testserver/patches/server/0435-Prevent-position-desync-in-playerconnection-causing-.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Spottedleaf <Spottedleaf@users.noreply.github.com>
Date: Fri, 12 Jun 2020 16:51:39 -0700
Subject: [PATCH] Prevent position desync in playerconnection causing tp
 exploit

Caused the server to revert to the player's overworld coordinates
after teleporting into the end.

Sidenote: The underlying issue is that the move call can teleport
entities and do other things like kill the entity. In the future,
to fix all exploits derieved from this usually unexpected
behaviour, we need to move all of this dangerous logic outside
of the move call and into an appropriate place in the tick method.

diff --git a/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java b/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
index 408c2071ea8f99721bc13cf4da27a17e64bc9e8a..a0f492b0c7783fc8c5ce2e1a60707ae2db74ab9f 100644
--- a/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
+++ b/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
@@ -1439,6 +1439,11 @@ public class ServerGamePacketListenerImpl implements ServerPlayerConnection, Tic
 
                             this.player.move(MoverType.PLAYER, new Vec3(d7, d8, d9));
                             this.player.onGround = packet.isOnGround(); // CraftBukkit - SPIGOT-5810, SPIGOT-5835, SPIGOT-6828: reset by this.player.move
+                            // Paper start - prevent position desync
+                            if (this.awaitingPositionFromClient != null) {
+                                return; // ... thanks Mojang for letting move calls teleport across dimensions.
+                            }
+                            // Paper end - prevent position desync
                             double d12 = d8;
 
                             d7 = d0 - this.player.getX();