lib/chown.c

   1 /* provide consistent interface to chown for systems that don't interpret
   2    an ID of -1 as meaning `don't change the corresponding ID'.
   3    Copyright (C) 1997, 2004 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 2, or (at your option)
   8    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, write to the Free Software Foundation,
  17    Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
  18
  19 /* written by Jim Meyering */
  20
  21 #include <config.h>
  22
  23 /* Disable the definition of chown to rpl_chown (from config.h) in this
  24    file.  Otherwise, we'd get conflicting prototypes for rpl_chown on
  25    most systems.  */
  26 #undef chown
  27
  28 #include <sys/types.h>
  29 #include <sys/stat.h>
  30 #if HAVE_UNISTD_H
  31 # include <unistd.h>
  32 #endif
  33 #if HAVE_FCNTL_H
  34 # include <fcntl.h>
  35 #else
  36 # include <sys/file.h>
  37 #endif
  38 #include <errno.h>
  39
  40 /* Provide a more-closely POSIX-conforming version of chown on
  41    systems with one or both of the following problems:
  42    - chown doesn't treat an ID of -1 as meaning
  43    `don't change the corresponding ID'.
  44    - chown doesn't dereference symlinks.  */
  45
  46 int
  47 rpl_chown (const char *file, uid_t uid, gid_t gid)
  48 {
  49 #if CHOWN_FAILS_TO_HONOR_ID_OF_NEGATIVE_ONE
  50   if (gid == (gid_t) -1 || uid == (uid_t) -1)
  51     {
  52       struct stat file_stats;
  53
  54       /* Stat file to get id(s) that should remain unchanged.  */
  55       if (stat (file, &file_stats))
  56         return 1;
  57
  58       if (gid == (gid_t) -1)
  59         gid = file_stats.st_gid;
  60
  61       if (uid == (uid_t) -1)
  62         uid = file_stats.st_uid;
  63     }
  64 #endif
  65
  66 #if CHOWN_MODIFIES_SYMLINK
  67   {
  68     /* Handle the case in which the system-supplied chown function
  69        does *not* follow symlinks.  Instead, it changes permissions
  70        on the symlink itself.  To work around that, we open the
  71        file (but this can fail due to lack of read or write permission) and
  72        use fchown on the resulting descriptor.  */
  73     int fd = open (file, O_RDONLY | O_NONBLOCK | O_NOCTTY);
  74     if (fd < 0
  75         && (fd = open (file, O_WRONLY | O_NONBLOCK | O_NOCTTY)) < 0)
  76       return -1;
  77     if (fchown (fd, uid, gid))
  78       {
  79         int saved_errno = errno;
  80         close (fd);
  81         errno = saved_errno;
  82         return -1;
  83       }
  84     return close (fd);
  85   }
  86 #else
  87   return chown (file, uid, gid);
  88 #endif
  89 }