Check at the start of the function

Author: oss-patch

Packet++/src/UdpLayer.cpp

@@ -160,12 +160,12 @@ namespace pcpp
 
 	void UdpLayer::computeCalculateFields()
 	{
-		udphdr* udpHdr = (udphdr*)m_Data;
 		if (m_DataLen < sizeof(udphdr))
 		{
 			PCPP_LOG_ERROR("Buffer too small to calculate fields");
 			return;
 		}
+		udphdr* udpHdr = (udphdr*)m_Data;
 		udpHdr->length = htobe16(m_DataLen);
 		calculateChecksum(true);
 	}