Add tempfile() - a secure tmpfile() replacement using O_TMPFILE.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

tempfile.c

@@ -0,0 +1,64 @@
+/* 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 <stdlib.h>		/* mkstemp() */
+#include <stdio.h>		/* fdopen() */
+#include <sys/stat.h>		/* umask() */
+
+/**
+ * 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.
+ *
+ * Returns:
+ * An open %FILE pointer, or %NULL on error.
+ */
+FILE *tempfile(void)
+{
+	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");
+}
+
+#ifdef UNITTEST
+int main(void)
+{
+	FILE *fp = tempfile(); system("ls -lrt "
+	_PATH_TMP " | tail -10"); return fclose(fp);
+}
+#endif
+
+/**
+ * Local Variables:
+ *  compile-command: "gcc -D_GNU_SOURCE -DUNITTEST -o tempy tempfile.c && ./tempy"
+ *  version-control: t
+ *  indent-tabs-mode: t
+ *  c-file-style: "linux"
+ * End:
+ */