telnetd.c

linux下telnet服务端的源码实现

/* Copyright (C) 1998, 2001, 2002, 2004x Free Software Foundation, Inc.

   This file is part of GNU Inetutils.

   GNU Inetutils 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, or (at your option)
   any later version.

   GNU Inetutils is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR 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 GNU Inetutils; see the file COPYING.  If not, write
   to the Free Software Foundation, Inc., 51 Franklin Street,
   Fifth Floor, Boston, MA 02110-1301 USA. */

#include "telnetd.h"
#include <getopt.h>
#ifdef HAVE_SYS_UTSNAME_H
# include <sys/utsname.h>
#endif
#include <libinetutils.h>

static char short_options[] = "a:D::d:E:HhLl::nS:Uu:VX:";

static struct option long_options[] =
{
  /* Help options */
  {"version", no_argument, NULL, 'V'},
  {"license", no_argument, NULL, 'L'},
  {"help",    no_argument, NULL, 'H'},
  /* Common options */
  {"authmode", required_argument, NULL, 'a'},
  {"debug", optional_argument, NULL, 'D'},
  {"exec-login", required_argument, NULL, 'E'},
  {"no-hostinfo", no_argument, NULL, 'h'},
  {"linemode", optional_argument, NULL, 'l'},
  {"no-keepalive", no_argument, NULL, 'n'},
  {"reverse-lookup", no_argument, NULL, 'U'},
  {"disable-auth-type", required_argument, NULL, 'X'},
  {NULL, 0, NULL, 0}
};

static void telnetd_version P((void));
static void telnetd_license P((void));
static void telnetd_help P((void));
static void parse_authmode P((char *str));
static void parse_linemode P((char *str));
static void parse_debug_level P((char *str));
static void telnetd_setup P((int fd));
static int telnetd_run P((void));
static void print_hostinfo P((void));

/* Template command line for invoking login program */

char *login_invocation =
#ifdef SOLARIS
"/bin/login -h %h %?T{TERM=%T}{-} %?u{%?a{-f }-- %u}"
#else
"/bin/login -p -h %h %?u{-f %u}"
#endif
;

int keepalive = 1;      /* Should the TCP keepalive bit be set */
int reverse_lookup = 0; /* Reject connects from hosts which IP numbers
			   cannot be reverse mapped to their hostnames */
int alwayslinemode;     /* Always set the linemode (1) */ 
int lmodetype;          /* Type of linemode (2) */
int hostinfo = 1;       /* Print the host-specific information before
			   login */

int auth_level = 0;     /* Authentication level */

int debug_level[debug_max_mode]; /* Debugging levels */
int debug_tcp = 0;               /* Should the SO_DEBUG be set? */

int net;      /* Network connection socket */
int pty;      /* PTY master descriptor */
char *remote_hostname;
char *local_hostname;
char *user_name;
char line[256];

char	options[256];
char	do_dont_resp[256];
char	will_wont_resp[256];
int	linemode;	/* linemode on/off */
int	uselinemode;	/* what linemode to use (on/off) */
int	editmode;	/* edit modes in use */
int	useeditmode;	/* edit modes to use */
int	alwayslinemode;	/* command line option */
int	lmodetype;	/* Client support for linemode */
int	flowmode;	/* current flow control state */
int	restartany;	/* restart output on any character state */
int	diagnostic;	/* telnet diagnostic capabilities */
#if defined(AUTHENTICATION)
int	auth_level;
int     autologin;
#endif

slcfun	slctab[NSLC + 1];	/* slc mapping table */

char	*terminaltype;

int	SYNCHing;		/* we are in TELNET SYNCH mode */
struct telnetd_clocks clocks;
char *program_name;

int
main (int argc, char **argv)
{
  int c;
  program_name = argv[0];
  while ((c = getopt_long (argc, argv, short_options, long_options, NULL))
	 != EOF)
    {
      switch (c)
	{
	case 'V': 
	  telnetd_version ();
	  exit (0);
	  
	case 'L':
	  telnetd_license ();
	  exit (0);
	  
	case 'H':
	  telnetd_help ();
	  exit (0);
	  
	case 'a':
	  parse_authmode (optarg);
	  break;
	  
	case 'D':
	  parse_debug_level (optarg);
	  break;
	  
	case 'E':
	  login_invocation = optarg;
	  break;
	  
	case 'h':
	  hostinfo = 0;
	  break;
	  
	case 'l':
	  parse_linemode (optarg);
	  break;
	  
	case 'n':
	  keepalive = 0;
	  break;
	  
	case 'U':
	  reverse_lookup = 1;
	  break;
	  
#ifdef	AUTHENTICATION
	case 'X':
	  auth_disable_name (optarg);
	  break;
#endif
	default:
	  fprintf (stderr, "telnetd: unknown command line option: %c\n", c);
	  exit (1);
	}
    }

  if (argc != optind)
    {
      fprintf (stderr, "telnetd: junk arguments in the command line\n");
      exit (1);
    }
  
  openlog ("telnetd", LOG_PID | LOG_ODELAY, LOG_DAEMON);
  telnetd_setup (0);
  return telnetd_run ();
}

void
parse_linemode (char *str)
{
  if (!str)
    alwayslinemode = 1;
  else if (strcmp (str, "nokludge") == 0)
    lmodetype = NO_AUTOKLUDGE;
  else
    fprintf (stderr,
	     "telnetd: invalid argument to --linemode\n");
}

void
parse_authmode (char *str)
{
  if (strcasecmp (str, "none") == 0) 
    auth_level = 0;
  else if (strcasecmp (str, "other") == 0) 
    auth_level = AUTH_OTHER;
  else if (strcasecmp (str, "user") == 0) 
    auth_level = AUTH_USER;
  else if (strcasecmp (str, "valid") == 0) 
    auth_level = AUTH_VALID;
  else if (strcasecmp (str, "off") == 0) 
    auth_level = -1;
  else 
    fprintf (stderr,
	     "telnetd: unknown authorization level for -a\n");
}

static struct {
  char *name;
  int modnum;
} debug_mode[debug_max_mode] = {
  "options", debug_options,
  "report",  debug_report,
  "netdata", debug_net_data,
  "ptydata", debug_pty_data,
  "auth", debug_auth,
};

void
parse_debug_level (char *str)
{
  int i;
  char *tok;

  if (!str)
    {
      for (i = 0; i < debug_max_mode; i++) 
	debug_level[ debug_mode[i].modnum ] = MAX_DEBUG_LEVEL;
      return;
    }
  
  for (tok = strtok (str, ","); tok; tok = strtok (NULL, ","))
    {
      int length, level;
      char *p;

      if (strcmp (tok, "tcp") == 0)
	{
	  debug_tcp = 1;
	  continue;
	}

      p = strchr (tok, '=');
      if (p)
	{
	  length = p - tok;
	  level  = strtoul (p+1, NULL, 0);
	}
      else
	{
	  length = strlen (tok);
	  level  = MAX_DEBUG_LEVEL;
	}

      for (i = 0; i < debug_max_mode; i++) 
	if (strncmp (debug_mode[i].name, tok, length) == 0)
	  {
	    debug_level[ debug_mode[i].modnum ] = level;
	    break;
	  }

      if (i == debug_max_mode)
	fprintf (stderr, "telnetd: unknown debug mode: %s", tok);
    }
}


typedef unsigned int ip_addr_t; /*FIXME*/

void
telnetd_setup (int fd)
{
#ifdef IPV6
  struct sockaddr_storage saddr;
  char buf[256], buf2[256]; /* FIXME: We should use dynamic allocation. */
  int err;
#else
  struct sockaddr_in saddr;
  struct hostent *hp;
#endif
  int true = 1;
  socklen_t len;
  char uname[256]; /*FIXME*/
  int level;
 
  len = sizeof (saddr);
  if (getpeername(fd, (struct sockaddr *)&saddr, &len) < 0)
    {
      syslog (LOG_ERR, "getpeername: %m");
      exit (1);
    }

#ifdef IPV6
  err = getnameinfo ((struct sockaddr *) &saddr, sizeof (saddr), buf,
		     sizeof (buf), NULL, 0, NI_NUMERICHOST);
  if (err)
    {
      const char *errmsg;
      
      if (err == EAI_SYSTEM)
	errmsg = strerror (errno);
      else
	errmsg = gai_strerror (err);
      
      syslog (LOG_AUTH|LOG_NOTICE, "Cannot get address: %s", errmsg);
      fatal (fd, "Cannot get address.");
    }

  /* We use a second buffer so we don't have to call getnameinfo again
     if we need the numeric host below.  */
  err = getnameinfo ((struct sockaddr *) &saddr, sizeof (saddr), buf2,
		     sizeof (buf2), NULL, 0, NI_NAMEREQD);

  if (reverse_lookup)
    {
      struct addrinfo *result, *aip;

      if (err)
	{
	  const char *errmsg;
	  
	  if (err == EAI_SYSTEM)
	    errmsg = strerror (errno);
	  else
	    errmsg = gai_strerror (err);
	  
	  syslog (LOG_AUTH|LOG_NOTICE, "Can't resolve %s: %s", buf, errmsg);
	  fatal (fd, "Cannot resolve address.");
	}

      remote_hostname = xstrdup (buf2);

      err = getaddrinfo (remote_hostname, NULL, NULL, &result);
      if (err)
	{
	  const char *errmsg;
	  
	  if (err == EAI_SYSTEM)
	    errmsg = strerror (errno);
	  else
	    errmsg = gai_strerror (err);
	  
	  syslog (LOG_AUTH|LOG_NOTICE, "Forward resolve of %s failed: %s",
		  remote_hostname, errmsg);
	  fatal (fd, "Cannot resolve address.");
	}

      for (aip = result; aip; aip = aip->ai_next)
	if (!memcmp (aip->ai_addr, &saddr, aip->ai_addrlen))
	  break;

      if (aip == NULL)
	{
	  syslog (LOG_AUTH|LOG_NOTICE,
		  "None of addresses of %s matched %s",
		  remote_hostname,
		  buf);
	  exit (0);
	}

      freeaddrinfo (result);
    }
  else
    {
      if (!err)
	remote_hostname = xstrdup (buf2);
      else
	remote_hostname = xstrdup (buf);
    }
#else
  hp = gethostbyaddr ((char*)&saddr.sin_addr.s_addr,
		      sizeof (saddr.sin_addr.s_addr), AF_INET);
  if (reverse_lookup)
    {
      char **ap;
      
      if (!hp)
	{