Paper/patches/server/0421-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 c5d1fc2e7c8090ed91cb6ca24135c5aaa2172fa9..fd3e8c2d3a415a6a3370784ec3c0d46d3c1122b7 100644
--- a/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
+++ b/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
@@ -1434,6 +1434,11 @@ 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();