Instead of using binary packet comparison, add a callback to the API to explicitly check whether paths should be used. Check in with this callback (if present) when learning new paths or sending initial packets.

include/ZeroTierOne.h

@@ -1097,13 +1097,42 @@ typedef int (*ZT_DataStorePutFunction)(
  * delivery. It only means that the packet appears to have been sent.
  */
 typedef int (*ZT_WirePacketSendFunction)(
-	ZT_Node *,                       /* Node */
-	void *,                          /* User ptr */
-	const struct sockaddr_storage *, /* Local address */
-	const struct sockaddr_storage *, /* Remote address */
-	const void *,                    /* Packet data */
-	unsigned int,                    /* Packet length */
-	unsigned int);                   /* TTL or 0 to use default */
+	ZT_Node *,                        /* Node */
+	void *,                           /* User ptr */
+	const struct sockaddr_storage *,  /* Local address */
+	const struct sockaddr_storage *,  /* Remote address */
+	const void *,                     /* Packet data */
+	unsigned int,                     /* Packet length */
+	unsigned int);                    /* TTL or 0 to use default */
+
+/**
+ * Function to check whether a path should be used for ZeroTier traffic
+ *
+ * Paramters:
+ *  (1) Node
+ *  (2) User pointer
+ *  (3) Local interface address
+ *  (4) Remote address
+ *
+ * This function must return nonzero (true) if the path should be used.
+ *
+ * If no path check function is specified, ZeroTier will still exclude paths
+ * that overlap with ZeroTier-assigned and managed IP address blocks. But the
+ * use of a path check function is recommended to ensure that recursion does
+ * not occur in cases where addresses are assigned by the OS or managed by
+ * an out of band mechanism like DHCP. The path check function should examine
+ * all configured ZeroTier interfaces and check to ensure that the supplied
+ * addresses will not result in ZeroTier traffic being sent over a ZeroTier
+ * interface (recursion).
+ *
+ * Obviously this is not required in configurations where this can't happen,
+ * such as network containers or embedded.
+ */
+typedef int (*ZT_PathCheckFunction)(
+	ZT_Node *,                        /* Node */
+	void *,                           /* User ptr */
+	const struct sockaddr_storage *,  /* Local address */
+	const struct sockaddr_storage *); /* Remote address */
 
 /****************************************************************************/
 /* C Node API                                                               */
@@ -1121,6 +1150,7 @@ typedef int (*ZT_WirePacketSendFunction)(
  * @param dataStoreGetFunction Function called to get objects from persistent storage
  * @param dataStorePutFunction Function called to put objects in persistent storage
  * @param virtualNetworkConfigFunction Function to be called when virtual LANs are created, deleted, or their config parameters change
+ * @param pathCheckFunction A function to check whether a path should be used for ZeroTier traffic, or NULL to allow any path
  * @param eventCallback Function to receive status updates and non-fatal error notices
  * @return OK (0) or error code if a fatal error condition has occurred
  */
@@ -1133,6 +1163,7 @@ enum ZT_ResultCode ZT_Node_new(
 	ZT_WirePacketSendFunction wirePacketSendFunction,
 	ZT_VirtualNetworkFrameFunction virtualNetworkFrameFunction,
 	ZT_VirtualNetworkConfigFunction virtualNetworkConfigFunction,
+	ZT_PathCheckFunction pathCheckFunction,
 	ZT_EventCallback eventCallback);
 
 /**

node/IncomingPacket.cpp

@@ -507,10 +507,12 @@ bool IncomingPacket::_doRENDEZVOUS(const RuntimeEnvironment *RR,const SharedPtr<
 				const unsigned int port = at<uint16_t>(ZT_PROTO_VERB_RENDEZVOUS_IDX_PORT);
 				const unsigned int addrlen = (*this)[ZT_PROTO_VERB_RENDEZVOUS_IDX_ADDRLEN];
 				if ((port > 0)&&((addrlen == 4)||(addrlen == 16))) {
+					peer->received(_localAddress,_remoteAddress,hops(),packetId(),Packet::VERB_RENDEZVOUS,0,Packet::VERB_NOP);
+
 					InetAddress atAddr(field(ZT_PROTO_VERB_RENDEZVOUS_IDX_ADDRESS,addrlen),addrlen,port);
 					TRACE("RENDEZVOUS from %s says %s might be at %s, starting NAT-t",peer->address().toString().c_str(),with.toString().c_str(),atAddr.toString().c_str());
-					peer->received(_localAddress,_remoteAddress,hops(),packetId(),Packet::VERB_RENDEZVOUS,0,Packet::VERB_NOP);
-					RR->sw->rendezvous(withPeer,_localAddress,atAddr);
+					if (RR->node->shouldUsePathForZeroTierTraffic(_localAddress,atAddr))
+						RR->sw->rendezvous(withPeer,_localAddress,atAddr);
 				} else {
 					TRACE("dropped corrupt RENDEZVOUS from %s(%s) (bad address or port)",peer->address().toString().c_str(),_remoteAddress.toString().c_str());
 				}
@@ -941,7 +943,7 @@ bool IncomingPacket::_doPUSH_DIRECT_PATHS(const RuntimeEnvironment *RR,const Sha
 			switch(addrType) {
 				case 4: {
 					InetAddress a(field(ptr,4),4,at<uint16_t>(ptr + 4));
-					if ( ((flags & 0x01) == 0) && (Path::isAddressValidForPath(a)) && (!peer->hasActivePathTo(now,a)) ) {
+					if ( ((flags & 0x01) == 0) && (Path::isAddressValidForPath(a)) && (!peer->hasActivePathTo(now,a)) && (RR->node->shouldUsePathForZeroTierTraffic(_localAddress,a)) ) {
 						if (++countPerScope[(int)a.ipScope()][0] <= ZT_PUSH_DIRECT_PATHS_MAX_PER_SCOPE_AND_FAMILY) {
 							TRACE("attempting to contact %s at pushed direct path %s",peer->address().toString().c_str(),a.toString().c_str());
 							peer->sendHELLO(_localAddress,a,now);
@@ -952,7 +954,7 @@ bool IncomingPacket::_doPUSH_DIRECT_PATHS(const RuntimeEnvironment *RR,const Sha
 				}	break;
 				case 6: {
 					InetAddress a(field(ptr,16),16,at<uint16_t>(ptr + 16));
-					if ( ((flags & 0x01) == 0) && (Path::isAddressValidForPath(a)) && (!peer->hasActivePathTo(now,a)) ) {
+					if ( ((flags & 0x01) == 0) && (Path::isAddressValidForPath(a)) && (!peer->hasActivePathTo(now,a)) && (RR->node->shouldUsePathForZeroTierTraffic(_localAddress,a)) ) {
 						if (++countPerScope[(int)a.ipScope()][1] <= ZT_PUSH_DIRECT_PATHS_MAX_PER_SCOPE_AND_FAMILY) {
 							TRACE("attempting to contact %s at pushed direct path %s",peer->address().toString().c_str(),a.toString().c_str());
 							peer->sendHELLO(_localAddress,a,now);

node/InetAddress.cpp

@@ -280,6 +280,30 @@ InetAddress InetAddress::network() const
 	return r;
 }
 
+bool InetAddress::containsAddress(const InetAddress &addr) const
+{
+	if (addr.ss_family == ss_family) {
+		switch(ss_family) {
+			case AF_INET: {
+				const unsigned int bits = netmaskBits();
+				return ( (Utils::ntoh((uint32_t)reinterpret_cast<const struct sockaddr_in *>(&addr)->sin_addr.s_addr) >> (32 - bits)) == (Utils::ntoh((uint32_t)reinterpret_cast<const struct sockaddr_in *>(this)->sin_addr.s_addr) >> (32 - bits)) );
+			}
+			case AF_INET6: {
+				const InetAddress mask(netmask());
+				const uint8_t *m = reinterpret_cast<const uint8_t *>(reinterpret_cast<const struct sockaddr_in6 *>(&mask)->sin6_addr.s6_addr);
+				const uint8_t *a = reinterpret_cast<const uint8_t *>(reinterpret_cast<const struct sockaddr_in6 *>(&addr)->sin6_addr.s6_addr);
+				const uint8_t *b = reinterpret_cast<const uint8_t *>(reinterpret_cast<const struct sockaddr_in6 *>(this)->sin6_addr.s6_addr);
+				for(unsigned int i=0;i<16;++i) {
+					if ((a[i] & m[i]) != b[i])
+						return false;
+				}
+				return true;
+			}
+		}
+	}
+	return false;
+}
+
 bool InetAddress::isNetwork() const
 	throw()
 {

node/InetAddress.hpp

@@ -325,6 +325,14 @@ struct InetAddress : public sockaddr_storage
 	 */
 	InetAddress network() const;
 
+	/**
+	 * Test whether this IP/netmask contains this address
+	 *
+	 * @param addr Address to check
+	 * @return True if this IP/netmask (route) contains this address
+	 */
+	bool containsAddress(const InetAddress &addr) const;
+
 	/**
 	 * @return True if this is an IPv4 address
 	 */

node/Node.cpp

@@ -64,6 +64,7 @@ Node::Node(
 	ZT_WirePacketSendFunction wirePacketSendFunction,
 	ZT_VirtualNetworkFrameFunction virtualNetworkFrameFunction,
 	ZT_VirtualNetworkConfigFunction virtualNetworkConfigFunction,
+	ZT_PathCheckFunction pathCheckFunction,
 	ZT_EventCallback eventCallback) :
 	_RR(this),
 	RR(&_RR),
@@ -73,6 +74,7 @@ Node::Node(
 	_wirePacketSendFunction(wirePacketSendFunction),
 	_virtualNetworkFrameFunction(virtualNetworkFrameFunction),
 	_virtualNetworkConfigFunction(virtualNetworkConfigFunction),
+	_pathCheckFunction(pathCheckFunction),
 	_eventCallback(eventCallback),
 	_networks(),
 	_networks_m(),
@@ -671,6 +673,27 @@ std::string Node::dataStoreGet(const char *name)
 	return r;
 }
 
+bool Node::shouldUsePathForZeroTierTraffic(const InetAddress &localAddress,const InetAddress &remoteAddress)
+{
+	{
+		Mutex::Lock _l(_networks_m);
+		for(std::vector< std::pair< uint64_t, SharedPtr<Network> > >::const_iterator i=_networks.begin();i!=_networks.end();++i) {
+			SharedPtr<NetworkConfig> nc(i->second->config2());
+			if (nc) {
+				for(std::vector<InetAddress>::const_iterator a(nc->staticIps().begin());a!=nc->staticIps().end();++a) {
+					if (a->containsAddress(remoteAddress)) {
+						return false;
+					}
+				}
+			}
+		}
+	}
+
+	if (_pathCheckFunction)
+		return (_pathCheckFunction(reinterpret_cast<ZT_Node *>(this),_uPtr,reinterpret_cast<const struct sockaddr_storage *>(&localAddress),reinterpret_cast<const struct sockaddr_storage *>(&remoteAddress)) != 0);
+	else return true;
+}
+
 #ifdef ZT_TRACE
 void Node::postTrace(const char *module,unsigned int line,const char *fmt,...)
 {
@@ -743,11 +766,12 @@ enum ZT_ResultCode ZT_Node_new(
 	ZT_WirePacketSendFunction wirePacketSendFunction,
 	ZT_VirtualNetworkFrameFunction virtualNetworkFrameFunction,
 	ZT_VirtualNetworkConfigFunction virtualNetworkConfigFunction,
+	ZT_PathCheckFunction pathCheckFunction,
 	ZT_EventCallback eventCallback)
 {
 	*node = (ZT_Node *)0;
 	try {
-		*node = reinterpret_cast<ZT_Node *>(new ZeroTier::Node(now,uptr,dataStoreGetFunction,dataStorePutFunction,wirePacketSendFunction,virtualNetworkFrameFunction,virtualNetworkConfigFunction,eventCallback));
+		*node = reinterpret_cast<ZT_Node *>(new ZeroTier::Node(now,uptr,dataStoreGetFunction,dataStorePutFunction,wirePacketSendFunction,virtualNetworkFrameFunction,virtualNetworkConfigFunction,pathCheckFunction,eventCallback));
 		return ZT_RESULT_OK;
 	} catch (std::bad_alloc &exc) {
 		return ZT_RESULT_FATAL_ERROR_OUT_OF_MEMORY;

node/Node.hpp

@@ -71,6 +71,7 @@ public:
 		ZT_WirePacketSendFunction wirePacketSendFunction,
 		ZT_VirtualNetworkFrameFunction virtualNetworkFrameFunction,
 		ZT_VirtualNetworkConfigFunction virtualNetworkConfigFunction,
+		ZT_PathCheckFunction pathCheckFunction,
 		ZT_EventCallback eventCallback);
 
 	~Node();
@@ -189,6 +190,13 @@ public:
 			len);
 	}
 
+	/**
+	 * @param localAddress Local address
+	 * @param remoteAddress Remote address
+	 * @return True if path should be used
+	 */
+	bool shouldUsePathForZeroTierTraffic(const InetAddress &localAddress,const InetAddress &remoteAddress);
+
 	inline SharedPtr<Network> network(uint64_t nwid) const
 	{
 		Mutex::Lock _l(_networks_m);
@@ -288,6 +296,7 @@ private:
 	ZT_WirePacketSendFunction _wirePacketSendFunction;
 	ZT_VirtualNetworkFrameFunction _virtualNetworkFrameFunction;
 	ZT_VirtualNetworkConfigFunction _virtualNetworkConfigFunction;
+	ZT_PathCheckFunction _pathCheckFunction;
 	ZT_EventCallback _eventCallback;
 
 	std::vector< std::pair< uint64_t, SharedPtr<Network> > > _networks;

node/Peer.cpp

@@ -156,7 +156,7 @@ void Peer::received(
 				}
 			}
 
-			if (!pathIsConfirmed) {
+			if ((!pathIsConfirmed)&&(RR->node->shouldUsePathForZeroTierTraffic(localAddr,remoteAddr))) {
 				if (verb == Packet::VERB_OK) {
 
 					Path *slot = (Path *)0;

service/OneService.cpp

@@ -397,6 +397,7 @@ static long SnodeDataStoreGetFunction(ZT_Node *node,void *uptr,const char *name,
 static int SnodeDataStorePutFunction(ZT_Node *node,void *uptr,const char *name,const void *data,unsigned long len,int secure);
 static int SnodeWirePacketSendFunction(ZT_Node *node,void *uptr,const struct sockaddr_storage *localAddr,const struct sockaddr_storage *addr,const void *data,unsigned int len,unsigned int ttl);
 static void SnodeVirtualNetworkFrameFunction(ZT_Node *node,void *uptr,uint64_t nwid,uint64_t sourceMac,uint64_t destMac,unsigned int etherType,unsigned int vlanId,const void *data,unsigned int len);
+static int SnodePathCheckFunction(ZT_Node *node,void *uptr,const struct sockaddr_storage *localAddr,const struct sockaddr_storage *remoteAddr);
 
 #ifdef ZT_ENABLE_CLUSTER
 static void SclusterSendFunction(void *uptr,unsigned int toMemberId,const void *data,unsigned int len);
@@ -592,6 +593,7 @@ public:
 				SnodeWirePacketSendFunction,
 				SnodeVirtualNetworkFrameFunction,
 				SnodeVirtualNetworkConfigFunction,
+				SnodePathCheckFunction,
 				SnodeEventCallback);
 
 #ifdef ZT_USE_MINIUPNPC
@@ -1393,6 +1395,22 @@ public:
 			t->second->put(MAC(sourceMac),MAC(destMac),etherType,data,len);
 	}
 
+	inline int nodePathCheckFunction(const struct sockaddr_storage *localAddr,const struct sockaddr_storage *remoteAddr)
+	{
+		Mutex::Lock _l(_taps_m);
+		for(std::map< uint64_t,EthernetTap * >::const_iterator t(_taps.begin());t!=_taps.end();++t) {
+			if (t->second) {
+				std::vector<InetAddress> ips(t->second->ips());
+				for(std::vector<InetAddress>::const_iterator i(ips.begin());i!=ips.end();++i) {
+					if (i->containsAddress(*(reinterpret_cast<const InetAddress *>(remoteAddr)))) {
+						return 0;
+					}
+				}
+			}
+		}
+		return 1;
+	}
+
 	inline void tapFrameHandler(uint64_t nwid,const MAC &from,const MAC &to,unsigned int etherType,unsigned int vlanId,const void *data,unsigned int len)
 	{
 		_node->processVirtualNetworkFrame(OSUtils::now(),nwid,from.toInt(),to.toInt(),etherType,vlanId,data,len,&_nextBackgroundTaskDeadline);
@@ -1527,6 +1545,8 @@ static int SnodeWirePacketSendFunction(ZT_Node *node,void *uptr,const struct soc
 { return reinterpret_cast<OneServiceImpl *>(uptr)->nodeWirePacketSendFunction(localAddr,addr,data,len,ttl); }
 static void SnodeVirtualNetworkFrameFunction(ZT_Node *node,void *uptr,uint64_t nwid,uint64_t sourceMac,uint64_t destMac,unsigned int etherType,unsigned int vlanId,const void *data,unsigned int len)
 { reinterpret_cast<OneServiceImpl *>(uptr)->nodeVirtualNetworkFrameFunction(nwid,sourceMac,destMac,etherType,vlanId,data,len); }
+static int SnodePathCheckFunction(ZT_Node *node,void *uptr,const struct sockaddr_storage *localAddr,const struct sockaddr_storage *remoteAddr)
+{ return reinterpret_cast<OneServiceImpl *>(uptr)->nodePathCheckFunction(localAddr,remoteAddr); }
 
 #ifdef ZT_ENABLE_CLUSTER
 static void SclusterSendFunction(void *uptr,unsigned int toMemberId,const void *data,unsigned int len)