lib/tmpfile-safer.c

   1 /* Invoke tmpfile, but avoid some glitches.
   2    Copyright (C) 2006, 2009-2024 Free Software Foundation, Inc.
   3
   4    This program is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation, either version 3 of the License, or
   7    (at your option) any later version.
   8
   9    This program 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
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  16
  17 /* Written by Eric Blake, based on ideas from Paul Eggert.  */
  18
  19 #include <config.h>
  20
  21 #include "stdio-safer.h"
  22
  23 #include <errno.h>
  24 #include <unistd.h>
  25 #include "unistd-safer.h"
  26
  27 #include "binary-io.h"
  28
  29 /* Like tmpfile, but do not return stdin, stdout, or stderr.
  30
  31    Remember that tmpfile can leave files behind if your program calls _exit,
  32    so this function should not be mixed with the close_stdout module.  */
  33
  34 FILE *
  35 tmpfile_safer (void)
  36 {
  37   FILE *fp = tmpfile ();
  38
  39   if (fp)
  40     {
  41       int fd = fileno (fp);
  42
  43       if (0 <= fd && fd <= STDERR_FILENO)
  44         {
  45           int f = dup_safer (fd);
  46
  47           if (f < 0)
  48             {
  49               int e = errno;
  50               fclose (fp);
  51               errno = e;
  52               return NULL;
  53             }
  54
  55           /* Keep the temporary file in binary mode, on platforms
  56              where that matters.  */
  57           if (fclose (fp) != 0
  58               || ! (fp = fdopen (f, O_BINARY ? "wb+" : "w+")))
  59             {
  60               int e = errno;
  61               close (f);
  62               errno = e;
  63               return NULL;
  64             }
  65         }
  66     }
  67
  68   return fp;
  69 }