coreutils/lib/dirchownmod.c

/* Change the ownership and mode bits of a directory.

   Copyright (C) 2006 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 2, 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, write to the Free Software Foundation,
   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */

/* Written by Paul Eggert.  */

#ifdef HAVE_CONFIG_H
# include <config.h>
#endif

#include "dirchownmod.h"

#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

#include "lchmod.h"
#include "stat-macros.h"

#ifndef O_DIRECTORY
# define O_DIRECTORY 0
#endif
#ifndef O_NOFOLLOW
# define O_NOFOLLOW 0
#endif

/* Change the ownership and mode bits of the directory DIR.

   If MKDIR_MODE is not (mode_t) -1, mkdir (DIR, MKDIR_MODE) has just
   been executed successfully with umask zero, so DIR should be a
   directory (not a symbolic link).

   First, set the file's owner to OWNER and group to GROUP, but leave
   the owner alone if OWNER is (uid_t) -1, and similarly for GROUP.

   Then, set the file's mode bits to MODE, except preserve any of the
   bits that correspond to zero bits in MODE_BITS.  In other words,
   MODE_BITS is a mask that specifies which of the file's mode bits
   should be set or cleared.  MODE should be a subset of MODE_BITS,
   which in turn should be a subset of CHMOD_MODE_BITS.

   This implementation assumes the current umask is zero.

   Return 0 if successful, -1 (setting errno) otherwise.  Unsuccessful
   calls may do the chown but not the chmod.  */

int
dirchownmod (char const *dir, mode_t mkdir_mode,
	     uid_t owner, gid_t group,
	     mode_t mode, mode_t mode_bits)
{
  struct stat st;
  int result;

  /* Manipulate DIR via a file descriptor if possible, to avoid some races.  */
  int open_flags = O_RDONLY | O_DIRECTORY | O_NOCTTY | O_NOFOLLOW | O_NONBLOCK;
  int fd = open (dir, open_flags);

  /* Fail if the directory is unreadable, the directory previously
     existed or was created without read permission.  Otherwise, get
     the file's status.  */
  if (0 <= fd)
    result = fstat (fd, &st);
  else if (errno != EACCES
	   || (mkdir_mode != (mode_t) -1 && mkdir_mode & S_IRUSR))
    return fd;
  else
    result = stat (dir, &st);

  if (result == 0)
    {
      mode_t dir_mode = st.st_mode;

      /* Check whether DIR is a directory.  If FD is nonnegative, this
	 check avoids changing the ownership and mode bits of the
	 wrong file in many cases.  This doesn't fix all the race
	 conditions, but it is better than nothing.  */
      if (! S_ISDIR (dir_mode))
	{
	  errno = ENOTDIR;
	  result = -1;
	}
      else
	{
	  /* If at least one of the S_IXUGO bits are set, chown might
	     clear the S_ISUID and S_SGID bits.  Keep track of any
	     file mode bits whose values are indeterminate due to this
	     issue.  */
	  mode_t indeterminate = 0;

	  /* On some systems, chown clears S_ISUID and S_ISGID, so do
	     chown before chmod.  On older System V hosts, ordinary
	     users can give their files away via chown; don't worry
	     about that here, since users shouldn't do that.  */

	  if ((owner != (uid_t) -1 && owner != st.st_uid)
	      || (group != (gid_t) -1 && group != st.st_gid))
	    {
	      result = (0 <= fd
			? fchown (fd, owner, group)
			: mkdir_mode != (mode_t) -1
			? lchown (dir, owner, group)
			: chown (dir, owner, group));

	      /* Either the user cares about an indeterminate bit and
		 it'll be set properly by chmod below, or the user
		 doesn't care and it's OK to use the bit's pre-chown
		 value.  So there's no need to re-stat DIR here.  */

	      if (result == 0 && (dir_mode & S_IXUGO))
		indeterminate = dir_mode & (S_ISUID | S_ISGID);
	    }

	  /* If the file mode bits might not be right, use chmod to
	     change them.  Don't change bits the user doesn't care
	     about.  */
	  if (result == 0 && (((dir_mode ^ mode) | indeterminate) & mode_bits))
	    {
	      mode_t chmod_mode =
		mode | (dir_mode & CHMOD_MODE_BITS & ~mode_bits);
	      result = (0 <= fd
			? fchmod (fd, chmod_mode)
			: mkdir_mode != (mode_t) -1
			? lchmod (dir, chmod_mode)
			: chmod (dir, chmod_mode));
	    }
	}
    }

  if (0 <= fd)
    {
      if (result == 0)
	result = close (fd);
      else
	{
	  int e = errno;
	  close (fd);
	  errno = e;
	}
    }

  return result;
}