Stricter Fat32 volume validation, fix Fat32 MkDir when volume name matches new directory name

filesystem/fat32/directory.go

@@ -1,6 +1,7 @@
 package fat32
 
 import (
+	"fmt"
 	"time"
 )
 
@@ -72,6 +73,10 @@ func (d *Directory) createEntry(name string, cluster uint32, dir bool) (*directo
 
 // createVolumeLabel create a volume label entry in the given directory, and return the handle to it
 func (d *Directory) createVolumeLabel(name string) (*directoryEntry, error) {
+	name, err := validateAndFormatVolumeLabel(name)
+	if err != nil {
+		return nil, fmt.Errorf("Unable to create a volume label entry: %w", err)
+	}
 	// allocate a slot for the new filename in the existing directory
 	entry := directoryEntry{
 		filenameLong:      "",

filesystem/fat32/fat32.go

@@ -1,6 +1,7 @@
 package fat32
 
 import (
+	"bytes"
 	"errors"
 	"fmt"
 	"os"
@@ -626,14 +627,36 @@ func (fs *FileSystem) Label() string {
 	return labelEntry.filenameShort + labelEntry.fileExtension
 }
 
-// SetLabel changes the filesystem label
-func (fs *FileSystem) SetLabel(volumeLabel string) error {
+// https://learn.microsoft.com/en-us/windows/win32/fileio/naming-a-file#naming-conventions
+// https://www.cs.fsu.edu/~cop4610t/assignments/project3/spec/fatspec.pdf
+func validateAndFormatVolumeLabel(volumeLabel string) (string, error) {
 	if volumeLabel == "" {
 		volumeLabel = "NO NAME"
 	}
+	if len(volumeLabel) > 11 {
+		return "", fmt.Errorf("Volume label |%s| must be less than 11 characters, got %d", volumeLabel, len(volumeLabel))
+	}
 
-	// ensure the volumeLabel is proper sized
-	volumeLabel = fmt.Sprintf("%-11.11s", volumeLabel)
+	// The following characters are not legal in any bytes of DIR_Name:
+	// • Values less than 0x20 except for the special case of 0x05 in DIR_Name[0] described above.
+	// TODO
+	// • 0x22, 0x2A, 0x2B, 0x2C, 0x2E, 0x2F, 0x3A, 0x3B, 0x3C, 0x3D, 0x3E, 0x3F, 0x5B, 0x5C, 0x5D,
+	// and 0x7C.
+	invalidBytes := string([]byte{0x22, 0x2A, 0x2B, 0x2C, 0x2E, 0x2F, 0x3A, 0x3B, 0x3C, 0x3D, 0x3E, 0x3F, 0x5B, 0x5C, 0x5D, 0x7C})
+	idx := bytes.IndexAny([]byte(volumeLabel), invalidBytes)
+	if idx != -1 {
+		return "", fmt.Errorf("Volume label cannot have invalid character %c", volumeLabel[idx])
+	}
+
+	return fmt.Sprintf("%-11.11s", volumeLabel), nil
+}
+
+// SetLabel changes the filesystem label
+func (fs *FileSystem) SetLabel(volumeLabel string) error {
+	volumeLabel, err := validateAndFormatVolumeLabel(volumeLabel)
+	if err != nil {
+		return fmt.Errorf("Error validating volume label %w", err)
+	}
 
 	// set the label in the superblock
 	bpb := fs.bootSector.biosParameterBlock
@@ -827,6 +850,9 @@ func (fs *FileSystem) readDirWithMkdir(p string, doMake bool) (*Directory, []*di
 		// do we have an entry whose name is the same as this name?
 		found := false
 		for _, e := range entries {
+			if e.isVolumeLabel {
+				continue
+			}
 			if e.filenameLong != subp && e.filenameShort != subp && (!e.lowercaseShortname || (e.lowercaseShortname && !strings.EqualFold(e.filenameShort, subp))) {
 				continue
 			}

filesystem/fat32/fat32_internal_test.go

@@ -348,3 +348,24 @@ func TestFat32ReadDirWithMkdir(t *testing.T) {
 		}
 	}
 }
+
+func TestFat32ValidateAndFormatVolumeLabel(t *testing.T) {
+	label, err := validateAndFormatVolumeLabel("foo")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if label != "foo        " {
+		t.Fatal("invalid format")
+	}
+
+	label, err = validateAndFormatVolumeLabel("ahfkjsdhfkjshdkjfhkhsdf")
+	if err == nil {
+		t.Fatal("expected error validating input over accepted length")
+	}
+
+	label, err = validateAndFormatVolumeLabel("*")
+	if err == nil {
+		t.Fatal("expected error validating input with bad character")
+	}
+
+}

filesystem/fat32/fat32_test.go

@@ -106,6 +106,20 @@ func TestFat32Type(t *testing.T) {
 }
 
 func TestFat32Mkdir(t *testing.T) {
+	t.Run("Creating directory at root with the same name as volume", func(t *testing.T) {
+		f, err := os.CreateTemp("", "*")
+		label := "boot"
+		// create an empty filesystem
+		fs, err := fat32.Create(f, 1000000, 0, 512, label)
+		if err != nil {
+			t.Fatalf("error creating fat32 filesystem: %v", err)
+		}
+		err = fs.Mkdir("/" + label)
+		if err != nil {
+			t.Fatalf("error creating directory with same name as label (%s): %v", label, err)
+		}
+	})
+
 	// only do this test if os.Getenv("TEST_IMAGE") contains a real image
 	if intImage == "" {
 		return