Don't limit dns wire data by size (#254)

* Don't limit dns wire data by size

* Check buffer size minimum

Author: leoparente

src/handlers/dns/DnsStreamHandler.cpp

@@ -180,26 +180,19 @@ void DnsStreamHandler::process_udp_packet_cb(pcpp::Packet &payload, PacketDirect
 
 void TcpSessionData::receive_dns_wire_data(const uint8_t *data, size_t len)
 {
-    const size_t MIN_DNS_QUERY_SIZE = 17;
-    const size_t MAX_DNS_QUERY_SIZE = 512;
-
     _buffer.append(reinterpret_cast<const char *>(data), len);
 
     for (;;) {
         std::uint16_t size;
 
-        if (_buffer.size() < sizeof(size)) {
+        // if buffer size < min DNS size, we know we need more data
+        if (_buffer.size() < MIN_DNS_QUERY_SIZE + sizeof(size)) {
             break;
         }
 
         // dns packet size is in network byte order.
         size = static_cast<unsigned char>(_buffer[1]) | static_cast<unsigned char>(_buffer[0]) << 8;
 
-        // ensure we never allocate more than max
-        if (size < MIN_DNS_QUERY_SIZE || size > MAX_DNS_QUERY_SIZE) {
-            break;
-        }
-
         if (_buffer.size() >= sizeof(size) + size) {
             auto data = std::make_unique<uint8_t[]>(size);
             std::memcpy(data.get(), _buffer.data() + sizeof(size), size);

src/handlers/dns/DnsStreamHandler.h

@@ -207,6 +207,7 @@ class DnsMetricsManager final : public visor::AbstractMetricsManager<DnsMetricsB
 class TcpSessionData final
 {
 public:
+    static constexpr size_t MIN_DNS_QUERY_SIZE = 17;
     using got_msg_cb = std::function<void(std::unique_ptr<uint8_t[]> data, size_t size)>;
 
 private: