fs: Add proper volume and path validation.

fs-utils.go

@@ -0,0 +1,56 @@
+/*
+ * Minio Cloud Storage, (C) 2016 Minio, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package main
+
+import (
+	"regexp"
+	"unicode/utf8"
+)
+
+// validVolname regexp.
+var validVolname = regexp.MustCompile(`^.{3,63}$`)
+
+// isValidVolname verifies a volname name in accordance with object
+// layer requirements.
+func isValidVolname(volname string) bool {
+	return validVolname.MatchString(volname)
+}
+
+// Keeping this as lower bound value supporting Linux, Darwin and Windows operating systems.
+const pathMax = 4096
+
+// isValidPath verifies if a path name is in accordance with FS limitations.
+func isValidPath(path string) bool {
+	// TODO: Make this FSType or Operating system specific.
+	if len(path) > pathMax || len(path) == 0 {
+		return false
+	}
+	if !utf8.ValidString(path) {
+		return false
+	}
+	return true
+}
+
+// isValidPrefix verifies where the prefix is a valid path.
+func isValidPrefix(prefix string) bool {
+	// Prefix can be empty.
+	if prefix == "" {
+		return true
+	}
+	// Verify if prefix is a valid path.
+	return isValidPath(prefix)
+}

fs.go

@@ -121,26 +121,63 @@ func checkDiskFree(diskPath string, minFreeDisk int64) (err error) {
 	return nil
 }
 
+// checkVolumeArg - will convert incoming volume names to
+// corresponding valid volume names on the backend in a platform
+// compatible way for all operating systems. If volume is not found
+// an error is generated.
+func (s fsStorage) checkVolumeArg(volume string) (string, error) {
+	if !isValidVolname(volume) {
+		return "", errInvalidArgument
+	}
+	volumeDir := filepath.Join(s.diskPath, volume)
+	_, err := os.Stat(volumeDir)
+	if err == nil {
+		return volumeDir, nil
+	}
+	if os.IsNotExist(err) {
+		var volumes []os.FileInfo
+		volumes, err = ioutil.ReadDir(s.diskPath)
+		if err != nil {
+			return volumeDir, errVolumeNotFound
+		}
+		for _, vol := range volumes {
+			if vol.IsDir() {
+				// Verify if lowercase version of the volume
+				// is equal to the incoming volume, then use the proper name.
+				if strings.ToLower(vol.Name()) == volume {
+					volumeDir = filepath.Join(s.diskPath, vol.Name())
+					return volumeDir, nil
+				}
+			}
+		}
+		return volumeDir, errVolumeNotFound
+	} else if os.IsPermission(err) {
+		return volumeDir, errVolumeAccessDenied
+	}
+	return volumeDir, err
+}
+
 // Make a volume entry.
 func (s fsStorage) MakeVol(volume string) (err error) {
-	if volume == "" {
+	volumeDir, err := s.checkVolumeArg(volume)
-		return errInvalidArgument
+	if err == nil {
-	}
+		// Volume already exists, return error.
-	if err = checkDiskFree(s.diskPath, s.minFreeDisk); err != nil {
-		return err
-	}
-
-	volumeDir := getVolumeDir(s.diskPath, volume)
-	if _, err = os.Stat(volumeDir); err == nil {
 		return errVolumeExists
 	}
 
-	// Make a volume entry.
+	// Validate if disk is free.
-	if err = os.Mkdir(volumeDir, 0700); err != nil {
+	if e := checkDiskFree(s.diskPath, s.minFreeDisk); e != nil {
-		return err
+		return e
 	}
 
-	return nil
+	// If volume not found create it.
+	if err == errVolumeNotFound {
+		// Make a volume entry.
+		return os.Mkdir(volumeDir, 0700)
+	}
+
+	// For all other errors return here.
+	return err
 }
 
 // removeDuplicateVols - remove duplicate volumes.
@@ -175,9 +212,15 @@ func (s fsStorage) ListVols() (volsInfo []VolInfo, err error) {
 			// If not directory, ignore all file types.
 			continue
 		}
+		// Volname on case sensitive fs backends can come in as
+		// capitalized, but object layer cannot consume it
+		// directly. Convert it as we see fit.
+		volName := strings.ToLower(file.Name())
+		// Modtime is used as created time.
+		createdTime := file.ModTime()
 		volInfo := VolInfo{
-			Name:    file.Name(),
+			Name:    volName,
-			Created: file.ModTime(),
+			Created: createdTime,
 		}
 		volsInfo = append(volsInfo, volInfo)
 	}
@@ -186,30 +229,13 @@ func (s fsStorage) ListVols() (volsInfo []VolInfo, err error) {
 	return volsInfo, nil
 }
 
-// getVolumeDir - will convert incoming volume names to
-// corresponding valid volume names on the backend in a platform
-// compatible way for all operating systems.
-func getVolumeDir(diskPath, volume string) string {
-	volumes, e := ioutil.ReadDir(diskPath)
-	if e != nil {
-		return volume
-	}
-	for _, vol := range volumes {
-		// Verify if lowercase version of the volume
-		// is equal to the incoming volume, then use the proper name.
-		if strings.ToLower(vol.Name()) == volume {
-			return filepath.Join(diskPath, vol.Name())
-		}
-	}
-	return filepath.Join(diskPath, volume)
-}
-
 // StatVol - get volume info.
 func (s fsStorage) StatVol(volume string) (volInfo VolInfo, err error) {
-	if volume == "" {
+	// Verify if volume is valid and it exists.
-		return VolInfo{}, errInvalidArgument
+	volumeDir, err := s.checkVolumeArg(volume)
+	if err != nil {
+		return VolInfo{}, err
 	}
-	volumeDir := getVolumeDir(s.diskPath, volume)
 	// Stat a volume entry.
 	var st os.FileInfo
 	st, err = os.Stat(volumeDir)
@@ -219,18 +245,23 @@ func (s fsStorage) StatVol(volume string) (volInfo VolInfo, err error) {
 		}
 		return VolInfo{}, err
 	}
+	// Modtime is used as created time since operating systems lack a
+	// portable way of knowing the actual created time of a directory.
+	createdTime := st.ModTime()
 	return VolInfo{
-		Name:    st.Name(),
+		Name:    volume,
-		Created: st.ModTime(),
+		Created: createdTime,
 	}, nil
 }
 
 // DeleteVol - delete a volume.
 func (s fsStorage) DeleteVol(volume string) error {
-	if volume == "" {
+	// Verify if volume is valid and it exists.
-		return errInvalidArgument
+	volumeDir, err := s.checkVolumeArg(volume)
+	if err != nil {
+		return err
 	}
-	err := os.Remove(getVolumeDir(s.diskPath, volume))
+	err = os.Remove(volumeDir)
 	if err != nil && os.IsNotExist(err) {
 		return errVolumeNotFound
 	}
@@ -281,23 +312,13 @@ var specialPrefixes = []string{
 
 // List operation.
 func (s fsStorage) ListFiles(volume, prefix, marker string, recursive bool, count int) ([]FileInfo, bool, error) {
-	if volume == "" {
+	// Verify if volume is valid and it exists.
-		return nil, true, errInvalidArgument
+	volumeDir, err := s.checkVolumeArg(volume)
+	if err != nil {
+		return nil, true, err
 	}
-
 	var fileInfos []FileInfo
 
-	volumeDir := getVolumeDir(s.diskPath, volume)
-	// Verify if volume directory exists
-	if exists, err := isDirExist(volumeDir); !exists {
-		if err == nil {
-			return nil, true, errVolumeNotFound
-		} else if os.IsNotExist(err) {
-			return nil, true, errVolumeNotFound
-		} else {
-			return nil, true, err
-		}
-	}
 	if marker != "" {
 		// Verify if marker has prefix.
 		if marker != "" && !strings.HasPrefix(marker, prefix) {
@@ -323,6 +344,7 @@ func (s fsStorage) ListFiles(volume, prefix, marker string, recursive bool, coun
 			// Prefix does not exist, not an error just respond empty list response.
 			return nil, true, nil
 		} else if strings.Contains(err.Error(), "not a directory") {
+			// Prefix exists as a file.
 			return nil, true, nil
 		}
 		// Rest errors should be treated as failure.
@@ -375,26 +397,18 @@ func (s fsStorage) ListFiles(volume, prefix, marker string, recursive bool, coun
 
 // ReadFile - read a file at a given offset.
 func (s fsStorage) ReadFile(volume string, path string, offset int64) (readCloser io.ReadCloser, err error) {
-	if volume == "" || path == "" {
+	volumeDir, err := s.checkVolumeArg(volume)
-		return nil, errInvalidArgument
+	if err != nil {
+		return nil, err
 	}
-	volumeDir := getVolumeDir(s.diskPath, volume)
+
-	// Verify if volume directory exists
+	filePath := filepath.Join(volumeDir, filepath.FromSlash(path))
-	var exists bool
-	if exists, err = isDirExist(volumeDir); !exists {
-		if err == nil {
-			return nil, errVolumeNotFound
-		} else if os.IsNotExist(err) {
-			return nil, errVolumeNotFound
-		} else {
-			return nil, err
-		}
-	}
-	filePath := filepath.Join(volumeDir, path)
 	file, err := os.Open(filePath)
 	if err != nil {
 		if os.IsNotExist(err) {
 			return nil, errFileNotFound
+		} else if os.IsPermission(err) {
+			return nil, errFileAccessDenied
 		}
 		return nil, err
 	}
@@ -416,22 +430,12 @@ func (s fsStorage) ReadFile(volume string, path string, offset int64) (readClose
 
 // CreateFile - create a file at path.
 func (s fsStorage) CreateFile(volume, path string) (writeCloser io.WriteCloser, err error) {
-	if volume == "" || path == "" {
+	volumeDir, err := s.checkVolumeArg(volume)
-		return nil, errInvalidArgument
+	if err != nil {
+		return nil, err
 	}
-	if e := checkDiskFree(s.diskPath, s.minFreeDisk); e != nil {
+	if err := checkDiskFree(s.diskPath, s.minFreeDisk); err != nil {
-		return nil, e
+		return nil, err
-	}
-	volumeDir := getVolumeDir(s.diskPath, volume)
-	// Verify if volume directory exists
-	if exists, err := isDirExist(volumeDir); !exists {
-		if err == nil {
-			return nil, errVolumeNotFound
-		} else if os.IsNotExist(err) {
-			return nil, errVolumeNotFound
-		} else {
-			return nil, err
-		}
 	}
 	filePath := filepath.Join(volumeDir, path)
 	// Verify if the file already exists and is not of regular type.
@@ -445,33 +449,26 @@ func (s fsStorage) CreateFile(volume, path string) (writeCloser io.WriteCloser,
 
 // StatFile - get file info.
 func (s fsStorage) StatFile(volume, path string) (file FileInfo, err error) {
-	if volume == "" || path == "" {
+	volumeDir, err := s.checkVolumeArg(volume)
-		return FileInfo{}, errInvalidArgument
+	if err != nil {
-	}
+		return FileInfo{}, err
-	volumeDir := getVolumeDir(s.diskPath, volume)
-	// Verify if volume directory exists
-	var exists bool
-	if exists, err = isDirExist(volumeDir); !exists {
-		if err == nil {
-			return FileInfo{}, errVolumeNotFound
-		} else if os.IsNotExist(err) {
-			return FileInfo{}, errVolumeNotFound
-		} else {
-			return FileInfo{}, err
-		}
 	}
 
-	filePath := filepath.Join(volumeDir, path)
+	filePath := filepath.Join(volumeDir, filepath.FromSlash(path))
 	st, err := os.Stat(filePath)
 	if err != nil {
+		// File is really not found.
 		if os.IsNotExist(err) {
 			return FileInfo{}, errFileNotFound
 		}
+		// File path cannot be verified since one of the parents is a file.
 		if strings.Contains(err.Error(), "not a directory") {
 			return FileInfo{}, errIsNotRegular
 		}
+		// Return all errors here.
 		return FileInfo{}, err
 	}
+	// If its a directory its not a regular file.
 	if st.Mode().IsDir() {
 		return FileInfo{}, errIsNotRegular
 	}
@@ -486,49 +483,55 @@ func (s fsStorage) StatFile(volume, path string) (file FileInfo, err error) {
 }
 
 // deleteFile - delete file path if its empty.
-func deleteFile(basePath, deletePath, volume, path string) error {
+func deleteFile(basePath, deletePath string) error {
 	if basePath == deletePath {
 		return nil
 	}
 	// Verify if the path exists.
-	pathSt, e := os.Stat(deletePath)
+	pathSt, err := os.Stat(deletePath)
-	if e != nil {
+	if err != nil {
-		return e
+		if os.IsNotExist(err) {
+			return errFileNotFound
+		} else if os.IsPermission(err) {
+			return errFileAccessDenied
+		}
+		return err
 	}
 	if pathSt.IsDir() {
 		// Verify if directory is empty.
-		empty, e := isDirEmpty(deletePath)
+		empty, err := isDirEmpty(deletePath)
-		if e != nil {
+		if err != nil {
-			return e
+			return err
 		}
 		if !empty {
 			return nil
 		}
 	}
 	// Attempt to remove path.
-	if e := os.Remove(deletePath); e != nil {
+	if err := os.Remove(deletePath); err != nil {
-		return e
+		return err
 	}
 	// Recursively go down the next path and delete again.
-	if e := deleteFile(basePath, filepath.Dir(deletePath), volume, path); e != nil {
+	if err := deleteFile(basePath, filepath.Dir(deletePath)); err != nil {
-		return e
+		return err
 	}
 	return nil
 }
 
 // DeleteFile - delete a file at path.
 func (s fsStorage) DeleteFile(volume, path string) error {
-	if volume == "" || path == "" {
+	volumeDir, err := s.checkVolumeArg(volume)
-		return errInvalidArgument
+	if err != nil {
+		return err
 	}
 
-	volumeDir := getVolumeDir(s.diskPath, volume)
-
 	// Following code is needed so that we retain "/" suffix if any in
-	// path argument. Do not use filepath.Join() since it would strip
+	// path argument.
-	// off any suffixes.
+	filePath := filepath.Join(volumeDir, filepath.FromSlash(path))
-	filePath := s.diskPath + string(os.PathSeparator) + volume + string(os.PathSeparator) + path
+	if strings.HasSuffix(filepath.FromSlash(path), string(os.PathSeparator)) {
+		filePath = filePath + string(os.PathSeparator)
+	}
 
 	// Delete file and delete parent directory as well if its empty.
-	return deleteFile(volumeDir, filePath, volume, path)
+	return deleteFile(volumeDir, filePath)
 }

object-api-multipart.go

@@ -22,7 +22,6 @@ import (
 	"fmt"
 	"io"
 	"path"
-	"path/filepath"
 	"strconv"
 	"strings"
 
@@ -111,10 +110,13 @@ func (o objectAPI) ListMultipartUploads(bucket, prefix, keyMarker, uploadIDMarke
 	}
 	result.IsTruncated = true
 	newMaxUploads := 0
-	prefixPath := bucket + slashPathSeparator + prefix // do not use filepath.Join so that we retain trailing '/' if any
+	prefixPath := path.Join(bucket, prefix)
-
+	if strings.HasSuffix(prefix, slashPathSeparator) {
+		// Add back the slash separator removed after 'path.Join'.
+		prefixPath = prefixPath + slashPathSeparator
+	}
 	if recursive {
-		keyMarkerPath := filepath.Join(keyMarker, uploadIDMarker)
+		keyMarkerPath := path.Join(keyMarker, uploadIDMarker)
 	outerLoop:
 		for {
 			fileInfos, eof, e := o.storage.ListFiles(minioMetaVolume, prefixPath, keyMarkerPath, recursive, maxUploads-newMaxUploads)
@@ -123,17 +125,17 @@ func (o objectAPI) ListMultipartUploads(bucket, prefix, keyMarker, uploadIDMarke
 			}
 			for _, fi := range fileInfos {
 				keyMarkerPath = fi.Name
-				fileName := filepath.Base(fi.Name)
+				fileName := path.Base(fi.Name)
 				if strings.Contains(fileName, ".") {
 					// fileName contains partnumber and md5sum info, skip this.
 					continue
 				}
 				result.Uploads = append(result.Uploads, uploadMetadata{
-					Object:    filepath.Dir(fi.Name),
+					Object:    path.Dir(fi.Name),
 					UploadID:  fileName,
 					Initiated: fi.ModTime,
 				})
-				result.NextKeyMarker = filepath.Dir(fi.Name)
+				result.NextKeyMarker = path.Dir(fi.Name)
 				result.NextUploadIDMarker = fileName
 				newMaxUploads++
 				if newMaxUploads == maxUploads {
@@ -244,7 +246,7 @@ func (o objectAPI) NewMultipartUpload(bucket, object string) (string, *probe.Err
 			return "", probe.NewError(e)
 		}
 		uploadID := uuid.String()
-		uploadIDFile := filepath.Join(bucket, object, uploadID)
+		uploadIDFile := path.Join(bucket, object, uploadID)
 		if _, e = o.storage.StatFile(minioMetaVolume, uploadIDFile); e != nil {
 			if e != errFileNotFound {
 				return "", probe.NewError(e)
@@ -266,7 +268,7 @@ func (o objectAPI) NewMultipartUpload(bucket, object string) (string, *probe.Err
 }
 
 func (o objectAPI) isUploadIDExist(bucket, object, uploadID string) (bool, error) {
-	st, e := o.storage.StatFile(minioMetaVolume, filepath.Join(bucket, object, uploadID))
+	st, e := o.storage.StatFile(minioMetaVolume, path.Join(bucket, object, uploadID))
 	if e != nil {
 		if e == errFileNotFound {
 			return false, nil
@@ -291,7 +293,7 @@ func (o objectAPI) PutObjectPart(bucket, object, uploadID string, partID int, si
 	}
 
 	partSuffix := fmt.Sprintf("%s.%d.%s", uploadID, partID, md5Hex)
-	fileWriter, e := o.storage.CreateFile(minioMetaVolume, filepath.Join(bucket, object, partSuffix))
+	fileWriter, e := o.storage.CreateFile(minioMetaVolume, path.Join(bucket, object, partSuffix))
 	if e != nil {
 		if e == errVolumeNotFound {
 			return "", probe.NewError(BucketNotFound{
@@ -356,7 +358,7 @@ func (o objectAPI) ListObjectParts(bucket, object, uploadID string, partNumberMa
 	marker := ""
 	nextPartNumberMarker := 0
 	if partNumberMarker > 0 {
-		fileInfos, _, e := o.storage.ListFiles(minioMetaVolume, filepath.Join(bucket, object, uploadID)+"."+strconv.Itoa(partNumberMarker)+".", "", false, 1)
+		fileInfos, _, e := o.storage.ListFiles(minioMetaVolume, path.Join(bucket, object, uploadID)+"."+strconv.Itoa(partNumberMarker)+".", "", false, 1)
 		if e != nil {
 			return result, probe.NewError(e)
 		}
@@ -365,12 +367,12 @@ func (o objectAPI) ListObjectParts(bucket, object, uploadID string, partNumberMa
 		}
 		marker = fileInfos[0].Name
 	}
-	fileInfos, eof, e := o.storage.ListFiles(minioMetaVolume, filepath.Join(bucket, object, uploadID)+".", marker, false, maxParts)
+	fileInfos, eof, e := o.storage.ListFiles(minioMetaVolume, path.Join(bucket, object, uploadID)+".", marker, false, maxParts)
 	if e != nil {
 		return result, probe.NewError(InvalidPart{})
 	}
 	for _, fileInfo := range fileInfos {
-		fileName := filepath.Base(fileInfo.Name)
+		fileName := path.Base(fileInfo.Name)
 		splitResult := strings.Split(fileName, ".")
 		partNum, e := strconv.Atoi(splitResult[1])
 		if e != nil {
@@ -415,7 +417,7 @@ func (o objectAPI) CompleteMultipartUpload(bucket string, object string, uploadI
 	for _, part := range parts {
 		partSuffix := fmt.Sprintf("%s.%d.%s", uploadID, part.PartNumber, part.ETag)
 		var fileReader io.ReadCloser
-		fileReader, e = o.storage.ReadFile(minioMetaVolume, filepath.Join(bucket, object, partSuffix), 0)
+		fileReader, e = o.storage.ReadFile(minioMetaVolume, path.Join(bucket, object, partSuffix), 0)
 		if e != nil {
 			return ObjectInfo{}, probe.NewError(e)
 		}
@@ -456,7 +458,8 @@ func (o objectAPI) removeMultipartUpload(bucket, object, uploadID string) *probe
 	}
 	marker := ""
 	for {
-		fileInfos, eof, e := o.storage.ListFiles(minioMetaVolume, filepath.Join(bucket, object, uploadID), marker, false, 1000)
+		uploadIDFile := path.Join(bucket, object, uploadID)
+		fileInfos, eof, e := o.storage.ListFiles(minioMetaVolume, uploadIDFile, marker, false, 1000)
 		if e != nil {
 			return probe.NewError(ObjectNotFound{Bucket: bucket, Object: object})
 		}

object-api.go

@@ -80,10 +80,15 @@ func (o objectAPI) ListBuckets() ([]BucketInfo, *probe.Error) {
 		return nil, probe.NewError(e)
 	}
 	for _, vol := range vols {
+		// StorageAPI can send volume names which are incompatible
+		// with buckets, handle it and skip them.
 		if !IsValidBucketName(vol.Name) {
 			continue
 		}
-		bucketInfos = append(bucketInfos, BucketInfo{vol.Name, vol.Created})
+		bucketInfos = append(bucketInfos, BucketInfo{
+			Name:    vol.Name,
+			Created: vol.Created,
+		})
 	}
 	return bucketInfos, nil
 }

object-handlers.go

@@ -1012,7 +1012,6 @@ func (api objectAPIHandlers) CompleteMultipartUploadHandler(w http.ResponseWrite
 		writeErrorResponse(w, r, ErrInternalError, r.URL.Path)
 		return
 	}
-	fmt.Println(string(completeMultipartBytes))
 	complMultipartUpload := &completeMultipartUpload{}
 	if e = xml.Unmarshal(completeMultipartBytes, complMultipartUpload); e != nil {
 		errorIf(probe.NewError(e), "XML Unmarshal failed", nil)

object-utils.go

@@ -18,6 +18,7 @@ package main
 
 import (
 	"regexp"
+	"strings"
 	"unicode/utf8"
 )
 
@@ -41,7 +42,27 @@ func IsValidBucketName(bucket string) bool {
 // IsValidObjectName verifies an object name in accordance with Amazon's
 // requirements. It cannot exceed 1024 characters and must be a valid UTF8
 // string.
-// See: http://docs.aws.amazon.com/AmazonS3/latest/dev/UsingMetadata.html
+//
+// See:
+// http://docs.aws.amazon.com/AmazonS3/latest/dev/UsingMetadata.html
+//
+// You should avoid the following characters in a key name because of
+// significant special handling for consistency across all
+// applications.
+//
+// Rejects strings with following characters.
+//
+// - Backslash ("\")
+// - Left curly brace ("{")
+// - Caret ("^")
+// - Right curly brace ("}")
+// - Grave accent / back tick ("`")
+// - Right square bracket ("]")
+// - Left square bracket ("[")
+// - Tilde ("~")
+// - 'Greater Than' symbol (">")
+// - 'Less Than' symbol ("<")
+// - Vertical bar / pipe ("|")
 func IsValidObjectName(object string) bool {
 	if len(object) > 1024 || len(object) == 0 {
 		return false
@@ -49,7 +70,8 @@ func IsValidObjectName(object string) bool {
 	if !utf8.ValidString(object) {
 		return false
 	}
-	return true
+	// Reject unsupported characters in object name.
+	return !strings.ContainsAny(object, "`^*{}[]|\\\"'")
 }
 
 // IsValidObjectPrefix verifies whether the prefix is a valid object name.

server_test.go

@@ -1172,6 +1172,7 @@ func (s *MyAPISuite) TestValidateObjectMultipartUploadID(c *C) {
 	c.Assert(err, IsNil)
 
 	response, err = client.Do(request)
+	c.Assert(err, IsNil)
 	c.Assert(response.StatusCode, Equals, http.StatusOK)
 
 	decoder := xml.NewDecoder(response.Body)

storage-errors.go

@@ -32,3 +32,11 @@ var errIsNotRegular = errors.New("Not a regular file type.")
 
 // errVolumeNotFound - cannot find the volume.
 var errVolumeNotFound = errors.New("Volume not found.")
+
+// errVolumeAccessDenied - cannot access volume, insufficient
+// permissions.
+var errVolumeAccessDenied = errors.New("Volume access denied.")
+
+// errVolumeAccessDenied - cannot access file, insufficient
+// permissions.
+var errFileAccessDenied = errors.New("File access denied.")