From 82d4d1927d7db22ea71f5b7e3f5396bcee3b5513 Mon Sep 17 00:00:00 2001
From: arvidn <arvid@libtorrent.org>
Date: Wed, 15 Jan 2020 19:47:41 +0100
Subject: [PATCH] restrict DHT nodes to the network they are associated with
 (multi-homed)

---
 ChangeLog             |  1 +
 src/kademlia/node.cpp | 56 ++++++++++++++++++++++++-------------------
 src/session_impl.cpp  |  3 ++-
 3 files changed, 34 insertions(+), 26 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index f5313bf54..b02c20381 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,4 @@
+	* fix external IP voting for multi-homed DHT nodes
 	* deprecate broadcast_lsd setting. Just use multicast
 	* deprecate upnp_ignore_nonrouters setting
 	* don't attempt sending event=stopped if event=start never succeeded
diff --git a/src/kademlia/node.cpp b/src/kademlia/node.cpp
index 89260cb59..efb403ea0 100644
--- a/src/kademlia/node.cpp
+++ b/src/kademlia/node.cpp
@@ -269,32 +269,37 @@ void node::incoming(aux::listen_socket_handle const& s, msg const& m)
 		return;
 	}
 
-	const char y = *(y_ent.string_ptr());
+	char const y = *(y_ent.string_ptr());
 
-	bdecode_node ext_ip = m.message.dict_find_string("ip");
+	// we can only ascribe the external IP this node is saying we have to the
+	// listen socket the packet was received on
+	if (s == m_sock)
+	{
+		bdecode_node ext_ip = m.message.dict_find_string("ip");
 
-	// backwards compatibility
-	if (!ext_ip)
-	{
-		bdecode_node const r = m.message.dict_find_dict("r");
-		if (r)
-			ext_ip = r.dict_find_string("ip");
-	}
+		// backwards compatibility
+		if (!ext_ip)
+		{
+			bdecode_node const r = m.message.dict_find_dict("r");
+			if (r)
+				ext_ip = r.dict_find_string("ip");
+		}
 
-	if (ext_ip && ext_ip.string_length() >= int(detail::address_size(udp::v6())))
-	{
-		// this node claims we use the wrong node-ID!
-		char const* ptr = ext_ip.string_ptr();
-		if (m_observer != nullptr)
-			m_observer->set_external_address(m_sock, detail::read_v6_address(ptr)
-				, m.addr.address());
-	}
-	else if (ext_ip && ext_ip.string_length() >= int(detail::address_size(udp::v4())))
-	{
-		char const* ptr = ext_ip.string_ptr();
-		if (m_observer != nullptr)
-			m_observer->set_external_address(m_sock, detail::read_v4_address(ptr)
-				, m.addr.address());
+		if (ext_ip && ext_ip.string_length() >= int(detail::address_size(udp::v6())))
+		{
+			// this node claims we use the wrong node-ID!
+			char const* ptr = ext_ip.string_ptr();
+			if (m_observer != nullptr)
+				m_observer->set_external_address(m_sock, detail::read_v6_address(ptr)
+					, m.addr.address());
+		}
+		else if (ext_ip && ext_ip.string_length() >= int(detail::address_size(udp::v4())))
+		{
+			char const* ptr = ext_ip.string_ptr();
+			if (m_observer != nullptr)
+				m_observer->set_external_address(m_sock, detail::read_v4_address(ptr)
+					, m.addr.address());
+		}
 	}
 
 	switch (y)
@@ -312,8 +317,9 @@ void node::incoming(aux::listen_socket_handle const& s, msg const& m)
 			// responds to 'query' messages that it receives.
 			if (m_settings.read_only) break;
 
-			// only respond to requests if they're addressed to this node
-			if (s != m_sock) break;
+			// ignore packets arriving on a different interface than the one we're
+			// associated with
+			if (s != m_sock) return;
 
 			if (!m_sock_man->has_quota())
 			{
diff --git a/src/session_impl.cpp b/src/session_impl.cpp
index 8fc07e50a..0f99cca1a 100644
--- a/src/session_impl.cpp
+++ b/src/session_impl.cpp
@@ -6908,7 +6908,8 @@ namespace aux {
 		, ip_source_t const source_type, address const& source)
 	{
 		auto sock = std::find_if(m_listen_sockets.begin(), m_listen_sockets.end()
-			, [&](std::shared_ptr<listen_socket_t> const& v) { return v->local_endpoint == local_endpoint; });
+			, [&](std::shared_ptr<listen_socket_t> const& v)
+			{ return v->local_endpoint.address() == local_endpoint.address(); });
 
 		if (sock != m_listen_sockets.end())
 			set_external_address(*sock, ip, source_type, source);