Prevent recursive transit of ZeroTier packets, toward GitHub issue #56

node/AntiRecursion.hpp

@@ -0,0 +1,110 @@
+/*
+ * ZeroTier One - Global Peer to Peer Ethernet
+ * Copyright (C) 2011-2014  ZeroTier Networks LLC
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * --
+ *
+ * ZeroTier may be used and distributed under the terms of the GPLv3, which
+ * are available at: http://www.gnu.org/licenses/gpl-3.0.html
+ *
+ * If you would like to embed ZeroTier into a commercial application or
+ * redistribute it in a modified binary form, please contact ZeroTier Networks
+ * LLC. Start here: http://www.zerotier.com/
+ */
+
+#ifndef ZT_ANTIRECURSION_HPP
+#define ZT_ANTIRECURSION_HPP
+
+#include <string.h>
+#include <stdlib.h>
+
+#include "Constants.hpp"
+
+namespace ZeroTier {
+
+#define ZT_ANTIRECURSION_TAIL_LEN 256
+
+/**
+ * Filter to prevent recursion (ZeroTier-over-ZeroTier)
+ *
+ * This works by logging ZeroTier packets that we send. It's then invoked
+ * again against packets read from local Ethernet taps. If the last N
+ * bytes representing the ZeroTier packet match in the tap frame, then
+ * the frame is a re-injection of a frame that we sent and is rejected.
+ *
+ * This means that ZeroTier packets simply will not traverse ZeroTier
+ * networks, which would cause all sorts of weird problems.
+ *
+ * NOTE: this is applied to low-level packets before they are sent to
+ * SocketManager and/or sockets, not to fully assembled packets before
+ * (possible) fragmentation.
+ */
+class AntiRecursion
+{
+public:
+	AntiRecursion()
+		throw()
+	{
+		memset(_history,0,sizeof(_history));
+		_ptr = 0;
+	}
+
+	/**
+	 * Add an outgoing ZeroTier packet to the circular log
+	 *
+	 * @param data ZT packet data
+	 * @param len Length of packet
+	 */
+	inline void logOutgoingZT(const void *data,unsigned int len)
+		throw()
+	{
+		ArItem *i = &(_history[_ptr++ % ZT_ANTIRECURSION_HISTORY_SIZE]);
+		const unsigned int tl = (len > ZT_ANTIRECURSION_TAIL_LEN) ? ZT_ANTIRECURSION_TAIL_LEN : len;
+		memcpy(i->tail,((const unsigned char *)data) + (len - tl),tl);
+		i->len = tl;
+	}
+
+	/**
+	 * Check an ethernet frame from a local tap against anti-recursion history
+	 *
+	 * @param data Raw frame data
+	 * @param len Length of frame
+	 * @return True if frame is OK to be passed, false if it's a ZT frame that we sent
+	 */
+	inline bool checkEthernetFrame(const void *data,unsigned int len)
+		throw()
+	{
+		for(unsigned int h=0;h<ZT_ANTIRECURSION_HISTORY_SIZE;++h) {
+			ArItem *i = &(_history[h]);
+			if ((len >= i->len)&&(!memcmp(((const unsigned char *)data) + (len - i->len),i->tail,i->len)))
+				return false;
+		}
+		return true;
+	}
+
+private:
+	struct ArItem
+	{
+		unsigned char tail[ZT_ANTIRECURSION_TAIL_LEN];
+		unsigned int len;
+	};
+	ArItem _history[ZT_ANTIRECURSION_HISTORY_SIZE];
+	volatile unsigned int _ptr;
+};
+
+} // namespace ZeroTier
+
+#endif