/*
  Copyright (C) 2002-2023 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 3 of the License, 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 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 this program.  If not, see `http://www.gnu.org/licenses/'. */

#include <config.h>

#include "telnetd.h"
#include <sys/wait.h>
#include <pty.h>

#ifdef AUTHENTICATION
# include <libtelnet/auth.h>
#endif
#include <libinetutils.h>

void
setup_utmp (char *line, char *host)
{
  char *ut_id = utmp_ptsid (line, "tn");
  utmp_init (line + sizeof (PATH_TTY_PFX) - 1, ".telnet", ut_id, host);
}


int
startslave (char *host, int autologin, char *autoname)
{
  pid_t pid;
  int master;

#ifdef AUTHENTICATION
  if (!autoname || !autoname[0])
    autologin = 0;

  if (autologin < auth_level)
    {
      fatal (net, "Authorization failed");
      exit (EXIT_FAILURE);
    }
#else /* !AUTHENTICATION */
  (void) autoname;		/* Silence warnings.  */
#endif

  pid = forkpty (&master, line, NULL, NULL);
  if (pid < 0)
    {
      if (errno == ENOENT)
	{
	  syslog (LOG_ERR, "Out of ptys");
	  fatal (net, "Out of ptys");
	}
      else
	{
	  syslog (LOG_ERR, "forkpty: %m");
	  fatal (net, "Forkpty");
	}
    }

  if (pid == 0)
    {
      /* Child */
      if (net > 2)
	close (net);

      setup_utmp (line, host);
      start_login (host, autologin, line);
    }

  /* Master */
  return master;
}

extern char **environ;
/*
 * scrub_env()
 *
 * Remove a few things from the environment that
 * don't need to be there.
 *
 * Security fix included in telnet-95.10.23.NE of David Borman <deb@cray.com>.
 */
static void
scrub_env (void)
{
  register char **cpp, **cpp2;

  for (cpp2 = cpp = environ; *cpp; cpp++)
    {
      if (strncmp (*cpp, "LD_", 3)
	  && strncmp (*cpp, "_RLD_", 5)
	  && strncmp (*cpp, "LIBPATH=", 8) && strncmp (*cpp, "IFS=", 4))
	*cpp2++ = *cpp;
    }
  *cpp2 = 0;
}

void
start_login (char *host, int autologin, char *name)
{
  char *cmd;
  int argc;
  char **argv;

  (void) host;			/* Silence warnings.  Diagnostic use?  */
  (void) autologin;
  (void) name;

  scrub_env ();

  /* Set the environment variable "LINEMODE" to indicate our linemode */
  if (lmodetype == REAL_LINEMODE)
    setenv ("LINEMODE", "real", 1);
  else if (lmodetype == KLUDGE_LINEMODE || lmodetype == KLUDGE_OK)
    setenv ("LINEMODE", "kludge", 1);

  cmd = expand_line (login_invocation);
  if (!cmd)
    fatal (net, "can't expand login command line");
  argcv_get (cmd, "", &argc, &argv);

  /* util-linux's "login" introduced an authentication bypass method
   * via environment variable "CREDENTIALS_DIRECTORY" in version 2.40.
   * Clear it from the environment before executing "login" to prevent
   * abuse via Telnet.
   */
  unsetenv ("CREDENTIALS_DIRECTORY");

  execv (argv[0], argv);
  syslog (LOG_ERR, "%s: %m\n", cmd);
  fatalperror (net, cmd);
}

/* SIG is generally naught every time the server itself
 * decides to close the connection out of an error condition.
 * In response to TELOPT_LOGOUT from the client, SIG is set
 * to SIGHUP, so we consider the exit as a success.  In other
 * cases, when the forked client process is caught exiting,
 * then SIG will be SIGCHLD.  Then we deliver the clients's
 * reported exit code.
 */
void
cleanup (int sig)
{
  int status = EXIT_FAILURE;
  char *p;

  if (sig == SIGCHLD)
    {
      pid_t pid = waitpid ((pid_t) - 1, &status, WNOHANG);
      syslog (LOG_INFO, "child process %ld exited: %d",
	      (long) pid, WEXITSTATUS (status));

      status = WEXITSTATUS (status);
    }
  else if (sig == SIGHUP)
    status = EXIT_SUCCESS;	/* Response to TELOPT_LOGOUT.  */

  p = line + sizeof (PATH_TTY_PFX) - 1;
  utmp_logout (p);
  chmod (line, 0644);
  chown (line, 0, 0);
  shutdown (net, 2);
  exit (status);
}
