This bug report is to track the fix for an issue I reported on the Samba mailing list:

https://lists.samba.org/archive/samba/2018-September/218233.html

In short:

===

Last night I attempted to upgrade from Samba 4.8.5 to 4.9.0, with disastrous results.  Upon starting Samba 4.9.0 my entire network came to a screaming halt a few seconds later, and upon shutting Samba down it came back to life again.

Just to be sure this wasn't a coincidence, I then started Samba again. Once again all connectivity stopped, but came back as soon as I was able to shut down Samba.

Network switches were all logging that they were shutting down physical ports due excessive numbers of broadcast packets being seen, and a Wireshark capture from my PC verified that indeed there really was a broadcast storm happening that was triggering this.

The capture showed that upon startup Samba 4.9.0 was sending thousands and thousands of broadcast packets onto the wire in very quick succession.  Wireshark counted around 6500 broadcasts in about 300ms. The packets are all Host Announcement packets sent from the IPv4 address of the host to the broadcast address of the subnet the Samba is on.

Upon reverting back to 4.8.5 with no other config changes, everything is back to normal again. 

===

This bug appears to be fixed with the following commit:


From 6a324eb8bdf4bb2d661aaf60efb270c55562f62f Mon Sep 17 00:00:00 2001
From: Andrew Bartlett <abartlet@samba.org>
Date: Sat, 15 Sep 2018 05:42:11 -0700
Subject: [PATCH] Revert "s3:nmbd: Fix possible integer overflow"

This reverts commit 3a383038ee7f74e5a9d2326a761b27950a14eb83.
---
 source3/nmbd/nmbd_sendannounce.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/source3/nmbd/nmbd_sendannounce.c b/source3/nmbd/nmbd_sendannounce.c
index 44d67e7..1d557c4 100644
--- a/source3/nmbd/nmbd_sendannounce.c
+++ b/source3/nmbd/nmbd_sendannounce.c
@@ -288,10 +288,8 @@ void announce_my_server_names(time_t t)
 			}
 
 			/* Announce every minute at first then progress to every 12 mins */
-			if (t > work->lastannounce_time &&
-			    (t - work->lastannounce_time) < work->announce_interval) {
+			if ((t - work->lastannounce_time) < work->announce_interval)
 				continue;
-			}
 
 			if (work->announce_interval < (CHECK_TIME_MAX_HOST_ANNCE * 60))
 				work->announce_interval += 60;
-- 

After applying this patch above, Samba functions normally again.