Paper/Spigot-Server-Patches/0299-Add-Velocity-IP-Forwarding-Support.patch

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 7178b37f7978c7e9031a22726005c5099fd78fe0..3139c194f9b1bc3510d51a81f13ae43d00a3dc29 100644
--- a/src/main/java/com/destroystokyo/paper/PaperConfig.java
+++ b/src/main/java/com/destroystokyo/paper/PaperConfig.java
@@ -8,6 +8,7 @@ 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;
@@ -252,7 +253,7 @@ 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;
@@ -324,4 +325,18 @@ 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);
+        }
+    }
 }
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..fdd8708f974700c7cde6e436c2f189d94d336f1f
--- /dev/null
+++ b/src/main/java/com/destroystokyo/paper/proxy/VelocityProxy.java
@@ -0,0 +1,67 @@
+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 net.minecraft.server.MinecraftKey;
+import net.minecraft.server.PacketDataSerializer;
+
+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;
+
+public class VelocityProxy {
+    private static final int SUPPORTED_FORWARDING_VERSION = 1;
+    public static final MinecraftKey PLAYER_INFO_CHANNEL = new MinecraftKey("velocity", "player_info");
+
+    public static boolean checkIntegrity(final PacketDataSerializer 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 PacketDataSerializer buf) {
+        return InetAddresses.forString(buf.readUTF(Short.MAX_VALUE));
+    }
+
+    public static GameProfile createProfile(final PacketDataSerializer buf) {
+        final GameProfile profile = new GameProfile(buf.readUUID(), buf.readUTF(16));
+        readProperties(buf, profile);
+        return profile;
+    }
+
+    private static void readProperties(final PacketDataSerializer 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/LoginListener.java b/src/main/java/net/minecraft/server/LoginListener.java
index 066b0dbdbc101a8235fb872c2d1e9d427dfd6bb8..ddad076c7eb6d30f2e0f187e004c9e198f7ff777 100644
--- a/src/main/java/net/minecraft/server/LoginListener.java
+++ b/src/main/java/net/minecraft/server/LoginListener.java
@@ -27,6 +27,7 @@ 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 LoginListener implements PacketLoginInListener {
 
@@ -43,6 +44,7 @@ public class LoginListener implements PacketLoginInListener {
     private SecretKey loginKey;
     private EntityPlayer l;
     public String hostname = ""; // CraftBukkit - add field
+    private int velocityLoginMessageId = -1; // Paper - Velocity support
 
     public LoginListener(MinecraftServer minecraftserver, NetworkManager networkmanager) {
         this.g = LoginListener.EnumProtocolState.HELLO;
@@ -194,6 +196,14 @@ public class LoginListener implements PacketLoginInListener {
             this.g = LoginListener.EnumProtocolState.KEY;
             this.networkManager.sendPacket(new PacketLoginOutEncryptionBegin("", this.server.getKeyPair().getPublic().getEncoded(), this.e));
         } else {
+            // Paper start - Velocity support
+            if (com.destroystokyo.paper.PaperConfig.velocitySupport) {
+                this.velocityLoginMessageId = java.util.concurrent.ThreadLocalRandom.current().nextInt();
+                PacketLoginOutCustomPayload packet = new PacketLoginOutCustomPayload(this.velocityLoginMessageId, com.destroystokyo.paper.proxy.VelocityProxy.PLAYER_INFO_CHANNEL, new PacketDataSerializer(Unpooled.EMPTY_BUFFER));
+                this.networkManager.sendPacket(packet);
+                return;
+            }
+            // Paper end
             // Spigot start
             // Paper start - Cache authenticator threads
             authenticatorPool.execute(new Runnable() {
@@ -295,6 +305,12 @@ public class LoginListener implements PacketLoginInListener {
     public class LoginHandler {
 
         public void fireEvents() throws Exception {
+                        // Paper start - Velocity support
+                        if (LoginListener.this.velocityLoginMessageId == -1 && com.destroystokyo.paper.PaperConfig.velocitySupport) {
+                            disconnect("This server requires you to connect with Velocity.");
+                            return;
+                        }
+                        // Paper end
                         String playerName = i.getName();
                         java.net.InetAddress address = ((java.net.InetSocketAddress) networkManager.getSocketAddress()).getAddress();
                         java.util.UUID uniqueId = i.getId();
@@ -342,6 +358,35 @@ public class LoginListener implements PacketLoginInListener {
     // Spigot end
 
     public void a(PacketLoginInCustomPayload packetloginincustompayload) {
+        // Paper start - Velocity support
+        if (com.destroystokyo.paper.PaperConfig.velocitySupport && packetloginincustompayload.getId() == this.velocityLoginMessageId) {
+            PacketDataSerializer buf = packetloginincustompayload.getBuf();
+            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;
+            }
+
+            this.networkManager.socketAddress = new java.net.InetSocketAddress(com.destroystokyo.paper.proxy.VelocityProxy.readAddress(buf), ((java.net.InetSocketAddress) this.networkManager.getSocketAddress()).getPort());
+
+            this.setGameProfile(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 " + i.getName(), ex);
+                }
+            });
+            return;
+        }
+        // Paper end
         this.disconnect(new ChatMessage("multiplayer.disconnect.unexpected_query_response"));
     }
 
diff --git a/src/main/java/net/minecraft/server/PacketDataSerializer.java b/src/main/java/net/minecraft/server/PacketDataSerializer.java
index 3a257d3b0a6adb4d0a43833b996d70765559eff8..8865e8e375f7cb437e5a7ff9f42a4156d8edd9e3 100644
--- a/src/main/java/net/minecraft/server/PacketDataSerializer.java
+++ b/src/main/java/net/minecraft/server/PacketDataSerializer.java
@@ -178,6 +178,7 @@ public class PacketDataSerializer extends ByteBuf {
         return this.d(oenum.ordinal());
     }
 
+    public int readVarInt() { return i(); } // Paper - OBFHELPER
     public int i() {
         int i = 0;
         int j = 0;
@@ -218,6 +219,7 @@ public class PacketDataSerializer extends ByteBuf {
         return this;
     }
 
+    public UUID readUUID() { return k(); } // Paper - OBFHELPER
     public UUID k() {
         return new UUID(this.readLong(), this.readLong());
     }
@@ -345,6 +347,7 @@ public class PacketDataSerializer extends ByteBuf {
         }
     }
 
+    public String readUTF(int maxLength) { return this.e(maxLength); } // Paper - OBFHELPER
     public String e(int i) {
         int j = this.i();
 
diff --git a/src/main/java/net/minecraft/server/PacketLoginInCustomPayload.java b/src/main/java/net/minecraft/server/PacketLoginInCustomPayload.java
index 4d1f44139535cae0df90615d29121ff85cc964de..c1ca6f950162f53ebcb16efabb3064809472673f 100644
--- a/src/main/java/net/minecraft/server/PacketLoginInCustomPayload.java
+++ b/src/main/java/net/minecraft/server/PacketLoginInCustomPayload.java
@@ -4,8 +4,8 @@ import java.io.IOException;
 
 public class PacketLoginInCustomPayload implements Packet<PacketLoginInListener> {
 
-    private int a;
-    private PacketDataSerializer b;
+    private int a; public int getId() { return a; } // Paper - OBFHELPER
+    private PacketDataSerializer b; public PacketDataSerializer getBuf() { return b; } // Paper - OBFHELPER
 
     public PacketLoginInCustomPayload() {}
 
diff --git a/src/main/java/net/minecraft/server/PacketLoginOutCustomPayload.java b/src/main/java/net/minecraft/server/PacketLoginOutCustomPayload.java
index b52e8b72eaee87e227b7cc2fd66101550262cb7e..990cfea6c2339cd3cf688e4645de76dcee1d351a 100644
--- a/src/main/java/net/minecraft/server/PacketLoginOutCustomPayload.java
+++ b/src/main/java/net/minecraft/server/PacketLoginOutCustomPayload.java
@@ -10,6 +10,14 @@ public class PacketLoginOutCustomPayload implements Packet<PacketLoginOutListene
 
     public PacketLoginOutCustomPayload() {}
 
+    // Paper start
+    public PacketLoginOutCustomPayload(int id, MinecraftKey channel, PacketDataSerializer buf) {
+        this.a = id;
+        this.b = channel;
+        this.c = buf;
+    }
+    // Paper end
+
     @Override
     public void a(PacketDataSerializer packetdataserializer) throws IOException {
         this.a = packetdataserializer.i();
diff --git a/src/main/java/org/bukkit/craftbukkit/CraftServer.java b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
index 82fe3ab9c5e05bd372f6c5721758742f866f3605..04d53310998fdb21636810b8e7dd9c359691090c 100644
--- a/src/main/java/org/bukkit/craftbukkit/CraftServer.java
+++ b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
@@ -685,7 +685,7 @@ 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");