Paper/Spigot-Server-Patches/0398-Add-Velocity-IP-Forwarding-Support.patch

From 42fb8acb4a8019d8f865997a568de0a6a1398c0b 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 35216672..70f650bb 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;
@@ -256,7 +257,7 @@ 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;
@@ -443,4 +444,18 @@ public class PaperConfig {
             }
         }
     }
+
+    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 00000000..fdd8708f
--- /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 5778a520..b6a3992a 100644
--- a/src/main/java/net/minecraft/server/LoginListener.java
+++ b/src/main/java/net/minecraft/server/LoginListener.java
@@ -43,6 +43,7 @@ public class LoginListener implements PacketLoginInListener, ITickable {
     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;
@@ -187,6 +188,14 @@ public class LoginListener implements PacketLoginInListener, ITickable {
             this.g = LoginListener.EnumProtocolState.KEY;
             this.networkManager.sendPacket(new PacketLoginOutEncryptionBegin("", this.server.E().getPublic(), 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(io.netty.buffer.Unpooled.EMPTY_BUFFER));
+                this.networkManager.sendPacket(packet);
+                return;
+            }
+            // Paper end
             // Spigot start
             // Paper start - Cache authenticator threads
             authenticatorPool.execute(new Runnable() {
@@ -278,6 +287,12 @@ public class LoginListener implements PacketLoginInListener, ITickable {
     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();
@@ -325,6 +340,35 @@ public class LoginListener implements PacketLoginInListener, ITickable {
     // 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.setSpoofedRemoteAddress(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", new Object[0]));
     }
 
diff --git a/src/main/java/net/minecraft/server/NetworkManager.java b/src/main/java/net/minecraft/server/NetworkManager.java
index b2afec5e..97a9dffe 100644
--- a/src/main/java/net/minecraft/server/NetworkManager.java
+++ b/src/main/java/net/minecraft/server/NetworkManager.java
@@ -48,7 +48,7 @@ public class NetworkManager extends SimpleChannelInboundHandler<Packet<?>> {
     private final ReentrantReadWriteLock j = new ReentrantReadWriteLock();
     public Channel channel;
     // Spigot Start // PAIL
-    public SocketAddress l;
+    public SocketAddress l; public void setSpoofedRemoteAddress(SocketAddress address) { this.l = address; } // Paper - OBFHELPER
     public java.util.UUID spoofedUUID;
     public com.mojang.authlib.properties.Property[] spoofedProfile;
     public boolean preparing = true;
diff --git a/src/main/java/net/minecraft/server/PacketDataSerializer.java b/src/main/java/net/minecraft/server/PacketDataSerializer.java
index cab83748..fb6e373f 100644
--- a/src/main/java/net/minecraft/server/PacketDataSerializer.java
+++ b/src/main/java/net/minecraft/server/PacketDataSerializer.java
@@ -140,6 +140,7 @@ public class PacketDataSerializer extends ByteBuf {
         return this.d(oenum.ordinal());
     }
 
+    public int readVarInt() { return this.g(); } // Paper - OBFHELPER
     public int g() {
         int i = 0;
         int j = 0;
@@ -180,6 +181,7 @@ public class PacketDataSerializer extends ByteBuf {
         return this;
     }
 
+    public UUID readUUID() { return this.i(); } // Paper - OBFHELPER
     public UUID i() {
         return new UUID(this.readLong(), this.readLong());
     }
@@ -298,6 +300,7 @@ public class PacketDataSerializer extends ByteBuf {
         }
     }
 
+    public String readUTF(int maxLength) { return this.e(maxLength); } // Paper - OBFHELPER
     public String e(int i) {
         int j = this.g();
 
diff --git a/src/main/java/net/minecraft/server/PacketLoginInCustomPayload.java b/src/main/java/net/minecraft/server/PacketLoginInCustomPayload.java
index e3c0094f..edfd4a50 100644
--- a/src/main/java/net/minecraft/server/PacketLoginInCustomPayload.java
+++ b/src/main/java/net/minecraft/server/PacketLoginInCustomPayload.java
@@ -3,8 +3,8 @@ package net.minecraft.server;
 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 9c5559ec..9de0421b 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
+
     public void a(PacketDataSerializer packetdataserializer) throws IOException {
         this.a = packetdataserializer.g();
         this.b = packetdataserializer.l();
-- 
2.19.1