net: Pass best block known height into CConnman

CConnman then passes the current best height into CNode at creation time.

This way CConnman/CNode have no dependency on main for height, and the signals
only move in one direction.

This also helps to prevent identity leakage a tiny bit. Before this change, an
attacker could theoretically make 2 connections on different interfaces. They
would connect fully on one, and only establish the initial connection on the
other. Once they receive a new block, they would relay it to your first
connection, and immediately commence the version handshake on the second. Since
the new block height is reflected immediately, they could attempt to learn
whether the two connections were correlated.

This is, of course, incredibly unlikely to work due to the small timings
involved and receipt from other senders. But it doesn't hurt to lock-in
nBestHeight at the time of connection, rather than letting the remote choose
the time.

1 files changed, 2 insertions, 8 deletions

diff --git a/src/main.cpp b/src/main.cpp
index a916cbc12d..1835d9712b 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -325,12 +325,6 @@ CNodeState *State(NodeId pnode) {
     return &it->second;
 }
 
-int GetHeight()
-{
-    LOCK(cs_main);
-    return chainActive.Height();
-}
-
 void UpdatePreferredDownload(CNode* node, CNodeState* state)
 {
     nPreferredDownload -= state->fPreferredDownload;
@@ -639,7 +633,6 @@ bool GetNodeStateStats(NodeId nodeid, CNodeStateStats &stats) {
 
 void RegisterNodeSignals(CNodeSignals& nodeSignals)
 {
-    nodeSignals.GetHeight.connect(&GetHeight);
     nodeSignals.ProcessMessages.connect(&ProcessMessages);
     nodeSignals.SendMessages.connect(&SendMessages);
     nodeSignals.InitializeNode.connect(&InitializeNode);
@@ -648,7 +641,6 @@ void RegisterNodeSignals(CNodeSignals& nodeSignals)
 
 void UnregisterNodeSignals(CNodeSignals& nodeSignals)
 {
-    nodeSignals.GetHeight.disconnect(&GetHeight);
     nodeSignals.ProcessMessages.disconnect(&ProcessMessages);
     nodeSignals.SendMessages.disconnect(&SendMessages);
     nodeSignals.InitializeNode.disconnect(&InitializeNode);
@@ -3058,6 +3050,8 @@ bool ActivateBestChain(CValidationState &state, const CChainParams& chainparams,
         // When we reach this point, we switched to a new tip (stored in pindexNewTip).
 
         // Notifications/callbacks that can run without cs_main
+        if(connman)
+            connman->SetBestHeight(nNewHeight);
 
         // throw all transactions though the signal-interface
         // while _not_ holding the cs_main lock