From bc20629b9f5c3a2192f563ca8e51fdaaa9287c31 Mon Sep 17 00:00:00 2001
From: Duke <duke@hush.is>
Date: Mon, 16 Sep 2024 11:18:16 -0400
Subject: [PATCH] Revert "Fix memory DoS"

This reverts commit 84377caae78116b817dbb64434def0b1ecffab74.
---
 src/main.cpp | 40 +++++++++++++++++++++-------------------
 1 file changed, 21 insertions(+), 19 deletions(-)

diff --git a/src/main.cpp b/src/main.cpp
index 4a9de15a7..ae5e27916 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -7320,8 +7320,6 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
         }
 
         LOCK(cs_main);
-        
-        const uint256* best_block{nullptr};
 
         std::vector<CInv> vToFetch;
 
@@ -7341,31 +7339,35 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
             if (inv.type == MSG_BLOCK) {
                 UpdateBlockAvailability(pfrom->GetId(), inv.hash);
                 if (!fAlreadyHave && !fImporting && !fReindex && !mapBlocksInFlight.count(inv.hash)) {
-                    // Headers-first is the primary method of announcement on
-                    // the network. If a node fell back to sending blocks by inv,
-                    // it's probably for a re-org. The final block hash
-                    // provided should be the highest, so send a getheaders and
-                    // then fetch the blocks we need to catch up.
-                    best_block = &inv.hash;
+                    // First request the headers preceding the announced block. In the normal fully-synced
+                    // case where a new block is announced that succeeds the current tip (no reorganization),
+                    // there are no such headers.
+                    // Secondly, and only when we are close to being synced, we request the announced block directly,
+                    // to avoid an extra round-trip. Note that we must *first* ask for the headers, so by the
+                    // time the block arrives, the header chain leading up to it is already validated. Not
+                    // doing this will result in the received block being rejected as an orphan in case it is
+                    // not a direct successor.
+                    pfrom->PushMessage(NetMsgType::GETHEADERS, chainActive.GetLocator(pindexBestHeader), inv.hash);
+                    CNodeState *nodestate = State(pfrom->GetId());
+                    if (chainActive.Tip()->GetBlockTime() > GetTime() - chainparams.GetConsensus().nPowTargetSpacing * 20 &&
+                        nodestate->nBlocksInFlight < MAX_BLOCKS_IN_TRANSIT_PER_PEER) {
+                        vToFetch.push_back(inv);
+                        // Mark block as in flight already, even though the actual "getdata" message only goes out
+                        // later (within the same cs_main lock, though).
+                        MarkBlockAsInFlight(pfrom->GetId(), inv.hash, chainparams.GetConsensus());
+                    }
+                    LogPrint("net", "getheaders (%d) %s to peer=%d\n", pindexBestHeader->GetHeight(), inv.hash.ToString(), pfrom->id);
                 }
-            } else {
-                pfrom->AddKnownWTxId(WTxId(inv.hash, inv.hashAux));
-                if (fBlocksOnly)
-                    LogPrint("net", "transaction (%s) inv sent in violation of protocol peer=%d\n", inv.hash.ToString(), pfrom->id);
-                else if (!fAlreadyHave && !IsInitialBlockDownload(chainparams.GetConsensus()))
-                    pfrom->AskFor(inv);
             }
+
             if (pfrom->nSendSize > (SendBufferSize() * 2)) {
                 Misbehaving(pfrom->GetId(), 50);
                 return error("send buffer size() = %u", pfrom->nSendSize);
             }
         }
 
-        if (best_block != nullptr) {
-            pfrom->PushMessage("getheaders", chainActive.GetLocator(pindexBestHeader), *best_block);
-            LogPrint("net", "getheaders (%d) %s to peer=%d\n", pindexBestHeader->GetHeight(), best_block->ToString(), pfrom->id);
-        }
-        
+        if (!vToFetch.empty())
+            pfrom->PushMessage(NetMsgType::GETDATA, vToFetch);
     } else if (strCommand == NetMsgType::GETDATA) {
         vector<CInv> vInv;
         vRecv >> vInv;