Handle select errors more robustly.

[fwd] / fw.c

/* -*-c-*-
 *
 * $Id: fw.c,v 1.9 2001/01/20 11:55:17 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 1.9  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 <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 "fw.h"
#include "scan.h"
#include "source.h"

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

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

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

static unsigned flags = 0;		/* Global state flags */
static unsigned active = 0;		/* Number of active things */

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

/*----- Main code ---------------------------------------------------------*/

/* --- @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 = "unexpected signal (bug!)";
  if (n == SIGTERM)
    sn = "SIGTERM";
  else if (n == SIGINT)
    sn = "SIGINT";

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

/* --- 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.logging [=] yes|no\n\
	socket.inet.[allow|deny] [from] address [/ address]\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_int;
  scanner sc;
  uid_t drop = -1;
  gid_t dropg = -1;

  enum {
    f_bogus = 1,
    f_file = 2,
    f_syslog = 4,
    f_fork = 8
  };

  /* --- 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);

  /* --- 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);
    sigaction(SIGINT, 0, &sa);
    if (sa.sa_handler != SIG_IGN)
      sig_add(&s_int, SIGINT, fw_tidy, 0);
  }

  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));
	  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);
  }

  /* --- 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 --- */

  conf_parse(&sc);

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

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