Replace insecure tmpfile() with mkstemp() based local tempfile()

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

exec.c

@@ -179,7 +179,7 @@ int run_interactive(char *cmd, char *fmt, ...)
 	}
 
 	/* Redirect output from cmd to a tempfile */
-	fp = tmpfile();
+	fp = tempfile();
 	if (fp && !debug) {
 		oldout = dup(STDOUT_FILENO);
 		olderr = dup(STDERR_FILENO);

helpers.c

@@ -126,6 +126,27 @@ int atonum(char *str)
 	return val;
 }
 
+/**
+ * tempfile - A secure tmpfile() replacement
+ *
+ * This is the secure replacement for tmpfile() that does not exist in GLIBC.
+ * The function uses mkstemp() for security.
+ *
+ * Returns:
+ * An open %FILE pointer, or %NULL on error.
+ */
+FILE *tempfile(void)
+{
+	int fd;
+	char *template = "/tmp/finit.XXXXXX";
+
+	fd = mkstemp(template);
+	if (-1 == fd)
+		return NULL;
+
+	return fdopen(fd, "rw");
+}
+
 static int encode(int lvl)
 {
 	if (!lvl) return 0;

helpers.h

@@ -69,6 +69,8 @@ int     makepath        (char *path);
 void    ifconfig        (char *ifname, char *addr, char *mask, int up);
 
 int     atonum          (char *str);
+FILE   *tempfile        (void);
+
 void    runlevel_set    (int pre, int now);
 int     runlevel_get    (void);
 char   *runlevel_string (int levels);