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/* Implement lchmod on platforms where it does not work correctly.
Copyright 2020-2023 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 <string.h>
#include <unistd.h>
#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)
{
char readlink_buf[1];
#ifdef O_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;
int err;
if (0 <= readlinkat (fd, "", readlink_buf, sizeof readlink_buf))
err = EOPNOTSUPP;
else if (errno == EINVAL)
{
static char const fmt[] = "/proc/self/fd/%d";
char buf[sizeof fmt - sizeof "%d" + INT_BUFSIZE_BOUND (int)];
sprintf (buf, fmt, fd);
err = chmod (buf, mode) == 0 ? 0 : errno == ENOENT ? -1 : errno;
}
else
err = errno == ENOENT ? -1 : errno;
close (fd);
errno = err;
if (0 <= err)
return err == 0 ? 0 : -1;
#endif
size_t len = strlen (file);
if (len && file[len - 1] == '/')
{
struct stat st;
if (lstat (file, &st) < 0)
return -1;
if (!S_ISDIR (st.st_mode))
{
errno = ENOTDIR;
return -1;
}
}
/* O_PATH + /proc is not supported. */
if (0 <= readlink (file, readlink_buf, sizeof readlink_buf))
{
errno = EOPNOTSUPP;
return -1;
}
/* Fall back on chmod, despite a possible race. */
return chmod (file, mode);
}
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