Allow enabling sand duping (#10191)

Because this exploit has been widely known for years and has not been fixed by Mojang, we decided that it was worth allowing people to toggle it on/off due to how easy it is to make it configurable.

It should be noted that this decision does not promise all future exploits will be configurable. 

1 files changed, 40 insertions, 0 deletions

diff --git a/patches/server/0731-Fix-NBT-pieces-overriding-a-block-entity-during-worl.patch b/patches/server/0731-Fix-NBT-pieces-overriding-a-block-entity-during-worl.patch
new file mode 100644
index 0000000000..aa5772fe8a
--- /dev/null
+++ b/patches/server/0731-Fix-NBT-pieces-overriding-a-block-entity-during-worl.patch
@@ -0,0 +1,40 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: etil2jz <[email protected]>
+Date: Sat, 2 Apr 2022 23:29:24 +0200
+Subject: [PATCH] Fix NBT pieces overriding a block entity during worldgen
+ deadlock
+
+By checking if the world passed into StructureTemplate's placeInWorld
+is not a WorldGenRegion, we can bypass the deadlock entirely.
+See https://bugs.mojang.com/browse/MC-246262
+
+diff --git a/src/main/java/net/minecraft/world/level/levelgen/structure/templatesystem/StructureTemplate.java b/src/main/java/net/minecraft/world/level/levelgen/structure/templatesystem/StructureTemplate.java
+index be8aab51a1b92a3a0cc94976975fc3aabc46f0b4..ae8a42261337bf736d0cc1bbe18da2b773417ca4 100644
+--- a/src/main/java/net/minecraft/world/level/levelgen/structure/templatesystem/StructureTemplate.java
++++ b/src/main/java/net/minecraft/world/level/levelgen/structure/templatesystem/StructureTemplate.java
+@@ -279,7 +279,11 @@ public class StructureTemplate {
+ 
+                         if (definedstructure_blockinfo.nbt != null) {
+                             tileentity = world.getBlockEntity(blockposition2);
+-                            Clearable.tryClear(tileentity);
++                            // Paper start - Fix NBT pieces overriding a block entity during worldgen deadlock
++                            if (!(world instanceof net.minecraft.world.level.WorldGenLevel)) {
++                                Clearable.tryClear(tileentity);
++                            }
++                            // Paper end - Fix NBT pieces overriding a block entity during worldgen deadlock
+                             world.setBlock(blockposition2, Blocks.BARRIER.defaultBlockState(), 20);
+                         }
+                         // CraftBukkit start
+@@ -406,7 +410,11 @@ public class StructureTemplate {
+                         if (pair1.getSecond() != null) {
+                             tileentity = world.getBlockEntity(blockposition6);
+                             if (tileentity != null) {
+-                                tileentity.setChanged();
++                                // Paper start - Fix NBT pieces overriding a block entity during worldgen deadlock
++                                if (!(world instanceof net.minecraft.world.level.WorldGenLevel)) {
++                                    tileentity.setChanged();
++                                }
++                                // Paper end - Fix NBT pieces overriding a block entity during worldgen deadlock
+                             }
+                         }
+                     }