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

@@ -5214,6 +5214,14 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
             return true;
         }
 
+        // 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)

src/net.cpp

@@ -2384,6 +2384,7 @@ CNode::CNode(SOCKET hSocketIn, const CAddress& addrIn, const std::string& addrNa
     nNextAddrSend = 0;
     nNextInvSend = 0;
     fRelayTxes = false;
+    fSentAddr = false;
     pfilter = new CBloomFilter();
     nPingNonceSent = 0;
     nPingUsecStart = 0;

src/net.h

@@ -358,6 +358,7 @@ public:
     // b) the peer may tell us in its version message that we should not relay tx invs
     //    unless it loads a bloom filter.
     bool fRelayTxes;
+    bool fSentAddr;
     CSemaphoreGrant grantOutbound;
     CCriticalSection cs_filter;
     CBloomFilter* pfilter;