fix: Bring support for symlink on regular files on NAS (#11383)

fixes #11203

cmd/os-readdir_other.go

@@ -56,6 +56,24 @@ func readDirFn(dirPath string, filter func(name string, typ os.FileMode) error)
 			return osErrToFileErr(err)
 		}
 		for _, fi := range fis {
+			if fi.Mode()&os.ModeSymlink == os.ModeSymlink {
+				fi, err = os.Stat(pathJoin(dirPath, fi.Name()))
+				if err != nil {
+					// It got deleted in the meantime, not found
+					// or returns too many symlinks ignore this
+					// file/directory.
+					if osIsNotExist(err) || isSysErrPathNotFound(err) ||
+						isSysErrTooManySymlinks(err) {
+						continue
+					}
+					return err
+				}
+
+				// Ignore symlinked directories.
+				if fi.IsDir() {
+					continue
+				}
+			}
 			if err = filter(fi.Name(), fi.Mode()); err == errDoneForNow {
 				// filtering requested to return by caller.
 				return nil
@@ -97,11 +115,26 @@ func readDirN(dirPath string, count int) (entries []string, err error) {
 			}
 		}
 		for _, fi := range fis {
-			// Not need to follow symlink.
 			if fi.Mode()&os.ModeSymlink == os.ModeSymlink {
+				fi, err = os.Stat(pathJoin(dirPath, fi.Name()))
+				if err != nil {
+					// It got deleted in the meantime, not found
+					// or returns too many symlinks ignore this
+					// file/directory.
+					if osIsNotExist(err) || isSysErrPathNotFound(err) ||
+						isSysErrTooManySymlinks(err) {
+						continue
+					}
+					return err
+				}
+
+				// Ignore symlinked directories.
+				if fi.IsDir() {
 					continue
 				}
-			if fi.Mode().IsDir() {
+			}
+
+			if fi.IsDir() {
 				// Append SlashSeparator instead of "\" so that sorting is achieved as expected.
 				entries = append(entries, fi.Name()+SlashSeparator)
 			} else if fi.Mode().IsRegular() {

cmd/os-readdir_test.go

@@ -149,7 +149,8 @@ func setupTestReadDirSymlink(t *testing.T) (testResults []result) {
 		}
 		// Add to entries.
 		entries = append(entries, name1)
-		// Symlinks are ignored.
+		// Symlinks are preserved for regular files
+		entries = append(entries, name2)
 	}
 	if err := os.MkdirAll(filepath.Join(dir, "mydir"), 0777); err != nil {
 		t.Fatalf("Unable to create \"mydir\", %s", err)

cmd/os-readdir_unix.go

@@ -123,9 +123,30 @@ func readDirFn(dirPath string, fn func(name string, typ os.FileMode) error) erro
 		if len(name) == 0 || bytes.Equal(name, []byte{'.'}) || bytes.Equal(name, []byte{'.', '.'}) {
 			continue
 		}
-		if typ&os.ModeSymlink == os.ModeSymlink {
+
+		// Fallback for filesystems (like old XFS) that don't
+		// support Dirent.Type and have DT_UNKNOWN (0) there
+		// instead.
+		if typ == unexpectedFileMode || typ&os.ModeSymlink == os.ModeSymlink {
+			fi, err := os.Stat(pathJoin(dirPath, string(name)))
+			if err != nil {
+				// It got deleted in the meantime, not found
+				// or returns too many symlinks ignore this
+				// file/directory.
+				if osIsNotExist(err) || isSysErrPathNotFound(err) ||
+					isSysErrTooManySymlinks(err) {
+					continue
+				}
+				return err
+			}
+
+			// Ignore symlinked directories.
+			if typ&os.ModeSymlink == os.ModeSymlink && fi.IsDir() {
 				continue
 			}
+
+			typ = fi.Mode() & os.ModeType
+		}
 		if err = fn(string(name), typ); err == errDoneForNow {
 			// fn() requested to return by caller.
 			return nil
@@ -176,11 +197,12 @@ func readDirN(dirPath string, count int) (entries []string, err error) {
 		if len(name) == 0 || bytes.Equal(name, []byte{'.'}) || bytes.Equal(name, []byte{'.', '.'}) {
 			continue
 		}
+
 		// Fallback for filesystems (like old XFS) that don't
 		// support Dirent.Type and have DT_UNKNOWN (0) there
 		// instead.
-		if typ == unexpectedFileMode {
+		if typ == unexpectedFileMode || typ&os.ModeSymlink == os.ModeSymlink {
-			fi, err := os.Lstat(pathJoin(dirPath, string(name)))
+			fi, err := os.Stat(pathJoin(dirPath, string(name)))
 			if err != nil {
 				// It got deleted in the meantime, not found
 				// or returns too many symlinks ignore this
@@ -191,22 +213,30 @@ func readDirN(dirPath string, count int) (entries []string, err error) {
 				}
 				return nil, err
 			}
-			typ = fi.Mode() & os.ModeType
+
-		}
+			// Ignore symlinked directories.
-		if typ&os.ModeSymlink == os.ModeSymlink {
+			if typ&os.ModeSymlink == os.ModeSymlink && fi.IsDir() {
 				continue
 			}
+
+			typ = fi.Mode() & os.ModeType
+		}
+
+		var nameStr string
 		if typ.IsRegular() {
-			entries = append(entries, string(name))
+			nameStr = string(name)
 		} else if typ.IsDir() {
 			// Use temp buffer to append a slash to avoid string concat.
 			tmp = tmp[:len(name)+1]
 			copy(tmp, name)
 			tmp[len(tmp)-1] = '/' // SlashSeparator
-			entries = append(entries, string(tmp))
+			nameStr = string(tmp)
 		}
+
 		count--
+		entries = append(entries, nameStr)
 	}
+
 	return
 }
 

cmd/os-readdir_windows.go

@@ -42,6 +42,15 @@ func readDirFn(dirPath string, filter func(name string, typ os.FileMode) error)
 	}
 	defer f.Close()
 
+	// Check if file or dir. This is the quickest way.
+	// Do not remove this check, on windows syscall.FindNextFile
+	// would throw an exception if Fd() points to a file
+	// instead of a directory, we need to quickly fail
+	// in such situations - this workadound is expected.
+	if _, err = f.Seek(0, io.SeekStart); err == nil {
+		return errFileNotFound
+	}
+
 	data := &syscall.Win32finddata{}
 	for {
 		e := syscall.FindNextFile(syscall.Handle(f.Fd()), data)
@@ -63,13 +72,33 @@ func readDirFn(dirPath string, filter func(name string, typ os.FileMode) error)
 		if name == "" || name == "." || name == ".." { // Useless names
 			continue
 		}
-		if data.FileAttributes&syscall.FILE_ATTRIBUTE_REPARSE_POINT != 0 {
+
+		var typ os.FileMode = 0 // regular file
+		switch {
+		case data.FileAttributes&syscall.FILE_ATTRIBUTE_REPARSE_POINT != 0:
+			// Reparse point is a symlink
+			fi, err := os.Stat(pathJoin(dirPath, string(name)))
+			if err != nil {
+				// It got deleted in the meantime, not found
+				// or returns too many symlinks ignore this
+				// file/directory.
+				if osIsNotExist(err) || isSysErrPathNotFound(err) ||
+					isSysErrTooManySymlinks(err) {
+					continue
+				}
+				return err
+			}
+
+			if fi.IsDir() {
+				// Ignore symlinked directories.
 				continue
 			}
-		var typ os.FileMode = 0 // regular file
+
-		if data.FileAttributes&syscall.FILE_ATTRIBUTE_DIRECTORY != 0 {
+			typ = fi.Mode()
+		case data.FileAttributes&syscall.FILE_ATTRIBUTE_DIRECTORY != 0:
 			typ = os.ModeDir
 		}
+
 		if e = filter(name, typ); e == errDoneForNow {
 			// filtering requested to return by caller.
 			return nil
@@ -88,10 +117,14 @@ func readDirN(dirPath string, count int) (entries []string, err error) {
 	defer f.Close()
 
 	// Check if file or dir. This is the quickest way.
-	_, err = f.Seek(0, io.SeekStart)
+	// Do not remove this check, on windows syscall.FindNextFile
-	if err == nil {
+	// would throw an exception if Fd() points to a file
+	// instead of a directory, we need to quickly fail
+	// in such situations - this workadound is expected.
+	if _, err = f.Seek(0, io.SeekStart); err == nil {
 		return nil, errFileNotFound
 	}
+
 	data := &syscall.Win32finddata{}
 	handle := syscall.Handle(f.Fd())
 
@@ -113,15 +146,33 @@ func readDirN(dirPath string, count int) (entries []string, err error) {
 		if name == "" || name == "." || name == ".." { // Useless names
 			continue
 		}
+
 		switch {
 		case data.FileAttributes&syscall.FILE_ATTRIBUTE_REPARSE_POINT != 0:
+			// Reparse point is a symlink
+			fi, err := os.Stat(pathJoin(dirPath, string(name)))
+			if err != nil {
+				// It got deleted in the meantime, not found
+				// or returns too many symlinks ignore this
+				// file/directory.
+				if osIsNotExist(err) || isSysErrPathNotFound(err) ||
+					isSysErrTooManySymlinks(err) {
+					continue
+				}
+				return nil, err
+			}
+
+			if fi.IsDir() {
+				// directory symlinks are ignored.
 				continue
+			}
 		case data.FileAttributes&syscall.FILE_ATTRIBUTE_DIRECTORY != 0:
-			entries = append(entries, name+SlashSeparator)
+			name = name + SlashSeparator
-		default:
-			entries = append(entries, name)
 		}
+
 		count--
+		entries = append(entries, name)
+
 	}
 
 	return entries, nil

docs/gateway/nas.md

@@ -79,6 +79,23 @@ export MINIO_NOTIFY_WEBHOOK_QUEUE_DIR_1=/tmp/webhk
 
 > NOTE: Please check the docs for the corresponding ENV setting. Alternatively, We can obtain other ENVs in the form `mc admin config set alias/ <sub-sys> --env`
 
+## Symlink support
+
+NAS gateway implementation allows symlinks on regular files,
+
+### Behavior
+
+- For reads symlink resolves to file symlink points to.
+- For deletes
+  - Delete of symlink deletes the symlink but not the real file to which the symlink points.
+  - Delete of actual file automatically makes symlink'ed file invisible, dangling symlinks won't be visible.
+
+#### Caveats
+- Disallows follow of directory symlinks to avoid security issues, and leaving them as is on namespace makes them very inconsistent.
+- Dangling symlinks are ignored automatically.
+
+*Directory symlinks is not and will not be supported as there are no safe ways to handle them.*
+
 ## Explore Further
 - [`mc` command-line interface](https://docs.min.io/docs/minio-client-quickstart-guide)
 - [`aws` command-line interface](https://docs.min.io/docs/aws-cli-with-minio)