mask tcp[tcpflags] with 0x0fff to provide tcp flags only

the-tcpdump-group · Dec 30, 2023 · cb04b97 · cb04b97
1 parent 31f3525
commit cb04b97
Showing 1 changed file with 4 additions and 1 deletion.
diff --git 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))); }