freopen-safer.c

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Hash : c08f85d7
Author :
Date : 2020-05-01T18:12:12

attribute: new module

This simplifies use of GCC and C2X attributes like ‘deprecated’.
* MODULES.html.sh: Add attribute.
* doc/attribute.texi, lib/attribute.h, modules/attribute: New files.
* doc/gnulib.texi (Particular Modules): Add Attributes.
* lib/backupfile.c, lib/fnmatch.c, lib/freopen-safer.c:
* lib/mbrtoc32.c, lib/mbrtowc.c, lib/nstrftime.c, lib/quotearg.c:
* lib/savewd.c, lib/unistr/u8-uctomb-aux.c, lib/unistr/u8-uctomb.c:
* lib/vasnprintf.c:
Include attribute.h, and let it define FALLTHROUGH.
* lib/bitset/base.h, lib/c-stack.c (__attribute__): Remove macro.
* lib/bitset/base.h (ATTRIBUTE_UNUSED): Define in terms of
_GL_ATTRIBUTE_MAYBE_UNUSED, for forwards compatibility to C2X.
* lib/dfa.c (FALLTHROUGH): Define consistently with gl_COMMON_BODY.
This is a copy since Gawk doesn’t use Gnulib.
* lib/di-set.h (_GL_ATTRIBUTE_NONNULL): Remove definition that
is incompatible with gl_COMMON_BODY’s.  All uses changed.
* lib/fts.c: Include attribte.h, for FALLTHROUGH.
Keep the existing FALLTHROUGH definition since Glibc might use it,
and it does no harm to Gnulib’s FALLTHROUGH.
* lib/fts_.h, lib/inttostr.h:
(__GNUC_PREREQ): Remove; no longer needed.
(__attribute_warn_unused_result__): Remove.  All uses
replaced by _GL_ATTRIBUTE_NODISCARD.
* lib/gl_list.h, lib/gl_map.h, lib/gl_omap.h, lib/gl_oset.h:
* lib/gl_set.h: Prefer _GL_ATTRIBUTE_NODISCARD to an ifdeffed
__attribute__ ((__warn_unused_result__)), for forward
compatibility to C2X.
* lib/hash.h (_GL_ATTRIBUTE_WUR): Remove.  All uses replaced by
_GL_ATTRIBUTE_NODISCARD.
(_GL_ATTRIBUTE_DEPRECATED): Remove, since gl_COMMON_BODY defines it.
* lib/ino-map.h (_GL_ATTRIBUTE_NONNULL): Remove.  All uses
replaced by gl_COMMON_BODY’s implementation, which has a
slightly different signature.
* lib/safe-alloc.h (_GL_ATTRIBUTE_RETURN_CHECK):
Remove.  All uses replaced by _GL_ATTRIBUTE_NODISCARD.
* lib/unused-parameter.h (_GL_UNUSED_PARAMETER):
Define in terms of _GL_ATTRIBUTE_MAYBE_UNUSED.
No doubt all uses should be replaced, at some point.
* m4/gnulib-common.m4 (_GL_GNUC_PREREQ): New macro.
(_Noreturn): Use it.
(_GL_HAS_ATTRIBUTE, _GL_ATTRIBUTE_ALLOC_SIZE)
(_GL_ATTRIBUTE_ALWAYS_INLINE, _GL_ATTRIBUTE_ARTIFICIAL)
(_GL_ATTRIBUTE_COLD)
(_GL_ATTRIBUTE_DEPRECATED, _GL_ATTRIBUTE_ERROR)
(_GL_ATTRIBUTE_WARNING, _GL_ATTRIBUTE_EXTERNALLY_VISIBLE)
(_GL_ATTRIBUTE_FALLTHROUGH, _GL_ATTRIBUTE_FORMAT)
(_GL_ATTRIBUTE_LEAF, _GL_ATTRIBUTE_MAY_ALIAS)
(_GL_ATTRIBUTE_MAYBE_UNUSED)
(_GL_ATTRIBUTE_NODISCARD, _GL_ATTRIBUTE_NOINLINE)
(_GL_ATTRIBUTE_NONNULL, _GL_ATTRIBUTE_NONSTRING)
(_GL_ATTRIBUTE_NOTHROW, _GL_ATTRIBUTE_PACKED, _GL_ATTRIBUTE_PURE)
(_GL_ATTRIBUTE_SENTINEL): New macros.
* modules/backup-rename, modules/backupfile, modules/c-vasnprintf:
* modules/fnmatch, modules/freopen-safer, modules/fts:
* modules/mbrtoc32, modules/mbrtowc, modules/nstrftime:
* modules/quotearg, modules/savewd:
* modules/unistdio/u16-u16-vasnprintf:
* modules/unistdio/u16-vasnprintf:
* modules/unistdio/u32-u32-vasnprintf:
* modules/unistdio/u32-vasnprintf:
* modules/unistdio/u8-u8-vasnprintf:
* modules/unistdio/u8-vasnprintf:
* modules/unistdio/ulc-vasnprintf:
* modules/unistr/u8-uctomb, modules/vasnprintf:
(Depends-on:): Add attribute module.

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lib/freopen-safer.c

/* Invoke freopen, but avoid some glitches.

   Copyright (C) 2009-2020 Free Software Foundation, Inc.

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program 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 General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */

/* Written by Eric Blake.  */

#include <config.h>

#include "stdio-safer.h"

#include "attribute.h"

#include <errno.h>
#include <fcntl.h>
#include <stdbool.h>
#include <unistd.h>

/* Guarantee that FD is open; all smaller FDs must already be open.
   Return true if successful.  */
static bool
protect_fd (int fd)
{
  int value = open ("/dev/null", O_RDONLY);
  if (value != fd)
    {
      if (0 <= value)
        {
          close (value);
          errno = EBADF; /* Unexpected; this is as good as anything else.  */
        }
      return false;
    }
  return true;
}

/* Like freopen, but guarantee that reopening stdin, stdout, or stderr
   preserves the invariant that STDxxx_FILENO==fileno(stdxxx), and
   that no other stream will interfere with the standard streams.
   This is necessary because most freopen implementations will change
   the associated fd of a stream to the lowest available slot.  */

FILE *
freopen_safer (char const *name, char const *mode, FILE *f)
{
  /* Unfortunately, we cannot use the fopen_safer approach of using
     fdopen (dup_safer (fileno (freopen (cmd, mode, f)))), because we
     need to return f itself.  The implementation of freopen(NULL,m,f)
     is system-dependent, so the best we can do is guarantee that all
     lower-valued standard fds are open prior to the freopen call,
     even though this puts more pressure on open fds.  */
  bool protect_in = false;
  bool protect_out = false;
  bool protect_err = false;
  int saved_errno;

  switch (fileno (f))
    {
    default: /* -1 or not a standard stream.  */
      if (dup2 (STDERR_FILENO, STDERR_FILENO) != STDERR_FILENO)
        protect_err = true;
      FALLTHROUGH;
    case STDERR_FILENO:
      if (dup2 (STDOUT_FILENO, STDOUT_FILENO) != STDOUT_FILENO)
        protect_out = true;
      FALLTHROUGH;
    case STDOUT_FILENO:
      if (dup2 (STDIN_FILENO, STDIN_FILENO) != STDIN_FILENO)
        protect_in = true;
      FALLTHROUGH;
    case STDIN_FILENO:
      /* Nothing left to protect.  */
      break;
    }
  if (protect_in && !protect_fd (STDIN_FILENO))
    f = NULL;
  else if (protect_out && !protect_fd (STDOUT_FILENO))
    f = NULL;
  else if (protect_err && !protect_fd (STDERR_FILENO))
    f = NULL;
  else
    f = freopen (name, mode, f);
  saved_errno = errno;
  if (protect_err)
    close (STDERR_FILENO);
  if (protect_out)
    close (STDOUT_FILENO);
  if (protect_in)
    close (STDIN_FILENO);
  if (!f)
    errno = saved_errno;
  return f;
}

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lib/freopen-safer.c