From 1346c272bea6b7378ecd97133f5d5f16a55e570e Mon Sep 17 00:00:00 2001
From: claudio <claudio@openbsd.org>
Date: Fri, 27 Oct 2023 14:22:43 +0000
Subject: [PATCH] Simplify the handling of optparamlen and RFC9072 support.

Use the ibuf_size() of the optional params (opb) when writing the various
headers. Only use optparamlen to write the Opt Parm Len field of the OPEN
message. Since there the size could be forced to 255 in case of a RFC9072
exended header. Also use size_t for optparamlen since the new ibuf API
no longer depends on using the right sized type.
OK tb@
---
 usr.sbin/bgpd/session.c | 26 +++++++++++++-------------
 1 file changed, 13 insertions(+), 13 deletions(-)

diff --git a/usr.sbin/bgpd/session.c b/usr.sbin/bgpd/session.c
index 5db8ebb1016..e7dbc3b32f1 100644
--- a/usr.sbin/bgpd/session.c
+++ b/usr.sbin/bgpd/session.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: session.c,v 1.452 2023/10/27 09:40:27 claudio Exp $ */
+/*	$OpenBSD: session.c,v 1.453 2023/10/27 14:22:43 claudio Exp $ */
 
 /*
  * Copyright (c) 2003, 2004, 2005 Henning Brauer <henning@openbsd.org>
@@ -1471,8 +1471,9 @@ session_open(struct peer *p)
 {
 	struct bgp_msg		*buf;
 	struct ibuf		*opb;
-	uint16_t		 len, optparamlen = 0, holdtime;
-	uint8_t			 i, op_type;
+	size_t			 optparamlen;
+	uint16_t		 holdtime;
+	uint8_t			 i;
 	int			 errs = 0, extlen = 0;
 	int			 mpcapa = 0;
 
@@ -1556,16 +1557,16 @@ session_open(struct peer *p)
 	if (optparamlen == 0) {
 		/* nothing */
 	} else if (optparamlen + 2 >= 255) {
-		/* RFC9072: 2 byte length instead of 1 + 3 byte extra header */
-		optparamlen += sizeof(op_type) + 2 + 3;
+		/* RFC9072: use 255 as magic size and request extra header */
 		optparamlen = 255;
 		extlen = 1;
 	} else {
-		optparamlen += sizeof(op_type) + 1;
+		/* regular capabilities header */
+		optparamlen += 2;
 	}
 
-	len = MSGSIZE_OPEN_MIN + optparamlen;
-	if (errs || (buf = session_newmsg(OPEN, len)) == NULL) {
+	if (errs || (buf = session_newmsg(OPEN,
+	    MSGSIZE_OPEN_MIN + optparamlen)) == NULL) {
 		ibuf_free(opb);
 		bgp_fsm(p, EVNT_CON_FATAL);
 		return;
@@ -1584,20 +1585,19 @@ session_open(struct peer *p)
 	errs += ibuf_add_n8(buf->buf, optparamlen);
 
 	if (extlen) {
-		/* write RFC9072 extra header */
+		/* RFC9072 extra header which spans over the capabilities hdr */
 		errs += ibuf_add_n8(buf->buf, OPT_PARAM_EXT_LEN);
-		errs += ibuf_add_n16(buf->buf, optparamlen - 3);
+		errs += ibuf_add_n16(buf->buf, ibuf_size(opb) + 1 + 2);
 	}
 
 	if (optparamlen) {
 		errs += ibuf_add_n8(buf->buf, OPT_PARAM_CAPABILITIES);
 
-		optparamlen = ibuf_size(opb);
 		if (extlen) {
 			/* RFC9072: 2-byte extended length */
-			errs += ibuf_add_n16(buf->buf, optparamlen);
+			errs += ibuf_add_n16(buf->buf, ibuf_size(opb));
 		} else {
-			errs += ibuf_add_n8(buf->buf, optparamlen);
+			errs += ibuf_add_n8(buf->buf, ibuf_size(opb));
 		}
 		errs += ibuf_add_buf(buf->buf, opb);
 	}
-- 
2.20.1