From cb04b97ecaf980bdf92ae0e23f55fe8791ce3e2b Mon Sep 17 00:00:00 2001
From: Richard Scheffenegger <rscheff@FreeBSD.org>
Date: Thu, 27 Jul 2023 23:30:24 +0200
Subject: [PATCH] mask tcp[tcpflags] with 0x0fff to provide tcp flags only

---
 grammar.y.in | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/grammar.y.in b/grammar.y.in
index c72f4e5521..999aa22d47 100644
--- a/grammar.y.in
+++ b/grammar.y.in
@@ -856,7 +856,10 @@ arth:	  pnum			{ CHECK_PTR_VAL(($$ = gen_loadi(cstate, $1))); }
 	;
 tcpflags: TCPFLAGS
 	;
-narth:	  pname '[' tcpflags ']'	{ CHECK_PTR_VAL(($$ = gen_load(cstate, $1, gen_loadi(cstate, 12), 2))); }
+narth:	  pname '[' tcpflags ']'	{ CHECK_PTR_VAL(($$ =
+						gen_arth(cstate, BPF_AND,
+						    gen_load(cstate, $1, gen_loadi(cstate, 12), 2),
+						    gen_loadi(cstate, 0x0FFF)))); }
 	| pname '[' arth ']'		{ CHECK_PTR_VAL(($$ = gen_load(cstate, $1, $3, 1))); }
 	| pname '[' arth ':' NUM ']'	{ CHECK_PTR_VAL(($$ = gen_load(cstate, $1, $3, $5))); }
 	| arth '+' arth			{ CHECK_PTR_VAL(($$ = gen_arth(cstate, BPF_ADD, $1, $3))); }