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chown.c revision 1.1.1.1.4.2 
      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, 2009-2022 Free Software 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 /* 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 (_GL_UNUSED const char *file, _GL_UNUSED uid_t uid,
     37        _GL_UNUSED gid_t gid)
     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 */
    152