pppd: Drop linux IPX support (#326)

[ppp.git] / pppd / main.c

/*
 * main.c - Point-to-Point Protocol main module
 *
 * Copyright (c) 1984-2000 Carnegie Mellon University. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The name "Carnegie Mellon University" must not be used to
 *    endorse or promote products derived from this software without
 *    prior written permission. For permission or any legal
 *    details, please contact
 *      Office of Technology Transfer
 *      Carnegie Mellon University
 *      5000 Forbes Avenue
 *      Pittsburgh, PA  15213-3890
 *      (412) 268-4387, fax: (412) 268-7395
 *      tech-transfer@andrew.cmu.edu
 *
 * 4. Redistributions of any form whatsoever must retain the following
 *    acknowledgment:
 *    "This product includes software developed by Computing Services
 *     at Carnegie Mellon University (http://www.cmu.edu/computing/)."
 *
 * CARNEGIE MELLON UNIVERSITY DISCLAIMS ALL WARRANTIES WITH REGARD TO
 * THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
 * AND FITNESS, IN NO EVENT SHALL CARNEGIE MELLON UNIVERSITY BE LIABLE
 * FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN
 * AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
 * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 *
 * Copyright (c) 1999-2020 Paul Mackerras. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. The name(s) of the authors of this software must not be used to
 *    endorse or promote products derived from this software without
 *    prior written permission.
 *
 * 3. Redistributions of any form whatsoever must retain the following
 *    acknowledgment:
 *    "This product includes software developed by Paul Mackerras
 *     <paulus@samba.org>".
 *
 * THE AUTHORS OF THIS SOFTWARE DISCLAIM ALL WARRANTIES WITH REGARD TO
 * THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
 * AND FITNESS, IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY
 * SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN
 * AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
 * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <signal.h>
#include <errno.h>
#include <fcntl.h>
#include <syslog.h>
#include <netdb.h>
#include <utmp.h>
#include <pwd.h>
#include <sys/param.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/time.h>
#include <sys/resource.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <inttypes.h>

#include "pppd.h"
#include "magic.h"
#include "fsm.h"
#include "lcp.h"
#include "ipcp.h"
#ifdef INET6
#include "ipv6cp.h"
#endif
#include "upap.h"
#include "chap-new.h"
#include "eap.h"
#include "ccp.h"
#include "ecp.h"
#include "pathnames.h"

#ifdef USE_TDB
#include "tdb.h"
#endif

#ifdef CBCP_SUPPORT
#include "cbcp.h"
#endif

#ifdef AT_CHANGE
#include "atcp.h"
#endif


/* interface vars */
char ifname[IFNAMSIZ];          /* Interface name */
int ifunit;                     /* Interface unit number */

struct channel *the_channel;

char *progname;                 /* Name of this program */
char hostname[MAXNAMELEN];      /* Our hostname */
static char pidfilename[MAXPATHLEN];    /* name of pid file */
static char linkpidfile[MAXPATHLEN];    /* name of linkname pid file */
char ppp_devnam[MAXPATHLEN];    /* name of PPP tty (maybe ttypx) */
uid_t uid;                      /* Our real user-id */
struct notifier *pidchange = NULL;
struct notifier *phasechange = NULL;
struct notifier *exitnotify = NULL;
struct notifier *sigreceived = NULL;
struct notifier *fork_notifier = NULL;

int hungup;                     /* terminal has been hung up */
int privileged;                 /* we're running as real uid root */
int need_holdoff;               /* need holdoff period before restarting */
int detached;                   /* have detached from terminal */
volatile int status;            /* exit status for pppd */
int unsuccess;                  /* # unsuccessful connection attempts */
int do_callback;                /* != 0 if we should do callback next */
int doing_callback;             /* != 0 if we are doing callback */
int ppp_session_number;         /* Session number, for channels with such a
                                   concept (eg PPPoE) */
int childwait_done;             /* have timed out waiting for children */

#ifdef USE_TDB
TDB_CONTEXT *pppdb;             /* database for storing status etc. */
#endif

char db_key[32];

int (*holdoff_hook)(void) = NULL;
int (*new_phase_hook)(int) = NULL;
void (*snoop_recv_hook)(unsigned char *p, int len) = NULL;
void (*snoop_send_hook)(unsigned char *p, int len) = NULL;

static int conn_running;        /* we have a [dis]connector running */
static int fd_loop;             /* fd for getting demand-dial packets */

int fd_devnull;                 /* fd for /dev/null */
int devfd = -1;                 /* fd of underlying device */
int fd_ppp = -1;                /* fd for talking PPP */
int phase;                      /* where the link is at */
int kill_link;
int asked_to_quit;
int open_ccp_flag;
int listen_time;
int got_sigusr2;
int got_sigterm;
int got_sighup;

static sigset_t signals_handled;
static int waiting;
static int sigpipe[2];

char **script_env;              /* Env. variable values for scripts */
int s_env_nalloc;               /* # words avail at script_env */

u_char outpacket_buf[PPP_MRU+PPP_HDRLEN]; /* buffer for outgoing packet */
u_char inpacket_buf[PPP_MRU+PPP_HDRLEN]; /* buffer for incoming packet */

static int n_children;          /* # child processes still running */
static int got_sigchld;         /* set if we have received a SIGCHLD */

int privopen;                   /* don't lock, open device as root */

char *no_ppp_msg = "Sorry - this system lacks PPP kernel support\n";

GIDSET_TYPE groups[NGROUPS_MAX];/* groups the user is in */
int ngroups;                    /* How many groups valid in groups */

static struct timeval start_time;       /* Time when link was started. */

static struct pppd_stats old_link_stats;
struct pppd_stats link_stats;
unsigned link_connect_time;
int link_stats_valid;

int error_count;

bool bundle_eof;
bool bundle_terminating;

/*
 * We maintain a list of child process pids and
 * functions to call when they exit.
 */
struct subprocess {
    pid_t       pid;
    char        *prog;
    void        (*done)(void *);
    void        *arg;
    int         killable;
    struct subprocess *next;
};

static struct subprocess *children;

/* Prototypes for procedures local to this file. */

static void setup_signals(void);
static void create_pidfile(int pid);
static void create_linkpidfile(int pid);
static void cleanup(void);
static void get_input(void);
static void calltimeout(void);
static struct timeval *timeleft(struct timeval *);
static void kill_my_pg(int);
static void hup(int);
static void term(int);
static void chld(int);
static void toggle_debug(int);
static void open_ccp(int);
static void bad_signal(int);
static void holdoff_end(void *);
static void forget_child(int pid, int status);
static int reap_kids(void);
static void childwait_end(void *);

#ifdef USE_TDB
static void update_db_entry(void);
static void add_db_key(const char *);
static void delete_db_key(const char *);
static void cleanup_db(void);
#endif

static void handle_events(void);
void print_link_stats(void);

extern  char    *getlogin(void);
int main(int, char *[]);

/*
 * PPP Data Link Layer "protocol" table.
 * One entry per supported protocol.
 * The last entry must be NULL.
 */
struct protent *protocols[] = {
    &lcp_protent,
    &pap_protent,
    &chap_protent,
#ifdef CBCP_SUPPORT
    &cbcp_protent,
#endif
    &ipcp_protent,
#ifdef INET6
    &ipv6cp_protent,
#endif
    &ccp_protent,
    &ecp_protent,
#ifdef AT_CHANGE
    &atcp_protent,
#endif
    &eap_protent,
    NULL
};

int
main(int argc, char *argv[])
{
    int i, t;
    char *p;
    struct passwd *pw;
    struct protent *protp;
    char numbuf[16];

    strlcpy(path_ipup, _PATH_IPUP, sizeof(path_ipup));
    strlcpy(path_ipdown, _PATH_IPDOWN, sizeof(path_ipdown));

#ifdef INET6
    strlcpy(path_ipv6up, _PATH_IPV6UP, sizeof(path_ipv6up));
    strlcpy(path_ipv6down, _PATH_IPV6DOWN, sizeof(path_ipv6down));
#endif
    link_stats_valid = 0;
    new_phase(PHASE_INITIALIZE);

    script_env = NULL;

    /* Initialize syslog facilities */
    reopen_log();

    if (gethostname(hostname, MAXNAMELEN) < 0 ) {
        option_error("Couldn't get hostname: %m");
        exit(1);
    }
    hostname[MAXNAMELEN-1] = 0;

    /* make sure we don't create world or group writable files. */
    umask(umask(0777) | 022);

    uid = getuid();
    privileged = uid == 0;
    slprintf(numbuf, sizeof(numbuf), "%d", uid);
    script_setenv("ORIG_UID", numbuf, 0);

    ngroups = getgroups(NGROUPS_MAX, groups);

    /*
     * Initialize magic number generator now so that protocols may
     * use magic numbers in initialization.
     */
    magic_init();

    /*
     * Initialize each protocol.
     */
    for (i = 0; (protp = protocols[i]) != NULL; ++i)
        (*protp->init)(0);

    /*
     * Initialize the default channel.
     */
    tty_init();

    progname = *argv;

    /*
     * Parse, in order, the system options file, the user's options file,
     * and the command line arguments.
     */
    if (!options_from_file(_PATH_SYSOPTIONS, !privileged, 0, 1)
        || !options_from_user()
        || !parse_args(argc-1, argv+1))
        exit(EXIT_OPTION_ERROR);
    devnam_fixed = 1;           /* can no longer change device name */

    /*
     * Work out the device name, if it hasn't already been specified,
     * and parse the tty's options file.
     */
    if (the_channel->process_extra_options)
        (*the_channel->process_extra_options)();

    if (debug)
        setlogmask(LOG_UPTO(LOG_DEBUG));

    /*
     * Check that we are running as root.
     */
    if (geteuid() != 0) {
        option_error("must be root to run %s, since it is not setuid-root",
                     argv[0]);
        exit(EXIT_NOT_ROOT);
    }

    if (!ppp_available()) {
        option_error("%s", no_ppp_msg);
        exit(EXIT_NO_KERNEL_SUPPORT);
    }

    /*
     * Check that the options given are valid and consistent.
     */
    check_options();
    if (!sys_check_options())
        exit(EXIT_OPTION_ERROR);
    auth_check_options();
#ifdef HAVE_MULTILINK
    mp_check_options();
#endif
    for (i = 0; (protp = protocols[i]) != NULL; ++i)
        if (protp->check_options != NULL)
            (*protp->check_options)();
    if (the_channel->check_options)
        (*the_channel->check_options)();


    if (dump_options || dryrun) {
        init_pr_log(NULL, LOG_INFO);
        print_options(pr_log, NULL);
        end_pr_log();
    }

    if (dryrun)
        die(0);

    /* Make sure fds 0, 1, 2 are open to somewhere. */
    fd_devnull = open(_PATH_DEVNULL, O_RDWR);
    if (fd_devnull < 0)
        fatal("Couldn't open %s: %m", _PATH_DEVNULL);
    while (fd_devnull <= 2) {
        i = dup(fd_devnull);
        if (i < 0)
            fatal("Critical shortage of file descriptors: dup failed: %m");
        fd_devnull = i;
    }

    /*
     * Initialize system-dependent stuff.
     */
    sys_init();

#ifdef USE_TDB
    pppdb = tdb_open(_PATH_PPPDB, 0, 0, O_RDWR|O_CREAT, 0644);
    if (pppdb != NULL) {
        slprintf(db_key, sizeof(db_key), "pppd%d", getpid());
        update_db_entry();
    } else {
        warn("Warning: couldn't open ppp database %s", _PATH_PPPDB);
        if (multilink) {
            warn("Warning: disabling multilink");
            multilink = 0;
        }
    }
#endif

    /*
     * Detach ourselves from the terminal, if required,
     * and identify who is running us.
     */
    if (!nodetach && !updetach)
        detach();
    p = getlogin();
    if (p == NULL) {
        pw = getpwuid(uid);
        if (pw != NULL && pw->pw_name != NULL)
            p = pw->pw_name;
        else
            p = "(unknown)";
    }
    syslog(LOG_NOTICE, "pppd %s started by %s, uid %d", VERSION, p, uid);
    script_setenv("PPPLOGNAME", p, 0);

    if (devnam[0])
        script_setenv("DEVICE", devnam, 1);
    slprintf(numbuf, sizeof(numbuf), "%d", getpid());
    script_setenv("PPPD_PID", numbuf, 1);

    setup_signals();

    create_linkpidfile(getpid());

    waiting = 0;

    /*
     * If we're doing dial-on-demand, set up the interface now.
     */
    if (demand) {
        /*
         * Open the loopback channel and set it up to be the ppp interface.
         */
        fd_loop = open_ppp_loopback();
        set_ifunit(1);
        /*
         * Configure the interface and mark it up, etc.
         */
        demand_conf();
    }

    do_callback = 0;
    for (;;) {

        bundle_eof = 0;
        bundle_terminating = 0;
        listen_time = 0;
        need_holdoff = 1;
        devfd = -1;
        status = EXIT_OK;
        ++unsuccess;
        doing_callback = do_callback;
        do_callback = 0;

        if (demand && !doing_callback) {
            /*
             * Don't do anything until we see some activity.
             */
            new_phase(PHASE_DORMANT);
            demand_unblock();
            add_fd(fd_loop);
            for (;;) {
                handle_events();
                if (asked_to_quit)
                    break;
                if (get_loop_output())
                    break;
            }
            remove_fd(fd_loop);
            if (asked_to_quit)
                break;

            /*
             * Now we want to bring up the link.
             */
            demand_block();
            info("Starting link");
        }

        get_time(&start_time);
        script_unsetenv("CONNECT_TIME");
        script_unsetenv("BYTES_SENT");
        script_unsetenv("BYTES_RCVD");

        lcp_open(0);            /* Start protocol */
        start_link(0);
        while (phase != PHASE_DEAD) {
            handle_events();
            get_input();
            if (kill_link)
                lcp_close(0, "User request");
            if (asked_to_quit) {
                bundle_terminating = 1;
                if (phase == PHASE_MASTER)
                    mp_bundle_terminated();
            }
            if (open_ccp_flag) {
                if (phase == PHASE_NETWORK || phase == PHASE_RUNNING) {
                    ccp_fsm[0].flags = OPT_RESTART; /* clears OPT_SILENT */
                    (*ccp_protent.open)(0);
                }
            }
        }
        /* restore FSMs to original state */
        lcp_close(0, "");

        if (!persist || asked_to_quit || (maxfail > 0 && unsuccess >= maxfail))
            break;

        if (demand)
            demand_discard();
        t = need_holdoff? holdoff: 0;
        if (holdoff_hook)
            t = (*holdoff_hook)();
        if (t > 0) {
            new_phase(PHASE_HOLDOFF);
            TIMEOUT(holdoff_end, NULL, t);
            do {
                handle_events();
                if (kill_link)
                    new_phase(PHASE_DORMANT); /* allow signal to end holdoff */
            } while (phase == PHASE_HOLDOFF);
            if (!persist)
                break;
        }
    }

    /* Wait for scripts to finish */
    reap_kids();
    if (n_children > 0) {
        if (child_wait > 0)
            TIMEOUT(childwait_end, NULL, child_wait);
        if (debug) {
            struct subprocess *chp;
            dbglog("Waiting for %d child processes...", n_children);
            for (chp = children; chp != NULL; chp = chp->next)
                dbglog("  script %s, pid %d", chp->prog, chp->pid);
        }
        while (n_children > 0 && !childwait_done) {
            handle_events();
            if (kill_link && !childwait_done)
                childwait_end(NULL);
        }
    }

    die(status);
    return 0;
}

/*
 * handle_events - wait for something to happen and respond to it.
 */
static void
handle_events(void)
{
    struct timeval timo;
    unsigned char buf[16];

    kill_link = open_ccp_flag = 0;

    /* alert via signal pipe */
    waiting = 1;
    /* flush signal pipe */
    for (; read(sigpipe[0], buf, sizeof(buf)) > 0; );
    add_fd(sigpipe[0]);
    /* wait if necessary */
    if (!(got_sighup || got_sigterm || got_sigusr2 || got_sigchld))
        wait_input(timeleft(&timo));
    waiting = 0;
    remove_fd(sigpipe[0]);

    calltimeout();
    if (got_sighup) {
        info("Hangup (SIGHUP)");
        kill_link = 1;
        got_sighup = 0;
        if (status != EXIT_HANGUP)
            status = EXIT_USER_REQUEST;
    }
    if (got_sigterm) {
        info("Terminating on signal %d", got_sigterm);
        kill_link = 1;
        asked_to_quit = 1;
        persist = 0;
        status = EXIT_USER_REQUEST;
        got_sigterm = 0;
    }
    if (got_sigchld) {
        got_sigchld = 0;
        reap_kids();    /* Don't leave dead kids lying around */
    }
    if (got_sigusr2) {
        open_ccp_flag = 1;
        got_sigusr2 = 0;
    }
}

/*
 * setup_signals - initialize signal handling.
 */
static void
setup_signals(void)
{
    struct sigaction sa;

    /* create pipe to wake up event handler from signal handler */
    if (pipe(sigpipe) < 0)
        fatal("Couldn't create signal pipe: %m");
    fcntl(sigpipe[0], F_SETFD, fcntl(sigpipe[0], F_GETFD) | FD_CLOEXEC);
    fcntl(sigpipe[1], F_SETFD, fcntl(sigpipe[1], F_GETFD) | FD_CLOEXEC);
    fcntl(sigpipe[0], F_SETFL, fcntl(sigpipe[0], F_GETFL) | O_NONBLOCK);
    fcntl(sigpipe[1], F_SETFL, fcntl(sigpipe[1], F_GETFL) | O_NONBLOCK);

    /*
     * Compute mask of all interesting signals and install signal handlers
     * for each.  Only one signal handler may be active at a time.  Therefore,
     * all other signals should be masked when any handler is executing.
     */
    sigemptyset(&signals_handled);
    sigaddset(&signals_handled, SIGHUP);
    sigaddset(&signals_handled, SIGINT);
    sigaddset(&signals_handled, SIGTERM);
    sigaddset(&signals_handled, SIGCHLD);
    sigaddset(&signals_handled, SIGUSR2);

#define SIGNAL(s, handler)      do { \
        sa.sa_handler = handler; \
        if (sigaction(s, &sa, NULL) < 0) \
            fatal("Couldn't establish signal handler (%d): %m", s); \
    } while (0)

    sa.sa_mask = signals_handled;
    sa.sa_flags = 0;
    SIGNAL(SIGHUP, hup);                /* Hangup */
    SIGNAL(SIGINT, term);               /* Interrupt */
    SIGNAL(SIGTERM, term);              /* Terminate */
    SIGNAL(SIGCHLD, chld);

    SIGNAL(SIGUSR1, toggle_debug);      /* Toggle debug flag */
    SIGNAL(SIGUSR2, open_ccp);          /* Reopen CCP */

    /*
     * Install a handler for other signals which would otherwise
     * cause pppd to exit without cleaning up.
     */
    SIGNAL(SIGABRT, bad_signal);
    SIGNAL(SIGALRM, bad_signal);
    SIGNAL(SIGFPE, bad_signal);
    SIGNAL(SIGILL, bad_signal);
    SIGNAL(SIGPIPE, bad_signal);
    SIGNAL(SIGQUIT, bad_signal);
    SIGNAL(SIGSEGV, bad_signal);
#ifdef SIGBUS
    SIGNAL(SIGBUS, bad_signal);
#endif
#ifdef SIGEMT
    SIGNAL(SIGEMT, bad_signal);
#endif
#ifdef SIGPOLL
    SIGNAL(SIGPOLL, bad_signal);
#endif
#ifdef SIGPROF
    SIGNAL(SIGPROF, bad_signal);
#endif
#ifdef SIGSYS
    SIGNAL(SIGSYS, bad_signal);
#endif
#ifdef SIGTRAP
    SIGNAL(SIGTRAP, bad_signal);
#endif
#ifdef SIGVTALRM
    SIGNAL(SIGVTALRM, bad_signal);
#endif
#ifdef SIGXCPU
    SIGNAL(SIGXCPU, bad_signal);
#endif
#ifdef SIGXFSZ
    SIGNAL(SIGXFSZ, bad_signal);
#endif

    /*
     * Apparently we can get a SIGPIPE when we call syslog, if
     * syslogd has died and been restarted.  Ignoring it seems
     * be sufficient.
     */
    signal(SIGPIPE, SIG_IGN);
}

/*
 * set_ifunit - do things we need to do once we know which ppp
 * unit we are using.
 */
void
set_ifunit(int iskey)
{
    char ifkey[32];

    if (req_ifname[0] != '\0')
        slprintf(ifname, sizeof(ifname), "%s", req_ifname);
    else
        slprintf(ifname, sizeof(ifname), "%s%d", PPP_DRV_NAME, ifunit);
    info("Using interface %s", ifname);
    script_setenv("IFNAME", ifname, iskey);
    slprintf(ifkey, sizeof(ifkey), "%d", ifunit);
    script_setenv("UNIT", ifkey, iskey);
    if (iskey) {
        create_pidfile(getpid());       /* write pid to file */
        create_linkpidfile(getpid());
    }
}

/*
 * detach - detach us from the controlling terminal.
 */
void
detach(void)
{
    int pid;
    int ret;
    char numbuf[16];
    int pipefd[2];

    if (detached)
        return;
    if (pipe(pipefd) == -1)
        pipefd[0] = pipefd[1] = -1;
    if ((pid = fork()) < 0) {
        error("Couldn't detach (fork failed: %m)");
        die(1);                 /* or just return? */
    }
    if (pid != 0) {
        /* parent */
        notify(pidchange, pid);
        /* update pid files if they have been written already */
        if (pidfilename[0])
            create_pidfile(pid);
        create_linkpidfile(pid);
        exit(0);                /* parent dies */
    }
    setsid();
    ret = chdir("/");
    if (ret != 0) {
        fatal("Could not change directory to '/', %m");
    }
    dup2(fd_devnull, 0);
    dup2(fd_devnull, 1);
    dup2(fd_devnull, 2);
    detached = 1;
    if (log_default)
        log_to_fd = -1;
    slprintf(numbuf, sizeof(numbuf), "%d", getpid());
    script_setenv("PPPD_PID", numbuf, 1);

    /* wait for parent to finish updating pid & lock files and die */
    close(pipefd[1]);
    complete_read(pipefd[0], numbuf, 1);
    close(pipefd[0]);
}

/*
 * reopen_log - (re)open our connection to syslog.
 */
void
reopen_log(void)
{
    openlog("pppd", LOG_PID | LOG_NDELAY, LOG_PPP);
    setlogmask(LOG_UPTO(LOG_INFO));
}

/*
 * Create a file containing our process ID.
 */
static void
create_pidfile(int pid)
{
    FILE *pidfile;

    slprintf(pidfilename, sizeof(pidfilename), "%s%s.pid",
             _PATH_VARRUN, ifname);
    if ((pidfile = fopen(pidfilename, "w")) != NULL) {
        fprintf(pidfile, "%d\n", pid);
        (void) fclose(pidfile);
    } else {
        error("Failed to create pid file %s: %m", pidfilename);
        pidfilename[0] = 0;
    }
}

void
create_linkpidfile(int pid)
{
    FILE *pidfile;

    if (linkname[0] == 0)
        return;
    script_setenv("LINKNAME", linkname, 1);
    slprintf(linkpidfile, sizeof(linkpidfile), "%sppp-%s.pid",
             _PATH_VARRUN, linkname);
    if ((pidfile = fopen(linkpidfile, "w")) != NULL) {
        fprintf(pidfile, "%d\n", pid);
        if (ifname[0])
            fprintf(pidfile, "%s\n", ifname);
        (void) fclose(pidfile);
    } else {
        error("Failed to create pid file %s: %m", linkpidfile);
        linkpidfile[0] = 0;
    }
}

/*
 * remove_pidfile - remove our pid files
 */
void remove_pidfiles(void)
{
    if (pidfilename[0] != 0 && unlink(pidfilename) < 0 && errno != ENOENT)
        warn("unable to delete pid file %s: %m", pidfilename);
    pidfilename[0] = 0;
    if (linkpidfile[0] != 0 && unlink(linkpidfile) < 0 && errno != ENOENT)
        warn("unable to delete pid file %s: %m", linkpidfile);
    linkpidfile[0] = 0;
}

/*
 * holdoff_end - called via a timeout when the holdoff period ends.
 */
static void
holdoff_end(void *arg)
{
    new_phase(PHASE_DORMANT);
}

/* List of protocol names, to make our messages a little more informative. */
struct protocol_list {
    u_short     proto;
    const char  *name;
} protocol_list[] = {
    { 0x21,     "IP" },
    { 0x23,     "OSI Network Layer" },
    { 0x25,     "Xerox NS IDP" },
    { 0x27,     "DECnet Phase IV" },
    { 0x29,     "Appletalk" },
    { 0x2b,     "Novell IPX" },
    { 0x2d,     "VJ compressed TCP/IP" },
    { 0x2f,     "VJ uncompressed TCP/IP" },
    { 0x31,     "Bridging PDU" },
    { 0x33,     "Stream Protocol ST-II" },
    { 0x35,     "Banyan Vines" },
    { 0x39,     "AppleTalk EDDP" },
    { 0x3b,     "AppleTalk SmartBuffered" },
    { 0x3d,     "Multi-Link" },
    { 0x3f,     "NETBIOS Framing" },
    { 0x41,     "Cisco Systems" },
    { 0x43,     "Ascom Timeplex" },
    { 0x45,     "Fujitsu Link Backup and Load Balancing (LBLB)" },
    { 0x47,     "DCA Remote Lan" },
    { 0x49,     "Serial Data Transport Protocol (PPP-SDTP)" },
    { 0x4b,     "SNA over 802.2" },
    { 0x4d,     "SNA" },
    { 0x4f,     "IP6 Header Compression" },
    { 0x51,     "KNX Bridging Data" },
    { 0x53,     "Encryption" },
    { 0x55,     "Individual Link Encryption" },
    { 0x57,     "IPv6" },
    { 0x59,     "PPP Muxing" },
    { 0x5b,     "Vendor-Specific Network Protocol" },
    { 0x61,     "RTP IPHC Full Header" },
    { 0x63,     "RTP IPHC Compressed TCP" },
    { 0x65,     "RTP IPHC Compressed non-TCP" },
    { 0x67,     "RTP IPHC Compressed UDP 8" },
    { 0x69,     "RTP IPHC Compressed RTP 8" },
    { 0x6f,     "Stampede Bridging" },
    { 0x73,     "MP+" },
    { 0xc1,     "NTCITS IPI" },
    { 0xfb,     "single-link compression" },
    { 0xfd,     "Compressed Datagram" },
    { 0x0201,   "802.1d Hello Packets" },
    { 0x0203,   "IBM Source Routing BPDU" },
    { 0x0205,   "DEC LANBridge100 Spanning Tree" },
    { 0x0207,   "Cisco Discovery Protocol" },
    { 0x0209,   "Netcs Twin Routing" },
    { 0x020b,   "STP - Scheduled Transfer Protocol" },
    { 0x020d,   "EDP - Extreme Discovery Protocol" },
    { 0x0211,   "Optical Supervisory Channel Protocol" },
    { 0x0213,   "Optical Supervisory Channel Protocol" },
    { 0x0231,   "Luxcom" },
    { 0x0233,   "Sigma Network Systems" },
    { 0x0235,   "Apple Client Server Protocol" },
    { 0x0281,   "MPLS Unicast" },
    { 0x0283,   "MPLS Multicast" },
    { 0x0285,   "IEEE p1284.4 standard - data packets" },
    { 0x0287,   "ETSI TETRA Network Protocol Type 1" },
    { 0x0289,   "Multichannel Flow Treatment Protocol" },
    { 0x2063,   "RTP IPHC Compressed TCP No Delta" },
    { 0x2065,   "RTP IPHC Context State" },
    { 0x2067,   "RTP IPHC Compressed UDP 16" },
    { 0x2069,   "RTP IPHC Compressed RTP 16" },
    { 0x4001,   "Cray Communications Control Protocol" },
    { 0x4003,   "CDPD Mobile Network Registration Protocol" },
    { 0x4005,   "Expand accelerator protocol" },
    { 0x4007,   "ODSICP NCP" },
    { 0x4009,   "DOCSIS DLL" },
    { 0x400B,   "Cetacean Network Detection Protocol" },
    { 0x4021,   "Stacker LZS" },
    { 0x4023,   "RefTek Protocol" },
    { 0x4025,   "Fibre Channel" },
    { 0x4027,   "EMIT Protocols" },
    { 0x405b,   "Vendor-Specific Protocol (VSP)" },
    { 0x8021,   "Internet Protocol Control Protocol" },
    { 0x8023,   "OSI Network Layer Control Protocol" },
    { 0x8025,   "Xerox NS IDP Control Protocol" },
    { 0x8027,   "DECnet Phase IV Control Protocol" },
    { 0x8029,   "Appletalk Control Protocol" },
    { 0x802b,   "Novell IPX Control Protocol" },
    { 0x8031,   "Bridging NCP" },
    { 0x8033,   "Stream Protocol Control Protocol" },
    { 0x8035,   "Banyan Vines Control Protocol" },
    { 0x803d,   "Multi-Link Control Protocol" },
    { 0x803f,   "NETBIOS Framing Control Protocol" },
    { 0x8041,   "Cisco Systems Control Protocol" },
    { 0x8043,   "Ascom Timeplex" },
    { 0x8045,   "Fujitsu LBLB Control Protocol" },
    { 0x8047,   "DCA Remote Lan Network Control Protocol (RLNCP)" },
    { 0x8049,   "Serial Data Control Protocol (PPP-SDCP)" },
    { 0x804b,   "SNA over 802.2 Control Protocol" },
    { 0x804d,   "SNA Control Protocol" },
    { 0x804f,   "IP6 Header Compression Control Protocol" },
    { 0x8051,   "KNX Bridging Control Protocol" },
    { 0x8053,   "Encryption Control Protocol" },
    { 0x8055,   "Individual Link Encryption Control Protocol" },
    { 0x8057,   "IPv6 Control Protocol" },
    { 0x8059,   "PPP Muxing Control Protocol" },
    { 0x805b,   "Vendor-Specific Network Control Protocol (VSNCP)" },
    { 0x806f,   "Stampede Bridging Control Protocol" },
    { 0x8073,   "MP+ Control Protocol" },
    { 0x80c1,   "NTCITS IPI Control Protocol" },
    { 0x80fb,   "Single Link Compression Control Protocol" },
    { 0x80fd,   "Compression Control Protocol" },
    { 0x8207,   "Cisco Discovery Protocol Control" },
    { 0x8209,   "Netcs Twin Routing" },
    { 0x820b,   "STP - Control Protocol" },
    { 0x820d,   "EDPCP - Extreme Discovery Protocol Ctrl Prtcl" },
    { 0x8235,   "Apple Client Server Protocol Control" },
    { 0x8281,   "MPLSCP" },
    { 0x8285,   "IEEE p1284.4 standard - Protocol Control" },
    { 0x8287,   "ETSI TETRA TNP1 Control Protocol" },
    { 0x8289,   "Multichannel Flow Treatment Protocol" },
    { 0xc021,   "Link Control Protocol" },
    { 0xc023,   "Password Authentication Protocol" },
    { 0xc025,   "Link Quality Report" },
    { 0xc027,   "Shiva Password Authentication Protocol" },
    { 0xc029,   "CallBack Control Protocol (CBCP)" },
    { 0xc02b,   "BACP Bandwidth Allocation Control Protocol" },
    { 0xc02d,   "BAP" },
    { 0xc05b,   "Vendor-Specific Authentication Protocol (VSAP)" },
    { 0xc081,   "Container Control Protocol" },
    { 0xc223,   "Challenge Handshake Authentication Protocol" },
    { 0xc225,   "RSA Authentication Protocol" },
    { 0xc227,   "Extensible Authentication Protocol" },
    { 0xc229,   "Mitsubishi Security Info Exch Ptcl (SIEP)" },
    { 0xc26f,   "Stampede Bridging Authorization Protocol" },
    { 0xc281,   "Proprietary Authentication Protocol" },
    { 0xc283,   "Proprietary Authentication Protocol" },
    { 0xc481,   "Proprietary Node ID Authentication Protocol" },
    { 0,        NULL },
};

/*
 * protocol_name - find a name for a PPP protocol.
 */
const char *
protocol_name(int proto)
{
    struct protocol_list *lp;

    for (lp = protocol_list; lp->proto != 0; ++lp)
        if (proto == lp->proto)
            return lp->name;
    return NULL;
}

/*
 * get_input - called when incoming data is available.
 */
static void
get_input(void)
{
    int len, i;
    u_char *p;
    u_short protocol;
    struct protent *protp;

    p = inpacket_buf;   /* point to beginning of packet buffer */

    len = read_packet(inpacket_buf);
    if (len < 0)
        return;

    if (len == 0) {
        if (bundle_eof && multilink_master) {
            notice("Last channel has disconnected");
            mp_bundle_terminated();
            return;
        }
        notice("Modem hangup");
        hungup = 1;
        status = EXIT_HANGUP;
        lcp_lowerdown(0);       /* serial link is no longer available */
        link_terminated(0);
        return;
    }

    if (len < PPP_HDRLEN) {
        dbglog("received short packet:%.*B", len, p);
        return;
    }

    dump_packet("rcvd", p, len);
    if (snoop_recv_hook) snoop_recv_hook(p, len);

    p += 2;                             /* Skip address and control */
    GETSHORT(protocol, p);
    len -= PPP_HDRLEN;

    /*
     * Toss all non-LCP packets unless LCP is OPEN.
     */
    if (protocol != PPP_LCP && lcp_fsm[0].state != OPENED) {
        dbglog("Discarded non-LCP packet when LCP not open");
        return;
    }

    /*
     * Until we get past the authentication phase, toss all packets
     * except LCP, LQR and authentication packets.
     */
    if (phase <= PHASE_AUTHENTICATE
        && !(protocol == PPP_LCP || protocol == PPP_LQR
             || protocol == PPP_PAP || protocol == PPP_CHAP ||
                protocol == PPP_EAP)) {
        dbglog("discarding proto 0x%x in phase %d",
                   protocol, phase);
        return;
    }

    /*
     * Upcall the proper protocol input routine.
     */
    for (i = 0; (protp = protocols[i]) != NULL; ++i) {
        if (protp->protocol == protocol && protp->enabled_flag) {
            (*protp->input)(0, p, len);
            return;
        }
        if (protocol == (protp->protocol & ~0x8000) && protp->enabled_flag
            && protp->datainput != NULL) {
            (*protp->datainput)(0, p, len);
            return;
        }
    }

    if (debug) {
        const char *pname = protocol_name(protocol);
        if (pname != NULL)
            warn("Unsupported protocol '%s' (0x%x) received", pname, protocol);
        else
            warn("Unsupported protocol 0x%x received", protocol);
    }
    lcp_sprotrej(0, p - PPP_HDRLEN, len + PPP_HDRLEN);
}

/*
 * ppp_send_config - configure the transmit-side characteristics of
 * the ppp interface.  Returns -1, indicating an error, if the channel
 * send_config procedure called error() (or incremented error_count
 * itself), otherwise 0.
 */
int
ppp_send_config(int unit, int mtu, u_int32_t accm, int pcomp, int accomp)
{
        int errs;

        if (the_channel->send_config == NULL)
                return 0;
        errs = error_count;
        (*the_channel->send_config)(mtu, accm, pcomp, accomp);
        return (error_count != errs)? -1: 0;
}

/*
 * ppp_recv_config - configure the receive-side characteristics of
 * the ppp interface.  Returns -1, indicating an error, if the channel
 * recv_config procedure called error() (or incremented error_count
 * itself), otherwise 0.
 */
int
ppp_recv_config(int unit, int mru, u_int32_t accm, int pcomp, int accomp)
{
        int errs;

        if (the_channel->recv_config == NULL)
                return 0;
        errs = error_count;
        (*the_channel->recv_config)(mru, accm, pcomp, accomp);
        return (error_count != errs)? -1: 0;
}

/*
 * new_phase - signal the start of a new phase of pppd's operation.
 */
void
new_phase(int p)
{
    phase = p;
    if (new_phase_hook)
        (*new_phase_hook)(p);
    notify(phasechange, p);
}

/*
 * die - clean up state and exit with the specified status.
 */
void
die(int status)
{
    if (!doing_multilink || multilink_master)
        print_link_stats();
    cleanup();
    notify(exitnotify, status);
    syslog(LOG_INFO, "Exit.");
    exit(status);
}

/*
 * cleanup - restore anything which needs to be restored before we exit
 */
/* ARGSUSED */
static void
cleanup(void)
{
    sys_cleanup();

    if (fd_ppp >= 0)
        the_channel->disestablish_ppp(devfd);
    if (the_channel->cleanup)
        (*the_channel->cleanup)();
    remove_pidfiles();

#ifdef USE_TDB
    if (pppdb != NULL)
        cleanup_db();
#endif

}

void
print_link_stats(void)
{
    /*
     * Print connect time and statistics.
     */
    if (link_stats_valid) {
       int t = (link_connect_time + 5) / 6;    /* 1/10ths of minutes */
       info("Connect time %d.%d minutes.", t/10, t%10);
       info("Sent %u bytes, received %u bytes.",
            link_stats.bytes_out, link_stats.bytes_in);
       link_stats_valid = 0;
    }
}

/*
 * reset_link_stats - "reset" stats when link goes up.
 */
void
reset_link_stats(int u)
{
    if (!get_ppp_stats(u, &old_link_stats))
        return;
    get_time(&start_time);
}

/*
 * update_link_stats - get stats at link termination.
 */
void
update_link_stats(int u)
{
    struct timeval now;
    char numbuf[32];

    if (!get_ppp_stats(u, &link_stats)
        || get_time(&now) < 0)
        return;
    link_connect_time = now.tv_sec - start_time.tv_sec;
    link_stats_valid = 1;

    link_stats.bytes_in  -= old_link_stats.bytes_in;
    link_stats.bytes_out -= old_link_stats.bytes_out;
    link_stats.pkts_in   -= old_link_stats.pkts_in;
    link_stats.pkts_out  -= old_link_stats.pkts_out;

    slprintf(numbuf, sizeof(numbuf), "%u", link_connect_time);
    script_setenv("CONNECT_TIME", numbuf, 0);
    snprintf(numbuf, sizeof(numbuf), "%" PRIu64, link_stats.bytes_out);
    script_setenv("BYTES_SENT", numbuf, 0);
    snprintf(numbuf, sizeof(numbuf), "%" PRIu64, link_stats.bytes_in);
    script_setenv("BYTES_RCVD", numbuf, 0);
}


struct  callout {
    struct timeval      c_time;         /* time at which to call routine */
    void                *c_arg;         /* argument to routine */
    void                (*c_func)(void *); /* routine */
    struct              callout *c_next;
};

static struct callout *callout = NULL;  /* Callout list */
static struct timeval timenow;          /* Current time */

/*
 * timeout - Schedule a timeout.
 */
void
timeout(void (*func)(void *), void *arg, int secs, int usecs)
{
    struct callout *newp, *p, **pp;

    /*
     * Allocate timeout.
     */
    if ((newp = (struct callout *) malloc(sizeof(struct callout))) == NULL)
        fatal("Out of memory in timeout()!");
    newp->c_arg = arg;
    newp->c_func = func;
    get_time(&timenow);
    newp->c_time.tv_sec = timenow.tv_sec + secs;
    newp->c_time.tv_usec = timenow.tv_usec + usecs;
    if (newp->c_time.tv_usec >= 1000000) {
        newp->c_time.tv_sec += newp->c_time.tv_usec / 1000000;
        newp->c_time.tv_usec %= 1000000;
    }

    /*
     * Find correct place and link it in.
     */
    for (pp = &callout; (p = *pp); pp = &p->c_next)
        if (newp->c_time.tv_sec < p->c_time.tv_sec
            || (newp->c_time.tv_sec == p->c_time.tv_sec
                && newp->c_time.tv_usec < p->c_time.tv_usec))
            break;
    newp->c_next = p;
    *pp = newp;
}


/*
 * untimeout - Unschedule a timeout.
 */
void
untimeout(void (*func)(void *), void *arg)
{
    struct callout **copp, *freep;

    /*
     * Find first matching timeout and remove it from the list.
     */
    for (copp = &callout; (freep = *copp); copp = &freep->c_next)
        if (freep->c_func == func && freep->c_arg == arg) {
            *copp = freep->c_next;
            free((char *) freep);
            break;
        }
}


/*
 * calltimeout - Call any timeout routines which are now due.
 */
static void
calltimeout(void)
{
    struct callout *p;

    while (callout != NULL) {
        p = callout;

        if (get_time(&timenow) < 0)
            fatal("Failed to get time of day: %m");
        if (!(p->c_time.tv_sec < timenow.tv_sec
              || (p->c_time.tv_sec == timenow.tv_sec
                  && p->c_time.tv_usec <= timenow.tv_usec)))
            break;              /* no, it's not time yet */

        callout = p->c_next;
        (*p->c_func)(p->c_arg);

        free((char *) p);
    }
}


/*
 * timeleft - return the length of time until the next timeout is due.
 */
static struct timeval *
timeleft(struct timeval *tvp)
{
    if (callout == NULL)
        return NULL;

    get_time(&timenow);
    tvp->tv_sec = callout->c_time.tv_sec - timenow.tv_sec;
    tvp->tv_usec = callout->c_time.tv_usec - timenow.tv_usec;
    if (tvp->tv_usec < 0) {
        tvp->tv_usec += 1000000;
        tvp->tv_sec -= 1;
    }
    if (tvp->tv_sec < 0)
        tvp->tv_sec = tvp->tv_usec = 0;

    return tvp;
}


/*
 * kill_my_pg - send a signal to our process group, and ignore it ourselves.
 * We assume that sig is currently blocked.
 */
static void
kill_my_pg(int sig)
{
    struct sigaction act, oldact;
    struct subprocess *chp;

    if (!detached) {
        /*
         * There might be other things in our process group that we
         * didn't start that would get hit if we did a kill(0), so
         * just send the signal individually to our children.
         */
        for (chp = children; chp != NULL; chp = chp->next)
            if (chp->killable)
                kill(chp->pid, sig);
        return;
    }

    /* We've done a setsid(), so we can just use a kill(0) */
    sigemptyset(&act.sa_mask);          /* unnecessary in fact */
    act.sa_handler = SIG_IGN;
    act.sa_flags = 0;
    kill(0, sig);
    /*
     * The kill() above made the signal pending for us, as well as
     * the rest of our process group, but we don't want it delivered
     * to us.  It is blocked at the moment.  Setting it to be ignored
     * will cause the pending signal to be discarded.  If we did the
     * kill() after setting the signal to be ignored, it is unspecified
     * (by POSIX) whether the signal is immediately discarded or left
     * pending, and in fact Linux would leave it pending, and so it
     * would be delivered after the current signal handler exits,
     * leading to an infinite loop.
     */
    sigaction(sig, &act, &oldact);
    sigaction(sig, &oldact, NULL);
}


/*
 * hup - Catch SIGHUP signal.
 *
 * Indicates that the physical layer has been disconnected.
 * We don't rely on this indication; if the user has sent this
 * signal, we just take the link down.
 */
static void
hup(int sig)
{
    /* can't log a message here, it can deadlock */
    got_sighup = 1;
    if (conn_running)
        /* Send the signal to the [dis]connector process(es) also */
        kill_my_pg(sig);
    notify(sigreceived, sig);
    if (waiting) {
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wunused-result"
        write(sigpipe[1], &sig, sizeof(sig));
#pragma GCC diagnostic pop
    }
}


/*
 * term - Catch SIGTERM signal and SIGINT signal (^C/del).
 *
 * Indicates that we should initiate a graceful disconnect and exit.
 */
/*ARGSUSED*/
static void
term(int sig)
{
    /* can't log a message here, it can deadlock */
    got_sigterm = sig;
    if (conn_running)
        /* Send the signal to the [dis]connector process(es) also */
        kill_my_pg(sig);
    notify(sigreceived, sig);
    if (waiting) {
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wunused-result"
        write(sigpipe[1], &sig, sizeof(sig));
#pragma GCC diagnostic pop
    }
}


/*
 * chld - Catch SIGCHLD signal.
 * Sets a flag so we will call reap_kids in the mainline.
 */
static void
chld(int sig)
{
    got_sigchld = 1;
    if (waiting) {
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wunused-result"
        write(sigpipe[1], &sig, sizeof(sig));
#pragma GCC diagnostic pop
    }
}


/*
 * toggle_debug - Catch SIGUSR1 signal.
 *
 * Toggle debug flag.
 */
/*ARGSUSED*/
static void
toggle_debug(int sig)
{
    debug = !debug;
    if (debug) {
        setlogmask(LOG_UPTO(LOG_DEBUG));
    } else {
        setlogmask(LOG_UPTO(LOG_WARNING));
    }
}


/*
 * open_ccp - Catch SIGUSR2 signal.
 *
 * Try to (re)negotiate compression.
 */
/*ARGSUSED*/
static void
open_ccp(int sig)
{
    got_sigusr2 = 1;
    if (waiting) {
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wunused-result"
        write(sigpipe[1], &sig, sizeof(sig));
#pragma GCC diagnostic pop
    }
}


/*
 * bad_signal - We've caught a fatal signal.  Clean up state and exit.
 */
static void
bad_signal(int sig)
{
    static int crashed = 0;

    if (crashed)
        _exit(127);
    crashed = 1;
    error("Fatal signal %d", sig);
    if (conn_running)
        kill_my_pg(SIGTERM);
    notify(sigreceived, sig);
    die(127);
}

/*
 * safe_fork - Create a child process.  The child closes all the
 * file descriptors that we don't want to leak to a script.
 * The parent waits for the child to do this before returning.
 * This also arranges for the specified fds to be dup'd to
 * fds 0, 1, 2 in the child.
 */
pid_t
safe_fork(int infd, int outfd, int errfd)
{
        pid_t pid;
        int fd, pipefd[2];
        char buf[1];

        /* make sure fds 0, 1, 2 are occupied (probably not necessary) */
        while ((fd = dup(fd_devnull)) >= 0) {
                if (fd > 2) {
                        close(fd);
                        break;
                }
        }

        if (pipe(pipefd) == -1)
                pipefd[0] = pipefd[1] = -1;
        pid = fork();
        if (pid < 0) {
                error("fork failed: %m");
                return -1;
        }
        if (pid > 0) {
                /* parent */
                close(pipefd[1]);
                /* this read() blocks until the close(pipefd[1]) below */
                complete_read(pipefd[0], buf, 1);
                close(pipefd[0]);
                return pid;
        }

        /* Executing in the child */
        sys_close();
#ifdef USE_TDB
        if (pppdb != NULL)
                tdb_close(pppdb);
#endif

        /* make sure infd, outfd and errfd won't get tromped on below */
        if (infd == 1 || infd == 2)
                infd = dup(infd);
        if (outfd == 0 || outfd == 2)
                outfd = dup(outfd);
        if (errfd == 0 || errfd == 1)
                errfd = dup(errfd);

        closelog();

        /* dup the in, out, err fds to 0, 1, 2 */
        if (infd != 0)
                dup2(infd, 0);
        if (outfd != 1)
                dup2(outfd, 1);
        if (errfd != 2)
                dup2(errfd, 2);

        if (log_to_fd > 2)
                close(log_to_fd);
        if (the_channel->close)
                (*the_channel->close)();
        else
                close(devfd);   /* some plugins don't have a close function */
        close(fd_ppp);
        close(fd_devnull);
        if (infd != 0)
                close(infd);
        if (outfd != 1)
                close(outfd);
        if (errfd != 2)
                close(errfd);

        notify(fork_notifier, 0);
        close(pipefd[0]);
        /* this close unblocks the read() call above in the parent */
        close(pipefd[1]);

        return 0;
}

static bool
add_script_env(int pos, char *newstring)
{
    if (pos + 1 >= s_env_nalloc) {
        int new_n = pos + 17;
        char **newenv = realloc(script_env, new_n * sizeof(char *));
        if (newenv == NULL) {
            free(newstring - 1);
            return 0;
        }
        script_env = newenv;
        s_env_nalloc = new_n;
    }
    script_env[pos] = newstring;
    script_env[pos + 1] = NULL;
    return 1;
}

static void
remove_script_env(int pos)
{
    free(script_env[pos] - 1);
    while ((script_env[pos] = script_env[pos + 1]) != NULL)
        pos++;
}

/*
 * update_system_environment - process the list of set/unset options
 * and update the system environment.
 */
static void
update_system_environment(void)
{
    struct userenv *uep;

    for (uep = userenv_list; uep != NULL; uep = uep->ue_next) {
        if (uep->ue_isset)
            setenv(uep->ue_name, uep->ue_value, 1);
        else
            unsetenv(uep->ue_name);
    }
}

/*
 * device_script - run a program to talk to the specified fds
 * (e.g. to run the connector or disconnector script).
 * stderr gets connected to the log fd or to the _PATH_CONNERRS file.
 */
int
device_script(char *program, int in, int out, int dont_wait)
{
    int pid;
    int status = -1;
    int errfd;
    int ret;

    if (log_to_fd >= 0)
        errfd = log_to_fd;
    else
        errfd = open(_PATH_CONNERRS, O_WRONLY | O_APPEND | O_CREAT, 0644);

    ++conn_running;
    pid = safe_fork(in, out, errfd);

    if (pid != 0 && log_to_fd < 0)
        close(errfd);

    if (pid < 0) {
        --conn_running;
        error("Failed to create child process: %m");
        return -1;
    }

    if (pid != 0) {
        record_child(pid, program, NULL, NULL, 1);
        status = 0;
        if (!dont_wait) {
            while (waitpid(pid, &status, 0) < 0) {
                if (errno == EINTR)
                    continue;
                fatal("error waiting for (dis)connection process: %m");
            }
            forget_child(pid, status);
            --conn_running;
        }
        return (status == 0 ? 0 : -1);
    }

    /* here we are executing in the child */
    ret = setgid(getgid());
    if (ret != 0) {
        perror("pppd: setgid failed\n");
        exit(1);
    }
    ret = setuid(uid);
    if (ret != 0 || getuid() != uid) {
        perror("pppd: setuid failed\n");
        exit(1);
    }
    update_system_environment();
    execl("/bin/sh", "sh", "-c", program, (char *)0);
    perror("pppd: could not exec /bin/sh");
    _exit(99);
    /* NOTREACHED */
}


/*
 * update_script_environment - process the list of set/unset options
 * and update the script environment.  Note that we intentionally do
 * not update the TDB.  These changes are layered on top right before
 * exec.  It is not possible to use script_setenv() or
 * script_unsetenv() safely after this routine is run.
 */
static void
update_script_environment(void)
{
    struct userenv *uep;

    for (uep = userenv_list; uep != NULL; uep = uep->ue_next) {
        int i;
        char *p, *newstring;
        int nlen = strlen(uep->ue_name);

        for (i = 0; (p = script_env[i]) != NULL; i++) {
            if (strncmp(p, uep->ue_name, nlen) == 0 && p[nlen] == '=')
                break;
        }
        if (uep->ue_isset) {
            nlen += strlen(uep->ue_value) + 2;
            newstring = malloc(nlen + 1);
            if (newstring == NULL)
                continue;
            *newstring++ = 0;
            slprintf(newstring, nlen, "%s=%s", uep->ue_name, uep->ue_value);
            if (p != NULL)
                script_env[i] = newstring;
            else
                add_script_env(i, newstring);
        } else if (p != NULL) {
            remove_script_env(i);
        }
    }
}

/*
 * run_program - execute a program with given arguments,
 * but don't wait for it unless wait is non-zero.
 * If the program can't be executed, logs an error unless
 * must_exist is 0 and the program file doesn't exist.
 * Returns -1 if it couldn't fork, 0 if the file doesn't exist
 * or isn't an executable plain file, or the process ID of the child.
 * If done != NULL, (*done)(arg) will be called later (within
 * reap_kids) iff the return value is > 0.
 */
pid_t
run_program(char *prog, char **args, int must_exist, void (*done)(void *), void *arg, int wait)
{
    int pid, status, ret;
    struct stat sbuf;

    /*
     * First check if the file exists and is executable.
     * We don't use access() because that would use the
     * real user-id, which might not be root, and the script
     * might be accessible only to root.
     */
    errno = EINVAL;
    if (stat(prog, &sbuf) < 0 || !S_ISREG(sbuf.st_mode)
        || (sbuf.st_mode & (S_IXUSR|S_IXGRP|S_IXOTH)) == 0) {
        if (must_exist || errno != ENOENT)
            warn("Can't execute %s: %m", prog);
        return 0;
    }

    pid = safe_fork(fd_devnull, fd_devnull, fd_devnull);
    if (pid == -1) {
        error("Failed to create child process for %s: %m", prog);
        return -1;
    }
    if (pid != 0) {
        if (debug)
            dbglog("Script %s started (pid %d)", prog, pid);
        record_child(pid, prog, done, arg, 0);
        if (wait) {
            while (waitpid(pid, &status, 0) < 0) {
                if (errno == EINTR)
                    continue;
                fatal("error waiting for script %s: %m", prog);
            }
            forget_child(pid, status);
        }
        return pid;
    }

    /* Leave the current location */
    (void) setsid();    /* No controlling tty. */
    (void) umask (S_IRWXG|S_IRWXO);
    ret = chdir ("/");  /* no current directory. */
    if (ret != 0) {
        fatal("Failed to change directory to '/', %m");
    }
    ret = setuid(0);            /* set real UID = root */
    if (ret != 0) {
        fatal("Failed to set uid, %m");
    }
    ret = setgid(getegid());
    if (ret != 0) {
        fatal("failed to set gid, %m");
    }

#ifdef BSD
    /* Force the priority back to zero if pppd is running higher. */
    if (setpriority (PRIO_PROCESS, 0, 0) < 0)
        warn("can't reset priority to 0: %m");
#endif

    /* run the program */
    update_script_environment();
    execve(prog, args, script_env);
    if (must_exist || errno != ENOENT) {
        /* have to reopen the log, there's nowhere else
           for the message to go. */
        reopen_log();
        syslog(LOG_ERR, "Can't execute %s: %m", prog);
        closelog();
    }
    _exit(99);
}


/*
 * record_child - add a child process to the list for reap_kids
 * to use.
 */
void
record_child(int pid, char *prog, void (*done)(void *), void *arg, int killable)
{
    struct subprocess *chp;

    ++n_children;

    chp = (struct subprocess *) malloc(sizeof(struct subprocess));
    if (chp == NULL) {
        warn("losing track of %s process", prog);
    } else {
        chp->pid = pid;
        chp->prog = prog;
        chp->done = done;
        chp->arg = arg;
        chp->next = children;
        chp->killable = killable;
        children = chp;
    }
}

/*
 * childwait_end - we got fed up waiting for the child processes to
 * exit, send them all a SIGTERM.
 */
static void
childwait_end(void *arg)
{
    struct subprocess *chp;

    for (chp = children; chp != NULL; chp = chp->next) {
        if (debug)
            dbglog("sending SIGTERM to process %d", chp->pid);
        kill(chp->pid, SIGTERM);
    }
    childwait_done = 1;
}

/*
 * forget_child - clean up after a dead child
 */
static void
forget_child(int pid, int status)
{
    struct subprocess *chp, **prevp;

    for (prevp = &children; (chp = *prevp) != NULL; prevp = &chp->next) {
        if (chp->pid == pid) {
            --n_children;
            *prevp = chp->next;
            break;
        }
    }
    if (WIFSIGNALED(status)) {
        warn("Child process %s (pid %d) terminated with signal %d",
             (chp? chp->prog: "??"), pid, WTERMSIG(status));
    } else if (debug)
        dbglog("Script %s finished (pid %d), status = 0x%x",
               (chp? chp->prog: "??"), pid,
               WIFEXITED(status) ? WEXITSTATUS(status) : status);
    if (chp && chp->done)
        (*chp->done)(chp->arg);
    if (chp)
        free(chp);
}

/*
 * reap_kids - get status from any dead child processes,
 * and log a message for abnormal terminations.
 */
static int
reap_kids(void)
{
    int pid, status;

    if (n_children == 0)
        return 0;
    while ((pid = waitpid(-1, &status, WNOHANG)) != -1 && pid != 0) {
        forget_child(pid, status);
    }
    if (pid == -1) {
        if (errno == ECHILD)
            return -1;
        if (errno != EINTR)
            error("Error waiting for child process: %m");
    }
    return 0;
}

/*
 * add_notifier - add a new function to be called when something happens.
 */
void
add_notifier(struct notifier **notif, notify_func func, void *arg)
{
    struct notifier *np;

    np = malloc(sizeof(struct notifier));
    if (np == 0)
        novm("notifier struct");
    np->next = *notif;
    np->func = func;
    np->arg = arg;
    *notif = np;
}

/*
 * remove_notifier - remove a function from the list of things to
 * be called when something happens.
 */
void
remove_notifier(struct notifier **notif, notify_func func, void *arg)
{
    struct notifier *np;

    for (; (np = *notif) != 0; notif = &np->next) {
        if (np->func == func && np->arg == arg) {
            *notif = np->next;
            free(np);
            break;
        }
    }
}

/*
 * notify - call a set of functions registered with add_notifier.
 */
void
notify(struct notifier *notif, int val)
{
    struct notifier *np;

    while ((np = notif) != 0) {
        notif = np->next;
        (*np->func)(np->arg, val);
    }
}

/*
 * novm - log an error message saying we ran out of memory, and die.
 */
void
novm(char *msg)
{
    fatal("Virtual memory exhausted allocating %s\n", msg);
}

/*
 * script_setenv - set an environment variable value to be used
 * for scripts that we run (e.g. ip-up, auth-up, etc.)
 */
void
script_setenv(char *var, char *value, int iskey)
{
    size_t varl = strlen(var);
    size_t vl = varl + strlen(value) + 2;
    int i;
    char *p, *newstring;

    newstring = (char *) malloc(vl+1);
    if (newstring == 0)
        return;
    *newstring++ = iskey;
    slprintf(newstring, vl, "%s=%s", var, value);

    /* check if this variable is already set */
    if (script_env != 0) {
        for (i = 0; (p = script_env[i]) != 0; ++i) {
            if (strncmp(p, var, varl) == 0 && p[varl] == '=') {
#ifdef USE_TDB
                if (p[-1] && pppdb != NULL)
                    delete_db_key(p);
#endif
                free(p-1);
                script_env[i] = newstring;
#ifdef USE_TDB
                if (pppdb != NULL) {
                    if (iskey)
                        add_db_key(newstring);
                    update_db_entry();
                }
#endif
                return;
            }
        }
    } else {
        /* no space allocated for script env. ptrs. yet */
        i = 0;
        script_env = malloc(16 * sizeof(char *));
        if (script_env == 0) {
            free(newstring - 1);
            return;
        }
        s_env_nalloc = 16;
    }

    if (!add_script_env(i, newstring))
        return;

#ifdef USE_TDB
    if (pppdb != NULL) {
        if (iskey)
            add_db_key(newstring);
        update_db_entry();
    }
#endif
}

/*
 * script_unsetenv - remove a variable from the environment
 * for scripts.
 */
void
script_unsetenv(char *var)
{
    int vl = strlen(var);
    int i;
    char *p;

    if (script_env == 0)
        return;
    for (i = 0; (p = script_env[i]) != 0; ++i) {
        if (strncmp(p, var, vl) == 0 && p[vl] == '=') {
#ifdef USE_TDB
            if (p[-1] && pppdb != NULL)
                delete_db_key(p);
#endif
            remove_script_env(i);
            break;
        }
    }
#ifdef USE_TDB
    if (pppdb != NULL)
        update_db_entry();
#endif
}

/*
 * Any arbitrary string used as a key for locking the database.
 * It doesn't matter what it is as long as all pppds use the same string.
 */
#define PPPD_LOCK_KEY   "pppd lock"

/*
 * lock_db - get an exclusive lock on the TDB database.
 * Used to ensure atomicity of various lookup/modify operations.
 */
void lock_db(void)
{
#ifdef USE_TDB
        TDB_DATA key;

        key.dptr = PPPD_LOCK_KEY;
        key.dsize = strlen(key.dptr);
        tdb_chainlock(pppdb, key);
#endif
}

/*
 * unlock_db - remove the exclusive lock obtained by lock_db.
 */
void unlock_db(void)
{
#ifdef USE_TDB
        TDB_DATA key;

        key.dptr = PPPD_LOCK_KEY;
        key.dsize = strlen(key.dptr);
        tdb_chainunlock(pppdb, key);
#endif
}

#ifdef USE_TDB
/*
 * update_db_entry - update our entry in the database.
 */
static void
update_db_entry(void)
{
    TDB_DATA key, dbuf;
    int vlen, i;
    char *p, *q, *vbuf;

    if (script_env == NULL)
        return;
    vlen = 0;
    for (i = 0; (p = script_env[i]) != 0; ++i)
        vlen += strlen(p) + 1;
    vbuf = malloc(vlen + 1);
    if (vbuf == 0)
        novm("database entry");
    q = vbuf;
    for (i = 0; (p = script_env[i]) != 0; ++i)
        q += slprintf(q, vbuf + vlen - q, "%s;", p);

    key.dptr = db_key;
    key.dsize = strlen(db_key);
    dbuf.dptr = vbuf;
    dbuf.dsize = vlen;
    if (tdb_store(pppdb, key, dbuf, TDB_REPLACE))
        error("tdb_store failed: %s", tdb_errorstr(pppdb));

    if (vbuf)
        free(vbuf);

}

/*
 * add_db_key - add a key that we can use to look up our database entry.
 */
static void
add_db_key(const char *str)
{
    TDB_DATA key, dbuf;

    key.dptr = (char *) str;
    key.dsize = strlen(str);
    dbuf.dptr = db_key;
    dbuf.dsize = strlen(db_key);
    if (tdb_store(pppdb, key, dbuf, TDB_REPLACE))
        error("tdb_store key failed: %s", tdb_errorstr(pppdb));
}

/*
 * delete_db_key - delete a key for looking up our database entry.
 */
static void
delete_db_key(const char *str)
{
    TDB_DATA key;

    key.dptr = (char *) str;
    key.dsize = strlen(str);
    tdb_delete(pppdb, key);
}

/*
 * cleanup_db - delete all the entries we put in the database.
 */
static void
cleanup_db(void)
{
    TDB_DATA key;
    int i;
    char *p;

    key.dptr = db_key;
    key.dsize = strlen(db_key);
    tdb_delete(pppdb, key);
    for (i = 0; (p = script_env[i]) != 0; ++i)
        if (p[-1])
            delete_db_key(p);
}
#endif /* USE_TDB */