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/* Implement lchmod on platforms where it does not work correctly.
Copyright 2020-2021 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 <https://www.gnu.org/licenses/>. */
/* written by Paul Eggert */
#include <config.h>
/* Specification. */
#include <sys/stat.h>
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#ifdef __osf__
/* Write "sys/stat.h" here, not <sys/stat.h>, otherwise OSF/1 5.1 DTK cc
eliminates this include because of the preliminary #include <sys/stat.h>
above. */
# include "sys/stat.h"
#else
# include <sys/stat.h>
#endif
#include <intprops.h>
/* Work like chmod, except when FILE is a symbolic link.
In that case, on systems where permissions on symbolic links are unsupported
(such as Linux), set errno to EOPNOTSUPP and return -1. */
int
lchmod (char const *file, mode_t mode)
{
#if defined O_PATH && defined AT_EMPTY_PATH
/* Open a file descriptor with O_NOFOLLOW, to make sure we don't
follow symbolic links, if /proc is mounted. O_PATH is used to
avoid a failure if the file is not readable.
Cf. <https://sourceware.org/bugzilla/show_bug.cgi?id=14578> */
int fd = open (file, O_PATH | O_NOFOLLOW | O_CLOEXEC);
if (fd < 0)
return fd;
/* Up to Linux 5.3 at least, when FILE refers to a symbolic link, the
chmod call below will change the permissions of the symbolic link
- which is undesired - and on many file systems (ext4, btrfs, jfs,
xfs, ..., but not reiserfs) fail with error EOPNOTSUPP - which is
misleading. Therefore test for a symbolic link explicitly.
Use fstatat because fstat does not work on O_PATH descriptors
before Linux 3.6. */
struct stat st;
if (fstatat (fd, "", &st, AT_EMPTY_PATH) != 0)
{
int stat_errno = errno;
close (fd);
errno = stat_errno;
return -1;
}
if (S_ISLNK (st.st_mode))
{
close (fd);
errno = EOPNOTSUPP;
return -1;
}
# if defined __linux__ || defined __ANDROID__ || defined __CYGWIN__
static char const fmt[] = "/proc/self/fd/%d";
char buf[sizeof fmt - sizeof "%d" + INT_BUFSIZE_BOUND (int)];
sprintf (buf, fmt, fd);
int chmod_result = chmod (buf, mode);
int chmod_errno = errno;
close (fd);
if (chmod_result == 0)
return chmod_result;
if (chmod_errno != ENOENT)
{
errno = chmod_errno;
return chmod_result;
}
# endif
/* /proc is not mounted or would not work as in GNU/Linux. */
#elif HAVE_LSTAT
struct stat st;
int lstat_result = lstat (file, &st);
if (lstat_result != 0)
return lstat_result;
if (S_ISLNK (st.st_mode))
{
errno = EOPNOTSUPP;
return -1;
}
#endif
/* Fall back on chmod, despite a possible race. */
return chmod (file, mode);
}
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