glibc/login/openpty.c

/* Copyright (C) 1998-2024 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library 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
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.  */

#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <pty.h>
#include <stdlib.h>
#include <string.h>
#include <termios.h>
#include <unistd.h>
#include <sys/types.h>
#include <shlib-compat.h>

/* Return the result of ptsname_r in the buffer pointed to by PTS,
   which should be of length BUF_LEN.  If it is too long to fit in
   this buffer, a sufficiently long buffer is allocated using malloc,
   and returned in PTS.  0 is returned upon success, -1 otherwise.  */
static int
pts_name (int fd, char **pts, size_t buf_len)
{
  int rv;
  char *buf = *pts;

  for (;;)
    {
      char *new_buf;

      if (buf_len)
	{
	  rv = __ptsname_r (fd, buf, buf_len);

	  if (rv != 0 || memchr (buf, '\0', buf_len))
	    /* We either got an error, or we succeeded and the
	       returned name fit in the buffer.  */
	    break;

	  /* Try again with a longer buffer.  */
	  buf_len += buf_len;	/* Double it */
	}
      else
	/* No initial buffer; start out by mallocing one.  */
	buf_len = 128;		/* First time guess.  */

      if (buf != *pts)
	/* We've already malloced another buffer at least once.  */
	new_buf = realloc (buf, buf_len);
      else
	new_buf = malloc (buf_len);
      if (! new_buf)
	{
	  rv = -1;
	  __set_errno (ENOMEM);
	  break;
	}
      buf = new_buf;
    }

  if (rv == 0)
    *pts = buf;		/* Return buffer to the user.  */
  else if (buf != *pts)
    free (buf);		/* Free what we malloced when returning an error.  */

  return rv;
}

/* Create pseudo tty multiplexer/terminal pair and set terminal attributes
   according to TERMP and WINP.  Return handles for both ends in
   *PPTMX and *PTERMINAL, and return the name of the terminal end in NAME.  */
int
__openpty (int *pptmx, int *pterminal, char *name,
	   const struct termios *termp, const struct winsize *winp)
{
#ifdef PATH_MAX
  char _buf[PATH_MAX];
#else
  char _buf[512];
#endif
  char *buf = _buf;
  int ptmx, ret = -1, terminal = -1;

  *buf = '\0';

  ptmx = __getpt ();
  if (ptmx == -1)
    return -1;

  if (grantpt (ptmx))
    goto on_error;

  if (unlockpt (ptmx))
    goto on_error;

#ifdef TIOCGPTPEER
  /* Try to allocate terminal fd solely based on PTMX fd first. */
  terminal = __ioctl (ptmx, TIOCGPTPEER, O_RDWR | O_NOCTTY);
#endif
  if (terminal == -1)
    {
      /* Fallback to path-based terminal fd allocation in case kernel doesn't
       * support TIOCGPTPEER.
       */
      if (pts_name (ptmx, &buf, sizeof (_buf)))
        goto on_error;

      terminal = __open64 (buf, O_RDWR | O_NOCTTY);
      if (terminal == -1)
        goto on_error;
    }

  /* XXX Should we ignore errors here?  */
  if (termp)
    tcsetattr (terminal, TCSAFLUSH, termp);
#ifdef TIOCSWINSZ
  if (winp)
    __ioctl (terminal, TIOCSWINSZ, winp);
#endif

  *pptmx = ptmx;
  *pterminal = terminal;
  if (name != NULL)
    {
      if (*buf == '\0')
        if (pts_name (ptmx, &buf, sizeof (_buf)))
          goto on_error;

      strcpy (name, buf);
    }

  ret = 0;

 on_error:
  if (ret == -1) {
    __close (ptmx);

    if (terminal != -1)
      __close (terminal);
  }

  if (buf != _buf)
    free (buf);

  return ret;
}
versioned_symbol (libc, __openpty, openpty, GLIBC_2_34);
libc_hidden_ver (__openpty, openpty)

#if OTHER_SHLIB_COMPAT (libutil, GLIBC_2_0, GLIBC_2_34)
compat_symbol (libutil, __openpty, openpty, GLIBC_2_0);
#endif