Update docco for new options.

[fwd] / fw.c

/* -*-c-*-
 *
 * $Id: fw.c,v 1.15 2003/11/25 14:46:50 mdw Exp $
 *
 * Port forwarding thingy
 *
 * (c) 1999 Straylight/Edgeware
 */

/*----- Licensing notice --------------------------------------------------* 
 *
 * This file is part of the `fw' port forwarder.
 *
 * `fw' is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 * 
 * `fw' is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with `fw'; if not, write to the Free Software Foundation,
 * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 */

/*----- Revision history --------------------------------------------------* 
 *
 * $Log: fw.c,v $
 * Revision 1.15  2003/11/25 14:46:50  mdw
 * Update docco for new options.
 *
 * Revision 1.14  2003/01/24 20:12:40  mdw
 * Correctly cast uid and gid sentinel values.
 *
 * Revision 1.13  2002/02/22 23:45:20  mdw
 * Add option to change the listen(2) parameter.  Receive `fw'-specific
 * code from `conf.c'.
 *
 * Revision 1.12  2002/01/13 14:49:17  mdw
 * Track @dstr_vputf@ change.
 *
 * Revision 1.11  2001/02/03 20:33:26  mdw
 * Fix flags to be unsigned.
 *
 * Revision 1.10  2001/02/03 20:30:03  mdw
 * Support re-reading config files on SIGHUP.
 *
 * Revision 1.9  2001/01/20 11:55:17  mdw
 * Handle select errors more robustly.
 *
 * Revision 1.8  2000/03/23 23:19:19  mdw
 * Fix changed options in parser table.
 *
 * Revision 1.7  2000/03/23 00:37:33  mdw
 * Add option to change user and group after initialization.  Naughtily
 * reassign short equivalents of --grammar and --options.
 *
 * Revision 1.6  1999/12/22 15:44:10  mdw
 * Make syslog a separate option, and do it better.
 *
 * Revision 1.5  1999/10/22 22:47:50  mdw
 * Grammar changes.  Also, don't enable SIGINT if it's currently ignored.
 *
 * Revision 1.4  1999/10/10 16:46:12  mdw
 * New resolver to initialize.  Also, include options for grammar and
 * options references.
 *
 * Revision 1.3  1999/07/26 23:30:42  mdw
 * Major reconstruction work for new design.
 *
 * Revision 1.2  1999/07/03 13:55:17  mdw
 * Various changes.  Add configuration grammar to help text.  Change to
 * root directory and open syslog when forking into background.
 *
 * Revision 1.1.1.1  1999/07/01 08:56:23  mdw
 * Initial revision.
 *
 */

/*----- Header files ------------------------------------------------------*/

#include "config.h"

#include <assert.h>
#include <ctype.h>
#include <errno.h>
#include <signal.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

#include <unistd.h>
#include <syslog.h>

#include <grp.h>
#include <pwd.h>

#include <mLib/bres.h>
#include <mLib/dstr.h>
#include <mLib/mdwopt.h>
#include <mLib/quis.h>
#include <mLib/report.h>
#include <mLib/sel.h>
#include <mLib/sig.h>
#include <mLib/sub.h>

#include "conf.h"
#include "endpt.h"
#include "exec.h"
#include "fattr.h"
#include "file.h"
#include "fw.h"
#include "scan.h"
#include "socket.h"
#include "source.h"

/*----- Global variables --------------------------------------------------*/

sel_state *sel;				/* Multiplexor for nonblocking I/O */

/*----- Static variables --------------------------------------------------*/

typedef struct conffile {
  struct conffile *next;
  char *name;
} conffile;

static unsigned flags = 0;		/* Global state flags */
static unsigned active = 0;		/* Number of active things */
static conffile *conffiles = 0;		/* List of configuration files */

#define FW_SYSLOG 1u
#define FW_QUIET 2u
#define FW_SET 4u

/*----- Configuration parsing ---------------------------------------------*/

/* --- @parse@ --- *
 *
 * Arguments:	@scanner *sc@ = pointer to scanner definition
 *
 * Returns:	---
 *
 * Use:		Parses a configuration file from the scanner.
 */

static source_ops *sources[] =
  { &xsource_ops, &fsource_ops, &ssource_ops, 0 };
static target_ops *targets[] =
  { &xtarget_ops, &ftarget_ops, &starget_ops, 0 };

void parse(scanner *sc)
{
  token(sc);

  for (;;) {
    if (sc->t == CTOK_EOF)
      break;
    if (sc->t != CTOK_WORD)
      error(sc, "parse error, keyword expected");

    /* --- Handle a forwarding request --- */

    if (strcmp(sc->d.buf, "forward") == 0 ||
	strcmp(sc->d.buf, "fw") == 0 ||
        strcmp(sc->d.buf, "from") == 0) {
      source *s;
      target *t;

      token(sc);

      /* --- Read a source description --- */

      {
	source_ops **sops;

	/* --- Try to find a source type which understands --- */

	s = 0;
	for (sops = sources; *sops; sops++) {
	  if ((s = (*sops)->read(sc)) != 0)
	    goto found_source;
	}
	error(sc, "unknown source name `%s'", sc->d.buf);

	/* --- Read any source-specific options --- */

      found_source:
	if (sc->t == '{') {
	  token(sc);
	  while (sc->t == CTOK_WORD) {
	    if (!s->ops->option || !s->ops->option(s, sc)) {
	      error(sc, "unknown %s source option `%s'",
		    s->ops->name, sc->d.buf);
	    }
	    if (sc->t == ';')
	      token(sc);
	  }
	  if (sc->t != '}')
	    error(sc, "parse error, missing `}'");
	  token(sc);
	}
      }

      /* --- Read a destination description --- */

      if (sc->t == CTOK_WORD && (strcmp(sc->d.buf, "to") == 0 ||
				 strcmp(sc->d.buf, "->") == 0))
	token(sc);

      {
	target_ops **tops;

	/* --- Try to find a target which understands --- */

	t = 0;
	for (tops = targets; *tops; tops++) {
	  if ((t = (*tops)->read(sc)) != 0)
	    goto found_target;
	}
	error(sc, "unknown target name `%s'", sc->d.buf);

	/* --- Read any target-specific options --- */

      found_target:
	if (sc->t == '{') {
	  token(sc);
	  while (sc->t == CTOK_WORD) {
	    if (!t->ops->option || !t->ops->option(t, sc)) {
	      error(sc, "unknown %s target option `%s'",
		    t->ops->name, sc->d.buf);
	    }
	    if (sc->t == ';')
	      token(sc);
	  }
	  if (sc->t != '}')
	    error(sc, "parse error, `}' expected");
	  token(sc);
	}
      }

      /* --- Combine the source and target --- */

      s->ops->attach(s, sc, t);
    }

    /* --- Include configuration from a file --- *
     *
     * Slightly tricky.  Scan the optional semicolon from the including
     * stream, not the included one.
     */

    else if (strcmp(sc->d.buf, "include") == 0) {
      FILE *fp;
      dstr d = DSTR_INIT;

      token(sc);
      conf_name(sc, '/', &d);
      if ((fp = fopen(d.buf, "r")) == 0)
	error(sc, "can't include `%s': %s", d.buf, strerror(errno));
      if (sc->t == ';')
	token(sc);
      pushback(sc);
      scan_push(sc, scan_file(fp, d.buf, 0));
      token(sc);
      dstr_destroy(&d);
      continue;				/* Don't parse a trailing `;' */
    }

    /* --- Other configuration is handled elsewhere --- */

    else {

      /* --- First try among the sources --- */

      {
	source_ops **sops;

	for (sops = sources; *sops; sops++) {
	  if ((*sops)->option && (*sops)->option(0, sc))
	    goto found_option;
	}
      }

      /* --- Then try among the targets --- */

      {
	target_ops **tops;

	for (tops = targets; *tops; tops++) {
	  if ((*tops)->option && (*tops)->option(0, sc))
	    goto found_option;
	}
      }

      /* --- Nobody wants the option --- */

      error(sc, "unknown global option or prefix `%s'", sc->d.buf);

    found_option:;
    }

    if (sc->t == ';')
      token(sc);
  }
}

/*----- General utility functions -----------------------------------------*/

/* --- @fw_log@ --- *
 *
 * Arguments:	@time_t t@ = when the connection occurred or (@-1@)
 *		@const char *fmt@ = format string to fill in
 *		@...@ = other arguments
 *
 * Returns:	---
 *
 * Use:		Logs a connection.
 */

void fw_log(time_t t, const char *fmt, ...)
{
  struct tm *tm;
  dstr d = DSTR_INIT;
  va_list ap;

  if (flags & FW_QUIET)
    return;

  if (t == -1)
    t = time(0);
  tm = localtime(&t);
  DENSURE(&d, 64);
  d.len += strftime(d.buf, d.sz, "%Y-%m-%d %H:%M:%S ", tm);
  va_start(ap, fmt);
  dstr_vputf(&d, fmt, &ap);
  va_end(ap);
  if (flags & FW_SYSLOG)
    syslog(LOG_NOTICE, "%s", d.buf);
  else {
    DPUTC(&d, '\n');
    dstr_write(&d, stderr);
  }
  DDESTROY(&d);
}

/* --- @fw_inc@, @fw_dec@ --- *
 *
 * Arguments:	---
 *
 * Returns:	---
 *
 * Use:		Increments or decrements the active thing count.  `fw' won't
 *		quit while there are active things.
 */

void fw_inc(void) { flags |= FW_SET; active++; }
void fw_dec(void) { if (active) active--; }

/* --- @fw_exit@ --- *
 *
 * Arguments:	---
 *
 * Returns:	---
 *
 * Use:		Exits when appropriate.
 */

static void fw_exit(void)
{
  endpt_killall();
  source_killall();
}

/* --- @fw_tidy@ --- *
 *
 * Arguments:	@int n@ = signal number
 *		@void *p@ = an uninteresting argument
 *
 * Returns:	---
 *
 * Use:		Handles various signals and causes a clean tidy-up.
 */

static void fw_tidy(int n, void *p)
{
  const char *sn = 0;
  switch (n) {
    case SIGTERM: sn = "SIGTERM"; break;
    case SIGINT: sn = "SIGINT"; break;
    default: abort();
  }

  fw_log(-1, "closing down gracefully on %s", sn);
  source_killall();
}

/* --- @fw_die@ --- *
 *
 * Arguments:	@int n@ = signal number
 *		@void *p@ = an uninteresting argument
 *
 * Returns:	---
 *
 * Use:		Handles various signals and causes an abrupt shutdown.
 */

static void fw_die(int n, void *p)
{
  const char *sn = 0;
  switch (n) {
    case SIGQUIT: sn = "SIGQUIT"; break;
    default: abort();
  }

  fw_log(-1, "closing down abruptly on %s", sn);
  source_killall();
  endpt_killall();
}

/* --- @fw_reload@ --- *
 *
 * Arguments:	@int n@ = a signal number
 *		@void *p@ = an uninteresting argument
 *
 * Returns:	---
 *
 * Use:		Handles a hangup signal by re-reading configuration files.
 */

static void fw_reload(int n, void *p)
{
  FILE *fp;
  scanner sc;
  conffile *cf;

  assert(n == SIGHUP);
  if (!conffiles) {
    fw_log(-1, "no configuration files to reload: ignoring SIGHUP");
    return;
  }
  fw_log(-1, "reloading configuration files...");
  source_killall();
  scan_create(&sc);
  for (cf = conffiles; cf; cf = cf->next) {
    if ((fp = fopen(cf->name, "r")) == 0)
      fw_log(-1, "error loading `%s': %s", cf->name, strerror(errno));
    else
      scan_add(&sc, scan_file(fp, cf->name, 0));
  }
  parse(&sc);
  fw_log(-1, "... reload completed OK");
}

/*----- Startup and options parsing ---------------------------------------*/

/* --- Standard GNU help options --- */

static void version(FILE *fp)
{
  pquis(fp, "$ version " VERSION "\n");
}

static void usage(FILE *fp)
{
  pquis(fp, "Usage: $ [-dql] [-f file] [config statements...]\n");
}

static void help(FILE *fp)
{
  version(fp);
  fputc('\n', fp);
  usage(fp);
  pquis(fp, "\n\
An excessively full-featured port-forwarder, which subsumes large chunks\n\
of the functionality of inetd, netcat, and normal cat.  Options available\n\
are:\n\
\n\
-h, --help	  Display this help message.\n\
-v, --version	  Display the program's version number.\n\
-u, --usage	  Display a terse usage summary.\n\
\n\
-G, --grammar	  Show a summary of the configuration language.\n\
-O, --options	  Show a summary of the source and target options.\n\
\n\
-f, --file=FILE	  Read configuration from a file.\n\
-q, --quiet	  Don't emit any logging information.\n\
-d, --daemon	  Fork into background after initializing.\n\
-l, --syslog	  Send log output to the system logger.\n\
-s, --setuid=USER Change uid to USER after initializing sources.\n\
-g, --setgid=GRP  Change gid to GRP after initializing sources.\n\
\n\
Configuration may be supplied in one or more configuration files, or on\n\
the command line (or both).  If no `-f' option is present, and no\n\
configuration is given on the command line, the standard input stream is\n\
read.\n\
\n\
Configuration is free-form.  Comments begin with a `#' character and\n\
continue to the end of the line.  Each command line argument is considered\n\
to be a separate line.\n\
\n\
The grammar is fairly complicated.  For a summary, run `$ --grammar'.\n\
For a summary of the various options, run `$ --options'.\n\
");
}

/* --- Other helpful options --- */

static void grammar(FILE *fp)
{
  version(fp);
  pquis(fp, "\n\
Grammar summary\n\
\n\
Basic syntax\n\
	FILE ::= EMPTY | FILE STMT [`;']\n\
	STMT ::= OPTION-STMT | FW-STMT\n\
	FW-STMT ::= `fw' SOURCE OPTIONS [`to'|`->'] TARGET OPTIONS\n\
	OPTIONS ::= `{' OPTION-SEQ `}'\n\
	OPTION-SEQ ::= EMPTY | OPTION-STMT [`;'] OPTION-SEQ\n\
\n\
Option syntax\n\
	OPTION-STMT ::= Q-OPTION\n\
	Q-OPTION ::= OPTION\n\
	     | PREFIX `.' Q-OPTION\n\
	     | PREFIX `{' OPTION-SEQ `}'\n\
	PREFIX ::= WORD\n\
\n\
File source and target\n\
	SOURCE ::= FILE\n\
	TARGET ::= FILE\n\
	FILE ::= `file' [`.'] FSPEC [`,' FSPEC]\n\
	FSPEC ::= FD-SPEC | NAME-SPEC | NULL-SPEC\n\
	FD-SPEC ::= [[`:']`fd'[`:']] NUMBER|`stdin'|`stdout'\n\
	NAME-SPEC ::= [[`:']`file'[`:']] FILE-NAME\n\
	FILE-NAME ::= PATH-SEQ | [ PATH-SEQ ]\n\
	PATH-SEQ ::= PATH-ELT | PATH-SEQ PATH-ELT\n\
	PATH-ELT ::= `/' | WORD\n\
	NULL-SPEC ::= [`:']`null'[`:']\n\
\n\
Exec source and target\n\
	SOURCE ::= EXEC\n\
	TARGET ::= EXEC\n\
	EXEC ::= `exec' [`.'] CMD-SPEC\n\
	CMD-SPEC ::= SHELL-CMD | [PROG-NAME] `[' ARGV0 ARG-SEQ `]'\n\
	ARG-SEQ ::= WORD | ARG-SEQ WORD\n\
	SHELL-CMD ::= WORD\n\
	ARGV0 ::= WORD\n\
\n\
Socket source and target\n\
	SOURCE ::= SOCKET-SOURCE\n\
	TARGET ::= SOCKET-TARGET\n\
	SOCKET-SOURCE ::= [`socket'[`.']] [[`:']ADDR-TYPE[`:']] SOURCE-ADDR\n\
	SOCKET-TARGET ::= [`socket'[`.']] [[`:']ADDR-TYPE[`:']] TARGET-ADDR\n\
\n\
	INET-SOURCE-ADDR ::= [`port'] PORT\n\
	INET-TARGET-ADDR ::= ADDRESS [`:'] PORT\n\
	ADDRESS ::= ADDR-ELT | ADDRESS ADDR-ELT\n\
	ADDR-ELT ::= `.' | WORD\n\
\n\
	UNIX-SOURCE-ADDR ::= FILE-NAME\n\
	UNIX-TARGET-ADDR ::= FILE-NAME\n\
");
}

static void options(FILE *fp)
{
  version(fp);
  pquis(fp, "\n\
Options summary\n\
\n\
File attributes (`fattr')\n\
	prefix.FATTR.MODE [=] MODE\n\
	prefix.FATTR.OWNER [=] USER\n\
	prefix.FATTR.GROUP [=] GROUP\n\
\n\
File options\n\
	file.create [=] yes|no\n\
	file.open [=] no|truncate|append\n\
	file.fattr.*\n\
\n\
Exec options\n\
	exec.logging [=] yes|no\n\
	exec.dir [=] FILE-NAME\n\
	exec.root [=] FILE-NAME\n\
	exec.user [=] USER\n\
	exec.group [=] GROUP\n\
	exec.rlimit.LIMIT[.hard|.soft] [=] VALUE\n\
	exec.env.clear\n\
	exec.env.unset VAR\n\
	exec.env.[set] VAR [=] VALUE\n\
\n\
Socket options\n\
	socket.conn [=] NUMBER|unlimited|one-shot\n\
	socket.listen [=] NUMBER\n\
	socket.logging [=] yes|no\n\
\n\
	socket.inet.source.[allow|deny] [host] ADDR [/ ADDR]\n\
	socket.inet.source.[allow|deny] priv-port\n\
	socket.inet.source.addr [=] any|ADDR\n\
	socket.inet.dest.addr [=] any|ADDR\n\
\n\
	socket.unix.fattr.*\n\
");
}

/* --- @main@ --- *
 *
 * Arguments:	@int argc@ = number of command line arguments
 *		@char *argv[]@ = vector of argument strings
 *
 * Returns:	---
 *
 * Use:		Simple port-forwarding server.
 */

int main(int argc, char *argv[])
{
  unsigned f = 0;
  sel_state sst;
  sig s_term, s_quit, s_int, s_hup;
  scanner sc;
  uid_t drop = -1;
  gid_t dropg = -1;
  conffile *cf, **cff = &conffiles;

#define f_bogus 1u
#define f_file 2u
#define f_syslog 4u
#define f_fork 8u

  /* --- Initialize things --- */

  ego(argv[0]);
  sel = &sst;
  sel_init(sel);
  sub_init();
  sig_init(sel);
  bres_init(sel);
  bres_exec(0);
  exec_init();
  fattr_init(&fattr_global);
  scan_create(&sc);

  atexit(fw_exit);

  /* --- Parse command line options --- */

  for (;;) {
    static struct option opts[] = {

      /* --- Standard GNU help options --- */

      { "help", 	0,		0,	'h' },
      { "version",	0,		0,	'v' },
      { "usage",	0,		0,	'u' },

      /* --- Other help options --- */

      { "grammar",	0,		0,	'G' },
      { "options",	0,		0,	'O' },

      /* --- Other useful arguments --- */

      { "file",		OPTF_ARGREQ,	0,	'f' },
      { "fork",		0,		0,	'd' },
      { "daemon",	0,		0,	'd' },
      { "syslog",	0,		0,	'l' },
      { "log",		0,		0,	'l' },
      { "quiet",	0,		0,	'q' },
      { "setuid",	OPTF_ARGREQ,	0,	's' },
      { "uid",		OPTF_ARGREQ,	0,	's' },
      { "setgid",	OPTF_ARGREQ,	0,	'g' },
      { "gid",		OPTF_ARGREQ,	0,	'g' },

      /* --- Magic terminator --- */

      { 0,		0,		0,	0 }
    };
    int i = mdwopt(argc, argv, "+hvu GO f:dls:g:", opts, 0, 0, 0);

    if (i < 0)
      break;
    switch (i) {
      case 'h':
	help(stdout);
	exit(0);
	break;
      case 'v':
	version(stdout);
	exit(0);
	break;
      case 'u':
	usage(stdout);
	exit(0);
	break;
      case 'G':
	grammar(stdout);
	exit(0);
	break;
      case 'O':
	options(stdout);
	exit(0);
	break;
      case 'f':
	if (strcmp(optarg, "-") == 0)
	  scan_add(&sc, scan_file(stdin, "<stdin>", SCF_NOCLOSE));
	else {
	  FILE *fp;
	  if ((fp = fopen(optarg, "r")) == 0)
	    die(1, "couldn't open file `%s': %s", optarg, strerror(errno));
	  cf = CREATE(conffile);
	  cf->name = optarg;
	  *cff = cf;
	  cff = &cf->next;
	  scan_add(&sc, scan_file(fp, optarg, 0));
	}
	f |= f_file;
	break;
      case 'd':
	f |= f_fork;
	break;
      case 'l':
	f |= f_syslog;
	break;
      case 'q':
	flags |= FW_QUIET;
	break;
      case 's':
        if (isdigit((unsigned char )optarg[0])) {
	  char *q;
	  drop = strtol(optarg, &q, 0);
	  if (*q)
	    die(1, "bad uid `%s'", optarg);
	} else {
	  struct passwd *pw = getpwnam(optarg);
	  if (!pw)
	    die(1, "unknown user `%s'", optarg);
	  drop = pw->pw_uid;
	}
	break;
      case 'g':
        if (isdigit((unsigned char )optarg[0])) {
	  char *q;
	  dropg = strtol(optarg, &q, 0);
	  if (*q)
	    die(1, "bad gid `%s'", optarg);
	} else {
	  struct group *gr = getgrnam(optarg);
	  if (!gr)
	    die(1, "unknown group `%s'", optarg);
	  dropg = gr->gr_gid;
	}
	break;
      default:
	f |= f_bogus;
	break;
    }
  }

  if (f & f_bogus) {
    usage(stderr);
    exit(1);
  }
  *cff = 0;

  /* --- Deal with the remaining arguments --- */

  if (optind < argc)
    scan_add(&sc, scan_argv(argv + optind));
  else if (f & f_file)
    /* Cool */;
  else if (!isatty(STDIN_FILENO))
    scan_add(&sc, scan_file(stdin, "<stdin>", SCF_NOCLOSE));
  else {
    moan("no configuration given and stdin is a terminal.");
    moan("type `%s --help' for usage information.", QUIS);
    exit(1);
  }

  /* --- Parse the configuration now gathered --- */

  parse(&sc);

  /* --- Set up some signal handlers --- *
   *
   * Don't enable @SIGINT@ if the caller already disabled it.
   */

  {
    struct sigaction sa;

    sig_add(&s_term, SIGTERM, fw_tidy, 0);
    sig_add(&s_quit, SIGQUIT, fw_die, 0);
    sigaction(SIGINT, 0, &sa);
    if (sa.sa_handler != SIG_IGN)
      sig_add(&s_int, SIGINT, fw_tidy, 0);
    sig_add(&s_hup, SIGHUP, fw_reload, 0);
  }

  /* --- Drop privileges --- */

#ifdef HAVE_SETGROUPS
  if ((dropg != (gid_t)-1 && (setgid(dropg) || setgroups(1, &dropg))) ||
      (drop != (uid_t)-1 && setuid(drop)))
    die(1, "couldn't drop privileges: %s", strerror(errno));
#else
  if ((dropg != (gid_t)-1 && setgid(dropg)) ||
      (drop != (uid_t)-1 && setuid(drop)))
    die(1, "couldn't drop privileges: %s", strerror(errno));
#endif

  /* --- Fork into the background --- */

  if (f & f_fork) {
    pid_t kid;

    kid = fork();
    if (kid == -1)
      die(1, "couldn't fork: %s", strerror(errno));
    if (kid != 0)
      _exit(0);

    close(0); close(1); close(2);
    chdir("/");
    setsid();

    kid = fork();
    if (kid != 0)
      _exit(0);
  }

  if (f & f_syslog) {
    flags |= FW_SYSLOG;
    openlog(QUIS, 0, LOG_DAEMON);
  }

  /* --- Let rip --- */

  if (!(flags & FW_SET))
    moan("nothing to do!");
  signal(SIGPIPE, SIG_IGN);

  {
    int selerr = 0;
    while (active) {
      if (!sel_select(sel))
        selerr = 0;
      else if (errno != EINTR && errno != EAGAIN) {
	fw_log(-1, "error from select: %s", strerror(errno));
	selerr++;
	if (selerr > 8) {
	  fw_log(-1, "too many consecutive select errors: bailing out");
	  exit(EXIT_FAILURE);
	}
      }
    }
  }
    
  return (0);
}

/*----- That's all, folks -------------------------------------------------*/