From f5157f12a4ac26a8f55ca50a276b6d457fc150a2 Mon Sep 17 00:00:00 2001
From: BoomEaro <21033866+BoomEaro@users.noreply.github.com>
Date: Wed, 1 Nov 2023 21:32:31 +1100
Subject: [PATCH] #3438: Fix possible race condition in duplicate player check

---
 proxy/src/main/java/net/md_5/bungee/BungeeCord.java        | 7 ++++++-
 proxy/src/main/java/net/md_5/bungee/UserConnection.java    | 4 +++-
 .../java/net/md_5/bungee/connection/InitialHandler.java    | 6 +++++-
 .../java/net/md_5/bungee/connection/UpstreamBridge.java    | 1 -
 4 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/proxy/src/main/java/net/md_5/bungee/BungeeCord.java b/proxy/src/main/java/net/md_5/bungee/BungeeCord.java
index 0bdde1e2..2024149f 100644
--- a/proxy/src/main/java/net/md_5/bungee/BungeeCord.java
+++ b/proxy/src/main/java/net/md_5/bungee/BungeeCord.java
@@ -753,7 +753,7 @@ public class BungeeCord extends ProxyServer
         }
     }
 
-    public void addConnection(UserConnection con)
+    public boolean addConnection(UserConnection con)
     {
         UUID offlineId = con.getPendingConnection().getOfflineId();
         if ( offlineId != null && offlineId.version() != 3 )
@@ -763,6 +763,10 @@ public class BungeeCord extends ProxyServer
         connectionLock.writeLock().lock();
         try
         {
+            if ( connections.containsKey( con.getName() ) || connectionsByUUID.containsKey( con.getUniqueId() ) || connectionsByOfflineUUID.containsKey( offlineId ) )
+            {
+                return false;
+            }
             connections.put( con.getName(), con );
             connectionsByUUID.put( con.getUniqueId(), con );
             connectionsByOfflineUUID.put( offlineId, con );
@@ -770,6 +774,7 @@ public class BungeeCord extends ProxyServer
         {
             connectionLock.writeLock().unlock();
         }
+        return true;
     }
 
     public void removeConnection(UserConnection con)
diff --git a/proxy/src/main/java/net/md_5/bungee/UserConnection.java b/proxy/src/main/java/net/md_5/bungee/UserConnection.java
index 18b1690d..04143a46 100644
--- a/proxy/src/main/java/net/md_5/bungee/UserConnection.java
+++ b/proxy/src/main/java/net/md_5/bungee/UserConnection.java
@@ -153,7 +153,7 @@ public final class UserConnection implements ProxiedPlayer
         }
     };
 
-    public void init()
+    public boolean init()
     {
         this.entityRewrite = EntityMap.getEntityMap( getPendingConnection().getVersion() );
 
@@ -172,6 +172,8 @@ public final class UserConnection implements ProxiedPlayer
 
         // Set whether the connection has a 1.8 FML marker in the handshake.
         forgeClientHandler.setFmlTokenInHandshake( this.getPendingConnection().getExtraDataInHandshake().contains( ForgeConstants.FML_HANDSHAKE_TOKEN ) );
+
+        return BungeeCord.getInstance().addConnection( this );
     }
 
     public void sendPacket(PacketWrapper packet)
diff --git a/proxy/src/main/java/net/md_5/bungee/connection/InitialHandler.java b/proxy/src/main/java/net/md_5/bungee/connection/InitialHandler.java
index 18570a7a..b1b087aa 100644
--- a/proxy/src/main/java/net/md_5/bungee/connection/InitialHandler.java
+++ b/proxy/src/main/java/net/md_5/bungee/connection/InitialHandler.java
@@ -613,7 +613,11 @@ public class InitialHandler extends PacketHandler implements PendingConnection
 
     private void finish2()
     {
-        userCon.init();
+        if ( !userCon.init() )
+        {
+            disconnect( bungee.getTranslation( "already_connected_proxy" ) );
+            return;
+        }
 
         ch.getHandle().pipeline().get( HandlerBoss.class ).setHandler( new UpstreamBridge( bungee, userCon ) );
         bungee.getPluginManager().callEvent( new PostLoginEvent( userCon ) );
diff --git a/proxy/src/main/java/net/md_5/bungee/connection/UpstreamBridge.java b/proxy/src/main/java/net/md_5/bungee/connection/UpstreamBridge.java
index 4b2e6269..460aa491 100644
--- a/proxy/src/main/java/net/md_5/bungee/connection/UpstreamBridge.java
+++ b/proxy/src/main/java/net/md_5/bungee/connection/UpstreamBridge.java
@@ -54,7 +54,6 @@ public class UpstreamBridge extends PacketHandler
         this.bungee = bungee;
         this.con = con;
 
-        BungeeCord.getInstance().addConnection( con );
         con.getTabListHandler().onConnect();
     }