login/openpty.c

   1 /* Copyright (C) 1998-2024 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.  */
  17
  18 #include <errno.h>
  19 #include <fcntl.h>
  20 #include <limits.h>
  21 #include <pty.h>
  22 #include <stdlib.h>
  23 #include <string.h>
  24 #include <termios.h>
  25 #include <unistd.h>
  26 #include <sys/types.h>
  27 #include <shlib-compat.h>
  28
  29 /* Return the result of ptsname_r in the buffer pointed to by PTS,
  30    which should be of length BUF_LEN.  If it is too long to fit in
  31    this buffer, a sufficiently long buffer is allocated using malloc,
  32    and returned in PTS.  0 is returned upon success, -1 otherwise.  */
  33 static int
  34 pts_name (int fd, char **pts, size_t buf_len)
  35 {
  36   int rv;
  37   char *buf = *pts;
  38
  39   for (;;)
  40     {
  41       char *new_buf;
  42
  43       if (buf_len)
  44         {
  45           rv = __ptsname_r (fd, buf, buf_len);
  46
  47           if (rv != 0 || memchr (buf, '\0', buf_len))
  48             /* We either got an error, or we succeeded and the
  49                returned name fit in the buffer.  */
  50             break;
  51
  52           /* Try again with a longer buffer.  */
  53           buf_len += buf_len;   /* Double it */
  54         }
  55       else
  56         /* No initial buffer; start out by mallocing one.  */
  57         buf_len = 128;          /* First time guess.  */
  58
  59       if (buf != *pts)
  60         /* We've already malloced another buffer at least once.  */
  61         new_buf = realloc (buf, buf_len);
  62       else
  63         new_buf = malloc (buf_len);
  64       if (! new_buf)
  65         {
  66           rv = -1;
  67           __set_errno (ENOMEM);
  68           break;
  69         }
  70       buf = new_buf;
  71     }
  72
  73   if (rv == 0)
  74     *pts = buf;         /* Return buffer to the user.  */
  75   else if (buf != *pts)
  76     free (buf);         /* Free what we malloced when returning an error.  */
  77
  78   return rv;
  79 }
  80
  81 /* Create pseudo tty multiplexer/terminal pair and set terminal attributes
  82    according to TERMP and WINP.  Return handles for both ends in
  83    *PPTMX and *PTERMINAL, and return the name of the terminal end in NAME.  */
  84 int
  85 __openpty (int *pptmx, int *pterminal, char *name,
  86            const struct termios *termp, const struct winsize *winp)
  87 {
  88 #ifdef PATH_MAX
  89   char _buf[PATH_MAX];
  90 #else
  91   char _buf[512];
  92 #endif
  93   char *buf = _buf;
  94   int ptmx, ret = -1, terminal = -1;
  95
  96   *buf = '\0';
  97
  98   ptmx = __getpt ();
  99   if (ptmx == -1)
 100     return -1;
 101
 102   if (grantpt (ptmx))
 103     goto on_error;
 104
 105   if (unlockpt (ptmx))
 106     goto on_error;
 107
 108 #ifdef TIOCGPTPEER
 109   /* Try to allocate terminal fd solely based on PTMX fd first. */
 110   terminal = __ioctl (ptmx, TIOCGPTPEER, O_RDWR | O_NOCTTY);
 111 #endif
 112   if (terminal == -1)
 113     {
 114       /* Fallback to path-based terminal fd allocation in case kernel doesn't
 115        * support TIOCGPTPEER.
 116        */
 117       if (pts_name (ptmx, &buf, sizeof (_buf)))
 118         goto on_error;
 119
 120       terminal = __open64 (buf, O_RDWR | O_NOCTTY);
 121       if (terminal == -1)
 122         goto on_error;
 123     }
 124
 125   /* XXX Should we ignore errors here?  */
 126   if (termp)
 127     tcsetattr (terminal, TCSAFLUSH, termp);
 128 #ifdef TIOCSWINSZ
 129   if (winp)
 130     __ioctl (terminal, TIOCSWINSZ, winp);
 131 #endif
 132
 133   *pptmx = ptmx;
 134   *pterminal = terminal;
 135   if (name != NULL)
 136     {
 137       if (*buf == '\0')
 138         if (pts_name (ptmx, &buf, sizeof (_buf)))
 139           goto on_error;
 140
 141       strcpy (name, buf);
 142     }
 143
 144   ret = 0;
 145
 146  on_error:
 147   if (ret == -1) {
 148     __close (ptmx);
 149
 150     if (terminal != -1)
 151       __close (terminal);
 152   }
 153
 154   if (buf != _buf)
 155     free (buf);
 156
 157   return ret;
 158 }
 159 versioned_symbol (libc, __openpty, openpty, GLIBC_2_34);
 160 libc_hidden_ver (__openpty, openpty)
 161
 162 #if OTHER_SHLIB_COMPAT (libutil, GLIBC_2_0, GLIBC_2_34)
 163 compat_symbol (libutil, __openpty, openpty, GLIBC_2_0);
 164 #endif