From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Wed, 13 May 2020 23:01:26 -0400
Subject: [PATCH] Protect Bedrock and End Portal/Frames from being destroyed

This fixes exploits that let players destroy bedrock by Pistons, explosions
and Mushrooom/Tree generation.

These blocks are designed to not be broken except by creative players/commands.
So protect them from a multitude of methods of destroying them.

A config is provided if you rather let players use these exploits, and let
them destroy the worlds End Portals and get on top of the nether easy.

diff --git a/src/main/java/com/destroystokyo/paper/PaperConfig.java b/src/main/java/com/destroystokyo/paper/PaperConfig.java
index 6f0c5a2d33001f59e560ec239c0edbd32de84ed8..ac6b291c103c432fdced603674345096326a9efe 100644
--- a/src/main/java/com/destroystokyo/paper/PaperConfig.java
+++ b/src/main/java/com/destroystokyo/paper/PaperConfig.java
@@ -411,4 +411,17 @@ public class PaperConfig {
     private static void midTickChunkTasks() {
         midTickChunkTasks = getInt("settings.chunk-tasks-per-tick", midTickChunkTasks);
     }
+
+    public static boolean allowBlockPermanentBreakingExploits = false;
+    private static void allowBlockPermanentBreakingExploits() {
+        if (config.contains("allow-perm-block-break-exploits")) {
+            allowBlockPermanentBreakingExploits = config.getBoolean("allow-perm-block-break-exploits", false);
+            config.set("allow-perm-block-break-exploits", null);
+        }
+
+        config.set("settings.unsupported-settings.allow-permanent-block-break-exploits-readme", "This setting controls if players should be able to break bedrock, end portals and other intended to be permanent blocks.");
+        allowBlockPermanentBreakingExploits = getBoolean("settings.unsupported-settings.allow-permanent-block-break-exploits", allowBlockPermanentBreakingExploits);
+
+    }
+
 }
diff --git a/src/main/java/net/minecraft/server/Block.java b/src/main/java/net/minecraft/server/Block.java
index b364ceafb4c3412b0d11b3b2e8b4321ed96769bb..a45ceff9ff970b996b2767379a2ecd4693f52d3a 100644
--- a/src/main/java/net/minecraft/server/Block.java
+++ b/src/main/java/net/minecraft/server/Block.java
@@ -23,6 +23,19 @@ public class Block extends BlockBase implements IMaterial {
     protected final BlockStateList<Block, IBlockData> blockStateList;
     private IBlockData blockData;
     // Paper start
+    public final boolean isDestroyable() {
+        return com.destroystokyo.paper.PaperConfig.allowBlockPermanentBreakingExploits ||
+            this != Blocks.BEDROCK &&
+            this != Blocks.END_PORTAL_FRAME &&
+            this != Blocks.END_PORTAL &&
+            this != Blocks.END_GATEWAY &&
+            this != Blocks.COMMAND_BLOCK &&
+            this != Blocks.REPEATING_COMMAND_BLOCK &&
+            this != Blocks.CHAIN_COMMAND_BLOCK &&
+            this != Blocks.BARRIER &&
+            this != Blocks.STRUCTURE_BLOCK &&
+            this != Blocks.JIGSAW;
+    }
     public co.aikar.timings.Timing timing;
     public co.aikar.timings.Timing getTiming() {
         if (timing == null) {
diff --git a/src/main/java/net/minecraft/server/BlockBase.java b/src/main/java/net/minecraft/server/BlockBase.java
index 62e7c6cb1b363d1ee626c4405f8c30e74aba03e9..1c06647fb6f8e757ca7a737a371cb1dec2aeb80e 100644
--- a/src/main/java/net/minecraft/server/BlockBase.java
+++ b/src/main/java/net/minecraft/server/BlockBase.java
@@ -138,7 +138,7 @@ public abstract class BlockBase {
 
     @Deprecated
     public boolean a(IBlockData iblockdata, BlockActionContext blockactioncontext) {
-        return this.material.isReplaceable() && (blockactioncontext.getItemStack().isEmpty() || blockactioncontext.getItemStack().getItem() != this.getItem());
+        return this.material.isReplaceable() && (blockactioncontext.getItemStack().isEmpty() || blockactioncontext.getItemStack().getItem() != this.getItem()) && (iblockdata.isDestroyable() || (blockactioncontext.getEntity() != null && blockactioncontext.getEntity().abilities.canInstantlyBuild)); // Paper
     }
 
     @Deprecated
@@ -342,7 +342,11 @@ public abstract class BlockBase {
         public Block getBlock() {
             return (Block) this.c;
         }
-
+        // Paper start
+        public final boolean isDestroyable() {
+            return getBlock().isDestroyable();
+        }
+        // Paper end
         public Material getMaterial() {
             return this.g;
         }
@@ -432,7 +436,7 @@ public abstract class BlockBase {
         }
 
         public EnumPistonReaction getPushReaction() {
-            return this.getBlock().getPushReaction(this.p());
+            return !isDestroyable() ? EnumPistonReaction.BLOCK : this.getBlock().getPushReaction(this.p()); // Paper
         }
 
         public boolean i(IBlockAccess iblockaccess, BlockPosition blockposition) {
diff --git a/src/main/java/net/minecraft/server/BlockPiston.java b/src/main/java/net/minecraft/server/BlockPiston.java
index 417d1a6c3dbd23905672a847939d92a953bbc91c..0bab7dfb053c1aa92f5417c25fed5484e09bbec3 100644
--- a/src/main/java/net/minecraft/server/BlockPiston.java
+++ b/src/main/java/net/minecraft/server/BlockPiston.java
@@ -165,6 +165,12 @@ public class BlockPiston extends BlockDirectional {
     @Override
     public boolean a(IBlockData iblockdata, World world, BlockPosition blockposition, int i, int j) {
         EnumDirection enumdirection = (EnumDirection) iblockdata.get(BlockPiston.FACING);
+        // Paper start - prevent retracting when we're facing the wrong way (we were replaced before retraction could occur)
+        EnumDirection directionQueuedAs = EnumDirection.fromType1(j & 7); // Paper - copied from below
+        if (!com.destroystokyo.paper.PaperConfig.allowBlockPermanentBreakingExploits && enumdirection != directionQueuedAs) {
+            return false;
+        }
+        // Paper end - prevent retracting when we're facing the wrong way
 
         if (!world.isClientSide) {
             boolean flag = this.a(world, blockposition, enumdirection);
@@ -196,7 +202,7 @@ public class BlockPiston extends BlockDirectional {
             IBlockData iblockdata1 = (IBlockData) ((IBlockData) Blocks.MOVING_PISTON.getBlockData().set(BlockPistonMoving.a, enumdirection)).set(BlockPistonMoving.b, this.sticky ? BlockPropertyPistonType.STICKY : BlockPropertyPistonType.DEFAULT);
 
             world.setTypeAndData(blockposition, iblockdata1, 20);
-            world.setTileEntity(blockposition, BlockPistonMoving.a((IBlockData) this.getBlockData().set(BlockPiston.FACING, EnumDirection.fromType1(j & 7)), enumdirection, false, true));
+            world.setTileEntity(blockposition, BlockPistonMoving.a((IBlockData) this.getBlockData().set(BlockPiston.FACING, EnumDirection.fromType1(j & 7)), enumdirection, false, true)); // Paper - diff on change, j is facing direction - copy this above
             world.update(blockposition, iblockdata1.getBlock());
             iblockdata1.a(world, blockposition, 2);
             if (this.sticky) {
@@ -225,7 +231,14 @@ public class BlockPiston extends BlockDirectional {
                     }
                 }
             } else {
-                world.a(blockposition.shift(enumdirection), false);
+                // Paper start - fix headless pistons breaking blocks
+                BlockPosition headPos = blockposition.shift(enumdirection);
+                if (com.destroystokyo.paper.PaperConfig.allowBlockPermanentBreakingExploits || world.getType(headPos) == Blocks.PISTON_HEAD.getBlockData().set(FACING, enumdirection)) { // double check to make sure we're not a headless piston.
+                    world.setAir(headPos, false);
+                } else {
+                    ((WorldServer)world).getChunkProvider().flagDirty(headPos); // ... fix client desync
+                }
+                // Paper end - fix headless pistons breaking blocks
             }
 
             world.playSound((EntityHuman) null, blockposition, SoundEffects.BLOCK_PISTON_CONTRACT, SoundCategory.BLOCKS, 0.5F, world.random.nextFloat() * 0.15F + 0.6F);
diff --git a/src/main/java/net/minecraft/server/Explosion.java b/src/main/java/net/minecraft/server/Explosion.java
index a552cc5bebb1a70db2e679a514769d0ad791ad68..72de544c0782e4daff222a0ca04e5bc870cf148c 100644
--- a/src/main/java/net/minecraft/server/Explosion.java
+++ b/src/main/java/net/minecraft/server/Explosion.java
@@ -125,6 +125,7 @@ public class Explosion {
                         for (float f1 = 0.3F; f > 0.0F; f -= 0.22500001F) {
                             BlockPosition blockposition = new BlockPosition(d4, d5, d6);
                             IBlockData iblockdata = this.world.getType(blockposition);
+                            if (!iblockdata.isDestroyable()) continue; // Paper
                             Fluid fluid = iblockdata.getFluid(); // Paper
                             Optional<Float> optional = this.l.a(this, this.world, blockposition, iblockdata, fluid);
 
@@ -278,7 +279,7 @@ public class Explosion {
                 IBlockData iblockdata = this.world.getType(blockposition);
                 Block block = iblockdata.getBlock();
 
-                if (!iblockdata.isAir()) {
+                if (!iblockdata.isAir() && iblockdata.isDestroyable()) { // Paper
                     BlockPosition blockposition1 = blockposition.immutableCopy();
 
                     this.world.getMethodProfiler().enter("explosion_blocks");
diff --git a/src/main/java/net/minecraft/server/World.java b/src/main/java/net/minecraft/server/World.java
index b479a25044ecf8c1a791729d643cf8dc90193b2b..8d59391befcbc2542a79758d2021ef51df59d815 100644
--- a/src/main/java/net/minecraft/server/World.java
+++ b/src/main/java/net/minecraft/server/World.java
@@ -362,6 +362,10 @@ public abstract class World implements GeneratorAccess, AutoCloseable {
     public boolean a(BlockPosition blockposition, IBlockData iblockdata, int i, int j) {
         // CraftBukkit start - tree generation
         if (this.captureTreeGeneration) {
+            // Paper start
+            IBlockData type = getType(blockposition);
+            if (!type.isDestroyable()) return false;
+            // Paper end
             CraftBlockState blockstate = capturedBlockStates.get(blockposition);
             if (blockstate == null) {
                 blockstate = CapturedBlockState.getTreeBlockState(this, blockposition, i);
