lib/login_tty.c

   1 /* Assign a given terminal as controlling terminal and as standard input,
   2    standard output, standard error of the current process.
   3    Copyright (C) 2010-2021 Free Software Foundation, Inc.
   4
   5    This program is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 3 of the License, or
   8    (at your option) any later version.
   9
  10    This program 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
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  17
  18 #include <config.h>
  19
  20 /* Currently no specification header.  */
  21
  22 #include <fcntl.h>
  23 #include <unistd.h>
  24 #include <sys/ioctl.h>
  25
  26 int
  27 login_tty (int slave_fd)
  28 {
  29   int i;
  30
  31   /* Create a new session.  */
  32   setsid ();
  33
  34   /* Make fd the controlling terminal for the current process.
  35      On BSD and OSF/1: There is ioctl TIOCSCTTY for this purpose.
  36      On Solaris:
  37        A terminal becomes the controlling terminal of a session
  38        if it is being open()ed, at a moment when
  39          1. it is not already the controlling terminal of some session, and
  40          2. the process that open()s it is a session leader that does not have
  41             a controlling terminal.
  42        We assume condition 1, try to ensure condition 2, and then open() it.
  43    */
  44   for (i = 0; i < 3; i++)
  45     if (i != slave_fd)
  46       close (i);
  47 #ifdef TIOCSCTTY
  48   if (ioctl (slave_fd, TIOCSCTTY, NULL) < 0)
  49     return -1;
  50 #else
  51   {
  52     char *slave_name;
  53     int dummy_fd;
  54
  55     slave_name = ttyname (slave_fd);
  56     if (slave_name == NULL)
  57       return -1;
  58     dummy_fd = open (slave_name, O_RDWR | O_CLOEXEC);
  59     if (dummy_fd < 0)
  60       return -1;
  61     close (dummy_fd);
  62   }
  63 #endif
  64
  65   /* Assign fd to the standard input, standard output, and standard error of
  66      the current process.  */
  67   for (i = 0; i < 3; i++)
  68     if (slave_fd != i)
  69       if (dup2 (slave_fd, i) < 0)
  70         return -1;
  71   if (slave_fd >= 3)
  72     close (slave_fd);
  73
  74   return 0;
  75 }