oksh-noxz [fork] Portable OpenBSD ksh, based on the Public Domain Korn Shell (pdksh).
	git clone https://noxz.tech/git/oksh-noxz.git
	oksh-noxz

commit: be763a7ece0c9e98519839ac31ecf5b8be619012
parent: 7a5f8be9f46ec5eaa34dcf3488737184c3b8b564
author: Brian Callahan <bcallah@openbsd.org>
date:   Mon, 5 Jul 2021 10:04:38 -0400

Sync with OpenBSD

CVSROOT:	/cvs
Module name:	src
Changes by:	millert@cvs.openbsd.org	2021/07/05 07:41:46

Modified files:
	bin/ksh        : syn.c

Log message:
Do not permit an empty list between "while" and "do".
This avoids a cpu loop for "while do done" and is consistent with
the behavior of AT&T ksh and most other shells.  OK jca@ halex@

diff --git a/syn.c b/syn.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: syn.c,v 1.39 2018/04/24 08:25:16 kn Exp $	*/
+/*	$OpenBSD: syn.c,v 1.40 2021/07/05 13:41:46 millert Exp $	*/
 
 /*
  * shell parser (C version)
@@ -331,6 +331,8 @@ get_command(int cf)
 		nesting_push(&old_nesting, c);
 		t = newtp((c == WHILE) ? TWHILE : TUNTIL);
 		t->left = c_list(true);
+		if (t->left == NULL)
+			syntaxerr(NULL);
 		t->right = dogroup();
 		nesting_pop(&old_nesting);
 		break;