1 files changed, 140 insertions, 3 deletions

diff --git a/src/net_processing.cpp b/src/net_processing.cpp
index 2e93809efc..35d73a6a2b 100644
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -23,6 +23,7 @@
 #include "primitives/transaction.h"
 #include "random.h"
 #include "reverse_iterator.h"
+#include "scheduler.h"
 #include "tinyformat.h"
 #include "txmempool.h"
 #include "ui_interface.h"
@@ -127,6 +128,9 @@ namespace {
     /** Number of outbound peers with m_chain_sync.m_protect. */
     int g_outbound_peers_with_protect_from_disconnect = 0;
 
+    /** When our tip was last updated. */
+    int64_t g_last_tip_update = 0;
+
     /** Relay map, protected by cs_main. */
     typedef std::map<uint256, CTransactionRef> MapRelay;
     MapRelay mapRelay;
@@ -231,6 +235,9 @@ struct CNodeState {
 
     ChainSyncTimeoutState m_chain_sync;
 
+    //! Time of last new block announcement
+    int64_t m_last_block_announcement;
+
     CNodeState(CAddress addrIn, std::string addrNameIn) : address(addrIn), name(addrNameIn) {
         fCurrentlyConnected = false;
         nMisbehavior = 0;
@@ -254,6 +261,7 @@ struct CNodeState {
         fWantsCmpctWitness = false;
         fSupportsDesiredCmpctVersion = false;
         m_chain_sync = { 0, nullptr, false, false };
+        m_last_block_announcement = 0;
     }
 };
 
@@ -427,6 +435,15 @@ void MaybeSetPeerAsAnnouncingHeaderAndIDs(NodeId nodeid, CConnman* connman) {
     }
 }
 
+bool TipMayBeStale(const Consensus::Params &consensusParams)
+{
+    AssertLockHeld(cs_main);
+    if (g_last_tip_update == 0) {
+        g_last_tip_update = GetTime();
+    }
+    return g_last_tip_update < GetTime() - consensusParams.nPowTargetSpacing * 3 && mapBlocksInFlight.empty();
+}
+
 // Requires cs_main
 bool CanDirectFetch(const Consensus::Params &consensusParams)
 {
@@ -533,6 +550,15 @@ void FindNextBlocksToDownload(NodeId nodeid, unsigned int count, std::vector<con
 
 } // namespace
 
+// This function is used for testing the stale tip eviction logic, see
+// DoS_tests.cpp
+void UpdateLastBlockAnnounceTime(NodeId node, int64_t time_in_seconds)
+{
+    LOCK(cs_main);
+    CNodeState *state = State(node);
+    if (state) state->m_last_block_announcement = time_in_seconds;
+}
+
 // Returns true for outbound peers, excluding manual connections, feelers, and
 // one-shots
 bool IsOutboundDisconnectionCandidate(const CNode *node)
@@ -764,9 +790,17 @@ static bool StaleBlockRequestAllowed(const CBlockIndex* pindex, const Consensus:
         (GetBlockProofEquivalentTime(*pindexBestHeader, *pindex, *pindexBestHeader, consensusParams) < STALE_RELAY_AGE_LIMIT);
 }
 
-PeerLogicValidation::PeerLogicValidation(CConnman* connmanIn) : connman(connmanIn) {
+PeerLogicValidation::PeerLogicValidation(CConnman* connmanIn, CScheduler &scheduler) : connman(connmanIn), m_stale_tip_check_time(0) {
     // Initialize global variables that cannot be constructed at startup.
     recentRejects.reset(new CRollingBloomFilter(120000, 0.000001));
+
+    const Consensus::Params& consensusParams = Params().GetConsensus();
+    // Stale tip checking and peer eviction are on two different timers, but we
+    // don't want them to get out of sync due to drift in the scheduler, so we
+    // combine them in one function and schedule at the quicker (peer-eviction)
+    // timer.
+    static_assert(EXTRA_PEER_CHECK_INTERVAL < STALE_CHECK_INTERVAL, "peer eviction timer should be less than stale tip check timer");
+    scheduler.scheduleEvery(std::bind(&PeerLogicValidation::CheckForStaleTipAndEvictPeers, this, consensusParams), EXTRA_PEER_CHECK_INTERVAL * 1000);
 }
 
 void PeerLogicValidation::BlockConnected(const std::shared_ptr<const CBlock>& pblock, const CBlockIndex* pindex, const std::vector<CTransactionRef>& vtxConflicted) {
@@ -797,6 +831,8 @@ void PeerLogicValidation::BlockConnected(const std::shared_ptr<const CBlock>& pb
         }
         LogPrint(BCLog::MEMPOOL, "Erased %d orphan tx included or conflicted by block\n", nErased);
     }
+
+    g_last_tip_update = GetTime();
 }
 
 // All of the following cache a recent block, and are protected by cs_most_recent_block
@@ -1215,6 +1251,7 @@ bool static ProcessHeadersMessage(CNode *pfrom, CConnman *connman, const std::ve
         return true;
     }
 
+    bool received_new_header = false;
     const CBlockIndex *pindexLast = nullptr;
     {
         LOCK(cs_main);
@@ -1255,6 +1292,12 @@ bool static ProcessHeadersMessage(CNode *pfrom, CConnman *connman, const std::ve
             }
             hashLastBlock = header.GetHash();
         }
+
+        // If we don't have the last header, then they'll have given us
+        // something new (if these headers are valid).
+        if (mapBlockIndex.find(hashLastBlock) == mapBlockIndex.end()) {
+            received_new_header = true;
+        }
     }
 
     CValidationState state;
@@ -1319,6 +1362,10 @@ bool static ProcessHeadersMessage(CNode *pfrom, CConnman *connman, const std::ve
         // because it is set in UpdateBlockAvailability. Some nullptr checks
         // are still present, however, as belt-and-suspenders.
 
+        if (received_new_header && pindexLast->nChainWork > chainActive.Tip()->nChainWork) {
+            nodestate->m_last_block_announcement = GetTime();
+        }
+
         if (nCount == MAX_HEADERS_RESULTS) {
             // Headers message had its maximum size; the peer may have more headers.
             // TODO: optimize: if pindexLast is an ancestor of chainActive.Tip or pindexBestHeader, continue
@@ -1403,6 +1450,7 @@ bool static ProcessHeadersMessage(CNode *pfrom, CConnman *connman, const std::ve
             // If this is an outbound peer, check to see if we should protect
             // it from the bad/lagging chain logic.
             if (g_outbound_peers_with_protect_from_disconnect < MAX_OUTBOUND_PEERS_TO_PROTECT_FROM_DISCONNECT && nodestate->pindexBestKnownBlock->nChainWork >= chainActive.Tip()->nChainWork && !nodestate->m_chain_sync.m_protect) {
+                LogPrint(BCLog::NET, "Protecting outbound peer=%d from eviction\n", pfrom->GetId());
                 nodestate->m_chain_sync.m_protect = true;
                 ++g_outbound_peers_with_protect_from_disconnect;
             }
@@ -2219,6 +2267,8 @@ bool static ProcessMessage(CNode* pfrom, const std::string& strCommand, CDataStr
         CBlockHeaderAndShortTxIDs cmpctblock;
         vRecv >> cmpctblock;
 
+        bool received_new_header = false;
+
         {
         LOCK(cs_main);
 
@@ -2228,6 +2278,10 @@ bool static ProcessMessage(CNode* pfrom, const std::string& strCommand, CDataStr
                 connman->PushMessage(pfrom, msgMaker.Make(NetMsgType::GETHEADERS, chainActive.GetLocator(pindexBestHeader), uint256()));
             return true;
         }
+
+        if (mapBlockIndex.find(cmpctblock.header.GetHash()) == mapBlockIndex.end()) {
+            received_new_header = true;
+        }
         }
 
         const CBlockIndex *pindex = nullptr;
@@ -2266,6 +2320,14 @@ bool static ProcessMessage(CNode* pfrom, const std::string& strCommand, CDataStr
         assert(pindex);
         UpdateBlockAvailability(pfrom->GetId(), pindex->GetBlockHash());
 
+        CNodeState *nodestate = State(pfrom->GetId());
+
+        // If this was a new header with more work than our tip, update the
+        // peer's last block announcement time
+        if (received_new_header && pindex->nChainWork > chainActive.Tip()->nChainWork) {
+            nodestate->m_last_block_announcement = GetTime();
+        }
+
         std::map<uint256, std::pair<NodeId, std::list<QueuedBlock>::iterator> >::iterator blockInFlightIt = mapBlocksInFlight.find(pindex->GetBlockHash());
         bool fAlreadyInFlight = blockInFlightIt != mapBlocksInFlight.end();
 
@@ -2288,8 +2350,6 @@ bool static ProcessMessage(CNode* pfrom, const std::string& strCommand, CDataStr
         if (!fAlreadyInFlight && !CanDirectFetch(chainparams.GetConsensus()))
             return true;
 
-        CNodeState *nodestate = State(pfrom->GetId());
-
         if (IsWitnessEnabled(pindex->pprev, chainparams.GetConsensus()) && !nodestate->fSupportsDesiredCmpctVersion) {
             // Don't bother trying to process compact blocks from v1 peers
             // after segwit activates.
@@ -2967,6 +3027,83 @@ void PeerLogicValidation::ConsiderEviction(CNode *pto, int64_t time_in_seconds)
     }
 }
 
+void PeerLogicValidation::EvictExtraOutboundPeers(int64_t time_in_seconds)
+{
+    // Check whether we have too many outbound peers
+    int extra_peers = connman->GetExtraOutboundCount();
+    if (extra_peers > 0) {
+        // If we have more outbound peers than we target, disconnect one.
+        // Pick the outbound peer that least recently announced
+        // us a new block, with ties broken by choosing the more recent
+        // connection (higher node id)
+        NodeId worst_peer = -1;
+        int64_t oldest_block_announcement = std::numeric_limits<int64_t>::max();
+
+        LOCK(cs_main);
+
+        connman->ForEachNode([&](CNode* pnode) {
+            // Ignore non-outbound peers, or nodes marked for disconnect already
+            if (!IsOutboundDisconnectionCandidate(pnode) || pnode->fDisconnect) return;
+            CNodeState *state = State(pnode->GetId());
+            if (state == nullptr) return; // shouldn't be possible, but just in case
+            // Don't evict our protected peers
+            if (state->m_chain_sync.m_protect) return;
+            if (state->m_last_block_announcement < oldest_block_announcement || (state->m_last_block_announcement == oldest_block_announcement && pnode->GetId() > worst_peer)) {
+                worst_peer = pnode->GetId();
+                oldest_block_announcement = state->m_last_block_announcement;
+            }
+        });
+        if (worst_peer != -1) {
+            bool disconnected = connman->ForNode(worst_peer, [&](CNode *pnode) {
+                // Only disconnect a peer that has been connected to us for
+                // some reasonable fraction of our check-frequency, to give
+                // it time for new information to have arrived.
+                // Also don't disconnect any peer we're trying to download a
+                // block from.
+                CNodeState &state = *State(pnode->GetId());
+                if (time_in_seconds - pnode->nTimeConnected > MINIMUM_CONNECT_TIME && state.nBlocksInFlight == 0) {
+                    LogPrint(BCLog::NET, "disconnecting extra outbound peer=%d (last block announcement received at time %d)\n", pnode->GetId(), oldest_block_announcement);
+                    pnode->fDisconnect = true;
+                    return true;
+                } else {
+                    LogPrint(BCLog::NET, "keeping outbound peer=%d chosen for eviction (connect time: %d, blocks_in_flight: %d)\n", pnode->GetId(), pnode->nTimeConnected, state.nBlocksInFlight);
+                    return false;
+                }
+            });
+            if (disconnected) {
+                // If we disconnected an extra peer, that means we successfully
+                // connected to at least one peer after the last time we
+                // detected a stale tip. Don't try any more extra peers until
+                // we next detect a stale tip, to limit the load we put on the
+                // network from these extra connections.
+                connman->SetTryNewOutboundPeer(false);
+            }
+        }
+    }
+}
+
+void PeerLogicValidation::CheckForStaleTipAndEvictPeers(const Consensus::Params &consensusParams)
+{
+    if (connman == nullptr) return;
+
+    int64_t time_in_seconds = GetTime();
+
+    EvictExtraOutboundPeers(time_in_seconds);
+
+    if (time_in_seconds > m_stale_tip_check_time) {
+        LOCK(cs_main);
+        // Check whether our tip is stale, and if so, allow using an extra
+        // outbound peer
+        if (TipMayBeStale(consensusParams)) {
+            LogPrintf("Potential stale tip detected, will try using extra outbound peer (last tip update: %d seconds ago)\n", time_in_seconds - g_last_tip_update);
+            connman->SetTryNewOutboundPeer(true);
+        } else if (connman->GetTryNewOutboundPeer()) {
+            connman->SetTryNewOutboundPeer(false);
+        }
+        m_stale_tip_check_time = time_in_seconds + STALE_CHECK_INTERVAL;
+    }
+}
+
 class CompareInvMempoolOrder
 {
     CTxMemPool *mp;