[service] Fix check for invalid kext handle (#1716)

* [service] Fix check for invalid kext handle

* [windows_kext] Use BTreeMap as cache structure

* [windows_kext] Fix synchronization bug

* Update windows_kext/kextinterface/kext_file.go

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

* Update windows_kext/kextinterface/kext_file.go

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

* Update windows_kext/kextinterface/kext_file.go

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

---------

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

windows_kext/kextinterface/kext_file.go

@@ -4,6 +4,8 @@
 package kextinterface
 
 import (
+	"fmt"
+
 	"golang.org/x/sys/windows"
 )
 
@@ -13,7 +15,16 @@ type KextFile struct {
 	read_slice []byte
 }
 
+// Read tries to read the supplied buffer length from the driver.
+// The data from the driver is read in chunks `len(f.buffer)` and the extra data is cached for the next call.
+// The performance penalty of calling the function with small buffers is very small.
+// The function will block until the next info packet is received from the kext.
 func (f *KextFile) Read(buffer []byte) (int, error) {
+	if err := f.IsValid(); err != nil {
+		return 0, fmt.Errorf("failed to read: %w", err)
+	}
+
+	// If no data is available from previous calls, read from kext.
 	if f.read_slice == nil || len(f.read_slice) == 0 {
 		err := f.refill_read_buffer()
 		if err != nil {
@@ -22,14 +33,19 @@ func (f *KextFile) Read(buffer []byte) (int, error) {
 	}
 
 	if len(f.read_slice) >= len(buffer) {
-		// Write all requested bytes.
+		// There is enough data to fill the requested buffer.
 		copy(buffer, f.read_slice[0:len(buffer)])
+		// Move the slice to contain the remaining data.
 		f.read_slice = f.read_slice[len(buffer):]
 	} else {
-		// Write all available bytes and read again.
+		// There is not enough data to fill the requested buffer.
+
+		// Write everything available.
 		copy(buffer[0:len(f.read_slice)], f.read_slice)
 		copiedBytes := len(f.read_slice)
 		f.read_slice = nil
+
+		// Read again.
 		_, err := f.Read(buffer[copiedBytes:])
 		if err != nil {
 			return 0, err
@@ -51,20 +67,33 @@ func (f *KextFile) refill_read_buffer() error {
 	return nil
 }
 
+// Write sends the buffer bytes to the kext. The function will block until the whole buffer is written to the kext.
 func (f *KextFile) Write(buffer []byte) (int, error) {
+	if err := f.IsValid(); err != nil {
+		return 0, fmt.Errorf("failed to write: %w", err)
+	}
 	var count uint32 = 0
 	overlapped := &windows.Overlapped{}
 	err := windows.WriteFile(f.handle, buffer, &count, overlapped)
 	return int(count), err
 }
 
+// Close closes the handle to the kext. This will cancel all active Reads and Writes.
 func (f *KextFile) Close() error {
+	if err := f.IsValid(); err != nil {
+		return fmt.Errorf("failed to close: %w", err)
+	}
 	err := windows.CloseHandle(f.handle)
-	f.handle = winInvalidHandleValue
+	f.handle = windows.InvalidHandle
 	return err
 }
 
+// deviceIOControl exists for compatibility with the old kext.
 func (f *KextFile) deviceIOControl(code uint32, inData []byte, outData []byte) (*windows.Overlapped, error) {
+	if err := f.IsValid(); err != nil {
+		return nil, fmt.Errorf("failed to send io control: %w", err)
+	}
+	// Prepare the input data
 	var inDataPtr *byte = nil
 	var inDataSize uint32 = 0
 	if inData != nil {
@@ -72,6 +101,7 @@ func (f *KextFile) deviceIOControl(code uint32, inData []byte, outData []byte) (
 		inDataSize = uint32(len(inData))
 	}
 
+	// Prepare the output data
 	var outDataPtr *byte = nil
 	var outDataSize uint32 = 0
 	if outData != nil {
@@ -79,6 +109,7 @@ func (f *KextFile) deviceIOControl(code uint32, inData []byte, outData []byte) (
 		outDataSize = uint32(len(outData))
 	}
 
+	// Make the request to the kext.
 	overlapped := &windows.Overlapped{}
 	err := windows.DeviceIoControl(f.handle,
 		code,
@@ -92,6 +123,20 @@ func (f *KextFile) deviceIOControl(code uint32, inData []byte, outData []byte) (
 	return overlapped, nil
 }
 
+// GetHandle returns the handle of the kext.
 func (f *KextFile) GetHandle() windows.Handle {
 	return f.handle
 }
+
+// IsValid checks if kext file holds a valid handle to the kext driver.
+func (f *KextFile) IsValid() error {
+	if f == nil {
+		return fmt.Errorf("nil kext file")
+	}
+
+	if f.handle == windows.Handle(0) || f.handle == windows.InvalidHandle {
+		return fmt.Errorf("invalid handle")
+	}
+
+	return nil
+}