From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Spottedleaf <Spottedleaf@users.noreply.github.com>
Date: Fri, 27 Dec 2019 09:42:26 -0800
Subject: [PATCH] Guard against serializing mismatching chunk coordinate

Should help if something dumb happens

diff --git a/src/main/java/net/minecraft/world/level/chunk/storage/ChunkStorage.java b/src/main/java/net/minecraft/world/level/chunk/storage/ChunkStorage.java
index 329e7eb1c3e92445b3fae9e1e79d0497b7e3e3f2..909acbf5b8c6edcb4529647c11464d911d6f8c15 100644
--- a/src/main/java/net/minecraft/world/level/chunk/storage/ChunkStorage.java
+++ b/src/main/java/net/minecraft/world/level/chunk/storage/ChunkStorage.java
@@ -172,8 +172,19 @@ public class ChunkStorage implements AutoCloseable {
     }
 
     public CompletableFuture<Void> write(ChunkPos chunkPos, Supplier<CompoundTag> nbtSupplier) {
+        // Paper start - guard against possible chunk pos desync
+        final Supplier<CompoundTag> guardedPosCheck = () -> {
+            CompoundTag nbt = nbtSupplier.get();
+            if (nbt != null && !chunkPos.equals(SerializableChunkData.getChunkCoordinate(nbt))) {
+                final String world = (ChunkStorage.this instanceof net.minecraft.server.level.ChunkMap) ? ((net.minecraft.server.level.ChunkMap) ChunkStorage.this).level.getWorld().getName() : null;
+                throw new IllegalArgumentException("Chunk coordinate and serialized data do not have matching coordinates, trying to serialize coordinate " + chunkPos
+                    + " but compound says coordinate is " + SerializableChunkData.getChunkCoordinate(nbt) + (world == null ? " for an unknown world" : (" for world: " + world)));
+            }
+            return nbt;
+        };
+        // Paper end - guard against possible chunk pos desync
         this.handleLegacyStructureIndex(chunkPos);
-        return this.worker.store(chunkPos, nbtSupplier);
+        return this.worker.store(chunkPos, guardedPosCheck); // Paper - guard against possible chunk pos desync
     }
 
     protected void handleLegacyStructureIndex(ChunkPos chunkPos) {
diff --git a/src/main/java/net/minecraft/world/level/chunk/storage/SerializableChunkData.java b/src/main/java/net/minecraft/world/level/chunk/storage/SerializableChunkData.java
index 4367ccc628bb4f404d6a081083002518442f462b..92ad7704a77c024afe090488764eaf59a4f7505f 100644
--- a/src/main/java/net/minecraft/world/level/chunk/storage/SerializableChunkData.java
+++ b/src/main/java/net/minecraft/world/level/chunk/storage/SerializableChunkData.java
@@ -91,13 +91,25 @@ public record SerializableChunkData(Registry<Biome> biomeRegistry, ChunkPos chun
     public static final String SECTIONS_TAG = "sections";
     public static final String BLOCK_LIGHT_TAG = "BlockLight";
     public static final String SKY_LIGHT_TAG = "SkyLight";
+    // Paper start - guard against serializing mismatching coordinates
+    // TODO Note: This needs to be re-checked each update
+    public static ChunkPos getChunkCoordinate(final CompoundTag chunkData) {
+        final int dataVersion = ChunkStorage.getVersion(chunkData);
+        if (dataVersion < 2842) { // Level tag is removed after this version
+            final CompoundTag levelData = chunkData.getCompound("Level");
+            return new ChunkPos(levelData.getInt("xPos"), levelData.getInt("zPos"));
+        } else {
+            return new ChunkPos(chunkData.getInt("xPos"), chunkData.getInt("zPos"));
+        }
+    }
+    // Paper end - guard against serializing mismatching coordinates
 
     @Nullable
     public static SerializableChunkData parse(LevelHeightAccessor world, RegistryAccess registryManager, CompoundTag nbt) {
         if (!nbt.contains("Status", 8)) {
             return null;
         } else {
-            ChunkPos chunkcoordintpair = new ChunkPos(nbt.getInt("xPos"), nbt.getInt("zPos"));
+            ChunkPos chunkcoordintpair = new ChunkPos(nbt.getInt("xPos"), nbt.getInt("zPos")); // Paper - guard against serializing mismatching coordinates; diff on change, see ChunkSerializer#getChunkCoordinate
             long i = nbt.getLong("LastUpdate");
             long j = nbt.getLong("InhabitedTime");
             ChunkStatus chunkstatus = ChunkStatus.byName(nbt.getString("Status"));