From 33f421fd6e68fcb8ed50071661d9704717c81b2b Mon Sep 17 00:00:00 2001
From: dmiller <dmiller@e0a8ed71-7df4-0310-8962-fdc924857419>
Date: Tue, 3 Dec 2019 17:04:13 +0000
Subject: [PATCH] Avoid assertion failure when unsolicited ARP response
 received

We probably want a more explicit handling of the case where we get an
ARP response to a request that we did not send (system's own, or another
Nmap scan running at the same time). In any case, this ought to solve
the crashes reported as #1797 and #1764.
---
 scan_engine.cc | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/scan_engine.cc b/scan_engine.cc
index bd73cc8ead..7a4766da26 100644
--- a/scan_engine.cc
+++ b/scan_engine.cc
@@ -1275,7 +1275,12 @@ int UltraScanInfo::removeCompletedHosts() {
       }
       if (timedout)
         gstats->num_hosts_timedout++;
-      hss->target->stopTimeOutClock(&now);
+      /* We may have received an ARP response before we sent a probe, which
+       * would mean the timeout clock is not running. Avoid an assertion
+       * failure here by checking first.  */
+      if (hss->target->timeOutClockRunning()) {
+        hss->target->stopTimeOutClock(&now);
+      }
     }
   }
   return hostsRemoved;