From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001 From: Minecrell Date: Wed, 11 Oct 2017 18:22:50 +0200 Subject: [PATCH] Make legacy ping handler more reliable The Minecraft server often fails to respond to old ("legacy") pings from old Minecraft versions using the protocol used before the switch to Netty in Minecraft 1.7. Due to packet fragmentation[1], we might not have all needed bytes available when the LegacyPingHandler is called. In this case, it will run into an error, remove the handler and continue using the modern protocol. This is unlikely to happen for the first two revisions of the legacy ping protocol (used in Minecraft 1.5.x and older) since the request consists of only one or two bytes, but happens frequently for the last/third revision introduced in Minecraft 1.6. It has much larger, variable packet sizes due to the inclusion of the virtual host (the hostname/port used to connect to the server). The solution[2] is simple: If we find more than two matching bytes, we buffer the remaining bytes until we have enough to fully read and respond to the request. [1]: https://netty.io/wiki/user-guide-for-4.x.html#wiki-h3-11 [2]: https://netty.io/wiki/user-guide-for-4.x.html#wiki-h4-13 diff --git a/src/main/java/net/minecraft/server/network/LegacyQueryHandler.java b/src/main/java/net/minecraft/server/network/LegacyQueryHandler.java index 33e3a81f8ec18f0ba7170d885c4717640bf40eab..738da83f82bf01bde94c956ac22525a638db3906 100644 --- a/src/main/java/net/minecraft/server/network/LegacyQueryHandler.java +++ b/src/main/java/net/minecraft/server/network/LegacyQueryHandler.java @@ -15,6 +15,7 @@ public class LegacyQueryHandler extends ChannelInboundHandlerAdapter { private static final Logger LOGGER = LogUtils.getLogger(); private final ServerInfo server; + private ByteBuf buf; // Paper public LegacyQueryHandler(ServerInfo server) { this.server = server; @@ -23,6 +24,16 @@ public class LegacyQueryHandler extends ChannelInboundHandlerAdapter { public void channelRead(ChannelHandlerContext channelhandlercontext, Object object) { ByteBuf bytebuf = (ByteBuf) object; + // Paper start - Make legacy ping handler more reliable + if (this.buf != null) { + try { + readLegacy1_6(channelhandlercontext, bytebuf); + } finally { + bytebuf.release(); + } + return; + } + // Paper end bytebuf.markReaderIndex(); boolean flag = true; @@ -34,7 +45,7 @@ public class LegacyQueryHandler extends ChannelInboundHandlerAdapter { SocketAddress socketaddress = channelhandlercontext.channel().remoteAddress(); int i = bytebuf.readableBytes(); - String s; + String s = null; // Paper org.bukkit.event.server.ServerListPingEvent event = org.bukkit.craftbukkit.event.CraftEventFactory.callServerListPingEvent(socketaddress, this.server.getMotd(), this.server.getPlayerCount(), this.server.getMaxPlayers()); // CraftBukkit if (i == 0) { @@ -47,16 +58,24 @@ public class LegacyQueryHandler extends ChannelInboundHandlerAdapter { } if (bytebuf.isReadable()) { - if (!LegacyQueryHandler.readCustomPayloadPacket(bytebuf)) { - return; + // Paper start - Replace with improved version below + if (bytebuf.readUnsignedByte() != 250) { + s = this.readLegacy1_6(channelhandlercontext, bytebuf); + if (s == null) { + return; + } } - - LegacyQueryHandler.LOGGER.debug("Ping: (1.6) from {}", socketaddress); + // if (!LegacyQueryHandler.readCustomPayloadPacket(bytebuf)) { + // return; + // } + // + // LegacyQueryHandler.LOGGER.debug("Ping: (1.6) from {}", socketaddress); + // Paper end } else { LegacyQueryHandler.LOGGER.debug("Ping: (1.4-1.5.x) from {}", socketaddress); } - s = LegacyQueryHandler.createVersion1Response(this.server, event); // CraftBukkit + if (s == null) s = LegacyQueryHandler.createVersion1Response(this.server, event); // CraftBukkit // Paper LegacyQueryHandler.sendFlushAndClose(channelhandlercontext, LegacyQueryHandler.createLegacyDisconnectPacket(channelhandlercontext.alloc(), s)); } @@ -107,6 +126,90 @@ public class LegacyQueryHandler extends ChannelInboundHandlerAdapter { } } + // Paper start + private static String readLegacyString(ByteBuf buf) { + int size = buf.readShort() * Character.BYTES; + if (!buf.isReadable(size)) { + return null; + } + + String result = buf.toString(buf.readerIndex(), size, java.nio.charset.StandardCharsets.UTF_16BE); + buf.skipBytes(size); // toString doesn't increase readerIndex automatically + return result; + } + + private String readLegacy1_6(ChannelHandlerContext ctx, ByteBuf part) { + ByteBuf buf = this.buf; + + if (buf == null) { + this.buf = buf = ctx.alloc().buffer(); + buf.markReaderIndex(); + } else { + buf.resetReaderIndex(); + } + + buf.writeBytes(part); + + if (!buf.isReadable(Short.BYTES + Short.BYTES + Byte.BYTES + Short.BYTES + Integer.BYTES)) { + return null; + } + + String s = readLegacyString(buf); + if (s == null) { + return null; + } + + if (!s.equals("MC|PingHost")) { + removeHandler(ctx); + return null; + } + + if (!buf.isReadable(Short.BYTES) || !buf.isReadable(buf.readShort())) { + return null; + } + + net.minecraft.server.MinecraftServer server = net.minecraft.server.MinecraftServer.getServer(); + int protocolVersion = buf.readByte(); + String host = readLegacyString(buf); + if (host == null) { + removeHandler(ctx); + return null; + } + int port = buf.readInt(); + + if (buf.isReadable()) { + removeHandler(ctx); + return null; + } + + buf.release(); + this.buf = null; + + LOGGER.debug("Ping: (1.6) from {}", ctx.channel().remoteAddress()); + + String response = String.format("\u00a71\u0000%d\u0000%s\u0000%s\u0000%d\u0000%d", + Byte.MAX_VALUE, server.getServerVersion(), server.getMotd(), server.getPlayerCount(), server.getMaxPlayers()); + return response; + } + + private void removeHandler(ChannelHandlerContext ctx) { + ByteBuf buf = this.buf; + this.buf = null; + + buf.resetReaderIndex(); + ctx.pipeline().remove(this); + ctx.fireChannelRead(buf); + } + + @Override + public void handlerRemoved(ChannelHandlerContext ctx) { + if (this.buf != null) { + this.buf.release(); + this.buf = null; + } + } + // Paper end + // CraftBukkit start private static String createVersion0Response(ServerInfo serverinfo, org.bukkit.event.server.ServerListPingEvent event) { return String.format(Locale.ROOT, "%s\u00a7%d\u00a7%d", event.getMotd(), event.getNumPlayers(), event.getMaxPlayers());