From 566e20e7740d8f032614c47b93c866a1d2c97840 Mon Sep 17 00:00:00 2001
From: Paul Stewart <pstew@chromium.org>
Date: Mon, 14 Jun 2021 12:32:58 +0000
Subject: [PATCH 15/19] Ensure gateway probe is broadcast

The arp_new() method does not always return a freshly
initialized arp_state structure.  For example, if
dhcp_probe_gw() is called while a probe from
start_unicast_arp() is still running, the arp_state
object from the unicast ARP call will be returned by
arp_new().  This can happen when a DHCP renew succeeds
while a unicast "GatewayArp" is still in progress.

In the above scenario we need to make sure the dest_hwlen
field of the arp_state structure is zero.  This signals a
broadcast ARP, and will ensure that the callbacks that are
invoked by the ARP state machine know which case we are in.

While here, add a small optimization that skips a
broadcast gateway ARP if a unicast ARP succeeds.

BUG=chromium:531042
TEST=Reconnect to WiFi network where ARP fails
---
 src/dhcp.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/dhcp.c b/src/dhcp.c
index c8ec40da..ac339a6a 100644
--- a/src/dhcp.c
+++ b/src/dhcp.c
@@ -2171,6 +2171,8 @@ dhcp_probe_gw_response(struct arp_state *astate, const struct arp_msg *amsg)
 		if (astate->dest_hwlen) {
 			/* Response to unicast ARP. */
 			rpc_notify_unicast_arp(astate->iface);
+			/* Unicast ARP succeeded; no need for broadcast ARP. */
+			astate->iface->options->options &= ~DHCPCD_ARPGW;
 		} else {
 			/* Response to arpgw request. */
 			save_gateway_addr(astate->iface, amsg->sha);
@@ -2199,6 +2201,8 @@ dhcp_probe_gw(struct interface *ifp)
 			    state->offer, state->offer_len, DHO_ROUTER) == 0) {
 		astate = arp_new(ifp, &gateway_addr);
 		if (astate) {
+			/* Make sure we're doing a broadcast ARP. */
+			astate->dest_hwlen = 0;
 			astate->src_addr.s_addr = state->offer->yiaddr;
 			astate->probed_cb = dhcp_probe_gw_timeout;
 			astate->conflicted_cb = dhcp_probe_gw_response;
-- 
2.33.0.800.g4c38ced690-goog