limit mininal received packet size to 40 bytes

libi2pd/SSU2.cpp

@@ -283,8 +283,15 @@ namespace transport
 		// but better to find out which host were sent it and mark that router as unreachable
 		{
 			i2p::transport::transports.UpdateReceivedBytes (bytes_transferred);
+			if (bytes_transferred < SSU2_MIN_RECEIVED_PACKET_SIZE)
+			{
+				// drop too short packets
+				m_PacketsPool.ReleaseMt (packet);
+				Receive (socket);
+				return;
+			}	
 			packet->len = bytes_transferred;
-
+			
 			boost::system::error_code ec;
 			size_t moreBytes = socket.available (ec);
 			if (!ec && moreBytes)

libi2pd/SSU2.h

@@ -1,5 +1,5 @@
 /*
-* Copyright (c) 2022-2023, The PurpleI2P Project
+* Copyright (c) 2022-2024, The PurpleI2P Project
 *
 * This file is part of Purple i2pd project and licensed under BSD3
 *
@@ -27,6 +27,7 @@ namespace transport
 	const size_t SSU2_SOCKET_RECEIVE_BUFFER_SIZE = 0x1FFFF; // 128K
 	const size_t SSU2_SOCKET_SEND_BUFFER_SIZE = 0x1FFFF; // 128K
 	const size_t SSU2_MAX_NUM_INTRODUCERS = 3;
+	const size_t SSU2_MIN_RECEIVED_PACKET_SIZE = 40; // 16 byte short header + 8 byte minimum payload + 16 byte MAC
 	const int SSU2_TO_INTRODUCER_SESSION_DURATION = 3600; // 1 hour
 	const int SSU2_TO_INTRODUCER_SESSION_EXPIRATION = 4800; // 80 minutes
 	const int SSU2_KEEP_ALIVE_INTERVAL = 15; // in seconds