ndhc.c

// Copyright 2004-2022 Nicholas J. Kain <njkain at gmail dot com>
// SPDX-License-Identifier: MIT
#include <stdio.h>
#include <sys/time.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/file.h>
#include <unistd.h>
#include <stdlib.h>
#include <signal.h>
#include <time.h>
#include <string.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <poll.h>
#include <sys/prctl.h>
#include <net/if.h>
#include <errno.h>
#include <pwd.h>
#include <grp.h>
#include <limits.h>
#include "nk/log.h"
#include "nk/privs.h"
#include "nk/io.h"

#include "ndhc.h"
#include "ndhc-defines.h"
#include "cfg.h"
#include "state.h"
#include "options.h"
#include "dhcp.h"
#include "sys.h"
#include "ifchange.h"
#include "arp.h"
#include "nl.h"
#include "netlink.h"
#include "leasefile.h"
#include "ifset.h"
#include "ifchd.h"
#include "duiaid.h"
#include "sockd.h"
#include "rfkill.h"
#include "scriptd.h"

struct client_state_t cs = {
    .program_init = true,
    .listenFd = -1,
    .arpFd = -1,
    .nlFd = -1,
    .nlPortId = 0,
    .rfkillFd = -1,
    .dhcp_wake_ts = -1,
    .routerArp = "\0\0\0\0\0\0",
    .serverArp = "\0\0\0\0\0\0",
};

struct client_config_t client_config = {
    .interface = "eth0",
    .arp = "\0\0\0\0\0\0",
    .s6_notify_fd = 3,
    .clientid_len = 0,
    .metric = 0,
};

static volatile sig_atomic_t l_signal_exit;
static volatile sig_atomic_t l_signal_renew;
static volatile sig_atomic_t l_signal_release;
// Intended to be called in a loop until SIGNAL_NONE is returned.
int signals_flagged(void)
{
    if (l_signal_exit) {
        l_signal_exit = 0;
        return SIGNAL_EXIT;
    }
    if (l_signal_renew) {
        l_signal_renew = 0;
        return SIGNAL_RENEW;
    }
    if (l_signal_release) {
        l_signal_release = 0;
        return SIGNAL_RELEASE;
    }
    return SIGNAL_NONE;
}

bool carrier_isup(void) { return cs.carrier_up; }

void set_client_addr(const char *v) { cs.clientAddr = inet_addr(v); }

void print_version(void)
{
    printf("ndhc %s, dhcp client.\n", NDHC_VERSION);
    printf("Copyright 2004-2022 Nicholas J. Kain\n\n"
"Permission is hereby granted, free of charge, to any person obtaining\n"
"a copy of this software and associated documentation files (the\n"
"\"Software\"), to deal in the Software without restriction, including\n"
"without limitation the rights to use, copy, modify, merge, publish,\n"
"distribute, sublicense, and/or sell copies of the Software, and to\n"
"permit persons to whom the Software is furnished to do so, subject to\n"
"the following conditions:\n\n"
"The above copyright notice and this permission notice shall be\n"
"included in all copies or substantial portions of the Software.\n\n"
"THE SOFTWARE IS PROVIDED \"AS IS\", WITHOUT WARRANTY OF ANY KIND,\n"
"EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF\n"
"MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND\n"
"NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE\n"
"LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION\n"
"OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION\n"
"WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.\n"
           );
    exit(EXIT_SUCCESS);
}

void show_usage(void)
{
    printf(
"ndhc " NDHC_VERSION ", dhcp client.\n"
"Copyright 2004-2022 Nicholas J. Kain\n"
"Usage: ndhc [OPTIONS]\n\n"
"  -c, --config=FILE               Path to ndhc configuration file\n"
"  -I, --clientid=CLIENTID         Client identifier\n"
"  -h, --hostname=HOSTNAME         Client hostname\n"
"  -V, --vendorid=VENDORID         Client vendor identification string\n"
"  -i, --interface=INTERFACE       Interface to use (default: eth0)\n"
"  -n, --now                       Exit with failure if lease cannot be\n"
"                                  immediately negotiated.\n"
"  -r, --request=IP                IP address to request (default: none)\n"
"  -u, --user=USER                 ndhc runs as this user\n"
"  -U, --ifch-user=USER            ndhc-ifch runs as this user\n"
"  -D, --sockd-user=USER           ndhc-sockd runs as this user\n"
"  -C, --chroot=DIR                Chroot to this directory\n"
"  -s, --state-dir=DIR             State storage dir (default: /etc/ndhc)\n"
"  -d, --relentless-defense        Never back off in defending IP against\n"
"                                  conflicting hosts (servers only)\n"
"  -w, --arp-probe-wait            Time to delay before first ARP probe\n"
"  -W, --arp-probe-num             Number of ARP probes before lease is ok\n"
"  -m, --arp-probe-min             Min ms to wait for ARP response\n"
"  -M, --arp-probe-max             Max ms to wait for ARP response\n"
"  -t, --gw-metric                 Route metric for default gw (default: 0)\n"
"  -R, --resolve-conf=FILE         Path to resolv.conf or equivalent\n"
"  -H, --dhcp-set-hostname         Allow DHCP to set machine hostname\n"
"  -v, --version                   Display version\n"
           );
    exit(EXIT_SUCCESS);
}

static void signal_handler(int signo)
{
    int serrno = errno;
    switch (signo) {
    case SIGCHLD: {
        static const char errstr[] = "ndhc-master: Subprocess terminated unexpectedly. Exiting.\n";
        safe_write(STDOUT_FILENO, errstr, sizeof errstr - 1);
        _exit(EXIT_FAILURE);
    }
    case SIGINT:
    case SIGTERM: l_signal_exit = 1; break;
    case SIGUSR1: l_signal_renew = 1; break;
    case SIGUSR2: l_signal_release = 1; break;
    default: break;
    }
    errno = serrno;
}

void signal_exit(int status)
{
    log_line("Received terminal signal. Exiting.\n");
    exit(status);
}

static void setup_signals_ndhc(void)
{
    static const int ss[] = {
        SIGCHLD, SIGINT, SIGTERM, SIGUSR1, SIGUSR2, SIGKILL
    };
    sigset_t mask;

    if (sigprocmask(0, 0, &mask) < 0)
        suicide("sigprocmask failed\n");
    for (int i = 0; ss[i] != SIGKILL; ++i)
        if (sigdelset(&mask, ss[i]))
            suicide("sigdelset failed\n");
    if (sigaddset(&mask, SIGPIPE))
        suicide("sigaddset failed\n");
    if (sigprocmask(SIG_SETMASK, &mask, (sigset_t *)0) < 0)
        suicide("sigprocmask failed\n");

    struct sigaction sa = {
        .sa_handler = signal_handler,
        .sa_flags = SA_RESTART,
    };
    if (sigemptyset(&sa.sa_mask))
        suicide("sigemptyset failed\n");
    for (int i = 0; ss[i] != SIGKILL; ++i)
        if (sigaction(ss[i], &sa, NULL))
            suicide("sigaction failed\n");
}

static void fail_if_state_dir_dne(void)
{
    if (strlen(state_dir) == 0)
        suicide("state_dir path is empty; it must be specified\n");
    struct stat st;
    if (stat(state_dir, &st) < 0)
        suicide("failed to stat state_dir path '%s': %s\n",
                state_dir, strerror(errno));
    if (!S_ISDIR(st.st_mode))
        suicide("state_dir path '%s' does not specify a directory\n", state_dir);
}

static void do_ndhc_work(void)
{
    static bool rfkill_set; // Is the rfkill switch set?
    static bool rfkill_nl_carrier_wentup; // iface carrier changed to up during rfkill
    struct dhcpmsg dhcp_packet;
    long long nowts;
    int timeout = 0;
    bool had_event;

    setup_signals_ndhc();
    start_dhcp_listen(&cs);

    struct pollfd pfds[] = {
        [0] = { .fd = cs.nlFd,          .events = POLLIN|POLLHUP|POLLERR|POLLRDHUP },
        [1] = { .fd = ifchStream[0],    .events = POLLHUP|POLLERR|POLLRDHUP },
        [2] = { .fd = sockdStream[0],   .events = POLLHUP|POLLERR|POLLRDHUP },
        [6] = { .fd = scriptdStream[0], .events = POLLHUP|POLLERR|POLLRDHUP },
        [3] = { .fd = cs.rfkillFd,      .events = POLLIN|POLLHUP|POLLERR|POLLRDHUP },
        // These can change on the fly.
        [4] = { .events = POLLIN|POLLHUP|POLLERR|POLLRDHUP },
        [5] = { .events = POLLIN|POLLHUP|POLLERR|POLLRDHUP },
    };
    for (;;) {
        pfds[4].fd = cs.arpFd;
        pfds[5].fd = cs.listenFd;
        had_event = false;
        if (poll(pfds, 7, timeout) < 0) {
            if (errno != EINTR) suicide("poll failed\n");
        }

        bool sev_dhcp = false;
        uint32_t dhcp_srcaddr = 0;
        uint8_t dhcp_msgtype = 0;
        bool sev_arp = false;
        int sev_nl = IFS_NONE;
        int sev_rfk = RFK_NONE;
        bool force_fingerprint = false;
        if (pfds[0].revents & POLLIN) {
            had_event = true;
            sev_nl = nl_event_get(&cs);
            if (!cs.carrier_up)
                cs.carrier_up = (sev_nl == IFS_UP);
        }
        if (pfds[0].revents & (POLLHUP|POLLERR|POLLRDHUP)) {
            suicide("nlfd closed unexpectedly\n");
        }
        if (pfds[1].revents & (POLLHUP|POLLERR|POLLRDHUP)) {
            exit(EXIT_FAILURE);
        }
        if (pfds[2].revents & (POLLHUP|POLLERR|POLLRDHUP)) {
            exit(EXIT_FAILURE);
        }
        if (pfds[6].revents & (POLLHUP|POLLERR|POLLRDHUP)) {
            exit(EXIT_FAILURE);
        }
        if (pfds[3].revents & POLLIN) {
            had_event = true;
            sev_rfk = rfkill_get(&cs, 1, client_config.rfkillIdx);
        }
        if (pfds[3].revents & (POLLHUP|POLLERR|POLLRDHUP)) {
            suicide("rfkillfd closed unexpectedly\n");
        }
        if (pfds[4].revents & POLLIN) {
            had_event = true;
            // Make sure the fd is still the same.
            if (pfds[4].fd == cs.arpFd)
                sev_arp = arp_packet_get(&cs);
        }
        if (pfds[4].revents & (POLLHUP|POLLERR|POLLRDHUP)) {
            suicide("arpfd closed unexpectedly\n");
        }
        if (pfds[5].revents & POLLIN) {
            had_event = true;
            // Make sure the fd is still the same.
            if (pfds[5].fd == cs.listenFd)
                sev_dhcp = dhcp_packet_get(&cs, &dhcp_packet, &dhcp_msgtype,
                                           &dhcp_srcaddr);
        }
        if (pfds[5].revents & (POLLHUP|POLLERR|POLLRDHUP)) {
            suicide("listenfd closed unexpectedly\n");
        }

        if (sev_rfk == RFK_ENABLED) {
            rfkill_set = 1;
            rfkill_nl_carrier_wentup = false;
            log_line("rfkill: radio now blocked\n");
        } else if (sev_rfk == RFK_DISABLED) {
            rfkill_set = 0;
            log_line("rfkill: radio now unblocked\n");
            cs.carrier_up = ifchange_carrier_isup();
            if (rfkill_nl_carrier_wentup && carrier_isup()) {
                // We might have changed networks while the radio was down.
                force_fingerprint = true;
            }
        }

        if (sev_nl != IFS_NONE && nl_event_carrier_wentup(sev_nl)) {
            if (!rfkill_set)
                force_fingerprint = true;
            else
                rfkill_nl_carrier_wentup = true;
        }

        if (rfkill_set || !carrier_isup()) {
            // We can't do anything while the iface is disabled, anyway.
            // Suspend might cause link state change notifications to be
            // missed, so we use a non-infinite timeout.
            timeout = 2000 + (int)(nk_random_u32(&cs.rnd_state) % 3000);
            continue;
        }

        // These two can change on the fly; make sure the event is current.
        if (pfds[4].fd != cs.arpFd) sev_arp = false;
        if (pfds[5].fd != cs.listenFd) sev_dhcp = false;

        nowts = curms();
        long long arp_wake_ts = arp_get_wake_ts();
        int dhcp_ok = dhcp_handle(&cs, nowts, sev_dhcp, &dhcp_packet,
                                  dhcp_msgtype, dhcp_srcaddr,
                                  sev_arp, force_fingerprint,
                                  cs.dhcp_wake_ts <= nowts,
                                  arp_wake_ts <= nowts);

        if (dhcp_ok == COR_ERROR) {
            timeout = 2000 + (int)(nk_random_u32(&cs.rnd_state) % 3000);
            continue;
        }

        int prev_timeout = timeout;
        long long tt;

        arp_wake_ts = arp_get_wake_ts();
        if (arp_wake_ts < 0 && cs.dhcp_wake_ts < 0) {
            timeout = -1;
            continue;
        } else if (arp_wake_ts < 0) {
            tt = cs.dhcp_wake_ts - nowts;
        } else if (cs.dhcp_wake_ts < 0) {
            tt = arp_wake_ts - nowts;
        } else {
            tt = (arp_wake_ts < cs.dhcp_wake_ts ?
                  arp_wake_ts : cs.dhcp_wake_ts) - nowts;
        }
        if (tt > INT_MAX) tt = INT_MAX;
        if (tt < INT_MIN) tt = INT_MIN;
        timeout = tt;
        if (timeout < 0)
            timeout = 0;

        // Failsafe to prevent busy-spin.
        if (timeout == 0 && prev_timeout == 0 && !had_event)
            timeout = 10000;
    }
}

char state_dir[PATH_MAX] = "/etc/ndhc";
char chroot_dir[PATH_MAX] = "";
char resolv_conf_d[PATH_MAX] = "";
char script_file[PATH_MAX] = "";
uid_t ndhc_uid = 0;
gid_t ndhc_gid = 0;
int ifchSock[2];
int ifchStream[2];
int sockdSock[2];
int sockdStream[2];
int scriptdSock[2];
int scriptdStream[2] = { -1, -1 };

static void create_ifch_ipc_sockets(void) {
    if (socketpair(AF_UNIX, SOCK_DGRAM, 0, ifchSock) < 0)
        suicide("FATAL - can't create ndhc/ifch socket: %s\n", strerror(errno));
    if (socketpair(AF_UNIX, SOCK_STREAM, 0, ifchStream) < 0)
        suicide("FATAL - can't create ndhc/ifch socket: %s\n", strerror(errno));
}

static void create_sockd_ipc_sockets(void) {
    if (socketpair(AF_UNIX, SOCK_DGRAM, 0, sockdSock) < 0)
        suicide("FATAL - can't create ndhc/sockd socket: %s\n", strerror(errno));
    if (socketpair(AF_UNIX, SOCK_STREAM, 0, sockdStream) < 0)
        suicide("FATAL - can't create ndhc/sockd socket: %s\n", strerror(errno));
}

static void create_scriptd_ipc_sockets(void) {
    if (socketpair(AF_UNIX, SOCK_DGRAM, 0, scriptdSock) < 0)
        suicide("FATAL - can't create ndhc/scriptd socket: %s\n", strerror(errno));
    if (socketpair(AF_UNIX, SOCK_STREAM, 0, scriptdStream) < 0)
        suicide("FATAL - can't create ndhc/scriptd socket: %s\n", strerror(errno));
}

static void spawn_ifch(void)
{
    create_ifch_ipc_sockets();
    pid_t ifch_pid = fork();
    if (ifch_pid == 0) {
        close(ifchSock[0]);
        close(ifchStream[0]);
        // Don't share the RNG state with the master process.
        nk_random_init(&cs.rnd_state);
        ifch_main();
    } else if (ifch_pid > 0) {
        close(ifchSock[1]);
        close(ifchStream[1]);
    } else
        suicide("failed to fork ndhc-ifch: %s\n", strerror(errno));
}

static void spawn_sockd(void)
{
    create_sockd_ipc_sockets();
    pid_t sockd_pid = fork();
    if (sockd_pid == 0) {
        close(sockdSock[0]);
        close(sockdStream[0]);
        // Don't share the RNG state with the master process.
        nk_random_init(&cs.rnd_state);
        sockd_main();
    } else if (sockd_pid > 0) {
        close(sockdSock[1]);
        close(sockdStream[1]);
    } else
        suicide("failed to fork ndhc-sockd: %s\n", strerror(errno));
}

static void spawn_scriptd(void)
{
    valid_script_file = access(script_file, R_OK | X_OK) == 0;
    if (!valid_script_file) return;

    log_line("Found script file: '%s'\n", script_file);

    create_scriptd_ipc_sockets();
    pid_t scriptd_pid = fork();
    if (scriptd_pid == 0) {
        close(scriptdSock[0]);
        close(scriptdStream[0]);
        // Don't share the RNG state with the master process.
        nk_random_init(&cs.rnd_state);
        scriptd_main();
    } else if (scriptd_pid > 0) {
        close(scriptdSock[1]);
        close(scriptdStream[1]);
    } else
        suicide("failed to fork ndhc-scriptd: %s\n", strerror(errno));
}

static void ndhc_main(void) {
    prctl(PR_SET_NAME, "ndhc: master");
    log_line("ndhc client " NDHC_VERSION " started on interface [%s].\n",
             client_config.interface);

    if ((cs.nlFd = nl_open(NETLINK_ROUTE, RTMGRP_LINK, &cs.nlPortId)) < 0)
        suicide("%s: failed to open netlink socket\n", __func__);

    cs.rfkillFd = rfkill_open(&client_config.enable_rfkill);

    open_leasefile();

    nk_set_chroot(chroot_dir);
    memset(chroot_dir, '\0', sizeof chroot_dir);
    nk_set_uidgid(ndhc_uid, ndhc_gid, (const unsigned char *)0, 0);

    cs.carrier_up = ifchange_carrier_isup();
    if (!carrier_isup()) {
        if (ifchange_deconfig(&cs) < 0)
            suicide("%s: can't deconfigure interface settings\n", __func__);
    }

    do_ndhc_work();
}

static void wait_for_rfkill()
{
    cs.rfkillFd = rfkill_open(&client_config.enable_rfkill);
    if (cs.rfkillFd < 0)
        suicide("can't wait for rfkill to end if /dev/rfkill can't be opened\n");

    struct pollfd pfds[1] = {0};
    pfds[0].events = POLLIN|POLLHUP|POLLERR|POLLRDHUP;
    for (;;) {
        pfds[0].fd = cs.rfkillFd;
        if (poll(pfds, 1, -1) < 0) {
            if (errno != EINTR) suicide("poll failed\n");
        }
        if (pfds[0].revents & POLLIN) {
            if (rfkill_get(&cs, 0, 0) == RFK_DISABLED) {
                switch (perform_ifup()) {
                case 1:
                case 0: goto rfkill_gone;
                case -3:
                    log_line("rfkill: radio immediately blocked again; spurious?\n");
                    break;
                default: suicide("failed to set the interface to up state\n");
                }
            }
        }
        if (pfds[0].revents & (POLLHUP|POLLERR|POLLRDHUP)) {
            suicide("rfkillFd closed unexpectedly\n");
        }
    }
rfkill_gone:
    // We always close because ifchd and sockd shouldn't keep
    // an rfkill fd open.
    close(cs.rfkillFd);
    cs.rfkillFd = -1;
}

int main(int argc, char *argv[])
{
    parse_cmdline(argc, argv);

    nk_random_init(&cs.rnd_state);
    cs.xid = nk_random_u32(&cs.rnd_state);

    if (getuid())
        suicide("I need to be started as root.\n");
    if (!strncmp(chroot_dir, "", sizeof chroot_dir))
        suicide("No chroot path is specified.  Refusing to run.\n");
    fail_if_state_dir_dne();

    if (nl_getifdata() < 0)
        suicide("failed to get interface MAC or index\n");

    get_clientid(&client_config);

    switch (perform_ifup()) {
    case 1: case 0: break;
    case -3: wait_for_rfkill(); break;
    default: suicide("failed to set the interface to up state\n");
    }

    if (setpgid(0, 0) < 0) {
        // EPERM is returned if we are already a process group leader.
        if (errno != EPERM)
            suicide("setpgid failed: %s\n", strerror(errno));
    }

    spawn_ifch();
    spawn_sockd();
    spawn_scriptd();
    ndhc_main();
    exit(EXIT_SUCCESS);
}