Index: sys/compat/linux/linux_misc.c
===================================================================
--- sys/compat/linux/linux_misc.c
+++ sys/compat/linux/linux_misc.c
@@ -1954,6 +1954,13 @@
 	struct thread *tdt;
 	int error;
 
+	/*
+	 * According to man in case the invalid pid specified
+	 * EINVAL should be returned.
+	 */
+	if (uap->pid < 0)
+		return (EINVAL);
+
 	tdt = linux_tdfind(td, uap->pid, -1);
 	if (tdt == NULL)
 		return (ESRCH);