From: Florian Obser <florian@openbsd.org>
Subject: Re: dhcpleased: patch xid problem
To: tech@openbsd.org
Date: Tue, 13 Feb 2024 12:32:11 +0100

On 2024-02-11 16:22 +01, Florian Obser <florian@openbsd.org> wrote:
> Amazing that anything works at all, ever. As far as I can tell only
> table 5 suggests that we need to keep the xid for the whole DHCPDISCOVER
> / DHCPOFFER / DHCPREQUEST / DHCPACK exchange of messages.
>
> Oh well, Could you try this instead? This only creates a new xid when we
> start a new exchange of messages to get a new lease / renew an existing
> lease.
>

Andre confirmed that this fixes their issue (not sure why it didn't make
it to the list).

OK?

diff --git engine.c engine.c
index 6d371a5a112..0268b247938 100644
--- engine.c
+++ engine.c
@@ -1385,8 +1385,6 @@ state_transition(struct dhcpleased_iface *iface, enum if_state new_state)
 	char		 ifnamebuf[IF_NAMESIZE], *if_name;
 
 	iface->state = new_state;
-	if (new_state != old_state)
-		iface->xid = arc4random();
 
 	switch (new_state) {
 	case IF_DOWN:
@@ -1426,6 +1424,7 @@ state_transition(struct dhcpleased_iface *iface, enum if_state new_state)
 		case IF_DOWN:
 		case IF_IPV6_ONLY:
 			iface->timo.tv_sec = START_EXP_BACKOFF;
+			iface->xid = arc4random();
 			break;
 		case IF_BOUND:
 			fatal("invalid transition Bound -> Init");
@@ -1436,8 +1435,10 @@ state_transition(struct dhcpleased_iface *iface, enum if_state new_state)
 	case IF_REBOOTING:
 		if (old_state == IF_REBOOTING)
 			iface->timo.tv_sec *= 2;
-		else
+		else {
 			iface->timo.tv_sec = START_EXP_BACKOFF;
+			iface->xid = arc4random();
+		}
 		request_dhcp_request(iface);
 		break;
 	case IF_REQUESTING:
@@ -1458,6 +1459,7 @@ state_transition(struct dhcpleased_iface *iface, enum if_state new_state)
 		if (old_state == IF_BOUND) {
 			iface->timo.tv_sec = (iface->rebinding_time -
 			    iface->renewal_time) / 2; /* RFC 2131 4.4.5 */
+			iface->xid = arc4random();
 		} else
 			iface->timo.tv_sec /= 2;
 

-- 
In my defence, I have been left unsupervised.