glibc/misc/getpass.c

/* Copyright (C) 1992-2023 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 <stdio.h>
#include <stdio_ext.h>
#include <string.h>		/* For string function builtin redirect.  */
#include <termios.h>
#include <unistd.h>

#include <wchar.h>
#define flockfile(s) _IO_flockfile (s)
#define funlockfile(s) _IO_funlockfile (s)
#include <libc-lock.h>

/* It is desirable to use this bit on systems that have it.
   The only bit of terminal state we want to twiddle is echoing, which is
   done in software; there is no need to change the state of the terminal
   hardware.  */

#ifndef TCSASOFT
#define TCSASOFT 0
#endif

static void
call_fclose (void *arg)
{
  if (arg != NULL)
    fclose (arg);
}

char *
getpass (const char *prompt)
{
  FILE *in, *out;
  struct termios s, t;
  int tty_changed;
  static char *buf;
  static size_t bufsize;
  ssize_t nread;

  /* Try to write to and read from the terminal if we can.
     If we can't open the terminal, use stderr and stdin.  */

  in = fopen ("/dev/tty", "w+ce");
  if (in == NULL)
    {
      in = stdin;
      out = stderr;
    }
  else
    {
      /* We do the locking ourselves.  */
      __fsetlocking (in, FSETLOCKING_BYCALLER);

      out = in;
    }

  /* Make sure the stream we opened is closed even if the thread is
     canceled.  */
  __libc_cleanup_push (call_fclose, in == out ? in : NULL);

  flockfile (out);

  /* Turn echoing off if it is on now.  */

  if (__tcgetattr (fileno (in), &t) == 0)
    {
      /* Save the old one. */
      s = t;
      /* Tricky, tricky. */
      t.c_lflag &= ~(ECHO|ISIG);
      tty_changed = (tcsetattr (fileno (in), TCSAFLUSH|TCSASOFT, &t) == 0);
    }
  else
    tty_changed = 0;

  /* Write the prompt.  */
  __fxprintf (out, "%s", prompt);
  __fflush_unlocked (out);

  /* Read the password.  */
  nread = __getline (&buf, &bufsize, in);
  if (buf != NULL)
    {
      if (nread < 0)
	buf[0] = '\0';
      else if (buf[nread - 1] == '\n')
	{
	  /* Remove the newline.  */
	  buf[nread - 1] = '\0';
	  if (tty_changed)
	    /* Write the newline that was not echoed.  */
	    __fxprintf (out, "\n");
	}
    }

  /* Restore the original setting.  */
  if (tty_changed)
    (void) tcsetattr (fileno (in), TCSAFLUSH|TCSASOFT, &s);

  funlockfile (out);

  __libc_cleanup_pop (0);

  if (in != stdin)
    /* We opened the terminal; now close it.  */
    fclose (in);

  return buf;
}