lib/dirchownmod.c

   1 /* Change the ownership and mode bits of a directory.
   2
   3    Copyright (C) 2006-2020 Free Software Foundation, Inc.
   4
   5    This program is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 3 of the License, or
   8    (at your option) any later version.
   9
  10    This program is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  17
  18 /* Written by Paul Eggert.  */
  19
  20 #include <config.h>
  21
  22 #include "dirchownmod.h"
  23
  24 #include <errno.h>
  25 #include <sys/types.h>
  26 #include <sys/stat.h>
  27 #include <unistd.h>
  28
  29 #include "stat-macros.h"
  30
  31 #ifndef HAVE_FCHMOD
  32 # define HAVE_FCHMOD 0
  33 # undef fchmod
  34 # define fchmod(fd, mode) (-1)
  35 #endif
  36
  37 /* Change the ownership and mode bits of a directory.  If FD is
  38    nonnegative, it should be a file descriptor associated with the
  39    directory; close it before returning.  DIR is the name of the
  40    directory.
  41
  42    If MKDIR_MODE is not (mode_t) -1, mkdir (DIR, MKDIR_MODE) has just
  43    been executed successfully with umask zero, so DIR should be a
  44    directory (not a symbolic link).
  45
  46    First, set the file's owner to OWNER and group to GROUP, but leave
  47    the owner alone if OWNER is (uid_t) -1, and similarly for GROUP.
  48
  49    Then, set the file's mode bits to MODE, except preserve any of the
  50    bits that correspond to zero bits in MODE_BITS.  In other words,
  51    MODE_BITS is a mask that specifies which of the file's mode bits
  52    should be set or cleared.  MODE should be a subset of MODE_BITS,
  53    which in turn should be a subset of CHMOD_MODE_BITS.
  54
  55    This implementation assumes the current umask is zero.
  56
  57    Return 0 if successful, -1 (setting errno) otherwise.  Unsuccessful
  58    calls may do the chown but not the chmod.  */
  59
  60 int
  61 dirchownmod (int fd, char const *dir, mode_t mkdir_mode,
  62              uid_t owner, gid_t group,
  63              mode_t mode, mode_t mode_bits)
  64 {
  65   struct stat st;
  66   int result = (fd < 0 ? stat (dir, &st) : fstat (fd, &st));
  67
  68   if (result == 0)
  69     {
  70       mode_t dir_mode = st.st_mode;
  71
  72       /* Check whether DIR is a directory.  If FD is nonnegative, this
  73          check avoids changing the ownership and mode bits of the
  74          wrong file in many cases.  This doesn't fix all the race
  75          conditions, but it is better than nothing.  */
  76       if (! S_ISDIR (dir_mode))
  77         {
  78           errno = ENOTDIR;
  79           result = -1;
  80         }
  81       else
  82         {
  83           /* If at least one of the S_IXUGO bits are set, chown might
  84              clear the S_ISUID and S_SGID bits.  Keep track of any
  85              file mode bits whose values are indeterminate due to this
  86              issue.  */
  87           mode_t indeterminate = 0;
  88
  89           /* On some systems, chown clears S_ISUID and S_ISGID, so do
  90              chown before chmod.  On older System V hosts, ordinary
  91              users can give their files away via chown; don't worry
  92              about that here, since users shouldn't do that.  */
  93
  94           if ((owner != (uid_t) -1 && owner != st.st_uid)
  95               || (group != (gid_t) -1 && group != st.st_gid))
  96             {
  97               result = (0 <= fd
  98                         ? fchown (fd, owner, group)
  99                         : mkdir_mode != (mode_t) -1
 100                         ? lchown (dir, owner, group)
 101                         : chown (dir, owner, group));
 102
 103               /* Either the user cares about an indeterminate bit and
 104                  it'll be set properly by chmod below, or the user
 105                  doesn't care and it's OK to use the bit's pre-chown
 106                  value.  So there's no need to re-stat DIR here.  */
 107
 108               if (result == 0 && (dir_mode & S_IXUGO))
 109                 indeterminate = dir_mode & (S_ISUID | S_ISGID);
 110             }
 111
 112           /* If the file mode bits might not be right, use chmod to
 113              change them.  Don't change bits the user doesn't care
 114              about.  */
 115           if (result == 0 && (((dir_mode ^ mode) | indeterminate) & mode_bits))
 116             {
 117               mode_t chmod_mode =
 118                 mode | (dir_mode & CHMOD_MODE_BITS & ~mode_bits);
 119               result = (HAVE_FCHMOD && 0 <= fd
 120                         ? fchmod (fd, chmod_mode)
 121                         : mkdir_mode != (mode_t) -1
 122                         ? lchmod (dir, chmod_mode)
 123                         : chmod (dir, chmod_mode));
 124             }
 125         }
 126     }
 127
 128   if (0 <= fd)
 129     {
 130       if (result == 0)
 131         result = close (fd);
 132       else
 133         {
 134           int e = errno;
 135           close (fd);
 136           errno = e;
 137         }
 138     }
 139
 140   return result;
 141 }