make DHT dos mitigation parameters configurable via dht_settings

include/libtorrent/kademlia/dos_blocker.hpp

@@ -36,12 +36,13 @@ POSSIBILITY OF SUCH DAMAGE.
 #include "libtorrent/config.hpp"
 #include "libtorrent/time.hpp"
 #include "libtorrent/address.hpp"
+#include "libtorrent/assert.hpp"
 
 namespace libtorrent { namespace dht
 {
 
-// this is a class that maintains a list of abusive DHT nodes,
-// blocking their access to our DHT node.
+	// this is a class that maintains a list of abusive DHT nodes,
+	// blocking their access to our DHT node.
 	struct TORRENT_EXTRA_EXPORT dos_blocker
 	{
 		dos_blocker();
@@ -51,6 +52,18 @@ namespace libtorrent { namespace dht
 		// it's blocked
 		bool incoming(address addr, ptime now);
 
+		void set_rate_limit(int l)
+		{
+			TORRENT_ASSERT(l > 0);
+			m_message_rate_limit = l;
+		}
+
+		void set_block_timer(int t)
+		{
+			TORRENT_ASSERT(t > 0);
+			m_block_timeout = t;
+		}
+
 	private:
 	
 		// used to ignore abusive dht nodes
@@ -64,12 +77,17 @@ namespace libtorrent { namespace dht
 
 		enum { num_ban_nodes = 20 };
 
+		// the max number of packets we can receive per second from a node before
+		// we block it.
+		int m_message_rate_limit;
+
+		// the number of seconds a node gets blocked for when it exceeds the rate
+		// limit
+		int m_block_timeout;
+
 		node_ban_entry m_ban_nodes[num_ban_nodes];
-
 	};
-
-}
-}
+}}
 
 #endif
 

include/libtorrent/session_settings.hpp

@@ -1495,6 +1495,8 @@ namespace libtorrent
 			, privacy_lookups(false)
 			, enforce_node_id(false)
 			, ignore_dark_internet(true)
+			, block_timeout(5 * 60)
+			, block_ratelimit(5)
 		{}
 		
 		// the maximum number of peers to send in a reply to ``get_peers``
@@ -1571,6 +1573,15 @@ namespace libtorrent
 		// ignore DHT messages from parts of the internet we wouldn't expect to
 		// see any traffic from
 		bool ignore_dark_internet;
+
+		// the number of seconds a DHT node is banned if it exceeds the rate
+		// limit. The rate limit is averaged over 10 seconds to allow for bursts
+		// above the limit.
+		int block_timeout;
+
+		// the max number of packets per second a DHT node is allowed to send
+		// without getting banned.
+		int block_ratelimit;
 	};
 
 

src/kademlia/dht_tracker.cpp

@@ -287,6 +287,11 @@ namespace libtorrent { namespace dht
 		if (e || m_abort) return;
 
 		m_dht.tick();
+
+		// periodically update the DOS blocker's settings from the dht_settings
+		m_blocker.set_block_timer(m_settings.block_timeout);
+		m_blocker.set_rate_limit(m_settings.block_ratelimit);
+
 		error_code ec;
 		m_refresh_timer.expires_from_now(seconds(5), ec);
 		m_refresh_timer.async_wait(

src/kademlia/dos_blocker.cpp

@@ -44,6 +44,8 @@ namespace libtorrent { namespace dht
 #endif
 
 	dos_blocker::dos_blocker()
+		: m_message_rate_limit(5)
+		, m_block_timeout(5 * 60)
 	{
 		for (int i = 0; i < num_ban_nodes; ++i)
 		{
@@ -72,28 +74,27 @@ namespace libtorrent { namespace dht
 		{
 			++match->count;
 
-			// TODO: 2 make these limits configurable
-			if (match->count >= 50)
+			if (match->count >= m_message_rate_limit * 10)
 			{
 				if (now < match->limit)
 				{
-					if (match->count == 50)
+					if (match->count == m_message_rate_limit * 10)
 					{
 #ifdef TORRENT_DHT_VERBOSE_LOGGING
 						TORRENT_LOG(dht_tracker) << " BANNING PEER [ ip: "
 							<< addr << " time: " << total_milliseconds((now - match->limit) + seconds(10)) / 1000.f
 							<< " count: " << match->count << " ]";
 #endif
-						// we've received 50 messages in less than 10 seconds from
-						// this node. Ignore it until it's silent for 5 minutes
-						match->limit = now + minutes(5);
+						// we've received too many messages in less than 10 seconds
+						// from this node. Ignore it until it's silent for 5 minutes
+						match->limit = now + seconds(m_block_timeout);
 					}
 		
 					return false;
 				}
 
-				// we got 50 messages from this peer, but it was in
-				// more than 10 seconds. Reset the counter and the timer
+				// the messages we received from this peer took more than 10
+				// seconds. Reset the counter and the timer
 				match->count = 0;
 				match->limit = now + seconds(10);
 			}
@@ -106,6 +107,5 @@ namespace libtorrent { namespace dht
 		}
 		return true;
 	}
-}
-}
+}}