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/* A more POSIX-compliant chown
Copyright (C) 1997, 2004-2007, 2009-2026 Free Software Foundation, Inc.
This file is free software: you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as
published by the Free Software Foundation; either version 2.1 of the
License, or (at your option) any later version.
This file 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 Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>. */
/* written by Jim Meyering */
#include <config.h>
/* Specification. */
#include <unistd.h>
#include <errno.h>
#include <fcntl.h>
#include <string.h>
#include <sys/stat.h>
#include "issymlink.h"
#include "stat-time.h"
#ifndef CHOWN_CHANGE_TIME_BUG
# define CHOWN_CHANGE_TIME_BUG 0
#endif
#ifndef CHOWN_FAILS_TO_HONOR_ID_OF_NEGATIVE_ONE
# define CHOWN_FAILS_TO_HONOR_ID_OF_NEGATIVE_ONE 0
#endif
#ifndef CHOWN_MODIFIES_SYMLINK
# define CHOWN_MODIFIES_SYMLINK 0
#endif
#ifndef CHOWN_TRAILING_SLASH_BUG
# define CHOWN_TRAILING_SLASH_BUG 0
#endif
/* Gnulib target platforms lacking utimensat do not need it,
because in practice the bug it works around does not occur. */
#if !HAVE_UTIMENSAT
# undef utimensat
# define utimensat(fd, file, times, flag) \
((void) (fd), (void) (file), (void) (times), (void) (flag), \
0)
#endif
#if !HAVE_CHOWN
/* Simple stub that always fails with ENOSYS, for mingw. */
int
chown (_GL_UNUSED const char *file, _GL_UNUSED uid_t owner,
_GL_UNUSED gid_t group)
{
errno = ENOSYS;
return -1;
}
#else /* HAVE_CHOWN */
/* Below we refer to the system's function. */
# undef chown
/* Provide a more-closely POSIX-conforming version. */
int
rpl_chown (const char *file, uid_t owner, gid_t group)
{
/* In some very old platforms, the system-supplied function
does not follow symlinks.
If the file is a symlink, open the file (following symlinks), and
fchown the resulting descriptor. Although the open might fail
due to lack of permissions, it's the best we can easily do. */
if (CHOWN_MODIFIES_SYMLINK && 0 < issymlink (file))
{
int open_flags = O_NONBLOCK | O_NOCTTY | O_CLOEXEC;
int fd = open (file, O_RDONLY | open_flags);
if (fd < 0
&& (errno != EACCES
|| ((fd = open (file, O_WRONLY | open_flags)) < 0))
&& (errno != EACCES || O_EXEC == O_RDONLY
|| ((fd = open (file, O_EXEC | open_flags)) < 0))
&& (errno != EACCES || O_SEARCH == O_RDONLY || O_SEARCH == O_EXEC
|| ((fd = open (file, O_SEARCH | open_flags)) < 0)))
return fd;
int r = fchown (fd, owner, group);
int err = errno;
close (fd);
errno = err;
return r;
}
struct stat st;
gid_t no_gid = -1;
uid_t no_uid = -1;
bool gid_noop = group == no_gid;
bool uid_noop = owner == no_uid;
bool change_time_check = CHOWN_CHANGE_TIME_BUG && !(gid_noop & uid_noop);
bool negative_one_check = (CHOWN_FAILS_TO_HONOR_ID_OF_NEGATIVE_ONE
&& (gid_noop | uid_noop));
if (change_time_check | negative_one_check
|| (CHOWN_TRAILING_SLASH_BUG
&& file[0] && file[strlen (file) - 1] == '/'))
{
int r = stat (file, &st);
/* EOVERFLOW means the file exists, which is all that the
trailing slash check needs. */
if (r < 0 && (change_time_check | negative_one_check
|| errno != EOVERFLOW))
return r;
}
gid_t uid = (CHOWN_FAILS_TO_HONOR_ID_OF_NEGATIVE_ONE && uid_noop
? st.st_uid : owner);
gid_t gid = (CHOWN_FAILS_TO_HONOR_ID_OF_NEGATIVE_ONE && gid_noop
? st.st_gid : group);
int result = chown (file, uid, gid);
/* If no change in ownership, but at least one argument was not -1,
update ctime indirectly via a no-change update to atime and mtime.
Do not use UTIME_NOW or UTIME_OMIT as they might run into bugs
on some platforms. Do not communicate any failure to the caller
as that would be worse than communicating the ownership change. */
if (result == 0 && change_time_check
&& (((uid == st.st_uid) | uid_noop)
& ((gid == st.st_gid) | gid_noop)))
utimensat (AT_FDCWD, file,
((struct timespec[]) { get_stat_atime (&st),
get_stat_mtime (&st) }),
0);
return result;
}
#endif /* HAVE_CHOWN */
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