lib/fchownat.c

   1 /* This function serves as replacement for a missing fchownat function,
   2    as well as a work around for the fchownat bug in glibc-2.4:
   3     <http://lists.ubuntu.com/archives/ubuntu-users/2006-September/093218.html>
   4    when the buggy fchownat-with-AT_SYMLINK_NOFOLLOW operates on a symlink, it
   5    mistakenly affects the symlink referent, rather than the symlink itself.
   6
   7    Copyright (C) 2006-2007, 2009-2017 Free Software Foundation, Inc.
   8
   9    This program is free software: you can redistribute it and/or modify
  10    it under the terms of the GNU General Public License as published by
  11    the Free Software Foundation; either version 3 of the License, or
  12    (at your option) any later version.
  13
  14    This program is distributed in the hope that it will be useful,
  15    but WITHOUT ANY WARRANTY; without even the implied warranty of
  16    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  17    GNU General Public License for more details.
  18
  19    You should have received a copy of the GNU General Public License
  20    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  21
  22 /* written by Jim Meyering */
  23
  24 #include <config.h>
  25
  26 #include <unistd.h>
  27
  28 #include <errno.h>
  29 #include <string.h>
  30
  31 #include "openat.h"
  32
  33 #if !HAVE_FCHOWNAT
  34
  35 /* Replacement for Solaris' function by the same name.
  36    Invoke chown or lchown on file, FILE, using OWNER and GROUP, in the
  37    directory open on descriptor FD.  If FLAG is AT_SYMLINK_NOFOLLOW, then
  38    use lchown, otherwise, use chown.  If possible, do it without changing
  39    the working directory.  Otherwise, resort to using save_cwd/fchdir,
  40    then (chown|lchown)/restore_cwd.  If either the save_cwd or the
  41    restore_cwd fails, then give a diagnostic and exit nonzero.  */
  42
  43 # define AT_FUNC_NAME fchownat
  44 # define AT_FUNC_F1 lchown
  45 # define AT_FUNC_F2 chown
  46 # define AT_FUNC_USE_F1_COND AT_SYMLINK_NOFOLLOW
  47 # define AT_FUNC_POST_FILE_PARAM_DECLS , uid_t owner, gid_t group, int flag
  48 # define AT_FUNC_POST_FILE_ARGS        , owner, group
  49 # include "at-func.c"
  50 # undef AT_FUNC_NAME
  51 # undef AT_FUNC_F1
  52 # undef AT_FUNC_F2
  53 # undef AT_FUNC_USE_F1_COND
  54 # undef AT_FUNC_POST_FILE_PARAM_DECLS
  55 # undef AT_FUNC_POST_FILE_ARGS
  56
  57 #else /* HAVE_FCHOWNAT */
  58
  59 # undef fchownat
  60
  61 # if FCHOWNAT_NOFOLLOW_BUG
  62
  63 /* Failure to handle AT_SYMLINK_NOFOLLOW requires the /proc/self/fd or
  64    fchdir workaround to call lchown for lchownat, but there is no need
  65    to penalize chownat.  */
  66 static int
  67 local_lchownat (int fd, char const *file, uid_t owner, gid_t group);
  68
  69 #  define AT_FUNC_NAME local_lchownat
  70 #  define AT_FUNC_F1 lchown
  71 #  define AT_FUNC_POST_FILE_PARAM_DECLS , uid_t owner, gid_t group
  72 #  define AT_FUNC_POST_FILE_ARGS        , owner, group
  73 #  include "at-func.c"
  74 #  undef AT_FUNC_NAME
  75 #  undef AT_FUNC_F1
  76 #  undef AT_FUNC_POST_FILE_PARAM_DECLS
  77 #  undef AT_FUNC_POST_FILE_ARGS
  78
  79 # endif
  80
  81 /* Work around bugs with trailing slash, using the same workarounds as
  82    chown and lchown.  */
  83
  84 int
  85 rpl_fchownat (int fd, char const *file, uid_t owner, gid_t group, int flag)
  86 {
  87 # if FCHOWNAT_NOFOLLOW_BUG
  88   if (flag == AT_SYMLINK_NOFOLLOW)
  89     return local_lchownat (fd, file, owner, group);
  90 # endif
  91 # if FCHOWNAT_EMPTY_FILENAME_BUG
  92   if (file[0] == '\0')
  93     {
  94       errno = ENOENT;
  95       return -1;
  96     }
  97 # endif
  98 # if CHOWN_TRAILING_SLASH_BUG
  99   {
 100     size_t len = strlen (file);
 101     struct stat st;
 102     if (len && file[len - 1] == '/')
 103       {
 104         if (statat (fd, file, &st))
 105           return -1;
 106         if (flag == AT_SYMLINK_NOFOLLOW)
 107           return fchownat (fd, file, owner, group, 0);
 108       }
 109   }
 110 # endif
 111   return fchownat (fd, file, owner, group, flag);
 112 }
 113
 114 #endif /* HAVE_FCHOWNAT */