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

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

Makefile

@@ -38,6 +38,7 @@ STRIPINST  := $(INSTALL) -s --strip-program=$(CROSS)strip -m 0755
 
 CFLAGS     += -fPIC
 CFLAGS     += -Os
+CPPFLAGS   += -D_GNU_SOURCE
 CPPFLAGS   += -W -Wall -Werror
 ARFLAGS     = crus
 MAKEFLAGS   = --no-print-directory --silent
@@ -45,7 +46,7 @@ MAKEFLAGS   = --no-print-directory --silent
 DISTFILES   = README LICENSE
 HEADERS     = lite.h
 OBJS       := chomp.o copyfile.o dir.o fexist.o fisdir.o fmode.o rsync.o
-OBJS       += strlcpy.o strlcat.o strtonum.o
+OBJS       += strlcpy.o strlcat.o strtonum.o tempfile.o
 DEPS       := $(OBJS:.o=.d)
 JUNK        = *~ *.bak *.map .*.d *.d DEADJOE semantic.cache *.gdb *.elf core core.*
 

lite.h

@@ -39,6 +39,7 @@ int     fexist     (char *file);
 int     fisdir     (char *file);
 mode_t  fmode      (char *file);
 
+FILE   *tempfile   (void);
 ssize_t copyfile   (char *src, char *dst, int len, int sym);
 int     movefile   (char *src, char *dst);
 int     copy_filep (FILE *src, FILE *dst);

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:
+ */