95 lines
2.5 KiB
C
95 lines
2.5 KiB
C
/* Implement lchmod on platforms where it does not work correctly.
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Copyright 2020-2024 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 <string.h>
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#include <unistd.h>
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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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char readlink_buf[1];
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#ifdef O_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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int err;
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if (0 <= readlinkat (fd, "", readlink_buf, sizeof readlink_buf))
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err = EOPNOTSUPP;
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else if (errno == EINVAL)
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{
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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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err = chmod (buf, mode) == 0 ? 0 : errno == ENOENT ? -1 : errno;
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}
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else
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err = errno == ENOENT ? -1 : errno;
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close (fd);
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errno = err;
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if (0 <= err)
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return err == 0 ? 0 : -1;
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#endif
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size_t len = strlen (file);
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if (len && file[len - 1] == '/')
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{
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struct stat st;
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if (lstat (file, &st) < 0)
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return -1;
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if (!S_ISDIR (st.st_mode))
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{
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errno = ENOTDIR;
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return -1;
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}
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}
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/* O_PATH + /proc is not supported. */
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if (0 <= readlink (file, readlink_buf, sizeof readlink_buf))
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{
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errno = EOPNOTSUPP;
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return -1;
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}
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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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