From 5bacfabae7061abf3e0a4e7dc6f7628d6c2f378d Mon Sep 17 00:00:00 2001
From: Neil Alexander <neilalexander@users.noreply.github.com>
Date: Wed, 13 Mar 2019 17:43:33 +0000
Subject: [PATCH] Handle cases where link-local addresses may disappear or
 change

---
 src/yggdrasil/multicast.go | 39 +++++++++++++++++++++++++++++++++++++-
 1 file changed, 38 insertions(+), 1 deletion(-)

diff --git a/src/yggdrasil/multicast.go b/src/yggdrasil/multicast.go
index dacad27e..ca3a1f75 100644
--- a/src/yggdrasil/multicast.go
+++ b/src/yggdrasil/multicast.go
@@ -122,11 +122,48 @@ func (m *multicast) announce() {
 		// There might be interfaces that we configured listeners for but are no
 		// longer up - if that's the case then we should stop the listeners
 		for name, listener := range m.listeners {
-			if _, ok := interfaces[name]; !ok {
+			// Prepare our stop function!
+			stop := func() {
 				listener.stop <- true
 				delete(m.listeners, name)
 				m.core.log.Debugln("No longer multicasting on", name)
 			}
+			// If the interface is no longer visible on the system then stop the
+			// listener, as another one will be started further down
+			if _, ok := interfaces[name]; !ok {
+				stop()
+				continue
+			}
+			// It's possible that the link-local listener address has changed so if
+			// that is the case then we should clean up the interface listener
+			found := false
+			listenaddr, err := net.ResolveTCPAddr("tcp6", listener.listener.Addr().String())
+			if err != nil {
+				stop()
+				continue
+			}
+			// Find the interface that matches the listener
+			if intf, err := net.InterfaceByName(name); err == nil {
+				if addrs, err := intf.Addrs(); err == nil {
+					// Loop through the addresses attached to that listener and see if any
+					// of them match the current address of the listener
+					for _, addr := range addrs {
+						if ip, _, err := net.ParseCIDR(addr.String()); err == nil {
+							// Does the interface address match our listener address?
+							if ip.Equal(listenaddr.IP) {
+								found = true
+								break
+							}
+						}
+					}
+				}
+			}
+			// If the address has not been found on the adapter then we should stop
+			// and clean up the TCP listener. A new one will be created below if a
+			// suitable link-local address is found
+			if !found {
+				stop()
+			}
 		}
 		// Now that we have a list of valid interfaces from the operating system,
 		// we can start checking if we can send multicasts on them