anatol / devmapper.go Goto Github PK

func myJourney(vol *luks.Volume) {
	tb, e1 := asTable(vol)
	dvol, e2 := devmapper.OpenUserspaceVolume(os.O_RDONLY, 0, tb)
	buf := make([]byte, vol.StorageSectorSize*1234)
	_, e3 := dvol.ReadAt(buf, 0)
// ... works perfectly for crypt devices without integrity.

}


var flagsKernelNames = map[string]string{
	luks.FlagAllowDiscards:       devmapper.CryptFlagAllowDiscards,
	luks.FlagSameCPUCrypt:        devmapper.CryptFlagSameCPUCrypt,
	luks.FlagSubmitFromCryptCPUs: devmapper.CryptFlagSubmitFromCryptCPUs,
	luks.FlagNoReadWorkqueue:     devmapper.CryptFlagNoReadWorkqueue,
	luks.FlagNoWriteWorkqueue:    devmapper.CryptFlagNoWriteWorkqueue,
}

func asTable(v *luks.Volume) (*devmapper.CryptTable, error) {
	kernelFlags := make([]string, 0, len(v.Flags))
	for _, f := range v.Flags {
		flag, ok := flagsKernelNames[f]
		if !ok {
			return nil, fmt.Errorf("unknown LUKS flag: %v", f)
		}
		kernelFlags = append(kernelFlags, flag)
	}

	if v.StorageSize%v.StorageSectorSize != 0 {
		return nil, fmt.Errorf("storage size must be multiple of sector size")
	}
	if v.StorageOffset%v.StorageSectorSize != 0 {
		return nil, fmt.Errorf("offset must be multiple of sector size")
	}

	volKey := fieldByName(*v, "key").Interface().([]byte) // This is actually AES key + integrity key

	return &devmapper.CryptTable{
		Start:         0,
		Length:        v.StorageSize,
		BackendDevice: v.BackingDevice,
		BackendOffset: v.StorageOffset,
		Encryption:    v.StorageEncryption,
		Key:           volKey[:64], // This hack wont work, even if I'm extracting the AES key
		IVTweak:       v.StorageIvTweak,
		Flags:         kernelFlags,
		SectorSize:    v.StorageSectorSize,
	}, nil
}

// not important, just hack to extract non-exported field values.
func fieldByName(obj any, name string) reflect.Value {
	origObj := reflect.ValueOf(obj)
	refObj := reflect.New(origObj.Type()).Elem()
	refObj.Set(origObj)
	refField := refObj.FieldByName(name)
	return reflect.
		NewAt(refField.Type(), unsafe.Pointer(refField.UnsafeAddr())).
		Elem()
}