From: Ivan Pustogarov <ivanpustogarov@users.noreply.github.com>
Date: Sun, 7 Dec 2014 16:30:57 +0000 (+0100)
Subject: Ignore getaddr messages on Outbound connections.
X-Git-Tag: nvc-v0.5.5~26^2
X-Git-Url: https://git.novaco.in/?p=novacoin.git;a=commitdiff_plain;h=f52c581475d6e701748f91480301354860c7c8c6

Ignore getaddr messages on Outbound connections.

The only time when a client sends a "getaddr" message is when he
esatblishes an Outbound connection (see ProcessMessage() in
src/main.cpp).  Another bitcoin client is expected to receive a
"getaddr" message only on Inbound connection. Ignoring "gettaddr"
requests on Outbound connections can resolve potential privacy issues
(and as was said such request normally do not happen anyway).

Rebased-From: dca799e1db6e319fdd47e0bfdb038eab0efabb85
Github-Pull: #5442
---

diff --git a/src/main.cpp b/src/main.cpp
index 9ff24e4..b3c3504 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -3619,7 +3619,12 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv)
     }
 
 
-    else if (strCommand == "getaddr")
+    // This asymmetric behavior for inbound and outbound connections was introduced
+    // to prevent a fingerprinting attack: an attacker can send specific fake addresses
+    // to users' AddrMan and later request them by sending getaddr messages. 
+    // Making users (which are behind NAT and can only make outgoing connections) ignore 
+    // getaddr message mitigates the attack.
+    else if ((strCommand == "getaddr") && (pfrom->fInbound))
     {
         // Don't return addresses older than nCutOff timestamp
         int64_t nCutOff = GetTime() - (nNodeLifespan * nOneDay);