/* Invoke opendir, but avoid some glitches.

   Copyright (C) 2009-2017 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 <http://www.gnu.org/licenses/>.  */

/* Written by Eric Blake.  */

#include <config.h>

#include "dirent-safer.h"

#include <errno.h>

#include <unistd.h>

#include "unistd-safer.h"

/* Like opendir, but do not clobber stdin, stdout, or stderr.  */

DIR *

opendir_safer (char const *name)

{

  DIR *dp = opendir (name);

  if (dp)

    {

      int fd = dirfd (dp);

      if (0 <= fd && fd <= STDERR_FILENO)

        {

          /* If fdopendir is native (as on Linux), then it is safe to

             assume dirfd(fdopendir(n))==n.  If we are using the

             gnulib module fdopendir, then this guarantee is not met,

             but fdopendir recursively calls opendir_safer up to 3

             times to at least get a safe fd.  If fdopendir is not

             present but dirfd is accurate (as on cygwin 1.5.x), then

             we recurse up to 3 times ourselves.  Finally, if dirfd

             always fails (as on mingw), then we are already safe.  */

          DIR *newdp;

          int e;

#if HAVE_FDOPENDIR || GNULIB_FDOPENDIR

          int f = dup_safer (fd);

          if (f < 0)

            {

              e = errno;

              newdp = NULL;

            }

          else

            {

              newdp = fdopendir (f);

              e = errno;

              if (! newdp)

                close (f);

            }

#else /* !FDOPENDIR */

          newdp = opendir_safer (name);

          e = errno;

#endif

          closedir (dp);

          errno = e;

          dp = newdp;

        }

    }

  return dp;

}