misc/getpass.c

   1 /* Copyright (C) 1992-2023 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 <stdio.h>
  19 #include <stdio_ext.h>
  20 #include <string.h>             /* For string function builtin redirect.  */
  21 #include <termios.h>
  22 #include <unistd.h>
  23
  24 #include <wchar.h>
  25 #define flockfile(s) _IO_flockfile (s)
  26 #define funlockfile(s) _IO_funlockfile (s)
  27 #include <libc-lock.h>
  28
  29 /* It is desirable to use this bit on systems that have it.
  30    The only bit of terminal state we want to twiddle is echoing, which is
  31    done in software; there is no need to change the state of the terminal
  32    hardware.  */
  33
  34 #ifndef TCSASOFT
  35 #define TCSASOFT 0
  36 #endif
  37
  38 static void
  39 call_fclose (void *arg)
  40 {
  41   if (arg != NULL)
  42     fclose (arg);
  43 }
  44
  45 char *
  46 getpass (const char *prompt)
  47 {
  48   FILE *in, *out;
  49   struct termios s, t;
  50   int tty_changed;
  51   static char *buf;
  52   static size_t bufsize;
  53   ssize_t nread;
  54
  55   /* Try to write to and read from the terminal if we can.
  56      If we can't open the terminal, use stderr and stdin.  */
  57
  58   in = fopen ("/dev/tty", "w+ce");
  59   if (in == NULL)
  60     {
  61       in = stdin;
  62       out = stderr;
  63     }
  64   else
  65     {
  66       /* We do the locking ourselves.  */
  67       __fsetlocking (in, FSETLOCKING_BYCALLER);
  68
  69       out = in;
  70     }
  71
  72   /* Make sure the stream we opened is closed even if the thread is
  73      canceled.  */
  74   __libc_cleanup_push (call_fclose, in == out ? in : NULL);
  75
  76   flockfile (out);
  77
  78   /* Turn echoing off if it is on now.  */
  79
  80   if (__tcgetattr (fileno (in), &t) == 0)
  81     {
  82       /* Save the old one. */
  83       s = t;
  84       /* Tricky, tricky. */
  85       t.c_lflag &= ~(ECHO|ISIG);
  86       tty_changed = (tcsetattr (fileno (in), TCSAFLUSH|TCSASOFT, &t) == 0);
  87     }
  88   else
  89     tty_changed = 0;
  90
  91   /* Write the prompt.  */
  92   __fxprintf (out, "%s", prompt);
  93   __fflush_unlocked (out);
  94
  95   /* Read the password.  */
  96   nread = __getline (&buf, &bufsize, in);
  97   if (buf != NULL)
  98     {
  99       if (nread < 0)
 100         buf[0] = '\0';
 101       else if (buf[nread - 1] == '\n')
 102         {
 103           /* Remove the newline.  */
 104           buf[nread - 1] = '\0';
 105           if (tty_changed)
 106             /* Write the newline that was not echoed.  */
 107             __fxprintf (out, "\n");
 108         }
 109     }
 110
 111   /* Restore the original setting.  */
 112   if (tty_changed)
 113     (void) tcsetattr (fileno (in), TCSAFLUSH|TCSASOFT, &s);
 114
 115   funlockfile (out);
 116
 117   __libc_cleanup_pop (0);
 118
 119   if (in != stdin)
 120     /* We opened the terminal; now close it.  */
 121     fclose (in);
 122
 123   return buf;
 124 }