chown.c

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/* provide consistent interface to chown for systems that don't interpret
   an ID of -1 as meaning `don't change the corresponding ID'.

   Copyright (C) 1997, 2004, 2005, 2006, 2007 Free Software Foundation, Inc.

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

/* written by Jim Meyering */

#include <config.h>

/* Specification.  */
#include <unistd.h>

#include <stdbool.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>

/* Below we refer to the system's chown().  */
#undef chown

/* The results of open() in this file are not used with fchdir,
   therefore save some unnecessary work in fchdir.c.  */
#undef open
#undef close

/* Provide a more-closely POSIX-conforming version of chown on
   systems with one or both of the following problems:
   - chown doesn't treat an ID of -1 as meaning
   `don't change the corresponding ID'.
   - chown doesn't dereference symlinks.  */

int
rpl_chown (const char *file, uid_t uid, gid_t gid)
{
#if CHOWN_FAILS_TO_HONOR_ID_OF_NEGATIVE_ONE
  if (gid == (gid_t) -1 || uid == (uid_t) -1)
    {
      struct stat file_stats;

      /* Stat file to get id(s) that should remain unchanged.  */
      if (stat (file, &file_stats))
	return -1;

      if (gid == (gid_t) -1)
	gid = file_stats.st_gid;

      if (uid == (uid_t) -1)
	uid = file_stats.st_uid;
    }
#endif

#if CHOWN_MODIFIES_SYMLINK
  {
    /* Handle the case in which the system-supplied chown function
       does *not* follow symlinks.  Instead, it changes permissions
       on the symlink itself.  To work around that, we open the
       file (but this can fail due to lack of read or write permission) and
       use fchown on the resulting descriptor.  */
    int open_flags = O_NONBLOCK | O_NOCTTY;
    int fd = open (file, O_RDONLY | open_flags);
    if (0 <= fd
	|| (errno == EACCES
	    && 0 <= (fd = open (file, O_WRONLY | open_flags))))
      {
	int result = fchown (fd, uid, gid);
	int saved_errno = errno;

	/* POSIX says fchown can fail with errno == EINVAL on sockets,
	   so fall back on chown in that case.  */
	struct stat sb;
	bool fchown_socket_failure =
	  (result != 0 && saved_errno == EINVAL
	   && fstat (fd, &sb) == 0 && S_ISFIFO (sb.st_mode));

	close (fd);

	if (! fchown_socket_failure)
	  {
	    errno = saved_errno;
	    return result;
	  }
      }
    else if (errno != EACCES)
      return -1;
  }
#endif

  return chown (file, uid, gid);
}