inetutils/libinetutils/ttymsg.c

/*
  Copyright (C) 1996-2025 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/'. */

/*
 * Copyright (c) 1989, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <config.h>

#include <sys/types.h>
#include <sys/uio.h>
#include <signal.h>
#include <fcntl.h>
#include <errno.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/wait.h>

#define MAX_ERRBUF 1024

static int fork2 (void);
static char *normalize_path (char *path, const char *delim);

/*
 * Display the contents of a uio structure on a terminal.  Used by wall(1),
 * syslogd(8), and talkd(8).  Forks and finishes in child if write would block,
 * waiting up to tmout seconds.  Returns pointer to error string on unexpected
 * error; string is not newline-terminated.  Various "normal" errors are
 * ignored (exclusive-use, lack of permission, etc.).
 */
char *
inetutils_ttymsg (struct iovec *iov, int iovcnt, char *line, int tmout)
{
  static char errbuf[MAX_ERRBUF];
  char *device;
  int cnt, fd, left, wret;
  struct iovec localiov[6];
  int forked = 0;

  if (iovcnt > (int) (sizeof (localiov) / sizeof (localiov[0])))
    return (char *) ("too many iov's (change code in wall/ttymsg.c)");

  device = malloc (sizeof PATH_TTY_PFX - 1 + strlen (line) + 1);
  if (!device)
    {
      snprintf (errbuf, sizeof errbuf,
		"Not enough memory for tty device name");
      return errbuf;
    }

  strcpy (device, PATH_TTY_PFX);
  strcat (device, line);
  normalize_path (device, "/");
  if (strncmp (device, PATH_TTY_PFX, strlen (PATH_TTY_PFX)))
    {
      /* An attempt to break security... */
      snprintf (errbuf, sizeof (errbuf), "bad line name: %s", line);
      return (errbuf);
    }

  /*
   * open will fail on slip lines or exclusive-use lines
   * if not running as root; not an error.
   */
  fd = open (device, O_WRONLY | O_NONBLOCK, 0);
  if (fd < 0)
    {
      if (errno == EBUSY || errno == EACCES)
	return (NULL);
#ifdef READUTMP_USE_SYSTEMD
      /*
       * GNU/Linux systems without utmp file but with utmp emulation
       * provided via Gnulib's read_utmp() function regularly return
       * non-existing TTYs for some active user sessions.  This is a
       * limitation of the utmp emulation.  Thus ignore this error on
       * such systems, but not others.
       */
      if (errno == ENOENT)
	return (NULL);
#endif
      snprintf (errbuf, sizeof (errbuf), "%s: %s", device, strerror (errno));
      free (device);
      return errbuf;
    }

  for (cnt = left = 0; cnt < iovcnt; ++cnt)
    left += iov[cnt].iov_len;

  for (;;)
    {
      wret = writev (fd, iov, iovcnt);
      if (wret >= left)
	break;
      if (wret >= 0)
	{
	  left -= wret;
	  if (iov != localiov)
	    {
	      memcpy (localiov, iov, iovcnt * sizeof (struct iovec));
	      iov = localiov;
	    }
	  for (cnt = 0; wret >= (int) iov->iov_len; ++cnt)
	    {
	      wret -= iov->iov_len;
	      ++iov;
	      --iovcnt;
	    }
	  if (wret)
	    {
	      iov->iov_base = (char *) iov->iov_base + wret;
	      iov->iov_len -= wret;
	    }
	  continue;
	}
      if (errno == EWOULDBLOCK)
	{
	  int cpid, off = 0;

	  if (forked)
	    {
	      close (fd);
	      _exit (EXIT_FAILURE);
	    }
	  cpid = fork2 ();
	  if (cpid < 0)
	    {
	      snprintf (errbuf, sizeof (errbuf),
			"fork: %s", strerror (errno));
	      close (fd);
	      free (device);
	      return (errbuf);
	    }
	  if (cpid)		/* Parent.  */
	    {
	      close (fd);
	      free (device);
	      return (NULL);
	    }
	  forked++;
	  /* wait at most tmout seconds */
	  signal (SIGALRM, SIG_DFL);
	  signal (SIGTERM, SIG_DFL);	/* XXX */
#ifdef HAVE_SIGACTION
	  {
	    sigset_t empty;
	    sigemptyset (&empty);
	    sigprocmask (SIG_SETMASK, &empty, 0);
	  }
#else
	  sigsetmask (0);
#endif
	  alarm ((unsigned int) tmout);
	  fcntl (fd, O_NONBLOCK, &off);
	  continue;
	}
      /*
       * We get ENODEV on a slip line if we're running as root,
       * and EIO if the line just went away.
       */
      if (errno == ENODEV || errno == EIO)
	break;
      close (fd);
      if (forked)
	_exit (EXIT_FAILURE);
      snprintf (errbuf, sizeof (errbuf), "%s: %s", device, strerror (errno));
      free (device);
      return (errbuf);
    }

  free (device);
  close (fd);
  if (forked)
    _exit (EXIT_SUCCESS);
  return (NULL);
}


/* This was part of the Unix-Faq, maintain by Andrew Gierth.
   fork2() -- like fork, but the new process is immediately orphaned
   (won't leave a zombie when it exits)
   Returns 1 to the parent, not any meaningful pid.
   The parent cannot wait() for the new process (it's unrelated).

   This version assumes that you *haven't* caught or ignored SIGCHLD.
   If you have, then you should just be using fork() instead anyway.  */

static int
fork2 (void)
{
  pid_t pid;
  int status;

  if (!(pid = fork ()))
    {
      switch (fork ())
	{
	case 0:		/* Child.  */
	  return 0;
	case -1:
	  _exit (errno);	/* Assumes all errnos are <256 */
	default:		/* Parent.  */
	  _exit (EXIT_SUCCESS);
	}
    }

  if (pid < 0 || waitpid (pid, &status, 0) < 0)
    return -1;

  if (WIFEXITED (status))
    if (WEXITSTATUS (status) == 0)
      return 1;
    else
      errno = WEXITSTATUS (status);
  else
    errno = EINTR;		/* well, sort of :-) */

  return -1;
}

char *
normalize_path (char *path, const char *delim)
{
  int len;
  char *p;

  if (!path)
    return path;

  len = strlen (path);

  /* Empty string is returned as is */
  if (len == 0)
    return path;

  /* delete trailing delimiter if any */
  if (len && path[len - 1] == delim[0])
    path[len - 1] = 0;

  /* Eliminate any /../ */
  for (p = strchr (path, '.'); p; p = strchr (p, '.'))
    {
      if (p > path && p[-1] == delim[0])
	{
	  if (p[1] == '.' && (p[2] == 0 || p[2] == delim[0]))
	    /* found */
	    {
	      char *q, *s;

	      /* Find previous delimiter */
	      for (q = p - 2; *q != delim[0] && q >= path; q--)
		;

	      if (q < path)
		break;
	      /* Copy stuff */
	      s = p + 2;
	      p = q;
	      while ((*q++ = *s++))
		;
	      continue;
	    }
	}

      p++;
    }

  if (path[0] == 0)
    {
      path[0] = delim[0];
      path[1] = 0;
    }

  return path;
}