nvmutil: new urandom fd every time (rlong)

otherwise, a stale descriptor could be manipulated
easily by an attacker over time

very theoretical to be honest

Signed-off-by: Leah Rowe <leah@libreboot.org>

util/nvmutil/nvmutil.c

@@ -992,7 +992,7 @@ rlong(void)
 	static unsigned long mix = 0;
 	static unsigned long counter = 0;
 
-	static int fd = -1;
+	int fd = -1;
 
 	struct x_st_timeval tv;
 
@@ -1055,6 +1055,9 @@ rlong(void)
 	    sizeof(unsigned long), 0, IO_READ, LOOP_EAGAIN,
 	    LOOP_EINTR, MAX_ZERO_RW_RETRY, OFF_ERR);
 
+	if (x_i_close(fd) < 0)
+		err(errno, "Can't close randomness fd");
+
 	if (nr == sizeof(unsigned long))
 		return rval;
 
@@ -3095,11 +3098,15 @@ int
 x_i_close(int fd)
 {
 	int r;
+	int saved_errno = errno;
 
 	do {
 		r = close(fd);
 	} while (r == -1 && errno == EINTR);
 
+	if (r > -1)
+		errno = saved_errno;
+
 	return r;
 }