111 lines
3.3 KiB
C
111 lines
3.3 KiB
C
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/* Implement lchmod on platforms where it does not work correctly.
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Copyright 2020 Free Software Foundation, Inc.
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <https://www.gnu.org/licenses/>. */
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/* written by Paul Eggert */
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#include <config.h>
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/* Specification. */
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#include <sys/stat.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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#include <unistd.h>
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#ifdef __osf__
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/* Write "sys/stat.h" here, not <sys/stat.h>, otherwise OSF/1 5.1 DTK cc
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eliminates this include because of the preliminary #include <sys/stat.h>
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above. */
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# include "sys/stat.h"
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#else
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# include <sys/stat.h>
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#endif
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#include <intprops.h>
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/* Work like chmod, except when FILE is a symbolic link.
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In that case, on systems where permissions on symbolic links are unsupported
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(such as Linux), set errno to EOPNOTSUPP and return -1. */
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int
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lchmod (char const *file, mode_t mode)
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{
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#if defined O_PATH && defined AT_EMPTY_PATH
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/* Open a file descriptor with O_NOFOLLOW, to make sure we don't
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follow symbolic links, if /proc is mounted. O_PATH is used to
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avoid a failure if the file is not readable.
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Cf. <https://sourceware.org/bugzilla/show_bug.cgi?id=14578> */
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int fd = open (file, O_PATH | O_NOFOLLOW | O_CLOEXEC);
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if (fd < 0)
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return fd;
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/* Up to Linux 5.3 at least, when FILE refers to a symbolic link, the
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chmod call below will change the permissions of the symbolic link
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- which is undesired - and on many file systems (ext4, btrfs, jfs,
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xfs, ..., but not reiserfs) fail with error EOPNOTSUPP - which is
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misleading. Therefore test for a symbolic link explicitly.
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Use fstatat because fstat does not work on O_PATH descriptors
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before Linux 3.6. */
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struct stat st;
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if (fstatat (fd, "", &st, AT_EMPTY_PATH) != 0)
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{
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int stat_errno = errno;
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close (fd);
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errno = stat_errno;
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return -1;
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}
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if (S_ISLNK (st.st_mode))
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{
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close (fd);
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errno = EOPNOTSUPP;
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return -1;
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}
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# if defined __linux__ || defined __ANDROID__
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static char const fmt[] = "/proc/self/fd/%d";
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char buf[sizeof fmt - sizeof "%d" + INT_BUFSIZE_BOUND (int)];
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sprintf (buf, fmt, fd);
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int chmod_result = chmod (buf, mode);
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int chmod_errno = errno;
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close (fd);
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if (chmod_result == 0)
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return chmod_result;
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if (chmod_errno != ENOENT)
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{
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errno = chmod_errno;
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return chmod_result;
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}
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# endif
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/* /proc is not mounted or would not work as in GNU/Linux. */
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#elif HAVE_LSTAT
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struct stat st;
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int lstat_result = lstat (file, &st);
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if (lstat_result != 0)
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return lstat_result;
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if (S_ISLNK (st.st_mode))
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{
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errno = EOPNOTSUPP;
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return -1;
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}
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#endif
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/* Fall back on chmod, despite a possible race. */
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return chmod (file, mode);
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}
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