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/*
* 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 ((i->len > 0)&&(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
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