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/* A secure tmpfile() replacement.
*
* Copyright (c) 2015 Joachim Nilsson <troglobit@gmail.com>
*
* Permission to use, copy, modify, and/or distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
#include <paths.h>
#include <fcntl.h> /* O_TMPFILE requires -D_GNU_SOURCE */
#include <linux/version.h>
#include <stdlib.h> /* mkstemp() */
#include <stdio.h> /* fdopen() */
#include <sys/stat.h> /* umask() */
#ifndef O_TMPFILE /* Too old GLIBC or kernel */
#warning O_TMPFILE missing on your system, tempfile() may not work!
#define O_TMPFILE 020200000 /* Define and let it fail at runtime */
#endif
/**
* tempfile - A secure tmpfile() replacement
*
* This is the secure replacement for tmpfile() that does not exist in
* GLIBC. The function uses the Linux specific %O_TMPFILE and %O_EXCL
* for security. When the %FILE is fclose()'ed the file contents is
* lost. The file is hidden in the %_PATH_TMP directory on the system.
*
* This function requires Linux 3.11, or later, due to %O_TMPFILE.
*
* Returns:
* An open %FILE pointer, or %NULL on error.
*/
FILE *tempfile(void)
{
#if LINUX_VERSION_CODE >= KERNEL_VERSION(3,11,0)
int fd;
mode_t oldmask;
oldmask = umask(0077);
fd = open(_PATH_TMP, O_TMPFILE | O_RDWR | O_EXCL | O_CLOEXEC, S_IRUSR | S_IWUSR);
umask(oldmask);
if (-1 == fd)
return NULL;
return fdopen(fd, "rw");
#else
#warning Too old kernel, reverting to wrap unsafe tmpfile() ...
return tmpfile();
#endif
}
#ifdef UNITTEST
int main(void)
{
FILE *fp = tempfile(); system("ls -lrt "
_PATH_TMP " | tail -10"); return fclose(fp);
}
#endif
/**
* Local Variables:
* compile-command: "make V=1 -f tempfile.mk"
* version-control: t
* indent-tabs-mode: t
* c-file-style: "linux"
* End:
*/
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