os,syscall: File.Stat to use file handle for directories on Windows

Updates syscall.Open to support opening directories via CreateFileW.

CreateFileW handles are more versatile than FindFirstFile handles.
They can be used in Win32 APIs like GetFileInformationByHandle and
SetFilePointerEx, which are needed by some Go APIs.

Fixes #52747
Fixes #36019

Change-Id: I26a00cef9844fb4abeeb18d2f9d854162a146651
Reviewed-on: https://go-review.googlesource.com/c/go/+/405275
Reviewed-by: Roland Shoemaker <roland@golang.org>
Reviewed-by: Patrik Nyblom <pnyb@google.com>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
Run-TryBot: Quim Muntal <quimmuntal@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

src/internal/poll/fd_windows.go

@@ -268,7 +268,6 @@ const (
 	kindNet fileKind = iota
 	kindFile
 	kindConsole
-	kindDir
 	kindPipe
 )
 
@@ -286,12 +285,10 @@ func (fd *FD) Init(net string, pollable bool) (string, error) {
 	}
 
 	switch net {
-	case "file":
+	case "file", "dir":
 		fd.kind = kindFile
 	case "console":
 		fd.kind = kindConsole
-	case "dir":
-		fd.kind = kindDir
 	case "pipe":
 		fd.kind = kindPipe
 	case "tcp", "tcp4", "tcp6",
@@ -371,8 +368,6 @@ func (fd *FD) destroy() error {
 	case kindNet:
 		// The net package uses the CloseFunc variable for testing.
 		err = CloseFunc(fd.Sysfd)
-	case kindDir:
-		err = syscall.FindClose(fd.Sysfd)
 	default:
 		err = syscall.CloseHandle(fd.Sysfd)
 	}
@@ -1008,15 +1003,6 @@ func (fd *FD) Seek(offset int64, whence int) (int64, error) {
 	return syscall.Seek(fd.Sysfd, offset, whence)
 }
 
-// FindNextFile wraps syscall.FindNextFile.
-func (fd *FD) FindNextFile(data *syscall.Win32finddata) error {
-	if err := fd.incref(); err != nil {
-		return err
-	}
-	defer fd.decref()
-	return syscall.FindNextFile(fd.Sysfd, data)
-}
-
 // Fchmod updates syscall.ByHandleFileInformation.Fileattributes when needed.
 func (fd *FD) Fchmod(mode uint32) error {
 	if err := fd.incref(); err != nil {

src/os/dir_windows.go

@@ -11,8 +11,15 @@ import (
 )
 
 func (file *File) readdir(n int, mode readdirMode) (names []string, dirents []DirEntry, infos []FileInfo, err error) {
-	if !file.isdir() {
-		return nil, nil, nil, &PathError{Op: "readdir", Path: file.name, Err: syscall.ENOTDIR}
+	// If this file has no dirinfo, create one.
+	needdata := true
+	if file.dirinfo == nil {
+		needdata = false
+		file.dirinfo, err = openDir(file.name)
+		if err != nil {
+			err = &PathError{Op: "readdir", Path: file.name, Err: err}
+			return
+		}
 	}
 	wantAll := n <= 0
 	if wantAll {
@@ -20,8 +27,8 @@ func (file *File) readdir(n int, mode readdirMode) (names []string, dirents []Di
 	}
 	d := &file.dirinfo.data
 	for n != 0 && !file.dirinfo.isempty {
-		if file.dirinfo.needdata {
-			e := file.pfd.FindNextFile(d)
+		if needdata {
+			e := syscall.FindNextFile(file.dirinfo.h, d)
 			runtime.KeepAlive(file)
 			if e != nil {
 				if e == syscall.ERROR_NO_MORE_FILES {
@@ -32,7 +39,7 @@ func (file *File) readdir(n int, mode readdirMode) (names []string, dirents []Di
 				}
 			}
 		}
-		file.dirinfo.needdata = true
+		needdata = true
 		name := syscall.UTF16ToString(d.FileName[0:])
 		if name == "." || name == ".." { // Useless names
 			continue

src/os/file.go

@@ -225,10 +225,6 @@ func (f *File) WriteAt(b []byte, off int64) (n int, err error) {
 // relative to the current offset, and 2 means relative to the end.
 // It returns the new offset and an error, if any.
 // The behavior of Seek on a file opened with O_APPEND is not specified.
-//
-// If f is a directory, the behavior of Seek varies by operating
-// system; you can seek to the beginning of the directory on Unix-like
-// operating systems, but not on Windows.
 func (f *File) Seek(offset int64, whence int) (ret int64, err error) {
 	if err := f.checkValid("seek"); err != nil {
 		return 0, err

src/os/file_windows.go

@@ -86,10 +86,14 @@ func NewFile(fd uintptr, name string) *File {
 
 // Auxiliary information if the File describes a directory
 type dirInfo struct {
-	data     syscall.Win32finddata
-	needdata bool
-	path     string
-	isempty  bool // set if FindFirstFile returns ERROR_FILE_NOT_FOUND
+	h       syscall.Handle // search handle created with FindFirstFile
+	data    syscall.Win32finddata
+	path    string
+	isempty bool // set if FindFirstFile returns ERROR_FILE_NOT_FOUND
+}
+
+func (d *dirInfo) close() error {
+	return syscall.FindClose(d.h)
 }
 
 func epipecheck(file *File, e error) {
@@ -99,17 +103,7 @@ func epipecheck(file *File, e error) {
 // On Unix-like systems, it is "/dev/null"; on Windows, "NUL".
 const DevNull = "NUL"
 
-func (f *file) isdir() bool { return f != nil && f.dirinfo != nil }
-
-func openFile(name string, flag int, perm FileMode) (file *File, err error) {
-	r, e := syscall.Open(fixLongPath(name), flag|syscall.O_CLOEXEC, syscallMode(perm))
-	if e != nil {
-		return nil, e
-	}
-	return newFile(r, name, "file"), nil
-}
-
-func openDir(name string) (file *File, err error) {
+func openDir(name string) (d *dirInfo, e error) {
 	var mask string
 
 	path := fixLongPath(name)
@@ -130,25 +124,27 @@ func openDir(name string) (file *File, err error) {
 	if e != nil {
 		return nil, e
 	}
-	d := new(dirInfo)
-	r, e := syscall.FindFirstFile(maskp, &d.data)
+	d = new(dirInfo)
+	d.h, e = syscall.FindFirstFile(maskp, &d.data)
 	if e != nil {
 		// FindFirstFile returns ERROR_FILE_NOT_FOUND when
 		// no matching files can be found. Then, if directory
 		// exists, we should proceed.
-		if e != syscall.ERROR_FILE_NOT_FOUND {
-			return nil, e
-		}
+		// If FindFirstFile failed because name does not point
+		// to a directory, we should return ENOTDIR.
 		var fa syscall.Win32FileAttributeData
-		pathp, e := syscall.UTF16PtrFromString(path)
-		if e != nil {
+		pathp, e1 := syscall.UTF16PtrFromString(path)
+		if e1 != nil {
 			return nil, e
 		}
-		e = syscall.GetFileAttributesEx(pathp, syscall.GetFileExInfoStandard, (*byte)(unsafe.Pointer(&fa)))
-		if e != nil {
+		e1 = syscall.GetFileAttributesEx(pathp, syscall.GetFileExInfoStandard, (*byte)(unsafe.Pointer(&fa)))
+		if e1 != nil {
 			return nil, e
 		}
 		if fa.FileAttributes&syscall.FILE_ATTRIBUTE_DIRECTORY == 0 {
+			return nil, syscall.ENOTDIR
+		}
+		if e != syscall.ERROR_FILE_NOT_FOUND {
 			return nil, e
 		}
 		d.isempty = true
@@ -157,12 +153,11 @@ func openDir(name string) (file *File, err error) {
 	if !isAbs(d.path) {
 		d.path, e = syscall.FullPath(d.path)
 		if e != nil {
+			d.close()
 			return nil, e
 		}
 	}
-	f := newFile(r, name, "dir")
-	f.dirinfo = d
-	return f, nil
+	return d, nil
 }
 
 // openFileNolog is the Windows implementation of OpenFile.
@@ -170,28 +165,36 @@ func openFileNolog(name string, flag int, perm FileMode) (*File, error) {
 	if name == "" {
 		return nil, &PathError{Op: "open", Path: name, Err: syscall.ENOENT}
 	}
-	r, errf := openFile(name, flag, perm)
-	if errf == nil {
-		return r, nil
-	}
-	r, errd := openDir(name)
-	if errd == nil {
-		if flag&O_WRONLY != 0 || flag&O_RDWR != 0 {
-			r.Close()
-			return nil, &PathError{Op: "open", Path: name, Err: syscall.EISDIR}
+	path := fixLongPath(name)
+	r, e := syscall.Open(path, flag|syscall.O_CLOEXEC, syscallMode(perm))
+	if e != nil {
+		// We should return EISDIR when we are trying to open a directory with write access.
+		if e == syscall.ERROR_ACCESS_DENIED && (flag&O_WRONLY != 0 || flag&O_RDWR != 0) {
+			pathp, e1 := syscall.UTF16PtrFromString(path)
+			if e1 == nil {
+				var fa syscall.Win32FileAttributeData
+				e1 = syscall.GetFileAttributesEx(pathp, syscall.GetFileExInfoStandard, (*byte)(unsafe.Pointer(&fa)))
+				if e1 == nil && fa.FileAttributes&syscall.FILE_ATTRIBUTE_DIRECTORY != 0 {
+					e = syscall.EISDIR
+				}
+			}
 		}
-		return r, nil
+		return nil, &PathError{Op: "open", Path: name, Err: e}
 	}
-	return nil, &PathError{Op: "open", Path: name, Err: errf}
+	f, e := newFile(r, name, "file"), nil
+	if e != nil {
+		return nil, &PathError{Op: "open", Path: name, Err: e}
+	}
+	return f, nil
 }
 
 func (file *file) close() error {
 	if file == nil {
 		return syscall.EINVAL
 	}
-	if file.isdir() && file.dirinfo.isempty {
-		// "special" empty directories
-		return nil
+	if file.dirinfo != nil {
+		file.dirinfo.close()
+		file.dirinfo = nil
 	}
 	var err error
 	if e := file.pfd.Close(); e != nil {
@@ -211,6 +214,12 @@ func (file *file) close() error {
 // relative to the current offset, and 2 means relative to the end.
 // It returns the new offset and an error, if any.
 func (f *File) seek(offset int64, whence int) (ret int64, err error) {
+	if f.dirinfo != nil {
+		// Free cached dirinfo, so we allocate a new one if we
+		// access this file as a directory again. See #35767 and #37161.
+		f.dirinfo.close()
+		f.dirinfo = nil
+	}
 	ret, err = f.pfd.Seek(offset, whence)
 	runtime.KeepAlive(f)
 	return ret, err

src/os/os_test.go

@@ -2564,9 +2564,6 @@ func TestUserHomeDir(t *testing.T) {
 }
 
 func TestDirSeek(t *testing.T) {
-	if runtime.GOOS == "windows" {
-		testenv.SkipFlaky(t, 36019)
-	}
 	wd, err := Getwd()
 	if err != nil {
 		t.Fatal(err)

src/os/os_windows_test.go

@@ -1252,3 +1252,28 @@ func TestWindowsReadlink(t *testing.T) {
 	mklink(t, "relfilelink", "file")
 	testReadlink(t, "relfilelink", "file")
 }
+
+func TestOpenDirTOCTOU(t *testing.T) {
+	// Check opened directories can't be renamed until the handle is closed.
+	// See issue 52747.
+	tmpdir := t.TempDir()
+	dir := filepath.Join(tmpdir, "dir")
+	if err := os.Mkdir(dir, 0777); err != nil {
+		t.Fatal(err)
+	}
+	f, err := os.Open(dir)
+	if err != nil {
+		t.Fatal(err)
+	}
+	newpath := filepath.Join(tmpdir, "dir1")
+	err = os.Rename(dir, newpath)
+	if err == nil || !errors.Is(err, windows.ERROR_SHARING_VIOLATION) {
+		f.Close()
+		t.Fatalf("Rename(%q, %q) = %v; want windows.ERROR_SHARING_VIOLATION", dir, newpath, err)
+	}
+	f.Close()
+	err = os.Rename(dir, newpath)
+	if err != nil {
+		t.Error(err)
+	}
+}

src/os/stat_windows.go

@@ -16,10 +16,6 @@ func (file *File) Stat() (FileInfo, error) {
 	if file == nil {
 		return nil, ErrInvalid
 	}
-	if file.isdir() {
-		// I don't know any better way to do that for directory
-		return Stat(file.dirinfo.path)
-	}
 	return statHandle(file.name, file.pfd.Sysfd)
 }
 

src/syscall/syscall_windows.go

@@ -371,8 +371,11 @@ func Open(path string, mode int, perm uint32) (fd Handle, err error) {
 			}
 		}
 	}
-	h, e := CreateFile(pathp, access, sharemode, sa, createmode, attrs, 0)
-	return h, e
+	if createmode == OPEN_EXISTING && access == GENERIC_READ {
+		// Necessary for opening directory handles.
+		attrs |= FILE_FLAG_BACKUP_SEMANTICS
+	}
+	return CreateFile(pathp, access, sharemode, sa, createmode, attrs, 0)
 }
 
 func Read(fd Handle, p []byte) (n int, err error) {

src/syscall/syscall_windows_test.go

@@ -15,6 +15,28 @@ import (
 	"testing"
 )
 
+func TestOpen_Dir(t *testing.T) {
+	dir := t.TempDir()
+
+	h, err := syscall.Open(dir, syscall.O_RDONLY, 0)
+	if err != nil {
+		t.Fatalf("Open failed: %v", err)
+	}
+	syscall.CloseHandle(h)
+	h, err = syscall.Open(dir, syscall.O_RDONLY|syscall.O_TRUNC, 0)
+	if err == nil {
+		t.Error("Open should have failed")
+	} else {
+		syscall.CloseHandle(h)
+	}
+	h, err = syscall.Open(dir, syscall.O_RDONLY|syscall.O_CREAT, 0)
+	if err == nil {
+		t.Error("Open should have failed")
+	} else {
+		syscall.CloseHandle(h)
+	}
+}
+
 func TestWin32finddata(t *testing.T) {
 	dir := t.TempDir()