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 74a4593853707f5dccba597fa903e5f1194cd5c5..ba7fdf482ef8536074fcc3867d7fc142fcfe8ce8 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;
@@ -244,7 +245,7 @@ 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;
@@ -316,4 +317,21 @@ 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 (!TimingsManager.hiddenConfigs.contains("settings.velocity-support.secret")) {
+            TimingsManager.hiddenConfigs.add("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 87dcb1688d1bf1221609a410c33a8d61b0761a1f..2b46943e094544611390758664f3b2a3e2949323 100644
--- a/src/main/java/net/minecraft/server/LoginListener.java
+++ b/src/main/java/net/minecraft/server/LoginListener.java
@@ -26,6 +26,7 @@ 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 {
 
@@ -42,6 +43,7 @@ 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;
@@ -193,6 +195,14 @@ 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() {
@@ -294,6 +304,12 @@ 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();
@@ -341,6 +357,35 @@ 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 ee24acdd5e843e5421bf83bd6c069a4ecca09115..f43193c1090238f2241b878120247d1b3d0d4e57 100644
--- a/src/main/java/net/minecraft/server/PacketDataSerializer.java
+++ b/src/main/java/net/minecraft/server/PacketDataSerializer.java
@@ -164,6 +164,7 @@ 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;
@@ -204,6 +205,7 @@ public class PacketDataSerializer extends ByteBuf {
         return this;
     }
 
+    public UUID readUUID() { return k(); } // Paper - OBFHELPER
     public UUID k() {
         return new UUID(this.readLong(), this.readLong());
     }
@@ -331,6 +333,7 @@ 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 dce11770da204b09cdc2f89dceccb3cf4fae7ac6..251433b5a0560cdfca298aca45c53191b74bc403 100644
--- a/src/main/java/org/bukkit/craftbukkit/CraftServer.java
+++ b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
@@ -678,7 +678,7 @@ 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");
