lib/lchown.c

   1 /* Provide a stub lchown function for systems that lack it.
   2
   3    Copyright (C) 1998-1999, 2002, 2004, 2006-2007, 2009-2024 Free Software
   4    Foundation, Inc.
   5
   6    This file is free software: you can redistribute it and/or modify
   7    it under the terms of the GNU Lesser General Public License as
   8    published by the Free Software Foundation; either version 2.1 of the
   9    License, or (at your option) any later version.
  10
  11    This file is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14    GNU Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public License
  17    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  18
  19 /* written by Jim Meyering */
  20
  21 #include <config.h>
  22
  23 #include <unistd.h>
  24
  25 #include <errno.h>
  26 #include <string.h>
  27 #include <sys/stat.h>
  28
  29 #if !HAVE_LCHOWN
  30
  31 /* If the system chown does not follow symlinks, we don't want it
  32    replaced by gnulib's chown, which does follow symlinks.  */
  33 # if CHOWN_MODIFIES_SYMLINK /* native Windows and some very old platforms */
  34 #  undef chown
  35 # endif
  36
  37 /* Work just like chown, except when FILE is a symbolic link.
  38    In that case, set errno to EOPNOTSUPP and return -1.
  39    But if autoconf tests determined that chown modifies
  40    symlinks, then just call chown.  */
  41
  42 int
  43 lchown (const char *file, uid_t uid, gid_t gid)
  44 {
  45 # if HAVE_CHOWN
  46 #  if ! CHOWN_MODIFIES_SYMLINK
  47   char readlink_buf[1];
  48
  49   if (0 <= readlink (file, readlink_buf, sizeof readlink_buf))
  50     {
  51       errno = EOPNOTSUPP;
  52       return -1;
  53     }
  54 #  endif
  55
  56   return chown (file, uid, gid);
  57
  58 # else /* !HAVE_CHOWN */
  59   errno = ENOSYS;
  60   return -1;
  61 # endif
  62 }
  63
  64 #else /* HAVE_LCHOWN */
  65
  66 # undef lchown
  67
  68 /* Work around trailing slash bugs in lchown.  */
  69 int
  70 rpl_lchown (const char *file, uid_t uid, gid_t gid)
  71 {
  72   bool stat_valid = false;
  73   int result;
  74
  75 # if CHOWN_CHANGE_TIME_BUG
  76   struct stat st;
  77
  78   if (gid != (gid_t) -1 || uid != (uid_t) -1)
  79     {
  80       if (lstat (file, &st))
  81         return -1;
  82       stat_valid = true;
  83       if (!S_ISLNK (st.st_mode))
  84         return chown (file, uid, gid);
  85     }
  86 # endif
  87
  88 # if CHOWN_TRAILING_SLASH_BUG
  89   if (!stat_valid)
  90     {
  91       size_t len = strlen (file);
  92       if (len && file[len - 1] == '/')
  93         return chown (file, uid, gid);
  94     }
  95 # endif
  96
  97   result = lchown (file, uid, gid);
  98
  99 # if CHOWN_CHANGE_TIME_BUG && HAVE_LCHMOD
 100   if (result == 0 && stat_valid
 101       && (uid == st.st_uid || uid == (uid_t) -1)
 102       && (gid == st.st_gid || gid == (gid_t) -1))
 103     {
 104       /* No change in ownership, but at least one argument was not -1,
 105          so we are required to update ctime.  Since lchown succeeded,
 106          we assume that lchmod will do likewise.  But if the system
 107          lacks lchmod and lutimes, we are out of luck.  Oh well.  */
 108       result = lchmod (file, st.st_mode & (S_IRWXU | S_IRWXG | S_IRWXO
 109                                            | S_ISUID | S_ISGID | S_ISVTX));
 110     }
 111 # endif
 112
 113   return result;
 114 }
 115
 116 #endif /* HAVE_LCHOWN */