fwd: Improve `source' and `target' lifecycle management.

[fwd] / fwd.c

/* -*-c-*-
 *
 * Port forwarding thingy
 *
 * (c) 1999 Straylight/Edgeware
 */

/*----- Licensing notice --------------------------------------------------*
 *
 * This file is part of the `fwd' port forwarder.
 *
 * `fwd' 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.
 *
 * `fwd' 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 `fwd'; if not, write to the Free Software Foundation,
 * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 */

#include "fwd.h"

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

sel_state *sel;				/* Multiplexor for nonblocking I/O */
unsigned flags = 0;			/* Global state flags */

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

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

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

/*----- 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, "fwd") == 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);
      if (t->ops->confirm)
	t->ops->confirm(t);
      source_dec(s); target_dec(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 == NOW)
    t = time(0);
  tm = localtime(&t);
  DENSURE(&d, 64);
  d.len += strftime(d.buf, d.sz, "%Y-%m-%d %H:%M:%S %z ", 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.  `fwd' 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(NOW, "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(NOW, "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(NOW, "no configuration files to reload: ignoring SIGHUP");
    return;
  }
  fw_log(NOW, "reloading configuration files...");
  source_killall();
  scan_create(&sc);
  for (cf = conffiles; cf; cf = cf->next) {
    if ((fp = fopen(cf->name, "r")) == 0)
      fw_log(NOW, "error loading `%s': %s", cf->name, strerror(errno));
    else
      scan_add(&sc, scan_file(fp, cf->name, 0));
  }
  parse(&sc);
  fw_log(NOW, "... 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] [-p PIDFILE] [-f FILE] [CONFIG-STMTS...]\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.\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\
\n\
Options available are:\n\
\n\
Help options:\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\
Configuration summary:\n\
  -G, --grammar        Show a summary of the configuration language.\n\
  -O, --options        Show a summary of the source and target options.\n\
\n\
Other options:\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\
  -p, --pidfile=FILE   Write process-id to the named FILE.\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\
");
}

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

static void grammar(FILE *fp)
{
  version(fp);
  fputs("\nGrammar summary\n\n", fp);
  fputs(grammar_text, fp);
}

static void options(FILE *fp)
{
  version(fp);
  fputs("\nOption summary\n\n", fp);
  fputs(option_text, fp);
}

/* --- @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;
  const char *pidfile = 0;
  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' },
      { "pidfile",	OPTF_ARGREQ,	0,	'p' },
      { "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:dp:lqs: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 'p':
	pidfile = optarg;
	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);
  }

  /* --- 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);
    if (chdir("/"))
      die(1, "couldn't change to root directory: %s", strerror(errno));
    setsid();

    kid = fork();
    if (kid != 0)
      _exit(0);
  }
  if (pidfile) {
    FILE *fp = fopen(pidfile, "w");
    if (!fp) {
      die(EXIT_FAILURE, "couldn't create pidfile `%s': %s",
	  pidfile, strerror(errno));
    }
    fprintf(fp, "%lu\n", (unsigned long)getpid());
    if (fflush(fp) || ferror(fp) || fclose(fp)) {
      die(EXIT_FAILURE, "couldn't write pidfile `%s': %s",
	  pidfile, strerror(errno));
    }
  }

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

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

  if (drop != (uid_t)-1)
    privconn_split(sel);
#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

  /* --- 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(NOW, "error from select: %s", strerror(errno));
	selerr++;
	if (selerr > 8) {
	  fw_log(NOW, "too many consecutive select errors: bailing out");
	  exit(EXIT_FAILURE);
	}
      }
    }
  }

  return (0);
}

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