check tunnel payload size

Tunnel.cpp

@@ -482,6 +482,11 @@ namespace tunnel
 		uint16_t len = bufbe16toh(payload + TUNNEL_GATEWAY_HEADER_LENGTH_OFFSET);
 		// we make payload as new I2NP message to send
 		msg->offset += I2NP_HEADER_SIZE + TUNNEL_GATEWAY_HEADER_SIZE;
+		if (msg->offset + len > msg->len)
+		{
+			LogPrint (eLogError, "Tunnel: gateway payload ", (int)len, " exceeds message length ", (int)msg->len);
+			return;
+		}
 		msg->len = msg->offset + len;
 		auto typeID = msg->GetTypeID ();
 		LogPrint (eLogDebug, "Tunnel: gateway of ", (int) len, " bytes for tunnel ", tunnel->GetTunnelID (), ", msg type ", (int)typeID);

TunnelEndpoint.cpp

@@ -90,6 +90,11 @@ namespace tunnel
 
 				msg->offset = fragment - msg->buf;
 				msg->len = msg->offset + size;
+				if (msg->len > msg->maxLen)
+				{
+					LogPrint (eLogError, "TunnelMessage: fragment is too long ", (int)size);
+					return;
+				}
 				if (fragment + size < decrypted + TUNNEL_DATA_ENCRYPTED_SIZE)
 				{
 					// this is not last message. we have to copy it