OpenWrt – Rev 4

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/* 464xlatcfg.c
 *
 * Copyright (c) 2015 Steven Barth <cyrus@openwrt.org>
 * Copyright (c) 2017 Hans Dedecker <dedeckeh@gmail.com>
 *
 * 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
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 */

#include <netinet/icmp6.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <net/if.h>
#include <unistd.h>
#include <stdlib.h>
#include <signal.h>
#include <stdio.h>
#include <netdb.h>

static void sighandler(__attribute__((unused)) int signal)
{
}

int main(int argc, const char *argv[])
{
        char buf[INET6_ADDRSTRLEN], prefix[INET6_ADDRSTRLEN + 4];
        int pid;

        if (argc <= 1) {
                fprintf(stderr, "Usage: %s <name> [ifname] [ipv6prefix] [ipv4addr] [ipv6addr]\n", argv[0]);
                return 1;
        }

        snprintf(buf, sizeof(buf), "/var/run/%s.pid", argv[1]);
        FILE *fp = fopen(buf, "r");
        if (fp) {
                if (fscanf(fp, "%d", &pid) == 1)
                        kill(pid, SIGTERM);

                unlink(buf);
                fclose(fp);
        }

        if (!argv[2])
                return 0;

        if (!argv[3] || !argv[4] || !(fp = fopen(buf, "wx")))
                return 1;

        signal(SIGTERM, SIG_DFL);
        setvbuf(fp, NULL, _IOLBF, 0);
        fprintf(fp, "%d\n", getpid());

        prefix[sizeof(prefix) - 1] = 0;
        strncpy(prefix, argv[3], sizeof(prefix) - 1);

        if (!prefix[0]) {
                struct addrinfo hints = { .ai_family = AF_INET6 }, *res;
                if (getaddrinfo("ipv4only.arpa", NULL, &hints, &res) || !res) {
                        sleep(3);
                        if (getaddrinfo("ipv4only.arpa", NULL, &hints, &res) || !res)
                                return 2;
                }

                struct sockaddr_in6 *sin6 = (struct sockaddr_in6*)res->ai_addr;
                inet_ntop(AF_INET6, &sin6->sin6_addr, prefix, sizeof(prefix) - 4);
                strcat(prefix, "/96");
                freeaddrinfo(res);
        }

        int i = 0;
        int sock;
        struct sockaddr_in6 saddr;

        do {
                socklen_t saddrlen = sizeof(saddr);
                struct icmp6_filter filt;

                sock = socket(AF_INET6, SOCK_RAW, IPPROTO_ICMPV6);
                ICMP6_FILTER_SETBLOCKALL(&filt);
                setsockopt(sock, IPPROTO_ICMPV6, ICMP6_FILTER, &filt, sizeof(filt));
                setsockopt(sock, SOL_SOCKET, SO_BINDTODEVICE, argv[2], strlen(argv[2]));
                memset(&saddr, 0, sizeof(saddr));
                saddr.sin6_family = AF_INET6;
                saddr.sin6_addr.s6_addr32[0] = htonl(0x2001);
                saddr.sin6_addr.s6_addr32[1] = htonl(0xdb8);
                if (connect(sock, (struct sockaddr*)&saddr, sizeof(saddr)) ||
                                getsockname(sock, (struct sockaddr*)&saddr, &saddrlen))
                        return 3;

                if (!IN6_IS_ADDR_LINKLOCAL(&saddr.sin6_addr) || argv[5])
                        break;

                close(sock);
                sleep(3);
                i++;
        } while (i < 3);

        struct ipv6_mreq mreq = {saddr.sin6_addr, if_nametoindex(argv[2])};
        if (!argv[5]) {
                if (IN6_IS_ADDR_LINKLOCAL(&mreq.ipv6mr_multiaddr))
                        return 5;

                srandom(mreq.ipv6mr_multiaddr.s6_addr32[0] ^ mreq.ipv6mr_multiaddr.s6_addr32[1] ^
                                mreq.ipv6mr_multiaddr.s6_addr32[2] ^ mreq.ipv6mr_multiaddr.s6_addr32[3]);
                mreq.ipv6mr_multiaddr.s6_addr32[2] = random();
                mreq.ipv6mr_multiaddr.s6_addr32[3] = random();
        } else if (inet_pton(AF_INET6, argv[5], &mreq.ipv6mr_multiaddr) != 1) {
                return 1;
        }

        if (setsockopt(sock, SOL_IPV6, IPV6_JOIN_ANYCAST, &mreq, sizeof(mreq)))
                return 3;

        inet_ntop(AF_INET6, &mreq.ipv6mr_multiaddr, buf, sizeof(buf));
        fputs(buf, stdout);
        fputc('\n', stdout);
        fflush(stdout);

        FILE *nat46 = fopen("/proc/net/nat46/control", "w");
        if (!nat46 || fprintf(nat46, "add %s\nconfig %s local.style NONE local.v4 %s/32 local.v6 %s/128 "
                        "remote.style RFC6052 remote.v6 %s\n", argv[1], argv[1], argv[4], buf, prefix) < 0 ||
                        fclose(nat46))
                return 4;

        if (!(pid = fork())) {
                fclose(fp);
                fclose(stdin);
                fclose(stdout);
                fclose(stderr);
                chdir("/");
                setsid();
                signal(SIGTERM, sighandler);
                pause();

                nat46 = fopen("/proc/net/nat46/control", "w");
                if (nat46) {
                        fprintf(nat46, "del %s\n", argv[1]);
                        fclose(nat46);
                }
        } else {
                rewind(fp);
                fprintf(fp, "%d\n", pid);
        }

        return 0;
}