Revert "Change in transaction pull scheduling to prevent InvBlock-related attacks"

This reverts commit 1cff3d6cb017aea87d16cbda0768bbab256d16da.

6 files changed, 81 insertions, 168 deletions

diff --git a/src/net.cpp b/src/net.cpp
index ccab4a1718..67c6a5c798 100644
--- a/src/net.cpp
+++ b/src/net.cpp
@@ -85,6 +85,8 @@ std::map<CNetAddr, LocalServiceInfo> mapLocalHost GUARDED_BY(cs_mapLocalHost);
 static bool vfLimited[NET_MAX] GUARDED_BY(cs_mapLocalHost) = {};
 std::string strSubVersion;
 
+limitedmap<uint256, int64_t> mapAlreadyAskedFor(MAX_INV_SZ);
+
 void CConnman::AddOneShot(const std::string& strDest)
 {
     LOCK(cs_vOneShots);
@@ -2648,6 +2650,40 @@ CNode::~CNode()
     CloseSocket(hSocket);
 }
 
+void CNode::AskFor(const CInv& inv)
+{
+    if (mapAskFor.size() > MAPASKFOR_MAX_SZ || setAskFor.size() > SETASKFOR_MAX_SZ)
+        return;
+    // a peer may not have multiple non-responded queue positions for a single inv item
+    if (!setAskFor.insert(inv.hash).second)
+        return;
+
+    // We're using mapAskFor as a priority queue,
+    // the key is the earliest time the request can be sent
+    int64_t nRequestTime;
+    limitedmap<uint256, int64_t>::const_iterator it = mapAlreadyAskedFor.find(inv.hash);
+    if (it != mapAlreadyAskedFor.end())
+        nRequestTime = it->second;
+    else
+        nRequestTime = 0;
+    LogPrint(BCLog::NET, "askfor %s  %d (%s) peer=%d\n", inv.ToString(), nRequestTime, FormatISO8601Time(nRequestTime/1000000), id);
+
+    // Make sure not to reuse time indexes to keep things in the same order
+    int64_t nNow = GetTimeMicros() - 1000000;
+    static int64_t nLastTime;
+    ++nLastTime;
+    nNow = std::max(nNow, nLastTime);
+    nLastTime = nNow;
+
+    // Each retry is 2 minutes after the last
+    nRequestTime = std::max(nRequestTime + 2 * 60 * 1000000, nNow);
+    if (it != mapAlreadyAskedFor.end())
+        mapAlreadyAskedFor.update(it, nRequestTime);
+    else
+        mapAlreadyAskedFor.insert(std::make_pair(inv.hash, nRequestTime));
+    mapAskFor.insert(std::make_pair(nRequestTime, inv));
+}
+
 bool CConnman::NodeFullyConnected(const CNode* pnode)
 {
     return pnode && pnode->fSuccessfullyConnected && !pnode->fDisconnect;
diff --git a/src/net.h b/src/net.h
index f1d09f5934..db44ec6333 100644
--- a/src/net.h
+++ b/src/net.h
@@ -67,6 +67,10 @@ static const bool DEFAULT_UPNP = USE_UPNP;
 #else
 static const bool DEFAULT_UPNP = false;
 #endif
+/** The maximum number of entries in mapAskFor */
+static const size_t MAPASKFOR_MAX_SZ = MAX_INV_SZ;
+/** The maximum number of entries in setAskFor (larger due to getdata latency)*/
+static const size_t SETASKFOR_MAX_SZ = 2 * MAX_INV_SZ;
 /** The maximum number of peer connections to maintain. */
 static const unsigned int DEFAULT_MAX_PEER_CONNECTIONS = 125;
 /** The default for -maxuploadtarget. 0 = Unlimited */
@@ -521,6 +525,8 @@ extern bool fDiscover;
 extern bool fListen;
 extern bool fRelayTxes;
 
+extern limitedmap<uint256, int64_t> mapAlreadyAskedFor;
+
 /** Subversion as sent to the P2P network in `version` messages */
 extern std::string strSubVersion;
 
@@ -709,6 +715,8 @@ public:
     // and in the order requested.
     std::vector<uint256> vInventoryBlockToSend GUARDED_BY(cs_inventory);
     CCriticalSection cs_inventory;
+    std::set<uint256> setAskFor;
+    std::multimap<int64_t, CInv> mapAskFor;
     int64_t nNextInvSend{0};
     // Used for headers announcements - unfiltered blocks to relay
     std::vector<uint256> vBlockHashesToAnnounce GUARDED_BY(cs_inventory);
@@ -857,6 +865,8 @@ public:
         vBlockHashesToAnnounce.push_back(hash);
     }
 
+    void AskFor(const CInv& inv);
+
     void CloseSocketDisconnect();
 
     void copyStats(CNodeStats &stats);
diff --git a/src/net_processing.cpp b/src/net_processing.cpp
index 53ff6a52ac..d524d626c3 100644
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -64,21 +64,6 @@ static constexpr int STALE_RELAY_AGE_LIMIT = 30 * 24 * 60 * 60;
 /// Age after which a block is considered historical for purposes of rate
 /// limiting block relay. Set to one week, denominated in seconds.
 static constexpr int HISTORICAL_BLOCK_AGE = 7 * 24 * 60 * 60;
-/** Maximum number of in-flight transactions from a peer */
-static constexpr int32_t MAX_PEER_TX_IN_FLIGHT = 100;
-/** Maximum number of announced transactions from a peer */
-static constexpr int32_t MAX_PEER_TX_ANNOUNCEMENTS = 2 * MAX_INV_SZ;
-/** How many microseconds to delay requesting transactions from inbound peers */
-static constexpr int64_t INBOUND_PEER_TX_DELAY = 2 * 1000000;
-/** How long to wait (in microseconds) before downloading a transaction from an additional peer */
-static constexpr int64_t GETDATA_TX_INTERVAL = 60 * 1000000;
-/** Maximum delay (in microseconds) for transaction requests to avoid biasing some peers over others. */
-static constexpr int64_t MAX_GETDATA_RANDOM_DELAY = 2 * 1000000;
-static_assert(INBOUND_PEER_TX_DELAY >= MAX_GETDATA_RANDOM_DELAY,
-"To preserve security, MAX_GETDATA_RANDOM_DELAY should not exceed INBOUND_PEER_DELAY");
-/** Limit to avoid sending big packets. Not used in processing incoming GETDATA for compatibility */
-static const unsigned int MAX_GETDATA_SZ = 1000;
-
 
 struct COrphanTx {
     // When modifying, adapt the copy of this definition in tests/DoS_tests.
@@ -292,66 +277,6 @@ struct CNodeState {
     //! Time of last new block announcement
     int64_t m_last_block_announcement;
 
-    /*
-     * State associated with transaction download.
-     *
-     * Tx download algorithm:
-     *
-     *   When inv comes in, queue up (process_time, txid) inside the peer's
-     *   CNodeState (m_tx_process_time) as long as m_tx_announced for the peer
-     *   isn't too big (MAX_PEER_TX_ANNOUNCEMENTS).
-     *
-     *   The process_time for a transaction is set to nNow for outbound peers,
-     *   nNow + 2 seconds for inbound peers. This is the time at which we'll
-     *   consider trying to request the transaction from the peer in
-     *   SendMessages(). The delay for inbound peers is to allow outbound peers
-     *   a chance to announce before we request from inbound peers, to prevent
-     *   an adversary from using inbound connections to blind us to a
-     *   transaction (InvBlock).
-     *
-     *   When we call SendMessages() for a given peer,
-     *   we will loop over the transactions in m_tx_process_time, looking
-     *   at the transactions whose process_time <= nNow. We'll request each
-     *   such transaction that we don't have already and that hasn't been
-     *   requested from another peer recently, up until we hit the
-     *   MAX_PEER_TX_IN_FLIGHT limit for the peer. Then we'll update
-     *   g_already_asked_for for each requested txid, storing the time of the
-     *   GETDATA request. We use g_already_asked_for to coordinate transaction
-     *   requests amongst our peers.
-     *
-     *   For transactions that we still need but we have already recently
-     *   requested from some other peer, we'll reinsert (process_time, txid)
-     *   back into the peer's m_tx_process_time at the point in the future at
-     *   which the most recent GETDATA request would time out (ie
-     *   GETDATA_TX_INTERVAL + the request time stored in g_already_asked_for).
-     *   We add an additional delay for inbound peers, again to prefer
-     *   attempting download from outbound peers first.
-     *   We also add an extra small random delay up to 2 seconds
-     *   to avoid biasing some peers over others. (e.g., due to fixed ordering
-     *   of peer processing in ThreadMessageHandler).
-     *
-     *   When we receive a transaction from a peer, we remove the txid from the
-     *   peer's m_tx_in_flight set and from their recently announced set
-     *   (m_tx_announced).  We also clear g_already_asked_for for that entry, so
-     *   that if somehow the transaction is not accepted but also not added to
-     *   the reject filter, then we will eventually redownload from other
-     *   peers.
-     */
-    struct TxDownloadState {
-        /* Track when to attempt download of announced transactions (process
-         * time in micros -> txid)
-         */
-        std::multimap<int64_t, uint256> m_tx_process_time;
-
-        //! Store all the transactions a peer has recently announced
-        std::set<uint256> m_tx_announced;
-
-        //! Store transactions which were requested by us
-        std::set<uint256> m_tx_in_flight;
-    };
-
-    TxDownloadState m_tx_download;
-
     CNodeState(CAddress addrIn, std::string addrNameIn) : address(addrIn), name(addrNameIn) {
         fCurrentlyConnected = false;
         nMisbehavior = 0;
@@ -379,9 +304,6 @@ struct CNodeState {
     }
 };
 
-// Keeps track of the time (in microseconds) when transactions were requested last time
-limitedmap<uint256, int64_t> g_already_asked_for GUARDED_BY(cs_main)(MAX_INV_SZ);
-
 /** Map maintaining per-node state. */
 static std::map<NodeId, CNodeState> mapNodeState GUARDED_BY(cs_main);
 
@@ -672,58 +594,6 @@ static void FindNextBlocksToDownload(NodeId nodeid, unsigned int count, std::vec
     }
 }
 
-void EraseTxRequest(const uint256& txid) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
-{
-    g_already_asked_for.erase(txid);
-}
-
-int64_t GetTxRequestTime(const uint256& txid) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
-{
-    auto it = g_already_asked_for.find(txid);
-    if (it != g_already_asked_for.end()) {
-        return it->second;
-    }
-    return 0;
-}
-
-void UpdateTxRequestTime(const uint256& txid, int64_t request_time) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
-{
-    auto it = g_already_asked_for.find(txid);
-    if (it == g_already_asked_for.end()) {
-        g_already_asked_for.insert(std::make_pair(txid, request_time));
-    } else {
-        g_already_asked_for.update(it, request_time);
-    }
-}
-
-
-void RequestTx(CNodeState* state, const uint256& txid, int64_t nNow) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
-{
-    CNodeState::TxDownloadState& peer_download_state = state->m_tx_download;
-    if (peer_download_state.m_tx_announced.size() >= MAX_PEER_TX_ANNOUNCEMENTS || peer_download_state.m_tx_announced.count(txid)) {
-        // Too many queued announcements from this peer, or we already have
-        // this announcement
-        return;
-    }
-    peer_download_state.m_tx_announced.insert(txid);
-
-    int64_t process_time;
-    int64_t last_request_time = GetTxRequestTime(txid);
-    // First time requesting this tx
-    if (last_request_time == 0) {
-        process_time = nNow;
-    } else {
-        // Randomize the delay to avoid biasing some peers over others (such as due to
-        // fixed ordering of peer processing in ThreadMessageHandler)
-        process_time = last_request_time + GETDATA_TX_INTERVAL + GetRand(MAX_GETDATA_RANDOM_DELAY);
-    }
-
-    // We delay processing announcements from non-preferred (eg inbound) peers
-    if (!state->fPreferredDownload) process_time += INBOUND_PEER_TX_DELAY;
-
-    peer_download_state.m_tx_process_time.emplace(process_time, txid);
-}
-
 } // namespace
 
 // This function is used for testing the stale tip eviction logic, see
@@ -2150,7 +2020,6 @@ bool static ProcessMessage(CNode* pfrom, const std::string& strCommand, CDataStr
         LOCK(cs_main);
 
         uint32_t nFetchFlags = GetFetchFlags(pfrom);
-        int64_t nNow = GetTimeMicros();
 
         for (CInv &inv : vInv)
         {
@@ -2182,7 +2051,7 @@ bool static ProcessMessage(CNode* pfrom, const std::string& strCommand, CDataStr
                 if (fBlocksOnly) {
                     LogPrint(BCLog::NET, "transaction (%s) inv sent in violation of protocol peer=%d\n", inv.hash.ToString(), pfrom->GetId());
                 } else if (!fAlreadyHave && !fImporting && !fReindex && !IsInitialBlockDownload()) {
-                    RequestTx(State(pfrom->GetId()), inv.hash, nNow);
+                    pfrom->AskFor(inv);
                 }
             }
         }
@@ -2415,10 +2284,8 @@ bool static ProcessMessage(CNode* pfrom, const std::string& strCommand, CDataStr
         bool fMissingInputs = false;
         CValidationState state;
 
-        CNodeState* nodestate = State(pfrom->GetId());
-        nodestate->m_tx_download.m_tx_announced.erase(inv.hash);
-        nodestate->m_tx_download.m_tx_in_flight.erase(inv.hash);
-        EraseTxRequest(inv.hash);
+        pfrom->setAskFor.erase(inv.hash);
+        mapAlreadyAskedFor.erase(inv.hash);
 
         std::list<CTransactionRef> lRemovedTxn;
 
@@ -2456,12 +2323,10 @@ bool static ProcessMessage(CNode* pfrom, const std::string& strCommand, CDataStr
             }
             if (!fRejectedParents) {
                 uint32_t nFetchFlags = GetFetchFlags(pfrom);
-                int64_t nNow = GetTimeMicros();
-
                 for (const CTxIn& txin : tx.vin) {
                     CInv _inv(MSG_TX | nFetchFlags, txin.prevout.hash);
                     pfrom->AddInventoryKnown(_inv);
-                    if (!AlreadyHave(_inv)) RequestTx(State(pfrom->GetId()), _inv.hash, nNow);
+                    if (!AlreadyHave(_inv)) pfrom->AskFor(_inv);
                 }
                 AddOrphanTx(ptx, pfrom->GetId());
 
@@ -3899,39 +3764,24 @@ bool PeerLogicValidation::SendMessages(CNode* pto)
         //
         // Message: getdata (non-blocks)
         //
-        auto& tx_process_time = state.m_tx_download.m_tx_process_time;
-        while (!tx_process_time.empty() && tx_process_time.begin()->first <= nNow && state.m_tx_download.m_tx_in_flight.size() < MAX_PEER_TX_IN_FLIGHT) {
-            const uint256& txid = tx_process_time.begin()->second;
-            CInv inv(MSG_TX | GetFetchFlags(pto), txid);
-            if (!AlreadyHave(inv)) {
-                // If this transaction was last requested more than 1 minute ago,
-                // then request.
-                int64_t last_request_time = GetTxRequestTime(inv.hash);
-                if (last_request_time <= nNow - GETDATA_TX_INTERVAL) {
-                    LogPrint(BCLog::NET, "Requesting %s peer=%d\n", inv.ToString(), pto->GetId());
-                    vGetData.push_back(inv);
-                    if (vGetData.size() >= MAX_GETDATA_SZ) {
-                        connman->PushMessage(pto, msgMaker.Make(NetMsgType::GETDATA, vGetData));
-                        vGetData.clear();
-                    }
-                    UpdateTxRequestTime(inv.hash, nNow);
-                    state.m_tx_download.m_tx_in_flight.insert(inv.hash);
-                } else {
-                    // This transaction is in flight from someone else; queue
-                    // up processing to happen after the download times out
-                    // (with a slight delay for inbound peers, to prefer
-                    // requests to outbound peers).
-                    RequestTx(&state, txid, nNow);
+        while (!pto->mapAskFor.empty() && (*pto->mapAskFor.begin()).first <= nNow)
+        {
+            const CInv& inv = (*pto->mapAskFor.begin()).second;
+            if (!AlreadyHave(inv))
+            {
+                LogPrint(BCLog::NET, "Requesting %s peer=%d\n", inv.ToString(), pto->GetId());
+                vGetData.push_back(inv);
+                if (vGetData.size() >= 1000)
+                {
+                    connman->PushMessage(pto, msgMaker.Make(NetMsgType::GETDATA, vGetData));
+                    vGetData.clear();
                 }
             } else {
-                // We have already seen this transaction, no need to download.
-                state.m_tx_download.m_tx_announced.erase(inv.hash);
-                state.m_tx_download.m_tx_in_flight.erase(inv.hash);
+                //If we're not going to ask, don't expect a response.
+                pto->setAskFor.erase(inv.hash);
             }
-            tx_process_time.erase(tx_process_time.begin());
+            pto->mapAskFor.erase(pto->mapAskFor.begin());
         }
-
-
         if (!vGetData.empty())
             connman->PushMessage(pto, msgMaker.Make(NetMsgType::GETDATA, vGetData));
 
diff --git a/src/test/util_tests.cpp b/src/test/util_tests.cpp
index 860f64bb11..71b6ec7425 100644
--- a/src/test/util_tests.cpp
+++ b/src/test/util_tests.cpp
@@ -169,6 +169,11 @@ BOOST_AUTO_TEST_CASE(util_FormatISO8601Date)
     BOOST_CHECK_EQUAL(FormatISO8601Date(1317425777), "2011-09-30");
 }
 
+BOOST_AUTO_TEST_CASE(util_FormatISO8601Time)
+{
+    BOOST_CHECK_EQUAL(FormatISO8601Time(1317425777), "23:36:17Z");
+}
+
 struct TestArgsManager : public ArgsManager
 {
     TestArgsManager() { m_network_only_args.clear(); }
diff --git a/src/util/time.cpp b/src/util/time.cpp
index c0ede98701..83a7937d8f 100644
--- a/src/util/time.cpp
+++ b/src/util/time.cpp
@@ -97,3 +97,14 @@ std::string FormatISO8601Date(int64_t nTime) {
 #endif
     return strprintf("%04i-%02i-%02i", ts.tm_year + 1900, ts.tm_mon + 1, ts.tm_mday);
 }
+
+std::string FormatISO8601Time(int64_t nTime) {
+    struct tm ts;
+    time_t time_val = nTime;
+#ifdef _MSC_VER
+    gmtime_s(&ts, &time_val);
+#else
+    gmtime_r(&time_val, &ts);
+#endif
+    return strprintf("%02i:%02i:%02iZ", ts.tm_hour, ts.tm_min, ts.tm_sec);
+}
diff --git a/src/util/time.h b/src/util/time.h
index 68de1c156e..f2e2747434 100644
--- a/src/util/time.h
+++ b/src/util/time.h
@@ -33,5 +33,6 @@ void MilliSleep(int64_t n);
  */
 std::string FormatISO8601DateTime(int64_t nTime);
 std::string FormatISO8601Date(int64_t nTime);
+std::string FormatISO8601Time(int64_t nTime);
 
 #endif // BITCOIN_UTIL_TIME_H