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