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/PlayerConnection.java b/src/main/java/net/minecraft/server/PlayerConnection.java
index cab29e756cd0f04c8c97e29ee2affaa39b425b9a..ab9714c0ed5eed66b6c6d44b686fe39dd1719d97 100644
--- a/src/main/java/net/minecraft/server/PlayerConnection.java
+++ b/src/main/java/net/minecraft/server/PlayerConnection.java
@@ -1180,6 +1180,11 @@ public class PlayerConnection implements PacketListenerPlayIn {
 
                             this.player.move(EnumMoveType.PLAYER, new Vec3D(d7, d8, d9));
                             this.player.setOnGround(packetplayinflying.b()); // CraftBukkit - SPIGOT-5810, SPIGOT-5835: reset by this.player.move
+                            // Paper start - prevent position desync
+                            if (this.teleportPos != null) {
+                                return; // ... thanks Mojang for letting move calls teleport across dimensions.
+                            }
+                            // Paper end - prevent position desync
                             double d12 = d8;
 
                             d7 = d4 - this.player.locX();