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.

6 files changed, 43 insertions, 31 deletions

diff --git a/src/init.cpp b/src/init.cpp
index 599dac39b2..4dce8be819 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -1510,7 +1510,7 @@ bool AppInit2(boost::thread_group& threadGroup, CScheduler& scheduler)
 
     std::string strNodeError;
     int nMaxOutbound = std::min(MAX_OUTBOUND_CONNECTIONS, nMaxConnections);
-    if(!StartNode(connman, threadGroup, scheduler, nLocalServices, nRelevantServices, nMaxConnections, nMaxOutbound, strNodeError))
+    if(!StartNode(connman, threadGroup, scheduler, nLocalServices, nRelevantServices, nMaxConnections, nMaxOutbound, chainActive.Height(), strNodeError))
         return InitError(strNodeError);
 
     // ********************************************************* Step 12: finished
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
diff --git a/src/net.cpp b/src/net.cpp
index fe4daaaebf..d510952551 100644
--- a/src/net.cpp
+++ b/src/net.cpp
@@ -392,7 +392,7 @@ CNode* CConnman::ConnectNode(CAddress addrConnect, const char *pszDest, bool fCo
         addrman.Attempt(addrConnect, fCountFailure);
 
         // Add node
-        CNode* pnode = new CNode(GetNewNodeId(), nLocalServices, hSocket, addrConnect, pszDest ? pszDest : "", false);
+        CNode* pnode = new CNode(GetNewNodeId(), nLocalServices, GetBestHeight(), hSocket, addrConnect, pszDest ? pszDest : "", false);
         GetNodeSignals().InitializeNode(pnode->GetId(), pnode);
         pnode->AddRef();
 
@@ -451,17 +451,15 @@ void CNode::CloseSocketDisconnect()
 
 void CNode::PushVersion()
 {
-    int nBestHeight = GetNodeSignals().GetHeight().get_value_or(0);
-
     int64_t nTime = (fInbound ? GetAdjustedTime() : GetTime());
     CAddress addrYou = (addr.IsRoutable() && !IsProxy(addr) ? addr : CAddress(CService(), addr.nServices));
     CAddress addrMe = GetLocalAddress(&addr, nLocalServices);
     if (fLogIPs)
-        LogPrint("net", "send version message: version %d, blocks=%d, us=%s, them=%s, peer=%d\n", PROTOCOL_VERSION, nBestHeight, addrMe.ToString(), addrYou.ToString(), id);
+        LogPrint("net", "send version message: version %d, blocks=%d, us=%s, them=%s, peer=%d\n", PROTOCOL_VERSION, nMyStartingHeight, addrMe.ToString(), addrYou.ToString(), id);
     else
-        LogPrint("net", "send version message: version %d, blocks=%d, us=%s, peer=%d\n", PROTOCOL_VERSION, nBestHeight, addrMe.ToString(), id);
+        LogPrint("net", "send version message: version %d, blocks=%d, us=%s, peer=%d\n", PROTOCOL_VERSION, nMyStartingHeight, addrMe.ToString(), id);
     PushMessage(NetMsgType::VERSION, PROTOCOL_VERSION, (uint64_t)nLocalServices, nTime, addrYou, addrMe,
-                nLocalHostNonce, strSubVersion, nBestHeight, ::fRelayTxes);
+                nLocalHostNonce, strSubVersion, nMyStartingHeight, ::fRelayTxes);
 }
 
 
@@ -1028,7 +1026,7 @@ void CConnman::AcceptConnection(const ListenSocket& hListenSocket) {
         }
     }
 
-    CNode* pnode = new CNode(GetNewNodeId(), nLocalServices, hSocket, addr, "", true);
+    CNode* pnode = new CNode(GetNewNodeId(), nLocalServices, GetBestHeight(), hSocket, addr, "", true);
     GetNodeSignals().InitializeNode(pnode->GetId(), pnode);
     pnode->AddRef();
     pnode->fWhitelisted = whitelisted;
@@ -2038,13 +2036,14 @@ CConnman::CConnman()
     semOutbound = NULL;
     nMaxConnections = 0;
     nMaxOutbound = 0;
+    nBestHeight = 0;
 }
 
-bool StartNode(CConnman& connman, boost::thread_group& threadGroup, CScheduler& scheduler, ServiceFlags nLocalServices, ServiceFlags nRelevantServices, int nMaxConnectionsIn, int nMaxOutboundIn, std::string& strNodeError)
+bool StartNode(CConnman& connman, boost::thread_group& threadGroup, CScheduler& scheduler, ServiceFlags nLocalServices, ServiceFlags nRelevantServices, int nMaxConnectionsIn, int nMaxOutboundIn, int nBestHeightIn, std::string& strNodeError)
 {
     Discover(threadGroup);
 
-    bool ret = connman.Start(threadGroup, scheduler, nLocalServices, nRelevantServices, nMaxConnectionsIn, nMaxOutboundIn, strNodeError);
+    bool ret = connman.Start(threadGroup, scheduler, nLocalServices, nRelevantServices, nMaxConnectionsIn, nMaxOutboundIn, nBestHeightIn, strNodeError);
 
     return ret;
 }
@@ -2054,7 +2053,7 @@ NodeId CConnman::GetNewNodeId()
     return nLastNodeId.fetch_add(1, std::memory_order_relaxed);
 }
 
-bool CConnman::Start(boost::thread_group& threadGroup, CScheduler& scheduler, ServiceFlags nLocalServicesIn, ServiceFlags nRelevantServicesIn, int nMaxConnectionsIn, int nMaxOutboundIn, std::string& strNodeError)
+bool CConnman::Start(boost::thread_group& threadGroup, CScheduler& scheduler, ServiceFlags nLocalServicesIn, ServiceFlags nRelevantServicesIn, int nMaxConnectionsIn, int nMaxOutboundIn, int nBestHeightIn, std::string& strNodeError)
 {
     nTotalBytesRecv = 0;
     nTotalBytesSent = 0;
@@ -2071,6 +2070,8 @@ bool CConnman::Start(boost::thread_group& threadGroup, CScheduler& scheduler, Se
     nSendBufferMaxSize = 1000*GetArg("-maxsendbuffer", DEFAULT_MAXSENDBUFFER);
     nReceiveFloodSize = 1000*GetArg("-maxreceivebuffer", DEFAULT_MAXRECEIVEBUFFER);
 
+    SetBestHeight(nBestHeightIn);
+
     uiInterface.InitMessage(_("Loading addresses..."));
     // Load addresses from peers.dat
     int64_t nStart = GetTimeMillis();
@@ -2115,7 +2116,7 @@ bool CConnman::Start(boost::thread_group& threadGroup, CScheduler& scheduler, Se
     if (pnodeLocalHost == NULL) {
         CNetAddr local;
         LookupHost("127.0.0.1", local, false);
-        pnodeLocalHost = new CNode(GetNewNodeId(), nLocalServices, INVALID_SOCKET, CAddress(CService(local, 0), nLocalServices));
+        pnodeLocalHost = new CNode(GetNewNodeId(), nLocalServices, GetBestHeight(), INVALID_SOCKET, CAddress(CService(local, 0), nLocalServices));
         GetNodeSignals().InitializeNode(pnodeLocalHost->GetId(), pnodeLocalHost);
     }
 
@@ -2471,6 +2472,16 @@ ServiceFlags CConnman::GetLocalServices() const
     return nLocalServices;
 }
 
+void CConnman::SetBestHeight(int height)
+{
+    nBestHeight.store(height, std::memory_order_release);
+}
+
+int CConnman::GetBestHeight() const
+{
+    return nBestHeight.load(std::memory_order_acquire);
+}
+
 void CNode::Fuzz(int nChance)
 {
     if (!fSuccessfullyConnected) return; // Don't fuzz initial handshake
@@ -2509,7 +2520,7 @@ void CNode::Fuzz(int nChance)
 unsigned int CConnman::GetReceiveFloodSize() const { return nReceiveFloodSize; }
 unsigned int CConnman::GetSendBufferSize() const{ return nSendBufferMaxSize; }
 
-CNode::CNode(NodeId idIn, ServiceFlags nLocalServicesIn, SOCKET hSocketIn, const CAddress& addrIn, const std::string& addrNameIn, bool fInboundIn) :
+CNode::CNode(NodeId idIn, ServiceFlags nLocalServicesIn, int nMyStartingHeightIn, SOCKET hSocketIn, const CAddress& addrIn, const std::string& addrNameIn, bool fInboundIn) :
     ssSend(SER_NETWORK, INIT_PROTO_VERSION),
     addr(addrIn),
     nKeyedNetGroup(CalculateKeyedNetGroup(addrIn)),
@@ -2567,6 +2578,7 @@ CNode::CNode(NodeId idIn, ServiceFlags nLocalServicesIn, SOCKET hSocketIn, const
     nLocalServices = nLocalServicesIn;
 
     GetRandBytes((unsigned char*)&nLocalHostNonce, sizeof(nLocalHostNonce));
+    nMyStartingHeight = nMyStartingHeightIn;
 
     BOOST_FOREACH(const std::string &msg, getAllNetMessageTypes())
         mapRecvBytesPerMsgCmd[msg] = 0;
diff --git a/src/net.h b/src/net.h
index 0859190d36..852822d85b 100644
--- a/src/net.h
+++ b/src/net.h
@@ -109,7 +109,7 @@ public:
 
     CConnman();
     ~CConnman();
-    bool Start(boost::thread_group& threadGroup, CScheduler& scheduler, ServiceFlags nLocalServicesIn, ServiceFlags nRelevantServicesIn, int nMaxConnectionsIn, int nMaxOutboundIn, std::string& strNodeError);
+    bool Start(boost::thread_group& threadGroup, CScheduler& scheduler, ServiceFlags nLocalServicesIn, ServiceFlags nRelevantServicesIn, int nMaxConnectionsIn, int nMaxOutboundIn, int nBestHeightIn, std::string& strNodeError);
     void Stop();
     bool BindListenPort(const CService &bindAddr, std::string& strError, bool fWhitelisted = false);
     bool OpenNetworkConnection(const CAddress& addrConnect, bool fCountFailure, CSemaphoreGrant *grantOutbound = NULL, const char *strDest = NULL, bool fOneShot = false, bool fFeeler = false);
@@ -199,6 +199,10 @@ public:
     uint64_t GetTotalBytesRecv();
     uint64_t GetTotalBytesSent();
 
+    void SetBestHeight(int height);
+    int GetBestHeight() const;
+
+
 private:
     struct ListenSocket {
         SOCKET socket;
@@ -288,12 +292,13 @@ private:
     CSemaphore *semOutbound;
     int nMaxConnections;
     int nMaxOutbound;
+    std::atomic<int> nBestHeight;
 };
 extern std::unique_ptr<CConnman> g_connman;
 void MapPort(bool fUseUPnP);
 unsigned short GetListenPort();
 bool BindListenPort(const CService &bindAddr, std::string& strError, bool fWhitelisted = false);
-bool StartNode(CConnman& connman, boost::thread_group& threadGroup, CScheduler& scheduler, ServiceFlags nLocalServices, ServiceFlags nRelevantServices, int nMaxConnections, int nMaxOutbound, std::string& strNodeError);
+bool StartNode(CConnman& connman, boost::thread_group& threadGroup, CScheduler& scheduler, ServiceFlags nLocalServices, ServiceFlags nRelevantServices, int nMaxConnections, int nMaxOutbound, int nBestHeightIn, std::string& strNodeError);
 bool StopNode(CConnman& connman);
 size_t SocketSendData(CNode *pnode);
 
@@ -315,7 +320,6 @@ struct CombinerAll
 // Signals for message handling
 struct CNodeSignals
 {
-    boost::signals2::signal<int ()> GetHeight;
     boost::signals2::signal<bool (CNode*, CConnman&), CombinerAll> ProcessMessages;
     boost::signals2::signal<bool (CNode*, CConnman&), CombinerAll> SendMessages;
     boost::signals2::signal<void (NodeId, const CNode*)> InitializeNode;
@@ -558,7 +562,7 @@ public:
     CAmount lastSentFeeFilter;
     int64_t nextSendTimeFeeFilter;
 
-    CNode(NodeId id, ServiceFlags nLocalServicesIn, SOCKET hSocketIn, const CAddress &addrIn, const std::string &addrNameIn = "", bool fInboundIn = false);
+    CNode(NodeId id, ServiceFlags nLocalServicesIn, int nMyStartingHeightIn, SOCKET hSocketIn, const CAddress &addrIn, const std::string &addrNameIn = "", bool fInboundIn = false);
     ~CNode();
 
 private:
@@ -569,6 +573,7 @@ private:
 
     uint64_t nLocalHostNonce;
     ServiceFlags nLocalServices;
+    int nMyStartingHeight;
 public:
 
     NodeId GetId() const {
diff --git a/src/test/DoS_tests.cpp b/src/test/DoS_tests.cpp
index 2265f43a6e..33f107d84b 100644
--- a/src/test/DoS_tests.cpp
+++ b/src/test/DoS_tests.cpp
@@ -48,7 +48,7 @@ BOOST_AUTO_TEST_CASE(DoS_banning)
 {
     connman->ClearBanned();
     CAddress addr1(ip(0xa0b0c001), NODE_NONE);
-    CNode dummyNode1(id++, NODE_NETWORK, INVALID_SOCKET, addr1, "", true);
+    CNode dummyNode1(id++, NODE_NETWORK, 0, INVALID_SOCKET, addr1, "", true);
     GetNodeSignals().InitializeNode(dummyNode1.GetId(), &dummyNode1);
     dummyNode1.nVersion = 1;
     Misbehaving(dummyNode1.GetId(), 100); // Should get banned
@@ -57,7 +57,7 @@ BOOST_AUTO_TEST_CASE(DoS_banning)
     BOOST_CHECK(!connman->IsBanned(ip(0xa0b0c001|0x0000ff00))); // Different IP, not banned
 
     CAddress addr2(ip(0xa0b0c002), NODE_NONE);
-    CNode dummyNode2(id++, NODE_NETWORK, INVALID_SOCKET, addr2, "", true);
+    CNode dummyNode2(id++, NODE_NETWORK, 0, INVALID_SOCKET, addr2, "", true);
     GetNodeSignals().InitializeNode(dummyNode2.GetId(), &dummyNode2);
     dummyNode2.nVersion = 1;
     Misbehaving(dummyNode2.GetId(), 50);
@@ -74,7 +74,7 @@ BOOST_AUTO_TEST_CASE(DoS_banscore)
     connman->ClearBanned();
     mapArgs["-banscore"] = "111"; // because 11 is my favorite number
     CAddress addr1(ip(0xa0b0c001), NODE_NONE);
-    CNode dummyNode1(id++, NODE_NETWORK, INVALID_SOCKET, addr1, "", true);
+    CNode dummyNode1(id++, NODE_NETWORK, 0, INVALID_SOCKET, addr1, "", true);
     GetNodeSignals().InitializeNode(dummyNode1.GetId(), &dummyNode1);
     dummyNode1.nVersion = 1;
     Misbehaving(dummyNode1.GetId(), 100);
@@ -96,7 +96,7 @@ BOOST_AUTO_TEST_CASE(DoS_bantime)
     SetMockTime(nStartTime); // Overrides future calls to GetTime()
 
     CAddress addr(ip(0xa0b0c001), NODE_NONE);
-    CNode dummyNode(id++, NODE_NETWORK, INVALID_SOCKET, addr, "", true);
+    CNode dummyNode(id++, NODE_NETWORK, 0, INVALID_SOCKET, addr, "", true);
     GetNodeSignals().InitializeNode(dummyNode.GetId(), &dummyNode);
     dummyNode.nVersion = 1;
 
diff --git a/src/test/net_tests.cpp b/src/test/net_tests.cpp
index 1019b12c1c..bc9a98ab04 100644
--- a/src/test/net_tests.cpp
+++ b/src/test/net_tests.cpp
@@ -154,6 +154,7 @@ BOOST_AUTO_TEST_CASE(cnode_simple_test)
 {
     SOCKET hSocket = INVALID_SOCKET;
     NodeId id = 0;
+    int height = 0;
 
     in_addr ipv4Addr;
     ipv4Addr.s_addr = 0xa0b0c001;
@@ -163,12 +164,12 @@ BOOST_AUTO_TEST_CASE(cnode_simple_test)
     bool fInboundIn = false;
 
     // Test that fFeeler is false by default.
-    CNode* pnode1 = new CNode(id++, NODE_NETWORK, hSocket, addr, pszDest, fInboundIn);
+    CNode* pnode1 = new CNode(id++, NODE_NETWORK, height, hSocket, addr, pszDest, fInboundIn);
     BOOST_CHECK(pnode1->fInbound == false);
     BOOST_CHECK(pnode1->fFeeler == false);
 
     fInboundIn = true;
-    CNode* pnode2 = new CNode(id++, NODE_NETWORK, hSocket, addr, pszDest, fInboundIn);
+    CNode* pnode2 = new CNode(id++, NODE_NETWORK, height, hSocket, addr, pszDest, fInboundIn);
     BOOST_CHECK(pnode2->fInbound == true);
     BOOST_CHECK(pnode2->fFeeler == false);
 }