Fix TFTP packets being dropped

src/net-ipv4.cpp

@@ -111,11 +111,25 @@ namespace Net::Ipv4
 		if (headerSize != Header::SerializedLength())
 		{
 			DEBUG_LOG(
-				"Dropped IPv4 packet (invalid buffer size %u, expected at least %u)\r\n",
+				"Dropped IPv4 header (invalid buffer size %u, expected at least %u)\r\n",
 				bufferSize,
 				headerSize);
 			return;
 		}
+		DEBUG_LOG(
+			"IPv4 { src=%08lx, dst=%08lx, len=%u, protocol=%u }\r\n",
+			header.sourceIp,
+			header.destinationIp,
+			header.totalLength,
+			static_cast<uint8_t>(header.protocol));
+		if (bufferSize < header.totalLength)
+		{
+			DEBUG_LOG(
+				"Dropped IPv4 packet (invalid buffer size %u, expected at least %u)\r\n",
+				bufferSize,
+				header.totalLength);
+			return;
+		}
 
 		// Update ARP table
 		Arp::ArpTable.insert(std::make_pair(header.sourceIp, ethernetHeader.macSource));

src/net-tftp.cpp

@@ -25,15 +25,16 @@ namespace Net::Tftp
 	Packet::Packet(const Opcode opcode) : opcode(opcode) {}
 
 	static std::unique_ptr<Packet>
-	handleTftpWriteRequest(const uint8_t* data, const size_t dataSize)
+	handleTftpWriteRequest(const uint8_t* buffer, const size_t bufferSize)
 	{
+		DEBUG_LOG("Received TFTP write request\r\n");
 		WriteReadRequestPacket packet;
-		const auto size = packet.Deserialize(data, dataSize);
+		const auto size = packet.Deserialize(buffer, bufferSize);
 		if (size == 0)
 		{
 			DEBUG_LOG(
 				"Dropped TFTP packet (invalid buffer size %u, expected at least %u)\r\n",
-				dataSize,
+				bufferSize,
 				sizeof(WriteReadRequestPacket::opcode) + 2);
 			return nullptr;
 		}
@@ -88,6 +89,7 @@ namespace Net::Tftp
 
 	static std::unique_ptr<Packet> handleTftpData(const uint8_t* buffer, size_t size)
 	{
+		DEBUG_LOG("Received TFTP data\r\n");
 		DataPacket packet;
 		const auto tftpSize = packet.Deserialize(buffer, size);
 		if (tftpSize == 0)
@@ -134,6 +136,7 @@ namespace Net::Tftp
 		const size_t reqBufferSize)
 	{
 		const auto opcode = static_cast<Opcode>(reqBuffer[0] << 8 | reqBuffer[1]);
+		DEBUG_LOG("Received TFTP %u packet\r\n", static_cast<uint16_t>(opcode));
 		std::unique_ptr<Packet> response;
 
 		const auto payloadSize = udpReqHeader.length - udpReqHeader.SerializedLength();
@@ -160,6 +163,7 @@ namespace Net::Tftp
 
 		if (response != nullptr)
 		{
+			DEBUG_LOG("Sending TFTP response\r\n");
 			Udp::Header udpRespHeader(
 				udpReqHeader.destinationPort,
 				udpReqHeader.sourcePort,
@@ -189,6 +193,10 @@ namespace Net::Tftp
 
 			USPiSendFrame(buffer, size);
 		}
+		else
+		{
+			DEBUG_LOG("TFTP response was nullptr\r\n");
+		}
 
 		// TODO Reboot the Pi when a system file was received
 	}
@@ -226,25 +234,33 @@ namespace Net::Tftp
 
 	size_t WriteReadRequestPacket::Deserialize(const uint8_t* buffer, const size_t bufferSize)
 	{
-		// Can't use SerializedLength here, as it's variable.
+		// Can't use SerializedLength here, as it's variable. Check each field separately instead.
-		// Check for each field instead.
 		size_t i = 0;
 
 		if (sizeof(Opcode) >= bufferSize - i)
 			return 0;
 		opcode = static_cast<Opcode>(buffer[i] << 8 | buffer[i + 1]);
-		i += 2;
+		i += sizeof(Opcode);
 
-		const char* filenameStr = reinterpret_cast<const char*>(buffer + i);
+		// Check if there's a null terminator within the remaining buffer
-		if (std::strlen(filenameStr) + 1 >= bufferSize - i)
+		size_t j;
+		for (j = i; j < bufferSize; j++)
+			if (buffer[j] == 0)
+				break;
+		if (j == bufferSize)
 			return 0;
-		filename = std::string(filenameStr);
+
+		filename = std::string(reinterpret_cast<const char*>(buffer + i));
 		i += filename.size() + 1;
 
-		const char* modeStr = reinterpret_cast<const char*>(buffer + i);
+		// Check if there's a null terminator within the remaining buffer
-		if (std::strlen(modeStr) + 1 >= bufferSize - i)
+		for (j = i; j < bufferSize; j++)
+			if (buffer[j] == 0)
+				break;
+		if (j == bufferSize)
 			return 0;
-		mode = std::string(modeStr);
+
+		mode = std::string(reinterpret_cast<const char*>(buffer + i));
 		i += mode.size() + 1;
 
 		return i;

src/net-udp.cpp

@@ -62,7 +62,14 @@ namespace Net::Udp
 				Header::SerializedLength());
 			return;
 		}
-		if (udpHeader.length <= bufferSize)
+
+		DEBUG_LOG(
+			"UDP { src=%u, dst=%u, len=%u, chk=%u }\r\n",
+			static_cast<uint16_t>(udpHeader.sourcePort),
+			static_cast<uint16_t>(udpHeader.destinationPort),
+			udpHeader.length,
+			udpHeader.checksum);
+		if (bufferSize < udpHeader.length)
 		{
 			DEBUG_LOG(
 				"Dropped UDP packet (invalid buffer size %u, expected at least %u)\r\n",