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#include <stdio.h>
35
36extern "C" int ___fchmod(int, mode_t);
37
38int fchmod(int fd, mode_t mode) {
39  int saved_errno = errno;
40  int result = ___fchmod(fd, mode);
41
42  if ((result == 0) || (errno != EBADF)) {
43    return result;
44  }
45
46  // fd could be an O_PATH file descriptor, and the kernel
47  // may not directly support fchmod() on such a file descriptor.
48  // Use /proc/self/fd instead to emulate this support.
49  // https://sourceware.org/bugzilla/show_bug.cgi?id=14578
50  //
51  // As of February 2015, there are no kernels which support fchmod
52  // on an O_PATH file descriptor, and "man open" documents fchmod
53  // on O_PATH file descriptors as returning EBADF.
54  int fd_flag = fcntl(fd, F_GETFL);
55  if ((fd_flag == -1) || ((fd_flag & O_PATH) == 0)) {
56    errno = EBADF;
57    return -1;
58  }
59
60  char buf[40];
61  snprintf(buf, sizeof(buf), "/proc/self/fd/%d", fd);
62  errno = saved_errno;
63  result = chmod(buf, mode);
64  if ((result == -1) && (errno == ELOOP)) {
65    // Linux does not support changing the mode of a symlink.
66    // For fchmodat(AT_SYMLINK_NOFOLLOW), POSIX requires a return
67    // value of ENOTSUP. Assume that's true here too.
68    errno = ENOTSUP;
69  }
70
71  return result;
72}
73