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87 lines
2.3 KiB
C
87 lines
2.3 KiB
C
/* A secure tmpfile() replacement.
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*
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* Copyright (c) 2015-2021 Joachim Wiberg <troglobit@gmail.com>
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*
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* Permission to use, copy, modify, and/or distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* copyright notice and this permission notice appear in all copies.
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*
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* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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*/
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/**
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* @file tempfile.c
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* @author Joachim Wiberg
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* @date 2015-2021
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* @copyright ISC License
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*/
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#include <errno.h>
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#include <paths.h>
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#include <fcntl.h> /* O_TMPFILE requires -D_GNU_SOURCE */
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#include <stdio.h> /* fdopen() */
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#include <stdlib.h> /* mkostemp() */
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#include <sys/stat.h> /* umask() */
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static FILE *fallback(void)
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{
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char nm[15] = _PATH_TMP "XXXXXXXX";
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int fd;
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fd = mkostemp(nm, O_CLOEXEC);
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if (-1 == fd)
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return NULL;
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return fdopen(fd, "w+");
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}
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/**
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* A secure tmpfile() replacement
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*
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* This is the secure replacement for tmpfile() that does not exist in
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* GLIBC. It uses the Linux specific @c O_TMPFILE and @c O_EXCL to hide
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* the filename. When the @c FILE is fclose()'ed, the file contents is
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* lost. The file is hidden in the @c _PATH_TMP ("/tmp") directory in
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* the system.
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*
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* This function requires Linux 3.11, or later, due to @c O_TMPFILE.
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* Not all file systems support hidden inodes, in which case this
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* function defaults to call tmpfile() as a fallback.
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*
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* @returns An open @c FILE pointer, or @c NULL on error.
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*/
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FILE *tempfile(void)
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{
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#ifdef O_TMPFILE /* Only on Linux, with fairly recent (G)LIBC */
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int fd;
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mode_t oldmask;
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oldmask = umask(0077);
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fd = open(_PATH_TMP, O_TMPFILE | O_RDWR | O_EXCL | O_CLOEXEC, S_IRUSR | S_IWUSR);
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umask(oldmask);
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if (-1 == fd) {
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if (errno == EOPNOTSUPP)
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return fallback();
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return NULL;
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}
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return fdopen(fd, "w+");
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#else
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return fallback();
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#endif
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}
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/**
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* Local Variables:
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* indent-tabs-mode: t
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* c-file-style: "linux"
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* End:
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*/
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