From: Claudio Jeker <cjeker@diehard.n-r-g.com>
Subject: bgpd: fix idle hold for failed peers
To: tech@openbsd.org
Date: Tue, 14 Jul 2026 09:32:16 +0200

Noticed with a bad peer that has a broken bgp implementation which sends
OTC updates with bad flags. It seems to constantly reconnect ignoring the
IdleHold timer of 30min+.

The culprit is the fast reopen in session_accept() which should only trigger
on first error (peer->errcnt < 2) but errcnt is never increased when bgpd
sends the notification. It is only done when a notification is received.

Add a errcnt++ in session_notification() similar to parse_notification().

On top of this adjust the exponential backoff of IdleHoldTime so that it
actually reaches MAX_IDLE_HOLD. Right now the * 2 game gets us to ~31min
and then stops since MAX_IDLE_HOLD is 1h. Just use the proper way of
clamping the number down to MAX_IDLE_HOLD.

-- 
:wq Claudio

Index: session_bgp.c
===================================================================
RCS file: /cvs/src/usr.sbin/bgpd/session_bgp.c,v
diff -u -p -r1.9 session_bgp.c
--- session_bgp.c	8 May 2026 12:03:50 -0000	1.9
+++ session_bgp.c	14 Jul 2026 06:58:34 -0000
@@ -512,6 +512,7 @@ session_notification(struct peer *p, uin
 
 	session_sendmsg(buf, p, BGP_NOTIFICATION);
 	p->stats.msg_sent_notification++;
+	p->errcnt++;
 	p->stats.last_sent_errcode = errcode;
 	p->stats.last_sent_suberr = subcode;
 }
@@ -1858,9 +1859,10 @@ change_state(struct peer *peer, enum ses
 			} else if (event != EVNT_STOP) {
 				timer_set(&peer->timers, Timer_IdleHold,
 				    peer->IdleHoldTime);
-				if (event != EVNT_NONE &&
-				    peer->IdleHoldTime < MAX_IDLE_HOLD / 2)
+				if (event != EVNT_NONE)
 					peer->IdleHoldTime *= 2;
+				if (peer->IdleHoldTime > MAX_IDLE_HOLD)
+					peer->IdleHoldTime = MAX_IDLE_HOLD;
 				session_down(peer);
 			} else {
 				session_down(peer);