gnulib/import/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
   4    Copyright (C) 1997, 2004-2007, 2009-2021 Free Software Foundation, Inc.
   5
   6    This program is free software: you can redistribute it and/or modify
   7    it under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 3 of the License, or
   9    (at your option) any later version.
  10
  11    This program 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 General Public License for more details.
  15
  16    You should have received a copy of the GNU 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 /* Specification.  */
  24 #include <unistd.h>
  25
  26 #include <errno.h>
  27 #include <fcntl.h>
  28 #include <stdbool.h>
  29 #include <string.h>
  30 #include <sys/stat.h>
  31
  32 #if !HAVE_CHOWN
  33
  34 /* Simple stub that always fails with ENOSYS, for mingw.  */
  35 int
  36 chown (const char *file _GL_UNUSED, uid_t uid _GL_UNUSED,
  37        gid_t gid _GL_UNUSED)
  38 {
  39   errno = ENOSYS;
  40   return -1;
  41 }
  42
  43 #else /* HAVE_CHOWN */
  44
  45 /* Below we refer to the system's chown().  */
  46 # undef chown
  47
  48 /* Provide a more-closely POSIX-conforming version of chown on
  49    systems with one or both of the following problems:
  50    - chown doesn't treat an ID of -1 as meaning
  51    "don't change the corresponding ID".
  52    - chown doesn't dereference symlinks.  */
  53
  54 int
  55 rpl_chown (const char *file, uid_t uid, gid_t gid)
  56 {
  57   struct stat st;
  58   bool stat_valid = false;
  59   int result;
  60
  61 # if CHOWN_CHANGE_TIME_BUG
  62   if (gid != (gid_t) -1 || uid != (uid_t) -1)
  63     {
  64       if (stat (file, &st))
  65         return -1;
  66       stat_valid = true;
  67     }
  68 # endif
  69
  70 # if CHOWN_FAILS_TO_HONOR_ID_OF_NEGATIVE_ONE
  71   if (gid == (gid_t) -1 || uid == (uid_t) -1)
  72     {
  73       /* Stat file to get id(s) that should remain unchanged.  */
  74       if (!stat_valid && stat (file, &st))
  75         return -1;
  76       if (gid == (gid_t) -1)
  77         gid = st.st_gid;
  78       if (uid == (uid_t) -1)
  79         uid = st.st_uid;
  80     }
  81 # endif
  82
  83 # if CHOWN_MODIFIES_SYMLINK
  84   {
  85     /* Handle the case in which the system-supplied chown function
  86        does *not* follow symlinks.  Instead, it changes permissions
  87        on the symlink itself.  To work around that, we open the
  88        file (but this can fail due to lack of read or write permission) and
  89        use fchown on the resulting descriptor.  */
  90     int open_flags = O_NONBLOCK | O_NOCTTY | O_CLOEXEC;
  91     int fd = open (file, O_RDONLY | open_flags);
  92     if (0 <= fd
  93         || (errno == EACCES
  94             && 0 <= (fd = open (file, O_WRONLY | open_flags))))
  95       {
  96         int saved_errno;
  97         bool fchown_socket_failure;
  98
  99         result = fchown (fd, uid, gid);
 100         saved_errno = errno;
 101
 102         /* POSIX says fchown can fail with errno == EINVAL on sockets
 103            and pipes, so fall back on chown in that case.  */
 104         fchown_socket_failure =
 105           (result != 0 && saved_errno == EINVAL
 106            && fstat (fd, &st) == 0
 107            && (S_ISFIFO (st.st_mode) || S_ISSOCK (st.st_mode)));
 108
 109         close (fd);
 110
 111         if (! fchown_socket_failure)
 112           {
 113             errno = saved_errno;
 114             return result;
 115           }
 116       }
 117     else if (errno != EACCES)
 118       return -1;
 119   }
 120 # endif
 121
 122 # if CHOWN_TRAILING_SLASH_BUG
 123   if (!stat_valid)
 124     {
 125       size_t len = strlen (file);
 126       if (len && file[len - 1] == '/' && stat (file, &st))
 127         return -1;
 128     }
 129 # endif
 130
 131   result = chown (file, uid, gid);
 132
 133 # if CHOWN_CHANGE_TIME_BUG
 134   if (result == 0 && stat_valid
 135       && (uid == st.st_uid || uid == (uid_t) -1)
 136       && (gid == st.st_gid || gid == (gid_t) -1))
 137     {
 138       /* No change in ownership, but at least one argument was not -1,
 139          so we are required to update ctime.  Since chown succeeded,
 140          we assume that chmod will do likewise.  Fortunately, on all
 141          known systems where a 'no-op' chown skips the ctime update, a
 142          'no-op' chmod still does the trick.  */
 143       result = chmod (file, st.st_mode & (S_IRWXU | S_IRWXG | S_IRWXO
 144                                           | S_ISUID | S_ISGID | S_ISVTX));
 145     }
 146 # endif
 147
 148   return result;
 149 }
 150
 151 #endif /* HAVE_CHOWN */