Backport Bitcoin PR#8084: Add recently accepted blocks and txn to Att…

…emptToEvictConnection (#1522)

* Add recently accepted blocks and txn to AttemptToEvictConnection.

This protects any not-already-protected peers who were the most
 recent four to relay transactions and most recent four to send
 blocks to us.

* Allow disconnecting a netgroup with only one member in eviction.

With the latest additions there are enough protective measures that
 we can take the training wheels off.

src/main.cpp

@@ -3963,8 +3963,9 @@ static bool AcceptBlockHeader(const CBlockHeader& block, CValidationState& state
 }
 
 /** Store block on disk. If dbp is non-NULL, the file is known to already reside on disk */
-static bool AcceptBlock(const CBlock& block, CValidationState& state, const CChainParams& chainparams, CBlockIndex** ppindex, bool fRequested, const CDiskBlockPos* dbp)
+static bool AcceptBlock(const CBlock& block, CValidationState& state, const CChainParams& chainparams, CBlockIndex** ppindex, bool fRequested, const CDiskBlockPos* dbp, bool* fNewBlock)
 {
+    if (fNewBlock) *fNewBlock = false;
     AssertLockHeld(cs_main);
 
     CBlockIndex *pindexDummy = NULL;
@@ -3993,6 +3994,7 @@ static bool AcceptBlock(const CBlock& block, CValidationState& state, const CCha
         if (!fHasMoreWork) return true;     // Don't process less-work chains
         if (fTooFarAhead) return true;      // Block height is too high
     }
+    if (fNewBlock) *fNewBlock = true;
 
     if ((!CheckBlock(block, state)) || !ContextualCheckBlock(block, state, pindex->pprev)) {
         if (state.IsInvalid() && !state.CorruptionPossible()) {
@@ -4040,7 +4042,7 @@ static bool IsSuperMajority(int minVersion, const CBlockIndex* pstart, unsigned
 }
 
 
-bool ProcessNewBlock(CValidationState& state, const CChainParams& chainparams, const CNode* pfrom, const CBlock* pblock, bool fForceProcessing, const CDiskBlockPos* dbp)
+bool ProcessNewBlock(CValidationState& state, const CChainParams& chainparams, CNode* pfrom, const CBlock* pblock, bool fForceProcessing, const CDiskBlockPos* dbp)
 {
     {
         LOCK(cs_main);
@@ -4049,9 +4051,11 @@ bool ProcessNewBlock(CValidationState& state, const CChainParams& chainparams, c
 
         // Store to disk
         CBlockIndex *pindex = NULL;
-        bool ret = AcceptBlock(*pblock, state, chainparams, &pindex, fRequested, dbp);
+        bool fNewBlock = false;
+        bool ret = AcceptBlock(*pblock, state, chainparams, &pindex, fRequested, dbp, &fNewBlock);
         if (pindex && pfrom) {
             mapBlockSource[pindex->GetBlockHash()] = pfrom->GetId();
+            if (fNewBlock) pfrom->nLastBlockTime = GetTime();
         }
         CheckBlockIndex(chainparams.GetConsensus());
         if (!ret)
@@ -4633,7 +4637,7 @@ bool LoadExternalBlockFile(const CChainParams& chainparams, FILE* fileIn, CDiskB
                 if (mapBlockIndex.count(hash) == 0 || (mapBlockIndex[hash]->nStatus & BLOCK_HAVE_DATA) == 0) {
                     LOCK(cs_main);
                     CValidationState state;
-                    if (AcceptBlock(block, state, chainparams, NULL, true, dbp))
+                    if (AcceptBlock(block, state, chainparams, NULL, true, dbp, NULL))
                         nLoaded++;
                     if (state.IsError())
                         break;
@@ -4666,7 +4670,7 @@ bool LoadExternalBlockFile(const CChainParams& chainparams, FILE* fileIn, CDiskB
                                     head.ToString());
                             LOCK(cs_main);
                             CValidationState dummy;
-                            if (AcceptBlock(block, dummy, chainparams, NULL, true, &it->second))
+                            if (AcceptBlock(block, dummy, chainparams, NULL, true, &it->second, NULL))
                             {
                                 nLoaded++;
                                 queue.push_back(block.GetHash());
@@ -5878,6 +5882,8 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
             RelayTransaction(tx);
             vWorkQueue.push_back(inv.hash);
 
+            pfrom->nLastTXTime = GetTime();
+
             LogPrint("mempool", "AcceptToMemoryPool: peer=%d: accepted %s (poolsz %u txn, %u kB)\n",
                 pfrom->id,
                 tx.GetHash().ToString(),

src/main.h

@@ -205,7 +205,7 @@ void UnregisterNodeSignals(CNodeSignals& nodeSignals);
  * @param[out]  dbp     The already known disk position of pblock, or NULL if not yet stored.
  * @return True if state.IsValid()
  */
-bool ProcessNewBlock(CValidationState& state, const CChainParams& chainparams, const CNode* pfrom, const CBlock* pblock, bool fForceProcessing, const CDiskBlockPos* dbp);
+bool ProcessNewBlock(CValidationState& state, const CChainParams& chainparams, CNode* pfrom, const CBlock* pblock, bool fForceProcessing, const CDiskBlockPos* dbp);
 /** Check whether enough disk space is available for an incoming block */
 bool CheckDiskSpace(uint64_t nAdditionalBytes = 0);
 /** Open a block file (blk?????.dat) */

src/net.cpp

@@ -870,13 +870,23 @@ struct NodeEvictionCandidate
         : id(pnode->id),
           nTimeConnected(pnode->nTimeConnected),
           nMinPingUsecTime(pnode->nMinPingUsecTime),
+          nLastBlockTime(pnode->nLastBlockTime),
+          nLastTXTime(pnode->nLastTXTime),
+          fNetworkNode(pnode->fNetworkNode),
+          fRelayTxes(pnode->fRelayTxes),
+          fBloomFilter(pnode->pfilter != NULL),
           vchNetGroup(pnode->addr.GetGroup()),
           vchKeyedNetGroup(pnode->vchKeyedNetGroup)
         {}
 
     int id;
     int64_t nTimeConnected;
     int64_t nMinPingUsecTime;
+    int64_t nLastBlockTime;
+    int64_t nLastTXTime;
+    bool fNetworkNode;
+    bool fRelayTxes;
+    bool fBloomFilter;
     std::vector<unsigned char> vchNetGroup;
     std::vector<unsigned char> vchKeyedNetGroup;
 };
@@ -896,7 +906,32 @@ static bool CompareKeyedNetGroup(const NodeEvictionCandidate& a, const NodeEvict
     return a.vchKeyedNetGroup < b.vchKeyedNetGroup;
 }
 
-static bool AttemptToEvictConnection(bool fPreferNewConnection) {
+static bool CompareNodeBlockTime(const NodeEvictionCandidate &a, const NodeEvictionCandidate &b)
+{
+    // There is a fall-through here because it is common for a node to have many peers which have not yet relayed a block.
+    if (a.nLastBlockTime != b.nLastBlockTime) return a.nLastBlockTime < b.nLastBlockTime;
+    if (a.fNetworkNode != b.fNetworkNode) return b.fNetworkNode;
+    return a.nTimeConnected > b.nTimeConnected;
+}
+
+static bool CompareNodeTXTime(const NodeEvictionCandidate &a, const NodeEvictionCandidate &b)
+{
+    // There is a fall-through here because it is common for a node to have more than a few peers that have not yet relayed txn.
+    if (a.nLastTXTime != b.nLastTXTime) return a.nLastTXTime < b.nLastTXTime;
+    if (a.fRelayTxes != b.fRelayTxes) return b.fRelayTxes;
+    if (a.fBloomFilter != b.fBloomFilter) return a.fBloomFilter;
+    return a.nTimeConnected > b.nTimeConnected;
+}
+
+/** Try to find a connection to evict when the node is full.
+ *  Extreme care must be taken to avoid opening the node to attacker
+ *   triggered network partitioning.
+ *  The strategy used here is to protect a small number of peers
+ *   for each of several distinct characteristics which are difficult
+ *   to forge.  In order to partition a node the attacker must be
+ *   simultaneously better at all of them than honest peers.
+ */
+static bool AttemptToEvictConnection() {
     std::vector<NodeEvictionCandidate> vEvictionCandidates;
     {
         LOCK(cs_vNodes);
@@ -931,6 +966,20 @@ static bool AttemptToEvictConnection(bool fPreferNewConnection) {
 
     if (vEvictionCandidates.empty()) return false;
 
+    // Protect 4 nodes that most recently sent us transactions.
+    // An attacker cannot manipulate this metric without performing useful work.
+    std::sort(vEvictionCandidates.begin(), vEvictionCandidates.end(), CompareNodeTXTime);
+    vEvictionCandidates.erase(vEvictionCandidates.end() - std::min(4, static_cast<int>(vEvictionCandidates.size())), vEvictionCandidates.end());
+
+    if (vEvictionCandidates.empty()) return false;
+
+    // Protect 4 nodes that most recently sent us blocks.
+    // An attacker cannot manipulate this metric without performing useful work.
+    std::sort(vEvictionCandidates.begin(), vEvictionCandidates.end(), CompareNodeBlockTime);
+    vEvictionCandidates.erase(vEvictionCandidates.end() - std::min(4, static_cast<int>(vEvictionCandidates.size())), vEvictionCandidates.end());
+
+    if (vEvictionCandidates.empty()) return false;
+
     // Protect the half of the remaining nodes which have been connected the longest.
     // This replicates the existing implicit behavior.
     std::sort(vEvictionCandidates.begin(), vEvictionCandidates.end(), ReverseCompareNodeTimeConnected);
@@ -964,12 +1013,6 @@ static bool AttemptToEvictConnection(bool fPreferNewConnection) {
         return false;
     }
 
-    // Do not disconnect peers if there is only one unprotected connection from their network group.
-    if (vEvictionNodes.size() <= 1)
-        // unless we prefer the new connection (for whitelisted peers)
-        if (!fPreferNewConnection)
-            return false;
-
     // Disconnect from the network group with the most connections
     int nEvictionId = vEvictionNodes[0].id;
     {
@@ -1039,7 +1082,7 @@ static void AcceptConnection(const ListenSocket& hListenSocket) {
 
     if (nInbound >= nMaxInbound)
     {
-        if (!AttemptToEvictConnection(whitelisted)) {
+        if (!AttemptToEvictConnection()) {
             // No connection to evict, disconnect the new connection
             LogPrint("net", "failed to find an eviction candidate - connection dropped (full)\n");
             CloseSocket(hSocket);
@@ -2498,6 +2541,8 @@ CNode::CNode(SOCKET hSocketIn, const CAddress& addrIn, const std::string& addrNa
     nNextInvSend = 0;
     fRelayTxes = false;
     pfilter = new CBloomFilter();
+    nLastBlockTime = 0;
+    nLastTXTime = 0;
     nPingNonceSent = 0;
     nPingUsecStart = 0;
     nPingUsecTime = 0;

src/net.h

@@ -417,6 +417,10 @@ class CNode
     // Also protected by cs_inventory
     std::vector<uint256> vBlockHashesToAnnounce;
 
+    // Block and TXN accept times
+    std::atomic<int64_t> nLastBlockTime;
+    std::atomic<int64_t> nLastTXTime;
+
     // Ping time measurement:
     // The pong reply we're expecting, or 0 if no pong expected.
     uint64_t nPingNonceSent;