2825f10b7f
Support O_PATH file descriptors when handling fgetxattr and fsetxattr.
This avoids requiring file read access to pull extended attributes.
This is needed to support O_PATH file descriptors when calling
SELinux's fgetfilecon() call. In particular, this allows the querying
and setting of SELinux file context by using something like the following
code:
int dirfd = open("/path/to/dir", O_DIRECTORY);
int fd = openat(dirfd, "file", O_PATH | O_NOFOLLOW);
char *context;
fgetfilecon(fd, &context);
This change was motivated by a comment in
https://android-review.googlesource.com/#/c/152680/1/toys/posix/ls.c
Change-Id: Ic0cdf9f9dd0e35a63b44a4c4a08400020041eddf
59 lines
2.2 KiB
C++
59 lines
2.2 KiB
C++
/*
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* Copyright (C) 2015 The Android Open Source Project
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* * Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* * Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
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* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#include <sys/stat.h>
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#include <sys/types.h>
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#include <sys/xattr.h>
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#include <errno.h>
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#include <fcntl.h>
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#include <stdio.h>
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extern "C" ssize_t ___fgetxattr(int, const char*, void*, size_t);
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ssize_t fgetxattr(int fd, const char *name, void *value, size_t size) {
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int saved_errno = errno;
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ssize_t result = ___fgetxattr(fd, name, value, size);
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if ((result != -1) || (errno != EBADF)) {
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return result;
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}
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// fd could be an O_PATH file descriptor, and the kernel
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// may not directly support fgetxattr() on such a file descriptor.
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// Use /proc/self/fd instead to emulate this support.
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int fd_flag = fcntl(fd, F_GETFL);
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if ((fd_flag == -1) || ((fd_flag & O_PATH) == 0)) {
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errno = EBADF;
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return -1;
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}
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char buf[40];
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snprintf(buf, sizeof(buf), "/proc/self/fd/%d", fd);
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errno = saved_errno;
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return getxattr(buf, name, value, size);
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}
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