Feeler connections ported from BTC core, eclipse attack mitigation

src/main.cpp

@@ -6862,10 +6862,16 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
         return true;
     }
 
-    //fprintf(stderr,"netmsg: %s\n", strCommand.c_str());
+    fprintf(stderr,"%s: netmsg: %s from %s\n", __func__, strCommand.c_str(), pfrom->addr.ToString().c_str() );
+
+    if (strCommand == "version") {
+        // Feeler connections exist only to verify if node is online
+        if (pfrom->fFeeler) {
+            assert(pfrom->fInbound == false);
+            pfrom->fDisconnect = true;
+            fprintf(stderr,"%s: disconnecting feelerconn from %s\n", __func__, pfrom->addr.ToString().c_str() );
+        }
 
-    if (strCommand == "version")
-    {
         // Each connection can only send one version message
         if (pfrom->nVersion != 0)
         {
@@ -6978,15 +6984,6 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
             }
         }
 
-        // Do Not Relay alerts
-        /*
-        {
-            LOCK(cs_mapAlerts);
-            BOOST_FOREACH(PAIRTYPE(const uint256, CAlert)& item, mapAlerts)
-            item.second.RelayTo(pfrom);
-        }
-        */
-
         pfrom->fSuccessfullyConnected = true;
 
         string remoteAddr;

src/net.cpp

@@ -62,6 +62,9 @@ using namespace hush;
 #endif
 #endif
 
+// We add a random period time (0 to 1 seconds) to feeler connections to prevent synchronization.
+#define FEELER_SLEEP_WINDOW 1
+
 #define USE_TLS "encrypted as fuck"
 
 #if defined(USE_TLS) && !defined(TLS1_3_VERSION)
@@ -75,6 +78,7 @@ using namespace std;
 namespace {
     //TODO: Make these CLI args
     const int MAX_OUTBOUND_CONNECTIONS = 64;
+    const int MAX_FEELER_CONNECTIONS   = 1;
     const int MAX_INBOUND_FROMIP       = 3;
 
     struct ListenSocket {
@@ -1023,8 +1027,8 @@ static void AcceptConnection(const ListenSocket& hListenSocket) {
     socklen_t len = sizeof(sockaddr);
     SOCKET hSocket = accept(hListenSocket.socket, (struct sockaddr*)&sockaddr, &len);
     CAddress addr;
-    int nInbound = 0;
+    int nInbound    = 0;
-    int nMaxInbound = nMaxConnections - MAX_OUTBOUND_CONNECTIONS;
+    int nMaxInbound = nMaxConnections - (MAX_OUTBOUND_CONNECTIONS + MAX_FEELER_CONNECTIONS);
 
     if (hSocket != INVALID_SOCKET)
         if (!addr.SetSockAddr((const struct sockaddr*)&sockaddr))
@@ -1412,6 +1416,11 @@ void static ProcessOneShot()
     }
 }
 
+int64_t PoissonNextSend(int64_t now, int average_interval_seconds)
+{
+    return now + (int64_t)(log1p(GetRand(1ULL << 48) * -0.0000000000000035527136788 /* -1/2^48 */) * average_interval_seconds * -1000000.0 + 0.5);
+}
+
 void ThreadOpenConnections()
 {
     // Connect to specific addresses
@@ -1436,8 +1445,11 @@ void ThreadOpenConnections()
 
     // Initiate network connections
     int64_t nStart = GetTime();
-    while (true)
+
-    {
+    // Minimum time before next feeler connection (in microseconds).
+    int64_t nNextFeeler = PoissonNextSend(nStart*1000*1000, FEELER_INTERVAL);
+
+    while (true) {
         ProcessOneShot();
 
         MilliSleep(500);
@@ -1450,19 +1462,17 @@ void ThreadOpenConnections()
         if (GetTime() - nStart > 60) {
             static bool done = false;
             if (!done) {
-                // skip DNS seeds for staked chains.
                 LogPrintf("Adding fixed seed nodes.\n");
                 addrman.Add(convertSeed6(Params().FixedSeeds()), CNetAddr("127.0.0.1"));
                 done = true;
             }
         }
 
-
         // Choose an address to connect to based on most recently seen
         CAddress addrConnect;
 
-        // Only connect out to one peer per network group (/16 for IPv4).
+        // Only connect out to one peer per network group. Originally /16 for IPv4, now ASNs via
-        // Use -asmap for ASN bucketing
+        // -asmap for ASN bucketing, which is enabled by default
         // Do this here so we don't have to critsect vNodes inside mapAddresses critsect.
         int nOutbound = 0;
         set<vector<unsigned char> > setConnected;
@@ -1475,13 +1485,38 @@ void ThreadOpenConnections()
                 }
             }
         }
+        assert(nOutbound <= (MAX_OUTBOUND_CONNECTIONS + MAX_FEELER_CONNECTIONS));
+
+        // "Feeler Connections" as per https://eprint.iacr.org/2015/263.pdf
+        // "Eclipse Attacks on Bitcoin’s Peer-to-Peer Network" by
+        // Ethan Heilman, Alison Kendler, Aviv Zohar, Sharon Goldberg.
+        //
+        // Design goals:
+        //  * Increase the number of connectable addresses in the tried table.
+        //
+        // Method:
+        //  * Choose a random address from new and attempt to connect to it if we can connect
+        //    successfully it is added to tried.
+        //  * Start attempting feeler connections only after node finishes making outbound
+        //    connections.
+        //  * Make feeler connections randomly with 120s average interval via PoissonNextSend.
+        //  Originally from https://github.com/bitcoin/bitcoin/pull/8282
+        //  Modified for API changes by Duke Leto
+        bool fFeeler = false;
+        if (nOutbound >= MAX_OUTBOUND_CONNECTIONS) {
+            int64_t nTime = GetTimeMicros(); // The current time right now (in microseconds).
+            if (nTime > nNextFeeler) {
+                nNextFeeler = PoissonNextSend(nTime, FEELER_INTERVAL);
+                fFeeler = true;
+            } else {
+                continue;
+            }
+        }
 
         int64_t nANow = GetTime();
-
+        int nTries    = 0;
-        int nTries = 0;
+        while (true) {
-        while (true)
+            CAddrInfo addr = addrman.Select(fFeeler);
-        {
-            CAddrInfo addr = addrman.Select();
 
             // if we selected an invalid address, restart
             if (!addr.IsValid() || setConnected.count(addr.GetGroup(addrman.m_asmap)) || IsLocal(addr))
@@ -1501,6 +1536,13 @@ void ThreadOpenConnections()
             if (nANow - addr.nLastTry < 600 && nTries < 30)
                 continue;
 
+            /* TODO: port this code
+            // only consider nodes missing relevant services after 40 failed attempts
+            if ((addr.nServices & nRelevantServices) != nRelevantServices && nTries < 40)
+                continue;
+            */
+
+            //TODO: why is this a good thing?
             // do not allow non-default ports, unless after 50 invalid addresses selected already
             if (addr.GetPort() != Params().GetDefaultPort() && nTries < 50)
                 continue;
@@ -1509,8 +1551,18 @@ void ThreadOpenConnections()
             break;
         }
 
-        if (addrConnect.IsValid())
+        if (addrConnect.IsValid()) {
-            OpenNetworkConnection(addrConnect, &grant);
+            if (fFeeler) {
+                // Add small amount of random noise before connection to avoid synchronization
+                int randsleep = GetRandInt(FEELER_SLEEP_WINDOW * 1000);
+                MilliSleep(randsleep);
+                LogPrint("net", "Making feeler connection to %s\n", addrConnect.ToString().c_str());
+                printf("%s: Making feeler connection to %s\n", __func__, addrConnect.ToString().c_str());
+            }
+
+            //int failures = setConnected.size() >= std::min(nMaxConnections - 1, 2);
+            OpenNetworkConnection(addrConnect,/*failures,*/ &grant, NULL, false, fFeeler);
+        }
     }
 }
 
@@ -1591,7 +1643,7 @@ void ThreadOpenAddedConnections()
 }
 
 // if successful, this moves the passed grant to the constructed node
-bool OpenNetworkConnection(const CAddress& addrConnect, CSemaphoreGrant *grantOutbound, const char *pszDest, bool fOneShot)
+bool OpenNetworkConnection(const CAddress& addrConnect, /* bool fCountFailure, */ CSemaphoreGrant *grantOutbound, const char *pszDest, bool fOneShot, bool fFeeler)
 {
     // Initiate outbound network connection
     boost::this_thread::interruption_point();
@@ -1604,6 +1656,7 @@ bool OpenNetworkConnection(const CAddress& addrConnect, CSemaphoreGrant *grantOu
         return false;
     
     CNode* pnode = ConnectNode(addrConnect, pszDest);
+    //CNode* pnode = ConnectNode(addrConnect, pszDest, fCountFailure);
     boost::this_thread::interruption_point();
     
     if (!pnode)
@@ -1611,8 +1664,11 @@ bool OpenNetworkConnection(const CAddress& addrConnect, CSemaphoreGrant *grantOu
     if (grantOutbound)
         grantOutbound->MoveTo(pnode->grantOutbound);
     pnode->fNetworkNode = true;
+
     if (fOneShot)
         pnode->fOneShot = true;
+    if (fFeeler)
+        pnode->fFeeler = true;
 
     return true;
 }
@@ -1858,7 +1914,7 @@ void StartNode(boost::thread_group& threadGroup, CScheduler& scheduler)
 
     if (semOutbound == NULL) {
         // initialize semaphore
-        int nMaxOutbound = min(MAX_OUTBOUND_CONNECTIONS, nMaxConnections);
+        int nMaxOutbound = min((MAX_OUTBOUND_CONNECTIONS + MAX_FEELER_CONNECTIONS), nMaxConnections);
         semOutbound = new CSemaphore(nMaxOutbound);
     }
 
@@ -1907,7 +1963,7 @@ bool StopNode()
 {
     LogPrintf("StopNode()\n");
     if (semOutbound)
-        for (int i=0; i<MAX_OUTBOUND_CONNECTIONS; i++)
+        for (int i=0; i<(MAX_OUTBOUND_CONNECTIONS + MAX_FEELER_CONNECTIONS); i++)
             semOutbound->post();
 
     if (HUSH_NSPV_FULLNODE && fAddressesInitialized)
@@ -2166,12 +2222,13 @@ CNode::CNode(SOCKET hSocketIn, const CAddress& addrIn, const std::string& addrNa
     nTimeOffset = 0;
     addr = addrIn;
     addrName = addrNameIn == "" ? addr.ToStringIPPort() : addrNameIn;
-    nVersion = 0;
+    nVersion     = 0;
-    strSubVer = "";
+    strSubVer    = "";
     fAllowlisted = false;
-    fOneShot = false;
+    fOneShot     = false;
-    fClient = false; // set by version message
+    fClient      = false; // set by version message
-    fInbound = fInboundIn;
+    fFeeler      = false;
+    fInbound     = fInboundIn;
     fNetworkNode = false;
     fSuccessfullyConnected = false;
     fDisconnect = false;

src/net.h

@@ -82,10 +82,13 @@ static const size_t SETASKFOR_MAX_SZ = 2 * MAX_INV_SZ;
 static const unsigned int DEFAULT_MAX_PEER_CONNECTIONS = 384;
 /** The period before a network upgrade activates, where connections to upgrading peers are preferred (in blocks). */
 static const int NETWORK_UPGRADE_PEER_PREFERENCE_BLOCK_PERIOD = 24 * 24 * 3;
+/** Run the feeler connection loop once every 120 seconds. **/
+static const int FEELER_INTERVAL = 120;
 
 unsigned int ReceiveFloodSize();
 unsigned int SendBufferSize();
 
+int64_t PoissonNextSend(int64_t now, int average_interval_seconds);
 void AddOneShot(const std::string& strDest);
 void AddressCurrentlyConnected(const CService& addr);
 CNode* FindNode(const CNetAddr& ip);
@@ -93,7 +96,7 @@ CNode* FindNode(const CSubNet& subNet);
 CNode* FindNode(const std::string& addrName);
 CNode* FindNode(const CService& ip);
 CNode* ConnectNode(CAddress addrConnect, const char *pszDest = NULL);
-bool OpenNetworkConnection(const CAddress& addrConnect, CSemaphoreGrant *grantOutbound = NULL, const char *strDest = NULL, bool fOneShot = false);
+bool OpenNetworkConnection(const CAddress& addrConnect, CSemaphoreGrant *grantOutbound = NULL, const char *strDest = NULL, bool fOneShot = false, bool fFeeler = false);
 unsigned short GetListenPort();
 bool BindListenPort(const CService &bindAddr, std::string& strError, bool fAllowlisted = false);
 void StartNode(boost::thread_group& threadGroup, CScheduler& scheduler);
@@ -220,7 +223,8 @@ public:
     int nStartingHeight;
     uint64_t nSendBytes;
     uint64_t nRecvBytes;
-    bool fAllowlisted;
+    bool fAllowlisted; // If true this node bypasses DoS ban limits
+    bool fFeeler;      // If true this node is being used as a short lived feeler.
     double dPingTime;
     double dPingWait;
     std::string addrLocal;
@@ -228,7 +232,7 @@ public:
     CAddress addr;
     // Bind address of our side of the connection
     // CAddress addrBind; // https://github.com/bitcoin/bitcoin/commit/a7e3c2814c8e49197889a4679461be42254e5c51
-    uint32_t m_mapped_as;
+    uint32_t m_mapped_as;  // Mapped ASN for this address
 };
 
 
@@ -273,9 +277,6 @@ public:
 };
 
 
-
-
-
 /** Information about a peer */
 class CNode
 {
@@ -323,6 +324,7 @@ public:
     bool fOneShot;
     bool fClient;
     bool fInbound;
+    bool fFeeler;
     bool fNetworkNode;
     bool fSuccessfullyConnected;
     bool fDisconnect;

src/test/netbase_tests.cpp

@@ -5,9 +5,7 @@
 
 #include "netbase.h"
 #include "test/test_bitcoin.h"
-
 #include <string>
-
 #include <boost/assign/list_of.hpp>
 #include <boost/test/unit_test.hpp>
 
@@ -24,6 +22,35 @@ BOOST_AUTO_TEST_CASE(netbase_networks)
     BOOST_CHECK(CNetAddr("FD87:D87E:EB43:edb1:8e4:3588:e546:35ca").GetNetwork() == NET_ONION);
 }
 
+
+/* TODO: port this feeler test
+BOOST_AUTO_TEST_CASE(cnode_simple_test)
+{
+    SOCKET hSocket = INVALID_SOCKET;
+
+    in_addr ipv4Addr;
+    ipv4Addr.s_addr = 0xa0b0c001;
+
+    CAddress addr = CAddress(CService(ipv4Addr, 7777), NODE_NETWORK);
+    std::string pszDest = "";
+    bool fInboundIn = false;
+
+    // Test that fFeeler is false by default.
+    CNode* pnode1 = new CNode(hSocket, addr, pszDest, fInboundIn);
+
+
+    BOOST_CHECK(pnode1->fInbound == false);
+    BOOST_CHECK(pnode1->fFeeler == false);
+
+    fInboundIn = true;
+    CNode* pnode2 = new CNode(hSocket, addr, pszDest, fInboundIn);
+    BOOST_CHECK(pnode2->fInbound == true);
+    BOOST_CHECK(pnode2->fFeeler == false);
+}
+
+*/
+
+
 BOOST_AUTO_TEST_CASE(netbase_properties)
 {
     BOOST_CHECK(CNetAddr("127.0.0.1").IsIPv4());