From a514cb29688a27aaba917ae535f3c75dcd67834b Mon Sep 17 00:00:00 2001
From: Gregory Maxwell <greg@xiph.org>
Date: Mon, 11 Apr 2016 01:09:34 +0000
Subject: [PATCH] Only send one GetAddr response per connection.

This conserves resources from abusive peers that just send
 getaddr in a loop. Also makes correlating addr messages
 against INVs less effective.
---
 src/main.cpp | 8 ++++++++
 src/net.cpp  | 1 +
 src/net.h    | 1 +
 3 files changed, 10 insertions(+)

diff --git a/src/main.cpp b/src/main.cpp
index 2b09a50d6..0368f56a9 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -4867,6 +4867,14 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
     // the getaddr message mitigates the attack.
     else if ((strCommand == "getaddr") && (pfrom->fInbound))
     {
+        // Only send one GetAddr response per connection to reduce resource waste
+        //  and discourage addr stamping of INV announcements.
+        if (pfrom->fSentAddr) {
+            LogPrint("net", "Ignoring repeated \"getaddr\". peer=%d\n", pfrom->id);
+            return true;
+        }
+        pfrom->fSentAddr = true;
+
         pfrom->vAddrToSend.clear();
         vector<CAddress> vAddr = addrman.GetAddr();
         BOOST_FOREACH(const CAddress &addr, vAddr)
diff --git a/src/net.cpp b/src/net.cpp
index 636e3d5e7..0a96d01f2 100644
--- a/src/net.cpp
+++ b/src/net.cpp
@@ -2142,6 +2142,7 @@ CNode::CNode(SOCKET hSocketIn, CAddress addrIn, std::string addrNameIn, bool fIn
     nStartingHeight = -1;
     fGetAddr = false;
     fRelayTxes = false;
+    fSentAddr = false;
     pfilter = new CBloomFilter();
     nPingNonceSent = 0;
     nPingUsecStart = 0;
diff --git a/src/net.h b/src/net.h
index 44f14fd43..50fb90dca 100644
--- a/src/net.h
+++ b/src/net.h
@@ -278,6 +278,7 @@ public:
     // b) the peer may tell us in its version message that we should not relay tx invs
     //    until it has initialized its bloom filter.
     bool fRelayTxes;
+    bool fSentAddr;
     CSemaphoreGrant grantOutbound;
     CCriticalSection cs_filter;
     CBloomFilter* pfilter;