fix offset when reading and writing fat32 files to avoid overruns

Signed-off-by: Avi Deitcher <[email protected]>

filesystem/fat32/fat32_test.go

@@ -7,13 +7,17 @@ package fat32_test
 
 import (
 	"bytes"
-	"crypto/rand"
 	"fmt"
 	"io"
+	"math/rand/v2"
 	"os"
+	"path"
+	"path/filepath"
 	"strings"
 	"testing"
 
+	"github.com/diskfs/go-diskfs"
+	"github.com/diskfs/go-diskfs/disk"
 	"github.com/diskfs/go-diskfs/filesystem"
 	"github.com/diskfs/go-diskfs/filesystem/fat32"
 	"github.com/diskfs/go-diskfs/testhelper"
@@ -245,6 +249,8 @@ func TestFat32Read(t *testing.T) {
 	}
 	//nolint:thelper // this is not a helper function
 	runTest := func(t *testing.T, pre, post int64) {
+		seed := [32]byte{}
+		chacha := rand.NewChaCha8(seed)
 		for _, t2 := range tests {
 			tt := t2
 			t.Run(fmt.Sprintf("blocksize %d filesize %d bytechange %d", tt.filesize, tt.blocksize, tt.bytechange), func(t *testing.T) {
@@ -258,7 +264,7 @@ func TestFat32Read(t *testing.T) {
 				corrupted := ""
 				if tt.bytechange >= 0 {
 					b := make([]byte, 1)
-					_, _ = rand.Read(b)
+					_, _ = chacha.Read(b)
 					_, _ = f.WriteAt(b, tt.bytechange+pre)
 					corrupted = fmt.Sprintf("corrupted %d", tt.bytechange+pre)
 				}
@@ -629,14 +635,16 @@ func TestFat32OpenFile(t *testing.T) {
 			bWrite := make([]byte, size)
 			header := fmt.Sprintf("OpenFile(%s, %s)", path, getOpenMode(mode))
 			readWriter, err := fs.OpenFile(path, mode)
+			seed := [32]byte{}
+			chacha := rand.NewChaCha8(seed)
 			switch {
 			case err != nil:
 				t.Errorf("%s: unexpected error: %v", header, err)
 			case readWriter == nil:
 				t.Errorf("%s: Unexpected nil output", header)
 			default:
 				// write and then read
-				_, _ = rand.Read(bWrite)
+				_, _ = chacha.Read(bWrite)
 				written, writeErr := readWriter.Write(bWrite)
 				_, _ = readWriter.Seek(0, 0)
 				bRead, readErr := io.ReadAll(readWriter)
@@ -689,14 +697,16 @@ func TestFat32OpenFile(t *testing.T) {
 		bWrite := make([]byte, size)
 		header := fmt.Sprintf("OpenFile(%s, %s)", path, getOpenMode(mode))
 		readWriter, err := fs.OpenFile(path, mode)
+		seed := [32]byte{}
+		chacha := rand.NewChaCha8(seed)
 		switch {
 		case err != nil:
 			t.Fatalf("%s: unexpected error: %v", header, err)
 		case readWriter == nil:
 			t.Fatalf("%s: Unexpected nil output", header)
 		default:
 			// write and then read
-			_, _ = rand.Read(bWrite)
+			_, _ = chacha.Read(bWrite)
 			written, writeErr := readWriter.Write(bWrite)
 			_, _ = readWriter.Seek(0, 0)
 
@@ -765,7 +775,9 @@ func TestFat32OpenFile(t *testing.T) {
 				// success
 			}
 
-			_, _ = rand.Read(bWrite)
+			seed := [32]byte{}
+			chacha := rand.NewChaCha8(seed)
+			_, _ = chacha.Read(bWrite)
 			writeSizes := []int{512, 1024, 256}
 			low := 0
 			for i := 0; low < len(bWrite); i++ {
@@ -1058,3 +1070,83 @@ func TestOpenFileCaseInsensitive(t *testing.T) {
 		}
 	}
 }
+
+func testMkFile(fs filesystem.FileSystem, path string, size int) error {
+	rw, err := fs.OpenFile(path, os.O_CREATE|os.O_RDWR)
+	if err != nil {
+		return err
+	}
+	smallFile := make([]byte, size)
+	_, err = rw.Write(smallFile)
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+func TestCreateFileTree(t *testing.T) {
+	filename := "fat32_test"
+	tmpDir := t.TempDir()
+	tmpImgPath := filepath.Join(tmpDir, filename)
+
+	// 6GB to test large disk
+	size := int64(6 * 1024 * 1024 * 1024)
+	d, err := diskfs.Create(tmpImgPath, size, diskfs.Raw, diskfs.SectorSizeDefault)
+	if err != nil {
+		t.Fatalf("error creating disk: %v", err)
+	}
+
+	spec := disk.FilesystemSpec{
+		Partition: 0,
+		FSType:    filesystem.TypeFat32,
+	}
+	fs, err := d.CreateFilesystem(spec)
+	if err != nil {
+		t.Fatalf("error creating filesystem: %v", err)
+	}
+
+	if err := fs.Mkdir("/A"); err != nil {
+		t.Errorf("Error making dir /A in root: %v", err)
+	}
+	if err := fs.Mkdir("/b"); err != nil {
+		t.Errorf("Error making dir /b in root: %v", err)
+	}
+	if err := testMkFile(fs, "/rootfile", 11); err != nil {
+		t.Errorf("Error making microfile in root: %v", err)
+	}
+	for i := 0; i < 100; i++ {
+		dir := fmt.Sprintf("/b/sub%d", i)
+		if err := fs.Mkdir(dir); err != nil {
+			t.Errorf("Error making directory %s: %v", dir, err)
+		}
+		blobdir := path.Join(dir, "blob")
+		if err := fs.Mkdir(blobdir); err != nil {
+			t.Errorf("Error making directory %s: %v", blobdir, err)
+		}
+		file := path.Join(blobdir, "microfile")
+		if err := testMkFile(fs, file, 11); err != nil {
+			t.Errorf("Error making microfile %s: %v", file, err)
+		}
+		file = path.Join(blobdir, "randfile")
+		if err := testMkFile(fs, file, rand.IntN(73)); err != nil { // #nosec G404
+			t.Errorf("Error making random file %s: %v", file, err)
+		}
+		file = path.Join(blobdir, "smallfile")
+		if err := testMkFile(fs, file, 5*1024*1024); err != nil {
+			t.Errorf("Error making small file %s: %v", file, err)
+		}
+	}
+	file := "/b/sub49/blob/gigfile1"
+	gb := 1024 * 1024 * 1024
+	if err := testMkFile(fs, file, gb); err != nil {
+		t.Errorf("Error making gigfile1 %s: %v", file, err)
+	}
+	file = "/b/sub50/blob/gigfile1"
+	if err := testMkFile(fs, file, gb); err != nil {
+		t.Errorf("Error making gigfile1 %s: %v", file, err)
+	}
+	file = "/b/sub51/blob/gigfile1"
+	if err := testMkFile(fs, file, gb); err != nil {
+		t.Errorf("Error making gigfile1 %s: %v", file, err)
+	}
+}

filesystem/fat32/file.go

@@ -78,8 +78,8 @@ func (fl *File) Read(b []byte) (int, error) {
 		if toRead > left {
 			toRead = left
 		}
-		offset := uint32(start) + (clusters[i]-2)*uint32(bytesPerCluster)
-		_, _ = file.ReadAt(b[totalRead:totalRead+toRead], int64(offset)+fs.start)
+		offset := int64(start) + int64(clusters[i]-2)*int64(bytesPerCluster)
+		_, _ = file.ReadAt(b[totalRead:totalRead+toRead], offset+fs.start)
 		totalRead += toRead
 		if totalRead >= maxRead {
 			break
@@ -161,8 +161,8 @@ func (fl *File) Write(p []byte) (int, error) {
 		if toWrite > left {
 			toWrite = left
 		}
-		offset := uint32(start) + (clusters[i]-2)*uint32(bytesPerCluster)
-		_, err := file.WriteAt(p[totalWritten:totalWritten+toWrite], int64(offset)+fs.start)
+		offset := int64(start) + int64(clusters[i]-2)*int64(bytesPerCluster)
+		_, err := file.WriteAt(p[totalWritten:totalWritten+toWrite], offset+fs.start)
 		if err != nil {
 			return totalWritten, fmt.Errorf("unable to write to file: %v", err)
 		}