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libite

    1: /* A secure tmpfile() replacement.
    2:  *
    3:  * Copyright (c) 2015  Joachim Nilsson <troglobit@gmail.com>
    4:  *
    5:  * Permission to use, copy, modify, and/or distribute this software for any
    6:  * purpose with or without fee is hereby granted, provided that the above
    7:  * copyright notice and this permission notice appear in all copies.
    8:  *
    9:  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
   10:  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
   11:  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
   12:  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
   13:  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
   14:  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
   15:  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
   16:  */
   17: 
   18: #include <paths.h>
   19: #include <fcntl.h>		/* O_TMPFILE requires -D_GNU_SOURCE */
   20: #include <linux/version.h>
   21: #include <stdlib.h>		/* mkstemp() */
   22: #include <stdio.h>		/* fdopen() */
   23: #include <sys/stat.h>		/* umask() */
   24: 
   25: #ifndef  O_TMPFILE		/* Too old GLIBC or kernel */
   26: #warning O_TMPFILE missing on your system, tempfile() may not work!
   27: #define  __O_TMPFILE 020000000
   28: #define  O_TMPFILE (__O_TMPFILE | O_DIRECTORY) /* Define and let it fail at runtime */
   29: #endif
   30: 
   31: /**
   32:  * tempfile - A secure tmpfile() replacement
   33:  *
   34:  * This is the secure replacement for tmpfile() that does not exist in
   35:  * GLIBC.  The function uses the Linux specific %O_TMPFILE and %O_EXCL
   36:  * for security.  When the %FILE is fclose()'ed the file contents is
   37:  * lost.  The file is hidden in the %_PATH_TMP directory on the system.
   38:  *
   39:  * This function requires Linux 3.11, or later, due to %O_TMPFILE.
   40:  *
   41:  * Returns:
   42:  * An open %FILE pointer, or %NULL on error.
   43:  */
   44: FILE *tempfile(void)
   45: {
   46: #if LINUX_VERSION_CODE >= KERNEL_VERSION(3,11,0)
   47: 	int fd;
   48: 	mode_t oldmask;
   49: 
   50: 	oldmask = umask(0077);
   51: 	fd = open(_PATH_TMP, O_TMPFILE | O_RDWR | O_EXCL | O_CLOEXEC, S_IRUSR | S_IWUSR);
   52: 	umask(oldmask);
   53: 	if (-1 == fd)
   54: 		return NULL;
   55: 
   56: 	return fdopen(fd, "rw");
   57: #else
   58: #warning Too old kernel, reverting to wrap unsafe tmpfile() ...
   59: 	return tmpfile();
   60: #endif
   61: }
   62: 
   63: #ifdef UNITTEST
   64: int main(void)
   65: {
   66: 	FILE *fp = tempfile(); system("ls -lrt "
   67: 	_PATH_TMP " | tail -10"); return fclose(fp);
   68: }
   69: #endif
   70: 
   71: /**
   72:  * Local Variables:
   73:  *  compile-command: "make V=1 -f tempfile.mk"
   74:  *  version-control: t
   75:  *  indent-tabs-mode: t
   76:  *  c-file-style: "linux"
   77:  * End:
   78:  */