From 010766fe9e3037502f351619ffc7c5f82c5c6487 Mon Sep 17 00:00:00 2001
From: Bryan Boreham <bjboreham@gmail.com>
Date: Mon, 21 Mar 2016 15:22:36 +0000
Subject: [PATCH] Check entries claiming to originate from us against our
 current data, and override if necessary

---
 nameserver/entry.go      | 20 ++++++++++++++++++--
 nameserver/nameserver.go | 25 +++++++++++++++++++++----
 2 files changed, 39 insertions(+), 6 deletions(-)

diff --git a/nameserver/entry.go b/nameserver/entry.go
index cb0830fa..89a48ca7 100644
--- a/nameserver/entry.go
+++ b/nameserver/entry.go
@@ -105,6 +105,11 @@ func (e1 *Entry) addLowercase() {
 	e1.lHostname = strings.ToLower(e1.Hostname)
 }
 
+func (e *Entry) tombstone() {
+	e.Version++
+	e.Tombstone = now()
+}
+
 func check(es SortableEntries) error {
 	if !sort.IsSorted(es) {
 		return fmt.Errorf("Not sorted!")
@@ -182,8 +187,7 @@ func (es *Entries) tombstone(ourname mesh.PeerName, f func(*Entry) bool) Entries
 	tombstoned := Entries{}
 	for i, e := range *es {
 		if f(&e) && e.Origin == ourname {
-			e.Version++
-			e.Tombstone = now()
+			e.tombstone()
 			(*es)[i] = e
 			tombstoned = append(tombstoned, e)
 		}
@@ -191,6 +195,7 @@ func (es *Entries) tombstone(ourname mesh.PeerName, f func(*Entry) bool) Entries
 	return tombstoned
 }
 
+// note f() may only modify entries such that they remain in order defined by less()
 func (es *Entries) filter(f func(*Entry) bool) {
 	defer es.checkAndPanic().checkAndPanic()
 
@@ -205,6 +210,17 @@ func (es *Entries) filter(f func(*Entry) bool) {
 	*es = (*es)[:i]
 }
 
+func (es Entries) findEqual(e *Entry) (*Entry, bool) {
+	i := sort.Search(len(es), func(i int) bool {
+		return !es[i].insensitiveLess(e)
+	})
+	if i < len(es) && es[i].equal(*e) {
+		return &es[i], true
+	} else {
+		return nil, false
+	}
+}
+
 func (es Entries) lookup(hostname string) Entries {
 	es.checkAndPanic()
 
diff --git a/nameserver/nameserver.go b/nameserver/nameserver.go
index 806db03b..002c7f29 100644
--- a/nameserver/nameserver.go
+++ b/nameserver/nameserver.go
@@ -203,16 +203,33 @@ func (n *Nameserver) receiveGossip(msg []byte) (mesh.GossipData, mesh.GossipData
 		return nil, nil, fmt.Errorf("clock skew of %d detected", delta)
 	}
 
-	n.Lock()
-	isKnownPeer := n.isKnownPeer
-	n.Unlock() // Don't hold the lock over call out to code elsewhere
+	// Filter to remove entries from unknown peers, done before we take
+	// the nameserver lock, so we don't have to worry what isKnownPeer locks.
 	gossip.Entries.filter(func(e *Entry) bool {
-		return isKnownPeer(e.Origin)
+		return n.isKnownPeer(e.Origin)
 	})
 
 	n.Lock()
 	defer n.Unlock()
 
+	// Check entries claiming to originate from us against our current data
+	gossip.Entries.filter(func(e *Entry) bool {
+		if e.Origin == n.ourName {
+			if ourEntry, ok := n.entries.findEqual(e); ok {
+				if ourEntry.Version < e.Version ||
+					(ourEntry.Version == e.Version && ourEntry.Tombstone != e.Tombstone) {
+					// Take our version of the data, but make the version higher than the incoming
+					nextVersion := e.Version + 1
+					*e = *ourEntry
+					e.Version = nextVersion
+				}
+			} else { // We have no entry matching the one that came in with us as Origin
+				e.tombstone()
+			}
+		}
+		return true
+	})
+
 	newEntries := n.entries.merge(gossip.Entries)
 	if len(newEntries) > 0 {
 		return &GossipData{Entries: newEntries, Timestamp: now()}, &gossip, nil