - ipv6 address
* returns: the IPv4 address
*/
uint32_t ipv6_addr_to_ipv4_addr(const struct in6_addr *addr6) {
if (is_in_plat_subnet(addr6)) {
// Assumes a /96 plat subnet.
return addr6->s6_addr32[3];
} else if (IN6_ARE_ADDR_EQUAL(addr6, &Global_Clatd_Config.ipv6_local_subnet)) {
// Special-case our own address.
return Global_Clatd_Config.ipv4_local_subnet.s_addr;
} else {
// Third party packet. Let the caller deal with it.
return INADDR_NONE;
}
}
/* function: ipv4_addr_to_ipv6_addr
* return the corresponding ipv6 address for the given ipv4 address
* addr4 - ipv4 address
*/
struct in6_addr ipv4_addr_to_ipv6_addr(uint32_t addr4) {
struct in6_addr addr6;
// Both addresses are in network byte order (addr4 comes from a network packet, and the config
// file entry is read using inet_ntop).
if (addr4 == Global_Clatd_Config.ipv4_local_subnet.s_addr) {
return Global_Clatd_Config.ipv6_local_subnet;
} else {
// Assumes a /96 plat subnet.
addr6 = Global_Clatd_Config.plat_subnet;
addr6.s6_addr32[3] = addr4;
return addr6;
}
}
/* function: fill_tun_header
* fill in the header for the tun fd
* tun_header - tunnel header, already allocated
* proto - ethernet protocol id: ETH_P_IP(ipv4) or ETH_P_IPV6(ipv6)
*/
void fill_tun_header(struct tun_pi *tun_header, uint16_t proto) {
tun_header->flags = 0;
tun_header->proto = htons(proto);
}
/* function: fill_ip_header
* generate an ipv4 header from an ipv6 header
* ip_targ - (ipv4) target packet header, source: original ipv4 addr, dest: local subnet addr
* payload_len - length of other data inside packet
* protocol - protocol number (tcp, udp, etc)
* old_header - (ipv6) source packet header, source: nat64 prefix, dest: local subnet prefix
*/
void fill_ip_header(struct iphdr *ip, uint16_t payload_len, uint8_t protocol,
const struct ip6_hdr *old_header) {
int ttl_guess;
memset(ip, 0, sizeof(struct iphdr));
ip->ihl = 5;
ip->version = 4;
ip->tos = 0;
ip->tot_len = htons(sizeof(struct iphdr) + payload_len);
ip->id = 0;
ip->frag_off = htons(IP_DF);
ip->ttl = old_header->ip6_hlim;
ip->protocol = protocol;
ip->check = 0;
ip->saddr = ipv6_addr_to_ipv4_addr(&old_header->ip6_src);
ip->daddr = ipv6_addr_to_ipv4_addr(&old_header->ip6_dst);
// Third-party ICMPv6 message. This may have been originated by an native IPv6 address.
// In that case, the source IPv6 address can't be translated and we need to make up an IPv4
// source address. For now, use 255.0.0.<ttl>, which at least looks useful in traceroute.
if ((uint32_t)ip->saddr == INADDR_NONE) {
ttl_guess = icmp_guess_ttl(old_header->ip6_hlim);
ip->saddr = htonl((0xff << 24) + ttl_guess);
}
}
/* function: fill_ip6_header
* generate an ipv6 header from an ipv4 header
* ip6 - (ipv6) target packet header, source: local subnet prefix, dest: nat64 prefix
* payload_len - length of other data inside packet
* protocol - protocol number (tcp, udp, etc)
* old_header - (ipv4) source packet header, source: local subnet addr, dest: internet's ipv4 addr
*/
void fill_ip6_header(struct ip6_hdr *ip6, uint16_t payload_len, uint8_t protocol,
const struct iphdr *old_header) {
memset(ip6, 0, sizeof(struct ip6_hdr));
ip6->ip6_vfc = 6 << 4;
ip6->ip6_plen = htons(payload_len);
ip6->ip6_nxt = protocol;
ip6->ip6_hlim = old_header->ttl;
ip6->ip6_src = ipv4_addr_to_ipv6_addr(old_header->saddr);
ip6->ip6_dst = ipv4_addr_to_ipv6_addr(old_header->daddr);
}
/* function: maybe_fill_frag_header
* fills a fragmentation header
* generate an ipv6 fragment header from an ipv4 header
* frag_hdr - target (ipv6) fragmentation header
* ip6_targ - target (ipv6) header
* old_header - (ipv4) source packet header
* returns: the length of the fragmentation header if present, or zero if not present
*/
size_t maybe_fill_frag_header(struct ip6_frag *frag_hdr, struct ip6_hdr *ip6_targ,
const struct iphdr *old_header) {
uint16_t frag_flags = ntohs(old_header->frag_off);
uint16_t frag_off = frag_flags & IP_OFFMASK;
if (frag_off == 0 && (frag_flags & IP_MF) == 0) {
// Not a fragment.
return 0;
}
frag_hdr->ip6f_nxt = ip6_targ->ip6_nxt;
frag_hdr->ip6f_reserved = 0;
// In IPv4, the offset is the bottom 13 bits; in IPv6 it's the top 13 bits.
frag_hdr->ip6f_offlg = htons(frag_off << 3);
if (frag_flags & IP_MF) {
frag_hdr->ip6f_offlg |= IP6F_MORE_FRAG;
}
frag_hdr->ip6f_ident = htonl(ntohs(old_header->id));
ip6_targ->ip6_nxt = IPPROTO_FRAGMENT;
return sizeof(*frag_hdr);
}
/* function: parse_frag_header
* return the length of the fragmentation header if present, or zero if not present
* generate an ipv6 fragment header from an ipv4 header
* frag_hdr - (ipv6) fragmentation header
* ip_targ - target (ipv4) header
* returns: the next header value
*/
uint8_t parse_frag_header(const struct ip6_frag *frag_hdr, struct iphdr *ip_targ) {
uint16_t frag_off = (ntohs(frag_hdr->ip6f_offlg & IP6F_OFF_MASK) >> 3);
if (frag_hdr->ip6f_offlg & IP6F_MORE_FRAG) {
frag_off |= IP_MF;
}
ip_targ->frag_off = htons(frag_off);
ip_targ->id = htons(ntohl(frag_hdr->ip6f_ident) & 0xffff);
ip_targ->protocol = frag_hdr->ip6f_nxt;
return frag_hdr->ip6f_nxt;
}
/* function: icmp_to_icmp6
* translate ipv4 icmp to ipv6 icmp
* out - output packet
* icmp - source packet icmp header
* checksum - pseudo-header checksum
* payload - icmp payload
* payload_size - size of payload
* returns: the highest position in the output clat_packet that's filled in
*/
int icmp_to_icmp6(clat_packet out, clat_packet_index pos, const struct icmphdr *icmp,
uint32_t checksum, const uint8_t *payload, size_t payload_size) {
struct icmp6_hdr *icmp6_targ = out[pos].iov_base;
uint8_t icmp6_type;
int clat_packet_len;
memset(icmp6_targ, 0, sizeof(struct icmp6_hdr));
icmp6_type = icmp_to_icmp6_type(icmp->type, icmp->code);
icmp6_targ->icmp6_type = icmp6_type;
icmp6_targ->icmp6_code = icmp_to_icmp6_code(icmp->type, icmp->code);
out[pos].iov_len = sizeof(struct icmp6_hdr);
if (pos == CLAT_POS_TRANSPORTHDR && is_icmp_error(icmp->type) && icmp6_type != ICMP6_PARAM_PROB) {
// An ICMP error we understand, one level deep.
// Translate the nested packet (the one that caused the error).
clat_packet_len = ipv4_packet(out, pos + 1, payload, payload_size);
// The pseudo-header checksum was calculated on the transport length of the original IPv4
// packet that we were asked to translate. This transport length is 20 bytes smaller than it
// needs to be, because the ICMP error contains an IPv4 header, which we will be translating to
// an IPv6 header, which is 20 bytes longer. Fix it up here.
// We only need to do this for ICMP->ICMPv6, not ICMPv6->ICMP, because ICMP does not use the
// pseudo-header when calculating its checksum (as the IPv4 header has its own checksum).
checksum = checksum + htons(20);
} else if (icmp6_type == ICMP6_ECHO_REQUEST || icmp6_type == ICMP6_ECHO_REPLY) {
// Ping packet.
icmp6_targ->icmp6_id = icmp->un.echo.id;
icmp6_targ->icmp6_seq = icmp->un.echo.sequence;
out[CLAT_POS_PAYLOAD].iov_base = (uint8_t *)payload;
out[CLAT_POS_PAYLOAD].iov_len = payload_size;
clat_packet_len = CLAT_POS_PAYLOAD + 1;
} else {
// Unknown type/code. The type/code conversion functions have already logged an error.
return 0;
}
icmp6_targ->icmp6_cksum = 0; // Checksum field must be 0 when calculating checksum.
icmp6_targ->icmp6_cksum = packet_checksum(checksum, out, pos);
return clat_packet_len;
}
/* function: icmp6_to_icmp
* translate ipv6 icmp to ipv4 icmp
* out - output packet
* icmp6 - source packet icmp6 header
* payload - icmp6 payload
* payload_size - size of payload
* returns: the highest position in the output clat_packet that's filled in
*/
int icmp6_to_icmp(clat_packet out, clat_packet_index pos, const struct icmp6_hdr *icmp6,
const uint8_t *payload, size_t payload_size) {
struct icmphdr *icmp_targ = out[pos].iov_base;
uint8_t icmp_type;
int clat_packet_len;
memset(icmp_targ, 0, sizeof(struct icmphdr));
icmp_type = icmp6_to_icmp_type(icmp6->icmp6_type, icmp6->icmp6_code);
icmp_targ->type = icmp_type;
icmp_targ->code = icmp6_to_icmp_code(icmp6->icmp6_type, icmp6->icmp6_code);
out[pos].iov_len = sizeof(struct icmphdr);
if (pos == CLAT_POS_TRANSPORTHDR && is_icmp6_error(icmp6->icmp6_type) &&
icmp_type != ICMP_PARAMETERPROB) {
// An ICMPv6 error we understand, one level deep.
// Translate the nested packet (the one that caused the error).
clat_packet_len = ipv6_packet(out, pos + 1, payload, payload_size);
} else if (icmp_type == ICMP_ECHO || icmp_type == ICMP_ECHOREPLY) {
// Ping packet.
icmp_targ->un.echo.id = icmp6->icmp6_id;
icmp_targ->un.echo.sequence = icmp6->icmp6_seq;
out[CLAT_POS_PAYLOAD].iov_base = (uint8_t *)payload;
out[CLAT_POS_PAYLOAD].iov_len = payload_size;
clat_packet_len = CLAT_POS_PAYLOAD + 1;
} else {
// Unknown type/code. The type/code conversion functions have already logged an error.
return 0;
}
icmp_targ->checksum = 0; // Checksum field must be 0 when calculating checksum.
icmp_targ->checksum = packet_checksum(0, out, pos);
return clat_packet_len;
}
/* function: generic_packet
* takes a generic IP packet and sets it up for translation
* out - output packet
* pos - position in the output packet of the transport header
* payload - pointer to IP payload
* len - size of ip payload
* returns: the highest position in the output clat_packet that's filled in
*/
int generic_packet(clat_packet out, clat_packet_index pos, const uint8_t *payload, size_t len) {
out[pos].iov_len = 0;
out[CLAT_POS_PAYLOAD].iov_base = (uint8_t *)payload;
out[CLAT_POS_PAYLOAD].iov_len = len;
return CLAT_POS_PAYLOAD + 1;
}
/* function: udp_packet
* takes a udp packet and sets it up for translation
* out - output packet
* udp - pointer to udp header in packet
* old_sum - pseudo-header checksum of old header
* new_sum - pseudo-header checksum of new header
* len - size of ip payload
*/
int udp_packet(clat_packet out, clat_packet_index pos, const struct udphdr *udp, uint32_t old_sum,
uint32_t new_sum, size_t len) {
const uint8_t *payload;
size_t payload_size;
if (len < sizeof(struct udphdr)) {
logmsg_dbg(ANDROID_LOG_ERROR, "udp_packet/(too small)");
return 0;
}
payload = (const uint8_t *)(udp + 1);
payload_size = len - sizeof(struct udphdr);
return udp_translate(out, pos, udp, old_sum, new_sum, payload, payload_size);
}
/* function: tcp_packet
* takes a tcp packet and sets it up for translation
* out - output packet
* tcp - pointer to tcp header in packet
* checksum - pseudo-header checksum
* len - size of ip payload
* returns: the highest position in the output clat_packet that's filled in
*/
int tcp_packet(clat_packet out, clat_packet_index pos, const struct tcphdr *tcp, uint32_t old_sum,
uint32_t new_sum, size_t len) {
const uint8_t *payload;
size_t payload_size, header_size;
if (len < sizeof(struct tcphdr)) {
logmsg_dbg(ANDROID_LOG_ERROR, "tcp_packet/(too small)");
return 0;
}
if (tcp->doff < 5) {
logmsg_dbg(ANDROID_LOG_ERROR, "tcp_packet/tcp header length set to less than 5: %x", tcp->doff);
return 0;
}
if ((size_t)tcp->doff * 4 > len) {
logmsg_dbg(ANDROID_LOG_ERROR, "tcp_packet/tcp header length set too large: %x", tcp->doff);
return 0;
}
header_size = tcp->doff * 4;
payload = ((const uint8_t *)tcp) + header_size;
payload_size = len - header_size;
return tcp_translate(out, pos, tcp, header_size, old_sum, new_sum, payload, payload_size);
}
/* function: udp_translate
* common between ipv4/ipv6 - setup checksum and send udp packet
* out - output packet
* udp - udp header
* old_sum - pseudo-header checksum of old header
* new_sum - pseudo-header checksum of new header
* payload - tcp payload
* payload_size - size of payload
* returns: the highest position in the output clat_packet that's filled in
*/
int udp_translate(clat_packet out, clat_packet_index pos, const struct udphdr *udp,
uint32_t old_sum, uint32_t new_sum, const uint8_t *payload, size_t payload_size) {
struct udphdr *udp_targ = out[pos].iov_base;
memcpy(udp_targ, udp, sizeof(struct udphdr));
out[pos].iov_len = sizeof(struct udphdr);
out[CLAT_POS_PAYLOAD].iov_base = (uint8_t *)payload;
out[CLAT_POS_PAYLOAD].iov_len = payload_size;
if (udp_targ->check) {
udp_targ->check = ip_checksum_adjust(udp->check, old_sum, new_sum);
} else {
// Zero checksums are special. RFC 768 says, "An all zero transmitted checksum value means that
// the transmitter generated no checksum (for debugging or for higher level protocols that
// don't care)." However, in IPv6 zero UDP checksums were only permitted by RFC 6935 (2013). So
// for safety we recompute it.
udp_targ->check = 0; // Checksum field must be 0 when calculating checksum.
udp_targ->check = packet_checksum(new_sum, out, pos);
}
// RFC 768: "If the computed checksum is zero, it is transmitted as all ones (the equivalent
// in one's complement arithmetic)."
if (!udp_targ->check) {
udp_targ->check = 0xffff;
}
return CLAT_POS_PAYLOAD + 1;
}
/* function: tcp_translate
* common between ipv4/ipv6 - setup checksum and send tcp packet
* out - output packet
* tcp - tcp header
* header_size - size of tcp header including options
* checksum - partial checksum covering ipv4/ipv6 header
* payload - tcp payload
* payload_size - size of payload
* returns: the highest position in the output clat_packet that's filled in
*/
int tcp_translate(clat_packet out, clat_packet_index pos, const struct tcphdr *tcp,
size_t header_size, uint32_t old_sum, uint32_t new_sum, const uint8_t *payload,
size_t payload_size) {
struct tcphdr *tcp_targ = out[pos].iov_base;
out[pos].iov_len = header_size;
if (header_size > MAX_TCP_HDR) {
// A TCP header cannot be more than MAX_TCP_HDR bytes long because it's a 4-bit field that
// counts in 4-byte words. So this can never happen unless there is a bug in the caller.
logmsg(ANDROID_LOG_ERROR, "tcp_translate: header too long %d > %d, truncating", header_size,
MAX_TCP_HDR);
header_size = MAX_TCP_HDR;
}
memcpy(tcp_targ, tcp, header_size);
out[CLAT_POS_PAYLOAD].iov_base = (uint8_t *)payload;
out[CLAT_POS_PAYLOAD].iov_len = payload_size;
tcp_targ->check = ip_checksum_adjust(tcp->check, old_sum, new_sum);
return CLAT_POS_PAYLOAD + 1;
}
// Weak symbol so we can override it in the unit test.
void send_rawv6(int fd, clat_packet out, int iov_len) __attribute__((weak));
void send_rawv6(int fd, clat_packet out, int iov_len) {
// A send on a raw socket requires a destination address to be specified even if the socket's
// protocol is IPPROTO_RAW. This is the address that will be used in routing lookups; the
// destination address in the packet header only affects what appears on the wire, not where the
// packet is sent to.
static struct sockaddr_in6 sin6 = { AF_INET6, 0, 0, { { { 0, 0, 0, 0 } } }, 0 };
static struct msghdr msg = {
.msg_name = &sin6,
.msg_namelen = sizeof(sin6),
};
msg.msg_iov = out, msg.msg_iovlen = iov_len,
sin6.sin6_addr = ((struct ip6_hdr *)out[CLAT_POS_IPHDR].iov_base)->ip6_dst;
sendmsg(fd, &msg, 0);
}
/* function: translate_packet
* takes a packet, translates it, and writes it to fd
* fd - fd to write translated packet to
* to_ipv6 - true if translating to ipv6, false if translating to ipv4
* packet - packet
* packetsize - size of packet
*/
void translate_packet(int fd, int to_ipv6, const uint8_t *packet, size_t packetsize) {
int iov_len = 0;
// Allocate buffers for all packet headers.
struct tun_pi tun_targ;
char iphdr[sizeof(struct ip6_hdr)];
char fraghdr[sizeof(struct ip6_frag)];
char transporthdr[MAX_TCP_HDR];
char icmp_iphdr[sizeof(struct ip6_hdr)];
char icmp_fraghdr[sizeof(struct ip6_frag)];
char icmp_transporthdr[MAX_TCP_HDR];
// iovec of the packets we'll send. This gets passed down to the translation functions.
clat_packet out = {
{ &tun_targ, 0 }, // Tunnel header.
{ iphdr, 0 }, // IP header.
{ fraghdr, 0 }, // Fragment header.
{ transporthdr, 0 }, // Transport layer header.
{ icmp_iphdr, 0 }, // ICMP error inner IP header.
{ icmp_fraghdr, 0 }, // ICMP error fragmentation header.
{ icmp_transporthdr, 0 }, // ICMP error transport layer header.
{ NULL, 0 }, // Payload. No buffer, it's a pointer to the original payload.
};
if (to_ipv6) {
iov_len = ipv4_packet(out, CLAT_POS_IPHDR, packet, packetsize);
if (iov_len > 0) {
send_rawv6(fd, out, iov_len);
}
} else {
iov_len = ipv6_packet(out, CLAT_POS_IPHDR, packet, packetsize);
if (iov_len > 0) {
fill_tun_header(&tun_targ, ETH_P_IP);
out[CLAT_POS_TUNHDR].iov_len = sizeof(tun_targ);
send_tun(fd, out, iov_len);
}
}
}