xref: /freebsd-11-stable/usr.sbin/ppp/main.c

/*
 *			User Process PPP
 *
 *	    Written by Toshiharu OHNO (tony-o@iij.ad.jp)
 *
 *   Copyright (C) 1993, Internet Initiative Japan, Inc. All rights reserverd.
 *
 * Redistribution and use in source and binary forms are permitted
 * provided that the above copyright notice and this paragraph are
 * duplicated in all such forms and that any documentation,
 * advertising materials, and other materials related to such
 * distribution and use acknowledge that the software was developed
 * by the Internet Initiative Japan, Inc.  The name of the
 * IIJ may not be used to endorse or promote products derived
 * from this software without specific prior written permission.
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 *
 * $Id: main.c,v 1.54 1997/05/23 04:54:03 brian Exp $
 *
 *	TODO:
 *		o Add commands for traffic summary, version display, etc.
 *		o Add signal handler for misc controls.
 */
#include "fsm.h"
#include <fcntl.h>
#include <paths.h>
#include <sys/time.h>
#include <termios.h>
#include <signal.h>
#include <sys/wait.h>
#include <errno.h>
#include <netdb.h>
#include <unistd.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <alias.h>
#include "modem.h"
#include "os.h"
#include "hdlc.h"
#include "ccp.h"
#include "lcp.h"
#include "ipcp.h"
#include "vars.h"
#include "auth.h"
#include "filter.h"
#include "systems.h"
#include "ip.h"
#include "sig.h"

#define LAUTH_M1 "Warning: No password entry for this host in ppp.secret\n"
#define LAUTH_M2 "Warning: All manipulation is allowed by anyone in the world\n"

#ifndef O_NONBLOCK
#ifdef O_NDELAY
#define	O_NONBLOCK O_NDELAY
#endif
#endif

extern void VjInit(), AsyncInit();
extern void AsyncInput();
extern int  SelectSystem();

extern void DecodeCommand(), Prompt();
extern int aft_cmd;
extern int IsInteractive();
static void DoLoop(void);
static void TerminalStop();
static char *ex_desc();

static struct termios oldtio;		/* Original tty mode */
static struct termios comtio;		/* Command level tty mode */
int TermMode;
static int server;
static pid_t BGPid = 0;
struct sockaddr_in ifsin;
static char pid_filename[MAXPATHLEN];
static char if_filename[MAXPATHLEN];
int tunno;

static void
TtyInit()
{
  struct termios newtio;
  int stat;

  stat = fcntl(0, F_GETFL, 0);
  if (stat > 0) {
	 stat |= O_NONBLOCK;
	 (void)fcntl(0, F_SETFL, stat);
  }
  newtio = oldtio;
  newtio.c_lflag &= ~(ECHO|ISIG|ICANON);
  newtio.c_iflag = 0;
  newtio.c_oflag &= ~OPOST;
  newtio.c_cc[VEOF] = _POSIX_VDISABLE;
  newtio.c_cc[VINTR] = _POSIX_VDISABLE;
  newtio.c_cc[VMIN] = 1;
  newtio.c_cc[VTIME] = 0;
  newtio.c_cflag |= CS8;
  tcsetattr(0, TCSADRAIN, &newtio);
  comtio = newtio;
}

/*
 *  Set tty into command mode. We allow canonical input and echo processing.
 */
void
TtyCommandMode(prompt)
int prompt;
{
  struct termios newtio;
  int stat;

  if (!(mode & MODE_INTER))
    return;
  tcgetattr(0, &newtio);
  newtio.c_lflag |= (ECHO|ISIG|ICANON);
  newtio.c_iflag = oldtio.c_iflag;
  newtio.c_oflag |= OPOST;
  tcsetattr(0, TCSADRAIN, &newtio);
  stat = fcntl(0, F_GETFL, 0);
  if (stat > 0) {
	 stat |= O_NONBLOCK;
	 (void)fcntl(0, F_SETFL, stat);
  }
  TermMode = 0;
  if(prompt) Prompt();
}

/*
 * Set tty into terminal mode which is used while we invoke term command.
 */
void
TtyTermMode()
{
  int stat;

  tcsetattr(0, TCSADRAIN, &comtio);
  stat = fcntl(0, F_GETFL, 0);
  if (stat > 0) {
	 stat &= ~O_NONBLOCK;
	 (void)fcntl(0, F_SETFL, stat);
  }
  TermMode = 1;
}

void
TtyOldMode()
{
  int stat;

  stat = fcntl(0, F_GETFL, 0);
  if (stat > 0) {
	  stat &= ~O_NONBLOCK;
	  (void)fcntl(0, F_SETFL, stat);
  }
  tcsetattr(0, TCSANOW, &oldtio);
}

void
Cleanup(excode)
int excode;
{

  OsLinkdown();
  OsCloseLink(1);
  sleep(1);
  if (mode & MODE_AUTO)
    DeleteIfRoutes(1);
  (void)unlink(pid_filename);
  (void)unlink(if_filename);
  OsInterfaceDown(1);
  if (mode & MODE_BACKGROUND && BGFiledes[1] != -1) {
    char c = EX_ERRDEAD;
    if (write(BGFiledes[1],&c,1) == 1)
      LogPrintf(LOG_PHASE_BIT,"Parent notified of failure.\n");
    else
      LogPrintf(LOG_PHASE_BIT,"Failed to notify parent of failure.\n");
    close(BGFiledes[1]);
  }
  LogPrintf(LOG_PHASE_BIT, "PPP Terminated (%s).\n",ex_desc(excode));
  LogClose();
  if (server >= 0) {
    close(server);
    server = -1;
  }

  TtyOldMode();

  exit(excode);
}

static void
Hangup(signo)
int signo;
{
  if (signo == SIGSEGV) {
	LogPrintf(LOG_PHASE_BIT, "Signal %d, core dump.\n", signo);
	LogClose();
	abort();
  }
  if (BGPid) {
      kill (BGPid, SIGTERM);
      exit (EX_HANGUP);
  }
  else {
      LogPrintf(LOG_PHASE_BIT, "Signal %d, hangup.\n", signo);
      Cleanup(EX_HANGUP);
  }
}

static void
CloseSession(signo)
int signo;
{
   if (BGPid) {
     kill (BGPid, SIGINT);
     exit (EX_TERM);
   }
   else {
     LogPrintf(LOG_PHASE_BIT, "Signal %d, terminate.\n", signo);
     LcpClose();
     reconnectCount = 0;
     Cleanup(EX_TERM);
   }
}

static void
TerminalCont()
{
  pending_signal(SIGCONT, SIG_DFL);
  pending_signal(SIGTSTP, TerminalStop);
  TtyCommandMode(getpgrp() == tcgetpgrp(0));
}

static void
TerminalStop(signo)
int signo;
{
  pending_signal(SIGCONT, TerminalCont);
  TtyOldMode();
  pending_signal(SIGTSTP, SIG_DFL);
  kill(getpid(), signo);
}

static char *
ex_desc(int ex)
{
  static char num[12];
  static char *desc[] = { "normal", "start", "sock",
    "modem", "dial", "dead", "done", "reboot", "errdead",
    "hangup", "term", "nodial", "nologin" };

  if (ex >= 0 && ex < sizeof(desc)/sizeof(*desc))
    return desc[ex];
  snprintf(num, sizeof num, "%d", ex);
  return num;
}

void
Usage()
{
  fprintf(stderr,
          "Usage: ppp [-auto | -background | -direct | -dedicated | -ddial ] [ -alias ] [system]\n");
  exit(EX_START);
}

void
ProcessArgs(int argc, char **argv)
{
  int optc;
  char *cp;

  optc = 0;
  while (argc > 0 && **argv == '-') {
    cp = *argv + 1;
    if (strcmp(cp, "auto") == 0)
      mode |= MODE_AUTO;
    else if (strcmp(cp, "background") == 0)
      mode |= MODE_BACKGROUND|MODE_AUTO;
    else if (strcmp(cp, "direct") == 0)
      mode |= MODE_DIRECT;
    else if (strcmp(cp, "dedicated") == 0)
      mode |= MODE_DEDICATED;
    else if (strcmp(cp, "ddial") == 0)
      mode |= MODE_DDIAL|MODE_AUTO;
    else if (strcmp(cp, "alias") == 0) {
      mode |= MODE_ALIAS;
      optc--;             /* this option isn't exclusive */
    }
    else
      Usage();
    optc++;
    argv++; argc--;
  }
  if (argc > 1) {
    fprintf(stderr, "specify only one system label.\n");
    exit(EX_START);
  }
  if (argc == 1) dstsystem = *argv;

  if (optc > 1) {
    fprintf(stderr, "specify only one mode.\n");
    exit(EX_START);
  }
}

static void
Greetings()
{
  printf("User Process PPP. Written by Toshiharu OHNO.\r\n");
  fflush(stdout);
}

void
main(argc, argv)
int argc;
char **argv;
{
  FILE *lockfile;
  argc--; argv++;

  mode = MODE_INTER;		/* default operation is interactive mode */
  netfd = server = modem = tun_in = -1;
  ProcessArgs(argc, argv);
  Greetings();
  GetUid();
  IpcpDefAddress();
  InitPacketAlias();

  if (SelectSystem("default", CONFFILE) < 0) {
    fprintf(stderr, "Warning: No default entry is given in config file.\n");
  }

  switch ( LocalAuthInit() ) {
    case NOT_FOUND:
    	fprintf(stderr,LAUTH_M1);
    	fprintf(stderr,LAUTH_M2);
	fflush (stderr);
	/* Fall down */
    case VALID:
	VarLocalAuth = LOCAL_AUTH;
	break;
    default:
	break;
  }

  if (OpenTunnel(&tunno) < 0) {
    perror("open_tun");
    exit(EX_START);
  }

  if (mode & (MODE_AUTO|MODE_DIRECT|MODE_DEDICATED))
    mode &= ~MODE_INTER;
  if (mode & MODE_INTER) {
    printf("Interactive mode\n");
    netfd = STDIN_FILENO;
  } else if (mode & MODE_AUTO) {
    printf("Automatic Dialer mode\n");
    if (dstsystem == NULL) {
      fprintf(stderr, "Destination system must be specified in"
              " auto, background or ddial mode.\n");
      exit(EX_START);
    }
  }

  tcgetattr(0, &oldtio);		/* Save original tty mode */

  pending_signal(SIGHUP, LogReOpen);
  pending_signal(SIGTERM, CloseSession);
  pending_signal(SIGINT, CloseSession);
  pending_signal(SIGQUIT, CloseSession);
#ifdef SIGSEGV
  signal(SIGSEGV, Hangup);
#endif
#ifdef SIGPIPE
  signal(SIGPIPE, SIG_IGN);
#endif
#ifdef SIGALRM
  pending_signal(SIGALRM, SIG_IGN);
#endif
  if(mode & MODE_INTER)
    {
#ifdef SIGTSTP
      pending_signal(SIGTSTP, TerminalStop);
#endif
#ifdef SIGTTIN
      pending_signal(SIGTTIN, TerminalStop);
#endif
#ifdef SIGTTOU
      pending_signal(SIGTTOU, SIG_IGN);
#endif
    }

  if (dstsystem) {
    if (SelectSystem(dstsystem, CONFFILE) < 0) {
      fprintf(stderr, "Destination system not found in conf file.\n");
      Cleanup(EX_START);
    }
    if ((mode & MODE_AUTO) && DefHisAddress.ipaddr.s_addr == INADDR_ANY) {
      fprintf(stderr, "Must specify dstaddr with"
              " auto, background or ddial mode.\n");
      Cleanup(EX_START);
    }
  }
  if (mode & MODE_DIRECT)
    printf("Packet mode enabled.\n");

  if (!(mode & MODE_INTER)) {
    int port = SERVER_PORT + tunno;

    if (mode & MODE_BACKGROUND) {
      if (pipe (BGFiledes)) {
	perror("pipe");
	Cleanup(EX_SOCK);
      }
    }

    /* Create server socket and listen at there. */
    server = socket(PF_INET, SOCK_STREAM, 0);
    if (server < 0) {
      perror("socket");
      Cleanup(EX_SOCK);
    }
    ifsin.sin_family = AF_INET;
    ifsin.sin_addr.s_addr = INADDR_ANY;
    ifsin.sin_port = htons(port);
    setsockopt(server, SOL_SOCKET, SO_REUSEADDR, &server, sizeof server);
    if (bind(server, (struct sockaddr *) &ifsin, sizeof(ifsin)) < 0) {
      perror("bind");
      if (errno == EADDRINUSE)
        fprintf(stderr, "Wait for a while, then try again.\n");
      Cleanup(EX_SOCK);
    }
    if (listen(server, 5) != 0) {
      fprintf(stderr, "Unable to listen to socket - OS overload?\n");
    }

    DupLog();
    if (!(mode & MODE_DIRECT)) {
      pid_t bgpid;

      bgpid = fork ();
      if (bgpid == -1) {
	perror ("fork");
	Cleanup (EX_SOCK);
      }
      if (bgpid) {
	char c = EX_NORMAL;

	if (mode & MODE_BACKGROUND) {
	  /* Wait for our child to close its pipe before we exit. */
	  BGPid = bgpid;
          close (BGFiledes[1]);
	  if (read(BGFiledes[0], &c, 1) != 1) {
	    printf("Child exit, no status.\n");
	    LogPrintf (LOG_PHASE_BIT, "Parent: Child exit, no status.\n");
	  } else if (c == EX_NORMAL) {
	    printf("PPP enabled.\n");
	    LogPrintf (LOG_PHASE_BIT, "Parent: PPP enabled.\n");
	  } else {
	    printf("Child failed (%s).\n",ex_desc((int)c));
	    LogPrintf(LOG_PHASE_BIT, "Parent: Child failed (%s).\n",
                      ex_desc((int)c));
          }
          close (BGFiledes[0]);
	}
        exit(c);
      } else if (mode & MODE_BACKGROUND)
          close(BGFiledes[0]);
    }

    snprintf(pid_filename, sizeof (pid_filename), "%stun%d.pid",
             _PATH_VARRUN, tunno);
    (void)unlink(pid_filename);

    if ((lockfile = fopen(pid_filename, "w")) != NULL) {
      fprintf(lockfile, "%d\n", (int)getpid());
      fclose(lockfile);
    } else
      logprintf("Warning: Can't create %s: %s\n", pid_filename, strerror(errno));

    snprintf(if_filename, sizeof if_filename, "%s%s.if",
             _PATH_VARRUN, VarBaseDevice);
    (void)unlink(if_filename);

    if ((lockfile = fopen(if_filename, "w")) != NULL) {
      fprintf(lockfile, "tun%d\n", tunno);
      fclose(lockfile);
    } else
      logprintf("Warning: Can't create %s: %s\n", if_filename, strerror(errno));

    if (server >= 0)
	LogPrintf(LOG_PHASE_BIT, "Listening at %d.\n", port);
#ifdef DOTTYINIT
    if (mode & (MODE_DIRECT|MODE_DEDICATED)) { /* } */
#else
    if (mode & MODE_DIRECT) {
#endif
      TtyInit();
    } else {
      int fd;

      setsid();			/* detach control tty */
      if ((fd = open(_PATH_DEVNULL, O_RDWR, 0)) != -1) {
	(void)dup2(fd, STDIN_FILENO);
	(void)dup2(fd, STDOUT_FILENO);
	(void)dup2(fd, STDERR_FILENO);
	if (fd > 2)
		(void)close (fd);
      }
    }
  } else {
    TtyInit();
    TtyCommandMode(1);
  }
  LogPrintf(LOG_PHASE_BIT, "PPP Started.\n");


  do
   DoLoop();
  while (mode & MODE_DEDICATED);

  Cleanup(EX_DONE);
}

/*
 *  Turn into packet mode, where we speak PPP.
 */
void
PacketMode()
{
  if (RawModem(modem) < 0) {
    fprintf(stderr, "Not connected.\r\n");
    return;
  }

  AsyncInit();
  VjInit();
  LcpInit();
  IpcpInit();
  CcpInit();
  LcpUp();

  LcpOpen(VarOpenMode);
  if ((mode & (MODE_INTER|MODE_AUTO)) == MODE_INTER) {
    TtyCommandMode(1);
    fprintf(stderr, "Packet mode.\r\n");
    aft_cmd = 1;
  }
}

static void
ShowHelp()
{
  fprintf(stderr, "The following commands are available:\r\n");
  fprintf(stderr, " ~p\tEnter to Packet mode\r\n");
  fprintf(stderr, " ~-\tDecrease log level\r\n");
  fprintf(stderr, " ~+\tIncrease log level\r\n");
  fprintf(stderr, " ~.\tTerminate program\r\n");
  fprintf(stderr, " ~?\tThis help\r\n");
}

static void
ReadTty()
{
  int n;
  char ch;
  static int ttystate;
#define MAXLINESIZE 200
  char linebuff[MAXLINESIZE];

#ifdef DEBUG
  logprintf("termode = %d, netfd = %d, mode = %d\n", TermMode, netfd, mode);
#endif
  if (!TermMode) {
    n = read(netfd, linebuff, sizeof(linebuff)-1);
    aft_cmd = 1;
    if (n > 0) {
      DecodeCommand(linebuff, n, 1);
    } else {
      LogPrintf(LOG_PHASE_BIT, "client connection closed.\n");
      VarLocalAuth = LOCAL_NO_AUTH;
      close(netfd);
      close(1);
      dup2(2, 1);     /* Have to have something here or the modem will be 1 */
      netfd = -1;
      mode &= ~MODE_INTER;
    }
    return;
  }

  /*
   *  We are in terminal mode, decode special sequences
   */
  n = read(0, &ch, 1);
#ifdef DEBUG
  logprintf("got %d bytes\n", n);
#endif

  if (n > 0) {
    switch (ttystate) {
    case 0:
      if (ch == '~')
	ttystate++;
      else
	write(modem, &ch, n);
      break;
    case 1:
      switch (ch) {
      case '?':
	ShowHelp();
	break;
      case '-':
	if (loglevel > 0) {
	  loglevel--;
	  fprintf(stderr, "New loglevel is %d\r\n", loglevel);
	}
	break;
      case '+':
	loglevel++;
	fprintf(stderr, "New loglevel is %d\r\n", loglevel);
	break;
#ifdef DEBUG
      case 'm':
	ShowMemMap();
	break;
#endif
      case 'p':
	/*
	 * XXX: Should check carrier.
	 */
	if (LcpFsm.state <= ST_CLOSED) {
	  VarOpenMode = OPEN_ACTIVE;
	  PacketMode();
	}
	break;
#ifdef DEBUG
      case 't':
	ShowTimers();
	break;
#endif
      case '.':
	TermMode = 1;
	TtyCommandMode(1);
	break;
      default:
	if (write(modem, &ch, n) < 0)
	  fprintf(stderr, "err in write.\r\n");
	break;
      }
      ttystate = 0;
      break;
    }
  }
}


/*
 *  Here, we'll try to detect HDLC frame
 */

static char *FrameHeaders[] = {
  "\176\377\003\300\041",
  "\176\377\175\043\300\041",
  "\176\177\175\043\100\041",
  "\176\175\337\175\043\300\041",
  "\176\175\137\175\043\100\041",
  NULL,
};

u_char *
HdlcDetect(cp, n)
u_char *cp;
int n;
{
  char *ptr, *fp, **hp;

  cp[n] = '\0';	/* be sure to null terminated */
  ptr = NULL;
  for (hp = FrameHeaders; *hp; hp++) {
    fp = *hp;
    if (DEV_IS_SYNC)
      fp++;
    ptr = strstr((char *)cp, fp);
    if (ptr)
      break;
  }
  return((u_char *)ptr);
}

static struct pppTimer RedialTimer;

static void
RedialTimeout()
{
  StopTimer(&RedialTimer);
  LogPrintf(LOG_PHASE_BIT, "Redialing timer expired.\n");
}

static void
StartRedialTimer(Timeout)
	int Timeout;
{
  StopTimer(&RedialTimer);

  if (Timeout) {
    RedialTimer.state = TIMER_STOPPED;

    if (Timeout > 0)
	RedialTimer.load = Timeout * SECTICKS;
    else
	RedialTimer.load = (random() % REDIAL_PERIOD) * SECTICKS;

    LogPrintf(LOG_PHASE_BIT, "Enter pause (%d) for redialing.\n",
	      RedialTimer.load / SECTICKS);

    RedialTimer.func = RedialTimeout;
    StartTimer(&RedialTimer);
  }
}


static void
DoLoop()
{
  fd_set rfds, wfds, efds;
  int pri, i, n, wfd, nfds;
  struct sockaddr_in hisaddr;
  struct timeval timeout, *tp;
  int ssize = sizeof(hisaddr);
  u_char *cp;
  u_char rbuff[MAX_MRU];
  int dial_up;
  int tries;
  int qlen;
  pid_t pgroup;

  pgroup = getpgrp();

  if (mode & MODE_DIRECT) {
    modem = OpenModem(mode);
    LogPrintf(LOG_PHASE_BIT, "Packet mode enabled\n");
    fflush(stderr);
    PacketMode();
  } else if (mode & MODE_DEDICATED) {
    if (modem < 0)
      modem = OpenModem(mode);
  }

  fflush(stdout);

  timeout.tv_sec = 0;
  timeout.tv_usec = 0;
  reconnectRequired = 0;

  if (mode & MODE_BACKGROUND)
    dial_up = TRUE;			/* Bring the line up */
  else
    dial_up = FALSE;			/* XXXX */
  tries = 0;
  for (;;) {
    nfds = 0;
    FD_ZERO(&rfds); FD_ZERO(&wfds); FD_ZERO(&efds);

    /*
     * If the link is down and we're in DDIAL mode, bring it back
     * up.
     */
    if (mode & MODE_DDIAL && LcpFsm.state <= ST_CLOSED)
        dial_up = TRUE;

    /*
     * If we lost carrier and want to re-establish the connection
     * due to the "set reconnect" value, we'd better bring the line
     * back up.
     */
    if (LcpFsm.state <= ST_CLOSED) {
      if (dial_up != TRUE && reconnectRequired) {
        if (++reconnectCount <= VarReconnectTries) {
          LogPrintf(LOG_PHASE_BIT, "Connection lost, re-establish (%d/%d)\n",
                    reconnectCount, VarReconnectTries);
	  StartRedialTimer(VarReconnectTimer);
          dial_up = TRUE;
        } else {
          if (VarReconnectTries)
            LogPrintf(LOG_PHASE_BIT, "Connection lost, maximum (%d) times\n",
                      VarReconnectTries);
          reconnectCount = 0;
          if (mode & MODE_BACKGROUND)
            Cleanup(EX_DEAD);
        }
      }
      reconnectRequired = 0;
    }

   /*
    * If Ip packet for output is enqueued and require dial up,
    * Just do it!
    */
    if ( dial_up && RedialTimer.state != TIMER_RUNNING ) {
#ifdef DEBUG
      logprintf("going to dial: modem = %d\n", modem);
#endif
      modem = OpenModem(mode);
      if (modem < 0) {
	StartRedialTimer(VarRedialTimeout);
      } else {
	tries++;    /* Tries are per number, not per list of numbers. */
        if (VarDialTries)
	  LogPrintf(LOG_CHAT_BIT, "Dial attempt %u of %d\n", tries,
		    VarDialTries);
        else
	  LogPrintf(LOG_CHAT_BIT, "Dial attempt %u\n", tries);
	if (DialModem()) {
	  sleep(1);	       /* little pause to allow peer starts */
	  ModemTimeout();
	  PacketMode();
	  dial_up = FALSE;
	  tries = 0;
	} else {
	  CloseModem();
	  if (mode & MODE_BACKGROUND) {
	    if (VarNextPhone == NULL)
	      Cleanup(EX_DIAL);  /* Tried all numbers - no luck */
	    else
	      /* Try all numbers in background mode */
	      StartRedialTimer(VarRedialNextTimeout);
	  } else if (VarDialTries && tries >= VarDialTries) {
	    /* I give up !  Can't get through :( */
	    StartRedialTimer(VarRedialTimeout);
	    dial_up = FALSE;
	    tries = 0;
	  } else if (VarNextPhone == NULL)
	    /* Dial failed. Keep quite during redial wait period. */
	    StartRedialTimer(VarRedialTimeout);
	  else
	    StartRedialTimer(VarRedialNextTimeout);
	}
      }
    }
    qlen = ModemQlen();

    if (qlen == 0) {
      IpStartOutput();
      qlen = ModemQlen();
    }

    if (modem >= 0) {
      if (modem + 1 > nfds)
	nfds = modem + 1;
      FD_SET(modem, &rfds);
      FD_SET(modem, &efds);
      if (qlen > 0) {
	FD_SET(modem, &wfds);
      }
    }
    if (server >= 0) {
      if (server + 1 > nfds)
	nfds = server + 1;
      FD_SET(server, &rfds);
    }

    /*  *** IMPORTANT ***
     *
     *  CPU is serviced every TICKUNIT micro seconds.
     *	This value must be chosen with great care. If this values is
     *  too big, it results loss of characters from modem and poor responce.
     *  If this values is too small, ppp process eats many CPU time.
     */
#ifndef SIGALRM
    usleep(TICKUNIT);
    TimerService();
#else
    handle_signals();
#endif

    /* If there are aren't many packets queued, look for some more. */
    if (qlen < 20 && tun_in >= 0) {
      if (tun_in + 1 > nfds)
	nfds = tun_in + 1;
      FD_SET(tun_in, &rfds);
    }

    if (netfd >= 0) {
      if (netfd + 1 > nfds)
	nfds = netfd + 1;
      FD_SET(netfd, &rfds);
      FD_SET(netfd, &efds);
    }

#ifndef SIGALRM
    /*
     *  Normally, select() will not block because modem is writable.
     *  In AUTO mode, select will block until we find packet from tun
     */
    tp = (RedialTimer.state == TIMER_RUNNING)? &timeout : NULL;
    i = select(nfds, &rfds, &wfds, &efds, tp);
#else
    /*
     * When SIGALRM timer is running, a select function will be
     * return -1 and EINTR after a Time Service signal hundler
     * is done.  If the redial timer is not running and we are
     * trying to dial, poll with a 0 value timer.
     */
    tp = (dial_up && RedialTimer.state != TIMER_RUNNING) ? &timeout : NULL;
    i = select(nfds, &rfds, &wfds, &efds, tp);
#endif

    if ( i == 0 ) {
        continue;
    }

    if ( i < 0 ) {
       if ( errno == EINTR ) {
          handle_signals();
          continue;
       }
       perror("select");
       break;
    }

    if ((netfd >= 0 && FD_ISSET(netfd, &efds)) || (modem >= 0 && FD_ISSET(modem, &efds))) {
      logprintf("Exception detected.\n");
      break;
    }

    if (server >= 0 && FD_ISSET(server, &rfds)) {
      LogPrintf(LOG_PHASE_BIT, "connected to client.\n");
      wfd = accept(server, (struct sockaddr *)&hisaddr, &ssize);
      if (wfd < 0) {
	perror("accept");
	continue;
      }
      if (netfd >= 0) {
	write(wfd, "already in use.\n", 16);
	close(wfd);
	continue;
      } else
	netfd = wfd;
      if (dup2(netfd, 1) < 0) {
	perror("dup2");
	close(netfd);
	netfd = -1;
	continue;
      }
      mode |= MODE_INTER;
      Greetings();
      switch ( LocalAuthInit() ) {
         case NOT_FOUND:
    	    fprintf(stdout,LAUTH_M1);
    	    fprintf(stdout,LAUTH_M2);
            fflush(stdout);
	    /* Fall down */
         case VALID:
	    VarLocalAuth = LOCAL_AUTH;
	    break;
         default:
	    break;
      }
      (void) IsInteractive();
      Prompt();
    }

    if ((mode & MODE_INTER) && (netfd >= 0 && FD_ISSET(netfd, &rfds)) &&
	((mode & MODE_AUTO) || pgroup == tcgetpgrp(0))) {
      /* something to read from tty */
      ReadTty();
    }
    if (modem >= 0) {
      if (FD_ISSET(modem, &wfds)) {	/* ready to write into modem */
	 ModemStartOutput(modem);
      }
      if (FD_ISSET(modem, &rfds)) {	/* something to read from modem */
	if (LcpFsm.state <= ST_CLOSED)
	  usleep(10000);
	n = read(modem, rbuff, sizeof(rbuff));
	if ((mode & MODE_DIRECT) && n <= 0) {
	  DownConnection();
	} else
          LogDumpBuff(LOG_ASYNC, "ReadFromModem", rbuff, n);

	if (LcpFsm.state <= ST_CLOSED) {
	  /*
	   *  In dedicated mode, we just discard input until LCP is started.
	   */
	  if (!(mode & MODE_DEDICATED)) {
	    cp = HdlcDetect(rbuff, n);
	    if (cp) {
	      /*
	       * LCP packet is detected. Turn ourselves into packet mode.
	       */
	      if (cp != rbuff) {
	        write(1, rbuff, cp - rbuff);
	        write(1, "\r\n", 2);
	      }
	      PacketMode();
	    } else
	      write(1, rbuff, n);
	  }
	} else {
	  if (n > 0)
	    AsyncInput(rbuff, n);
	}
      }
    }

    if (tun_in >= 0 && FD_ISSET(tun_in, &rfds)) {       /* something to read from tun */
      n = read(tun_in, rbuff, sizeof(rbuff));
      if (n < 0) {
	perror("read from tun");
	continue;
      }
      /*
       *  Process on-demand dialup. Output packets are queued within tunnel
       *  device until IPCP is opened.
       */
      if (LcpFsm.state <= ST_CLOSED && (mode & MODE_AUTO)) {
	pri = PacketCheck(rbuff, n, FL_DIAL);
	if (pri >= 0) {
	  if (mode & MODE_ALIAS) {
	    PacketAliasOut(rbuff, sizeof rbuff);
	    n = ntohs(((struct ip *)rbuff)->ip_len);
	  }
	  IpEnqueue(pri, rbuff, n);
	  dial_up = TRUE;		/* XXX */
	}
	continue;
      }
      pri = PacketCheck(rbuff, n, FL_OUT);
      if (pri >= 0) {
        if (mode & MODE_ALIAS) {
          PacketAliasOut(rbuff, sizeof rbuff);
          n = ntohs(((struct ip *)rbuff)->ip_len);
        }
	IpEnqueue(pri, rbuff, n);
      }
    }
  }
  logprintf("job done.\n");
}