Index: kern_fork.c
===================================================================
--- kern_fork.c	(wersja 237276)
+++ kern_fork.c	(kopia robocza)
@@ -125,6 +125,11 @@
 	int error, fd;
 	struct proc *p2;
 
+	fd = -1;
+	error = copyout(&fd, uap->fdp, sizeof(fd));
+	if (error != 0)
+		return (error);
+
 	/*
 	 * It is necessary to return fd by reference because 0 is a valid file
 	 * descriptor number, and the child needs to be able to distinguish
@@ -135,7 +140,7 @@
 	if (error == 0) {
 		td->td_retval[0] = p2->p_pid;
 		td->td_retval[1] = 0;
-		error = copyout(&fd, uap->fdp, sizeof(fd));
+		(void)copyout(&fd, uap->fdp, sizeof(fd));
 	}
 	return (error);
 #else