Paper/patches/server/0272-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/proxy/VelocityProxy.java b/src/main/java/com/destroystokyo/paper/proxy/VelocityProxy.java
new file mode 100644
index 0000000000000000000000000000000000000000..980e2b4dc308adf9a6cb2596b28eaeee65d629a8
--- /dev/null
+++ b/src/main/java/com/destroystokyo/paper/proxy/VelocityProxy.java
@@ -0,0 +1,68 @@
+package com.destroystokyo.paper.proxy;
+
+import io.papermc.paper.configuration.GlobalConfiguration;
+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;
+import net.minecraft.world.entity.player.ProfilePublicKey;
+
+public class VelocityProxy {
+    private static final int SUPPORTED_FORWARDING_VERSION = 1;
+    public static final int MODERN_FORWARDING_WITH_KEY = 2;
+    public static final byte MAX_SUPPORTED_FORWARDING_VERSION = 2;
+    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(GlobalConfiguration.get().proxies.velocity.secret.getBytes(java.nio.charset.StandardCharsets.UTF_8), "HmacSHA256"));
+            final byte[] mySignature = mac.doFinal(data);
+            if (!MessageDigest.isEqual(signature, mySignature)) {
+                return false;
+            }
+        } catch (final InvalidKeyException | NoSuchAlgorithmException e) {
+            throw new AssertionError(e);
+        }
+
+        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));
+        }
+    }
+
+    public static ProfilePublicKey.Data readForwardedKey(FriendlyByteBuf buf) {
+        return new ProfilePublicKey.Data(buf);
+    }
+}
diff --git a/src/main/java/net/minecraft/server/network/ServerLoginPacketListenerImpl.java b/src/main/java/net/minecraft/server/network/ServerLoginPacketListenerImpl.java
index 1b075033f0640433341957f6e26ebe25f18928ee..8b5eddce4845619603ccfeec158d97cb86568e0d 100644
--- a/src/main/java/net/minecraft/server/network/ServerLoginPacketListenerImpl.java
+++ b/src/main/java/net/minecraft/server/network/ServerLoginPacketListenerImpl.java
@@ -69,6 +69,7 @@ public class ServerLoginPacketListenerImpl implements ServerLoginPacketListener
     @Nullable
     private ProfilePublicKey playerProfilePublicKey;
     public String hostname = ""; // CraftBukkit - add field
+    private int velocityLoginMessageId = -1; // Paper - Velocity support
 
     public ServerLoginPacketListenerImpl(MinecraftServer server, Connection connection) {
         this.state = ServerLoginPacketListenerImpl.State.HELLO;
@@ -279,6 +280,16 @@ 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 (io.papermc.paper.configuration.GlobalConfiguration.get().proxies.velocity.enabled) {
+                    this.velocityLoginMessageId = java.util.concurrent.ThreadLocalRandom.current().nextInt();
+                    net.minecraft.network.FriendlyByteBuf buf = new net.minecraft.network.FriendlyByteBuf(io.netty.buffer.Unpooled.buffer());
+                    buf.writeByte(com.destroystokyo.paper.proxy.VelocityProxy.MAX_SUPPORTED_FORWARDING_VERSION);
+                    net.minecraft.network.protocol.login.ClientboundCustomQueryPacket packet1 = new net.minecraft.network.protocol.login.ClientboundCustomQueryPacket(this.velocityLoginMessageId, com.destroystokyo.paper.proxy.VelocityProxy.PLAYER_INFO_CHANNEL, buf);
+                    this.connection.send(packet1);
+                    return;
+                }
+                // Paper end
                 // Spigot start
             // Paper start - Cache authenticator threads
             authenticatorPool.execute(new Runnable() {
@@ -388,6 +399,12 @@ public class ServerLoginPacketListenerImpl implements ServerLoginPacketListener
     public class LoginHandler {
 
         public void fireEvents() throws Exception {
+                            // Paper start - Velocity support
+                            if (ServerLoginPacketListenerImpl.this.velocityLoginMessageId == -1 && io.papermc.paper.configuration.GlobalConfiguration.get().proxies.velocity.enabled) {
+                                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();
@@ -435,6 +452,58 @@ public class ServerLoginPacketListenerImpl implements ServerLoginPacketListener
     // Spigot end
 
     public void handleCustomQueryPacket(ServerboundCustomQueryPacket packet) {
+        // Paper start - Velocity support
+        if (io.papermc.paper.configuration.GlobalConfiguration.get().proxies.velocity.enabled && packet.getTransactionId() == this.velocityLoginMessageId) {
+            net.minecraft.network.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;
+            }
+
+            int version = buf.readVarInt();
+            if (version > com.destroystokyo.paper.proxy.VelocityProxy.MAX_SUPPORTED_FORWARDING_VERSION) {
+                throw new IllegalStateException("Unsupported forwarding version " + version + ", wanted upto " + com.destroystokyo.paper.proxy.VelocityProxy.MAX_SUPPORTED_FORWARDING_VERSION);
+            }
+
+            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);
+
+            // We should already have this, but, we'll read it out anyway
+            //noinspection NonStrictComparisonCanBeEquality
+            if (version >= com.destroystokyo.paper.proxy.VelocityProxy.MODERN_FORWARDING_WITH_KEY) {
+                final ProfilePublicKey.Data forwardedKey = com.destroystokyo.paper.proxy.VelocityProxy.readForwardedKey(buf);
+                if (this.playerProfilePublicKey == null) {
+                    try {
+                        this.playerProfilePublicKey = ProfilePublicKey.createValidated(this.server.getServiceSignatureValidator(), forwardedKey);
+                    } catch (CryptException e) {
+                        this.disconnect("Unable to validate forwarded player key");
+                    }
+                }
+            }
+
+            // 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(Component.translatable("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 c2bda04775fd4406ee44ac99c56e592eca31bc9f..6a2e65401130ca885864e9952f594237d089769d 100644
--- a/src/main/java/org/bukkit/craftbukkit/CraftServer.java
+++ b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
@@ -755,7 +755,7 @@ 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 || io.papermc.paper.configuration.GlobalConfiguration.get().proxies.velocity.enabled) { // Paper - Velocity support
             return -1;
         } else {
             return this.configuration.getInt("settings.connection-throttle");