From 362fbcf90fdd136d58525d7e30ad53fb280b0d6f Mon Sep 17 00:00:00 2001
From: Ignotus Peverell <igno.peverell@protonmail.com>
Date: Wed, 1 Nov 2017 18:56:59 -0400
Subject: [PATCH] Proper p2p remote address detection when accepting conn

A receiving peer trusts the address advertised by a client.
However as we do not have external address detection (and there is
generally no very good way to do that), the address detected by
a peer is the loopback, which is useless. So we attempt to detect
these cases and use the IP detected by the TCP connection while
keeping the advertised port.
---
 p2p/src/handshake.rs | 27 ++++++++++++++++++++++++++-
 p2p/src/msg.rs       |  6 ++----
 2 files changed, 28 insertions(+), 5 deletions(-)

diff --git a/p2p/src/handshake.rs b/p2p/src/handshake.rs
index 1829c8a50..1f355b231 100644
--- a/p2p/src/handshake.rs
+++ b/p2p/src/handshake.rs
@@ -124,11 +124,12 @@ impl Handshake {
 							}));
 						}
 					}
+
 					// all good, keep peer info
 					let peer_info = PeerInfo {
 						capabilities: hand.capabilities,
 						user_agent: hand.user_agent,
-						addr: hand.sender_addr.0,
+						addr: extract_ip(&hand.sender_addr.0, &conn),
 						version: hand.version,
 						total_difficulty: hand.total_difficulty,
 					};
@@ -163,3 +164,27 @@ impl Handshake {
 		nonce
 	}
 }
+
+// Attempts to make a best guess at the correct remote IP by checking if the
+// advertised address is the loopback and our TCP connection. Note that the
+// port reported by the connection is always incorrect for receiving
+// connections as it's dynamically allocated by the server.
+fn extract_ip(advertised: &SocketAddr, conn: &TcpStream) -> SocketAddr {
+  match advertised {
+    &SocketAddr::V4(v4sock) => {
+      if v4sock.ip().is_loopback() {
+        if let Ok(addr) =  conn.peer_addr() {
+          return SocketAddr::new(addr.ip(), advertised.port());
+        }
+      }
+    }
+    &SocketAddr::V6(v6sock) => {
+      if v6sock.ip().is_loopback() {
+        if let Ok(addr) =  conn.peer_addr() {
+          return SocketAddr::new(addr.ip(), advertised.port());
+        }
+      }
+    }
+  }
+  advertised.clone()
+}
diff --git a/p2p/src/msg.rs b/p2p/src/msg.rs
index 4a39a5d2c..41d50b77f 100644
--- a/p2p/src/msg.rs
+++ b/p2p/src/msg.rs
@@ -190,8 +190,7 @@ pub struct Hand {
 	/// randomly generated for each handshake, helps detect self
 	pub nonce: u64,
 	/// total difficulty accumulated by the sender, used to check whether sync
-	/// may
-	/// be needed
+	/// may be needed
 	pub total_difficulty: Difficulty,
 	/// network address of the sender
 	pub sender_addr: SockAddr,
@@ -245,8 +244,7 @@ pub struct Shake {
 	/// sender capabilities
 	pub capabilities: Capabilities,
 	/// total difficulty accumulated by the sender, used to check whether sync
-	/// may
-	/// be needed
+	/// may be needed
 	pub total_difficulty: Difficulty,
 	/// name of version of the software
 	pub user_agent: String,