login/openpty.c

   1 /* Copyright (C) 1998-2020 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Zack Weinberg <zack@rabi.phys.columbia.edu>, 1998.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <errno.h>
  20 #include <fcntl.h>
  21 #include <limits.h>
  22 #include <pty.h>
  23 #include <stdlib.h>
  24 #include <string.h>
  25 #include <termios.h>
  26 #include <unistd.h>
  27 #include <sys/types.h>
  28
  29
  30 /* Return the result of ptsname_r in the buffer pointed to by PTS,
  31    which should be of length BUF_LEN.  If it is too long to fit in
  32    this buffer, a sufficiently long buffer is allocated using malloc,
  33    and returned in PTS.  0 is returned upon success, -1 otherwise.  */
  34 static int
  35 pts_name (int fd, char **pts, size_t buf_len)
  36 {
  37   int rv;
  38   char *buf = *pts;
  39
  40   for (;;)
  41     {
  42       char *new_buf;
  43
  44       if (buf_len)
  45         {
  46           rv = ptsname_r (fd, buf, buf_len);
  47
  48           if (rv != 0 || memchr (buf, '\0', buf_len))
  49             /* We either got an error, or we succeeded and the
  50                returned name fit in the buffer.  */
  51             break;
  52
  53           /* Try again with a longer buffer.  */
  54           buf_len += buf_len;   /* Double it */
  55         }
  56       else
  57         /* No initial buffer; start out by mallocing one.  */
  58         buf_len = 128;          /* First time guess.  */
  59
  60       if (buf != *pts)
  61         /* We've already malloced another buffer at least once.  */
  62         new_buf = realloc (buf, buf_len);
  63       else
  64         new_buf = malloc (buf_len);
  65       if (! new_buf)
  66         {
  67           rv = -1;
  68           __set_errno (ENOMEM);
  69           break;
  70         }
  71       buf = new_buf;
  72     }
  73
  74   if (rv == 0)
  75     *pts = buf;         /* Return buffer to the user.  */
  76   else if (buf != *pts)
  77     free (buf);         /* Free what we malloced when returning an error.  */
  78
  79   return rv;
  80 }
  81
  82 /* Create pseudo tty master slave pair and set terminal attributes
  83    according to TERMP and WINP.  Return handles for both ends in
  84    AMASTER and ASLAVE, and return the name of the slave end in NAME.  */
  85 int
  86 openpty (int *amaster, int *aslave, char *name,
  87          const struct termios *termp, const struct winsize *winp)
  88 {
  89 #ifdef PATH_MAX
  90   char _buf[PATH_MAX];
  91 #else
  92   char _buf[512];
  93 #endif
  94   char *buf = _buf;
  95   int master, ret = -1, slave = -1;
  96
  97   *buf = '\0';
  98
  99   master = getpt ();
 100   if (master == -1)
 101     return -1;
 102
 103   if (grantpt (master))
 104     goto on_error;
 105
 106   if (unlockpt (master))
 107     goto on_error;
 108
 109 #ifdef TIOCGPTPEER
 110   /* Try to allocate slave fd solely based on master fd first. */
 111   slave = ioctl (master, TIOCGPTPEER, O_RDWR | O_NOCTTY);
 112 #endif
 113   if (slave == -1)
 114     {
 115       /* Fallback to path-based slave fd allocation in case kernel doesn't
 116        * support TIOCGPTPEER.
 117        */
 118       if (pts_name (master, &buf, sizeof (_buf)))
 119         goto on_error;
 120
 121       slave = open (buf, O_RDWR | O_NOCTTY);
 122       if (slave == -1)
 123         goto on_error;
 124     }
 125
 126   /* XXX Should we ignore errors here?  */
 127   if (termp)
 128     tcsetattr (slave, TCSAFLUSH, termp);
 129 #ifdef TIOCSWINSZ
 130   if (winp)
 131     ioctl (slave, TIOCSWINSZ, winp);
 132 #endif
 133
 134   *amaster = master;
 135   *aslave = slave;
 136   if (name != NULL)
 137     {
 138       if (*buf == '\0')
 139         if (pts_name (master, &buf, sizeof (_buf)))
 140           goto on_error;
 141
 142       strcpy (name, buf);
 143     }
 144
 145   ret = 0;
 146
 147  on_error:
 148   if (ret == -1) {
 149     close (master);
 150
 151     if (slave != -1)
 152       close (slave);
 153   }
 154
 155   if (buf != _buf)
 156     free (buf);
 157
 158   return ret;
 159 }
 160 libutil_hidden_def (openpty)