From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Andrew Steinborn <git@steinborn.me>
Date: Mon, 8 Oct 2018 14:36:14 -0400
Subject: [PATCH] Add Velocity IP Forwarding Support

While Velocity supports BungeeCord-style IP forwarding, it is not secure. Users
have a lot of problems setting up firewalls or setting up plugins like IPWhitelist.
Further, the BungeeCord IP forwarding protocol still retains essentially its original
form, when there is brand new support for custom login plugin messages in 1.13.

Velocity's modern IP forwarding uses an HMAC-SHA256 code to ensure authenticity
of messages, is packed into a binary format that is smaller than BungeeCord's
forwarding, and is integrated into the Minecraft login process by using the 1.13
login plugin message packet.

diff --git a/src/main/java/com/destroystokyo/paper/PaperConfig.java b/src/main/java/com/destroystokyo/paper/PaperConfig.java
index da21f1623a90ade429723d4eb12d646aaf28071e..1015fcc6c77bd64c3f3cbf234e85a6602dbfa0d7 100644
--- a/src/main/java/com/destroystokyo/paper/PaperConfig.java
+++ b/src/main/java/com/destroystokyo/paper/PaperConfig.java
@@ -9,6 +9,7 @@ import java.io.IOException;
 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
 import java.lang.reflect.Modifier;
+import java.nio.charset.StandardCharsets;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -265,7 +266,7 @@ public class PaperConfig {
     }
 
     public static boolean isProxyOnlineMode() {
-        return Bukkit.getOnlineMode() || (SpigotConfig.bungee && bungeeOnlineMode);
+        return Bukkit.getOnlineMode() || (SpigotConfig.bungee && bungeeOnlineMode) || (velocitySupport && velocityOnlineMode);
     }
 
     public static int packetInSpamThreshold = 300;
@@ -347,6 +348,20 @@ public class PaperConfig {
         tabSpamLimit = getInt("settings.spam-limiter.tab-spam-limit", tabSpamLimit);
     }
 
+    public static boolean velocitySupport;
+    public static boolean velocityOnlineMode;
+    public static byte[] velocitySecretKey;
+    private static void velocitySupport() {
+        velocitySupport = getBoolean("settings.velocity-support.enabled", false);
+        velocityOnlineMode = getBoolean("settings.velocity-support.online-mode", false);
+        String secret = getString("settings.velocity-support.secret", "");
+        if (velocitySupport && secret.isEmpty()) {
+            fatal("Velocity support is enabled, but no secret key was specified. A secret key is required!");
+        } else {
+            velocitySecretKey = secret.getBytes(StandardCharsets.UTF_8);
+        }
+    }
+
     public static boolean asyncChunks = false;
     private static void asyncChunks() {
         ConfigurationSection section;
diff --git a/src/main/java/com/destroystokyo/paper/proxy/VelocityProxy.java b/src/main/java/com/destroystokyo/paper/proxy/VelocityProxy.java
new file mode 100644
index 0000000000000000000000000000000000000000..41d73aa91fb401612e087aa1b7278ba61d28bf3a
--- /dev/null
+++ b/src/main/java/com/destroystokyo/paper/proxy/VelocityProxy.java
@@ -0,0 +1,66 @@
+package com.destroystokyo.paper.proxy;
+
+import com.destroystokyo.paper.PaperConfig;
+import com.google.common.net.InetAddresses;
+import com.mojang.authlib.GameProfile;
+import com.mojang.authlib.properties.Property;
+import java.net.InetAddress;
+import java.security.InvalidKeyException;
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+
+import javax.crypto.Mac;
+import javax.crypto.spec.SecretKeySpec;
+import net.minecraft.network.FriendlyByteBuf;
+import net.minecraft.resources.ResourceLocation;
+
+public class VelocityProxy {
+    private static final int SUPPORTED_FORWARDING_VERSION = 1;
+    public static final ResourceLocation PLAYER_INFO_CHANNEL = new ResourceLocation("velocity", "player_info");
+
+    public static boolean checkIntegrity(final FriendlyByteBuf buf) {
+        final byte[] signature = new byte[32];
+        buf.readBytes(signature);
+
+        final byte[] data = new byte[buf.readableBytes()];
+        buf.getBytes(buf.readerIndex(), data);
+
+        try {
+            final Mac mac = Mac.getInstance("HmacSHA256");
+            mac.init(new SecretKeySpec(PaperConfig.velocitySecretKey, "HmacSHA256"));
+            final byte[] mySignature = mac.doFinal(data);
+            if (!MessageDigest.isEqual(signature, mySignature)) {
+                return false;
+            }
+        } catch (final InvalidKeyException | NoSuchAlgorithmException e) {
+            throw new AssertionError(e);
+        }
+
+        int version = buf.readVarInt();
+        if (version != SUPPORTED_FORWARDING_VERSION) {
+            throw new IllegalStateException("Unsupported forwarding version " + version + ", wanted " + SUPPORTED_FORWARDING_VERSION);
+        }
+
+        return true;
+    }
+
+    public static InetAddress readAddress(final FriendlyByteBuf buf) {
+        return InetAddresses.forString(buf.readUtf(Short.MAX_VALUE));
+    }
+
+    public static GameProfile createProfile(final FriendlyByteBuf buf) {
+        final GameProfile profile = new GameProfile(buf.readUUID(), buf.readUtf(16));
+        readProperties(buf, profile);
+        return profile;
+    }
+
+    private static void readProperties(final FriendlyByteBuf buf, final GameProfile profile) {
+        final int properties = buf.readVarInt();
+        for (int i1 = 0; i1 < properties; i1++) {
+            final String name = buf.readUtf(Short.MAX_VALUE);
+            final String value = buf.readUtf(Short.MAX_VALUE);
+            final String signature = buf.readBoolean() ? buf.readUtf(Short.MAX_VALUE) : null;
+            profile.getProperties().put(name, new Property(name, value, signature));
+        }
+    }
+}
diff --git a/src/main/java/net/minecraft/server/network/ServerLoginPacketListenerImpl.java b/src/main/java/net/minecraft/server/network/ServerLoginPacketListenerImpl.java
index 67b300574655854249c1f7440f56a6e8f0fad351..bb767f5b626225e70a8af273384bb74dbd21430d 100644
--- a/src/main/java/net/minecraft/server/network/ServerLoginPacketListenerImpl.java
+++ b/src/main/java/net/minecraft/server/network/ServerLoginPacketListenerImpl.java
@@ -18,6 +18,7 @@ import javax.crypto.Cipher;
 import javax.crypto.SecretKey;
 import net.minecraft.DefaultUncaughtExceptionHandler;
 import net.minecraft.network.Connection;
+import net.minecraft.network.FriendlyByteBuf;
 import net.minecraft.network.chat.Component;
 import net.minecraft.network.chat.TextComponent;
 import net.minecraft.network.chat.TranslatableComponent;
@@ -44,6 +45,7 @@ import org.bukkit.craftbukkit.util.Waitable;
 import org.bukkit.event.player.AsyncPlayerPreLoginEvent;
 import org.bukkit.event.player.PlayerPreLoginEvent;
 // CraftBukkit end
+import io.netty.buffer.Unpooled; // Paper
 
 public class ServerLoginPacketListenerImpl implements ServerLoginPacketListener {
 
@@ -62,6 +64,7 @@ public class ServerLoginPacketListenerImpl implements ServerLoginPacketListener
     @Nullable
     private ServerPlayer delayedAcceptPlayer;
     public String hostname = ""; // CraftBukkit - add field
+    private int velocityLoginMessageId = -1; // Paper - Velocity support
 
     public ServerLoginPacketListenerImpl(MinecraftServer server, Connection connection) {
         this.state = ServerLoginPacketListenerImpl.State.HELLO;
@@ -234,6 +237,14 @@ public class ServerLoginPacketListenerImpl implements ServerLoginPacketListener
             this.state = ServerLoginPacketListenerImpl.State.KEY;
             this.connection.send(new ClientboundHelloPacket("", this.server.getKeyPair().getPublic().getEncoded(), this.nonce));
         } else {
+            // Paper start - Velocity support
+            if (com.destroystokyo.paper.PaperConfig.velocitySupport) {
+                this.velocityLoginMessageId = java.util.concurrent.ThreadLocalRandom.current().nextInt();
+                net.minecraft.network.protocol.login.ClientboundCustomQueryPacket packet1 = new net.minecraft.network.protocol.login.ClientboundCustomQueryPacket(this.velocityLoginMessageId, com.destroystokyo.paper.proxy.VelocityProxy.PLAYER_INFO_CHANNEL, new FriendlyByteBuf(Unpooled.EMPTY_BUFFER));
+                this.connection.send(packet1);
+                return;
+            }
+            // Paper end
             // Spigot start
             // Paper start - Cache authenticator threads
             authenticatorPool.execute(new Runnable() {
@@ -335,6 +346,12 @@ public class ServerLoginPacketListenerImpl implements ServerLoginPacketListener
     public class LoginHandler {
 
         public void fireEvents() throws Exception {
+                            // Paper start - Velocity support
+                            if (ServerLoginPacketListenerImpl.this.velocityLoginMessageId == -1 && com.destroystokyo.paper.PaperConfig.velocitySupport) {
+                                disconnect("This server requires you to connect with Velocity.");
+                                return;
+                            }
+                            // Paper end
                         String playerName = ServerLoginPacketListenerImpl.this.gameProfile.getName();
                         java.net.InetAddress address = ((java.net.InetSocketAddress) ServerLoginPacketListenerImpl.this.connection.getRemoteAddress()).getAddress();
                         java.util.UUID uniqueId = ServerLoginPacketListenerImpl.this.gameProfile.getId();
@@ -382,6 +399,40 @@ public class ServerLoginPacketListenerImpl implements ServerLoginPacketListener
     // Spigot end
 
     public void handleCustomQueryPacket(ServerboundCustomQueryPacket packet) {
+        // Paper start - Velocity support
+        if (com.destroystokyo.paper.PaperConfig.velocitySupport && packet.getTransactionId() == this.velocityLoginMessageId) {
+            FriendlyByteBuf buf = packet.getData();
+            if (buf == null) {
+                this.disconnect("This server requires you to connect with Velocity.");
+                return;
+            }
+
+            if (!com.destroystokyo.paper.proxy.VelocityProxy.checkIntegrity(buf)) {
+                this.disconnect("Unable to verify player details");
+                return;
+            }
+
+            java.net.SocketAddress listening = this.connection.getRemoteAddress();
+            int port = 0;
+            if (listening instanceof java.net.InetSocketAddress) {
+                port = ((java.net.InetSocketAddress) listening).getPort();
+            }
+            this.connection.address = new java.net.InetSocketAddress(com.destroystokyo.paper.proxy.VelocityProxy.readAddress(buf), port);
+
+            this.gameProfile = com.destroystokyo.paper.proxy.VelocityProxy.createProfile(buf);
+
+            // Proceed with login
+            authenticatorPool.execute(() -> {
+                try {
+                    new LoginHandler().fireEvents();
+                } catch (Exception ex) {
+                    disconnect("Failed to verify username!");
+                    server.server.getLogger().log(java.util.logging.Level.WARNING, "Exception verifying " + gameProfile.getName(), ex);
+                }
+            });
+            return;
+        }
+        // Paper end
         this.disconnect(new TranslatableComponent("multiplayer.disconnect.unexpected_query_response"));
     }
 
diff --git a/src/main/java/org/bukkit/craftbukkit/CraftServer.java b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
index e4af349ab368ab561f6ef929395020fc260fe159..5eaf046724b7354b84c9a40f73c2f4d3d21fc601 100644
--- a/src/main/java/org/bukkit/craftbukkit/CraftServer.java
+++ b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
@@ -744,7 +744,7 @@ public final class CraftServer implements Server {
     @Override
     public long getConnectionThrottle() {
         // Spigot Start - Automatically set connection throttle for bungee configurations
-        if (org.spigotmc.SpigotConfig.bungee) {
+        if (org.spigotmc.SpigotConfig.bungee || com.destroystokyo.paper.PaperConfig.velocitySupport) { // Paper - Velocity support
             return -1;
         } else {
             return this.configuration.getInt("settings.connection-throttle");
