Do not use third party services for IP detection.

This is a simplified re-do of closed pull #3088.

This patch eliminates the privacy and reliability problematic use
of centralized web services for discovering the node's addresses
for advertisement.

The Bitcoin protocol already allows your peers to tell you what
IP they think you have, but this data isn't trustworthy since
they could lie. So the challenge is using it without creating a
DOS vector.

To accomplish this we adopt an approach similar to the one used
by P2Pool: If we're announcing and don't have a better address
discovered (e.g. via UPNP) or configured we just announce to
each peer the address that peer told us. Since peers could
already replace, forge, or drop our address messages this cannot
create a new vulnerability... but if even one of our peers is
giving us a good address we'll eventually make a useful
advertisement.

We also may randomly use the peer-provided address for the
daily rebroadcast even if we otherwise have a seemingly routable
address, just in case we've been misconfigured (e.g. by UPNP).

To avoid privacy problems, we only do these things if discovery
is enabled.

1 files changed, 20 insertions, 21 deletions

diff --git a/src/main.cpp b/src/main.cpp
index 82d52913a0..9f87a11007 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -3474,12 +3474,6 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
         else
             pfrom->fRelayTxes = true;
 
-        if (pfrom->fInbound && addrMe.IsRoutable())
-        {
-            pfrom->addrLocal = addrMe;
-            SeenLocal(addrMe);
-        }
-
         // Disconnect if we connected to ourself
         if (nNonce == nLocalHostNonce && nNonce > 1)
         {
@@ -3488,6 +3482,12 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
             return true;
         }
 
+        pfrom->addrLocal = addrMe;
+        if (pfrom->fInbound && addrMe.IsRoutable())
+        {
+            SeenLocal(addrMe);
+        }
+
         // Be shy and don't send version until we hear
         if (pfrom->fInbound)
             pfrom->PushVersion();
@@ -3508,7 +3508,12 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
             {
                 CAddress addr = GetLocalAddress(&pfrom->addr);
                 if (addr.IsRoutable())
+                {
+                    pfrom->PushAddress(addr);
+                } else if (IsPeerAddrLocalGood(pfrom)) {
+                    addr.SetIP(pfrom->addrLocal);
                     pfrom->PushAddress(addr);
+                }
             }
 
             // Get recent addresses
@@ -4371,24 +4376,18 @@ bool SendMessages(CNode* pto, bool fSendTrickle)
         static int64_t nLastRebroadcast;
         if (!IsInitialBlockDownload() && (GetTime() - nLastRebroadcast > 24 * 60 * 60))
         {
+            LOCK(cs_vNodes);
+            BOOST_FOREACH(CNode* pnode, vNodes)
             {
-                LOCK(cs_vNodes);
-                BOOST_FOREACH(CNode* pnode, vNodes)
-                {
-                    // Periodically clear setAddrKnown to allow refresh broadcasts
-                    if (nLastRebroadcast)
-                        pnode->setAddrKnown.clear();
+                // Periodically clear setAddrKnown to allow refresh broadcasts
+                if (nLastRebroadcast)
+                    pnode->setAddrKnown.clear();
 
-                    // Rebroadcast our address
-                    if (fListen)
-                    {
-                        CAddress addr = GetLocalAddress(&pnode->addr);
-                        if (addr.IsRoutable())
-                            pnode->PushAddress(addr);
-                    }
-                }
+                // Rebroadcast our address
+                AdvertizeLocal(pnode);
             }
-            nLastRebroadcast = GetTime();
+            if (!vNodes.empty())
+                nLastRebroadcast = GetTime();
         }
 
         //