1/*
2 * Copyright (C) 2015 The Android Open Source Project
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 *  * Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 *  * Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in
12 *    the documentation and/or other materials provided with the
13 *    distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
16 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
17 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
18 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
19 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
21 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
22 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
23 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
24 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
25 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * SUCH DAMAGE.
27 */
28
29#include <fcntl.h>
30#include <sys/stat.h>
31#include <sys/types.h>
32#include <errno.h>
33#include <unistd.h>
34
35#include "private/ErrnoRestorer.h"
36
37extern "C" int ___fchmodat(int, const char*, mode_t);
38
39int fchmodat(int dirfd, const char* pathname, mode_t mode, int flags) {
40  if ((flags & ~AT_SYMLINK_NOFOLLOW) != 0) {
41    errno = EINVAL;
42    return -1;
43  }
44
45  if (flags & AT_SYMLINK_NOFOLLOW) {
46    // Emulate AT_SYMLINK_NOFOLLOW using the mechanism described
47    // at https://sourceware.org/bugzilla/show_bug.cgi?id=14578
48    // comment #10
49
50    int fd = openat(dirfd, pathname, O_PATH | O_NOFOLLOW | O_CLOEXEC);
51    if (fd == -1) {
52      return -1; // returns errno from openat
53    }
54
55    // POSIX requires that ENOTSUP be returned when the system
56    // doesn't support setting the mode of a symbolic link.
57    // This is true for all Linux kernels.
58    // We rely on the O_PATH compatibility layer added in the
59    // fchmod() function to get errno correct.
60    int result = fchmod(fd, mode);
61    ErrnoRestorer errno_restorer; // don't let close() clobber errno
62    close(fd);
63    return result;
64  }
65
66  return ___fchmodat(dirfd, pathname, mode);
67}
68