From 15b514130eb861cb44ddc787aa152f73e259dbb1 Mon Sep 17 00:00:00 2001
From: Andrew Steinborn <git@steinborn.me>
Date: Sun, 19 Jul 2020 08:54:54 +1000
Subject: [PATCH] #2908: Don't frame packets for dead connections

---
 .../java/net/md_5/bungee/protocol/LegacyDecoder.java   |  7 +++++++
 .../net/md_5/bungee/protocol/MinecraftDecoder.java     |  7 +++++++
 .../net/md_5/bungee/protocol/Varint21FrameDecoder.java | 10 ++++++++++
 3 files changed, 24 insertions(+)

diff --git a/protocol/src/main/java/net/md_5/bungee/protocol/LegacyDecoder.java b/protocol/src/main/java/net/md_5/bungee/protocol/LegacyDecoder.java
index 334a8eabb..5518bf268 100644
--- a/protocol/src/main/java/net/md_5/bungee/protocol/LegacyDecoder.java
+++ b/protocol/src/main/java/net/md_5/bungee/protocol/LegacyDecoder.java
@@ -14,6 +14,13 @@ public class LegacyDecoder extends ByteToMessageDecoder
     @Override
     protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception
     {
+        // See check in Varint21FrameDecoder for more details
+        if ( !ctx.channel().isActive() )
+        {
+            in.skipBytes( in.readableBytes() );
+            return;
+        }
+
         if ( !in.isReadable() )
         {
             return;
diff --git a/protocol/src/main/java/net/md_5/bungee/protocol/MinecraftDecoder.java b/protocol/src/main/java/net/md_5/bungee/protocol/MinecraftDecoder.java
index ea44573d1..d36b7f3c0 100644
--- a/protocol/src/main/java/net/md_5/bungee/protocol/MinecraftDecoder.java
+++ b/protocol/src/main/java/net/md_5/bungee/protocol/MinecraftDecoder.java
@@ -20,6 +20,13 @@ public class MinecraftDecoder extends MessageToMessageDecoder<ByteBuf>
     @Override
     protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception
     {
+        // See Varint21FrameDecoder for the general reasoning. We add this here as ByteToMessageDecoder#handlerRemoved()
+        // will fire any cumulated data through the pipeline, so we want to try and stop it here.
+        if ( !ctx.channel().isActive() )
+        {
+            return;
+        }
+
         Protocol.DirectionData prot = ( server ) ? protocol.TO_SERVER : protocol.TO_CLIENT;
         ByteBuf slice = in.copy(); // Can't slice this one due to EntityMap :(
 
diff --git a/protocol/src/main/java/net/md_5/bungee/protocol/Varint21FrameDecoder.java b/protocol/src/main/java/net/md_5/bungee/protocol/Varint21FrameDecoder.java
index e903fd092..647394bae 100644
--- a/protocol/src/main/java/net/md_5/bungee/protocol/Varint21FrameDecoder.java
+++ b/protocol/src/main/java/net/md_5/bungee/protocol/Varint21FrameDecoder.java
@@ -15,6 +15,16 @@ public class Varint21FrameDecoder extends ByteToMessageDecoder
     @Override
     protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception
     {
+        // If we decode an invalid packet and an exception is thrown (thus triggering a close of the connection),
+        // the Netty ByteToMessageDecoder will continue to frame more packets and potentially call fireChannelRead()
+        // on them, likely with more invalid packets. Therefore, check if the connection is no longer active and if so
+        // sliently discard the packet.
+        if ( !ctx.channel().isActive() )
+        {
+            in.skipBytes( in.readableBytes() );
+            return;
+        }
+
         in.markReaderIndex();
 
         final byte[] buf = new byte[ 3 ];