at_windows.go

     1  // Copyright 2024 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package windows
     6  
     7  import (
     8  	"runtime"
     9  	"structs"
    10  	"syscall"
    11  	"unsafe"
    12  )
    13  
    14  // Openat flags supported by syscall.Open.
    15  const (
    16  	O_DIRECTORY = 0x04000 // target must be a directory
    17  )
    18  
    19  // Openat flags not supported by syscall.Open.
    20  //
    21  // These are invented values, use values in the 33-63 bit range
    22  // to avoid overlap with flags and attributes supported by [syscall.Open].
    23  //
    24  // When adding a new flag here, add an unexported version to
    25  // the set of invented O_ values in syscall/types_windows.go
    26  // to avoid overlap.
    27  const (
    28  	O_NOFOLLOW_ANY = 0x200000000 // disallow symlinks anywhere in the path
    29  	O_OPEN_REPARSE = 0x400000000 // FILE_OPEN_REPARSE_POINT, used by Lstat
    30  	O_WRITE_ATTRS  = 0x800000000 // FILE_WRITE_ATTRIBUTES, used by Chmod
    31  )
    32  
    33  func Openat(dirfd syscall.Handle, name string, flag uint64, perm uint32) (_ syscall.Handle, e1 error) {
    34  	if len(name) == 0 {
    35  		return syscall.InvalidHandle, syscall.ERROR_FILE_NOT_FOUND
    36  	}
    37  
    38  	var access, options uint32
    39  	switch flag & (syscall.O_RDONLY | syscall.O_WRONLY | syscall.O_RDWR) {
    40  	case syscall.O_RDONLY:
    41  		// FILE_GENERIC_READ includes FILE_LIST_DIRECTORY.
    42  		access = FILE_GENERIC_READ
    43  	case syscall.O_WRONLY:
    44  		access = FILE_GENERIC_WRITE
    45  		options |= FILE_NON_DIRECTORY_FILE
    46  	case syscall.O_RDWR:
    47  		access = FILE_GENERIC_READ | FILE_GENERIC_WRITE
    48  		options |= FILE_NON_DIRECTORY_FILE
    49  	default:
    50  		// Stat opens files without requesting read or write permissions,
    51  		// but we still need to request SYNCHRONIZE.
    52  		access = SYNCHRONIZE
    53  	}
    54  	if flag&syscall.O_CREAT != 0 {
    55  		access |= FILE_GENERIC_WRITE
    56  	}
    57  	if flag&syscall.O_APPEND != 0 {
    58  		access |= FILE_APPEND_DATA
    59  		// Remove FILE_WRITE_DATA access unless O_TRUNC is set,
    60  		// in which case we need it to truncate the file.
    61  		if flag&syscall.O_TRUNC == 0 {
    62  			access &^= FILE_WRITE_DATA
    63  		}
    64  	}
    65  	if flag&O_DIRECTORY != 0 {
    66  		options |= FILE_DIRECTORY_FILE
    67  		access |= FILE_LIST_DIRECTORY
    68  	}
    69  	if flag&syscall.O_SYNC != 0 {
    70  		options |= FILE_WRITE_THROUGH
    71  	}
    72  	if flag&O_WRITE_ATTRS != 0 {
    73  		access |= FILE_WRITE_ATTRIBUTES
    74  	}
    75  	// Allow File.Stat.
    76  	access |= STANDARD_RIGHTS_READ | FILE_READ_ATTRIBUTES | FILE_READ_EA
    77  
    78  	objAttrs := &OBJECT_ATTRIBUTES{}
    79  	if flag&O_NOFOLLOW_ANY != 0 {
    80  		objAttrs.Attributes |= OBJ_DONT_REPARSE
    81  	}
    82  	if flag&syscall.O_CLOEXEC == 0 {
    83  		objAttrs.Attributes |= OBJ_INHERIT
    84  	}
    85  	if err := objAttrs.init(dirfd, name); err != nil {
    86  		return syscall.InvalidHandle, err
    87  	}
    88  
    89  	if flag&O_OPEN_REPARSE != 0 {
    90  		options |= FILE_OPEN_REPARSE_POINT
    91  	}
    92  
    93  	// We don't use FILE_OVERWRITE/FILE_OVERWRITE_IF, because when opening
    94  	// a file with FILE_ATTRIBUTE_READONLY these will replace an existing
    95  	// file with a new, read-only one.
    96  	//
    97  	// Instead, we ftruncate the file after opening when O_TRUNC is set.
    98  	var disposition uint32
    99  	switch {
   100  	case flag&(syscall.O_CREAT|syscall.O_EXCL) == (syscall.O_CREAT | syscall.O_EXCL):
   101  		disposition = FILE_CREATE
   102  		options |= FILE_OPEN_REPARSE_POINT // don't follow symlinks
   103  	case flag&syscall.O_CREAT == syscall.O_CREAT:
   104  		disposition = FILE_OPEN_IF
   105  	default:
   106  		disposition = FILE_OPEN
   107  	}
   108  
   109  	fileAttrs := uint32(FILE_ATTRIBUTE_NORMAL)
   110  	if perm&syscall.S_IWRITE == 0 {
   111  		fileAttrs = FILE_ATTRIBUTE_READONLY
   112  	}
   113  
   114  	var h syscall.Handle
   115  	err := NtCreateFile(
   116  		&h,
   117  		SYNCHRONIZE|access,
   118  		objAttrs,
   119  		&IO_STATUS_BLOCK{},
   120  		nil,
   121  		fileAttrs,
   122  		FILE_SHARE_READ|FILE_SHARE_WRITE|FILE_SHARE_DELETE,
   123  		disposition,
   124  		FILE_SYNCHRONOUS_IO_NONALERT|FILE_OPEN_FOR_BACKUP_INTENT|options,
   125  		nil,
   126  		0,
   127  	)
   128  	if err != nil {
   129  		return h, ntCreateFileError(err, flag)
   130  	}
   131  
   132  	if flag&syscall.O_TRUNC != 0 {
   133  		err = syscall.Ftruncate(h, 0)
   134  		if err != nil {
   135  			syscall.CloseHandle(h)
   136  			return syscall.InvalidHandle, err
   137  		}
   138  	}
   139  
   140  	return h, nil
   141  }
   142  
   143  // ntCreateFileError maps error returns from NTCreateFile to user-visible errors.
   144  func ntCreateFileError(err error, flag uint64) error {
   145  	s, ok := err.(NTStatus)
   146  	if !ok {
   147  		// Shouldn't really be possible, NtCreateFile always returns NTStatus.
   148  		return err
   149  	}
   150  	switch s {
   151  	case STATUS_REPARSE_POINT_ENCOUNTERED:
   152  		return syscall.ELOOP
   153  	case STATUS_NOT_A_DIRECTORY:
   154  		// ENOTDIR is the errno returned by open when O_DIRECTORY is specified
   155  		// and the target is not a directory.
   156  		//
   157  		// NtCreateFile can return STATUS_NOT_A_DIRECTORY under other circumstances,
   158  		// such as when opening "file/" where "file" is not a directory.
   159  		// (This might be Windows version dependent.)
   160  		//
   161  		// Only map STATUS_NOT_A_DIRECTORY to ENOTDIR when O_DIRECTORY is specified.
   162  		if flag&O_DIRECTORY != 0 {
   163  			return syscall.ENOTDIR
   164  		}
   165  	case STATUS_FILE_IS_A_DIRECTORY:
   166  		return syscall.EISDIR
   167  	case STATUS_OBJECT_NAME_COLLISION:
   168  		return syscall.EEXIST
   169  	}
   170  	return s.Errno()
   171  }
   172  
   173  func Mkdirat(dirfd syscall.Handle, name string, mode uint32) error {
   174  	objAttrs := &OBJECT_ATTRIBUTES{}
   175  	if err := objAttrs.init(dirfd, name); err != nil {
   176  		return err
   177  	}
   178  	var h syscall.Handle
   179  	err := NtCreateFile(
   180  		&h,
   181  		FILE_GENERIC_READ,
   182  		objAttrs,
   183  		&IO_STATUS_BLOCK{},
   184  		nil,
   185  		syscall.FILE_ATTRIBUTE_NORMAL,
   186  		syscall.FILE_SHARE_READ|syscall.FILE_SHARE_WRITE|syscall.FILE_SHARE_DELETE,
   187  		FILE_CREATE,
   188  		FILE_DIRECTORY_FILE,
   189  		nil,
   190  		0,
   191  	)
   192  	if err != nil {
   193  		return ntCreateFileError(err, 0)
   194  	}
   195  	syscall.CloseHandle(h)
   196  	return nil
   197  }
   198  
   199  func Deleteat(dirfd syscall.Handle, name string, options uint32) error {
   200  	if name == "." {
   201  		// NtOpenFile's documentation isn't explicit about what happens when deleting ".".
   202  		// Make this an error consistent with that of POSIX.
   203  		return syscall.EINVAL
   204  	}
   205  	objAttrs := &OBJECT_ATTRIBUTES{}
   206  	if err := objAttrs.init(dirfd, name); err != nil {
   207  		return err
   208  	}
   209  	var h syscall.Handle
   210  	err := NtOpenFile(
   211  		&h,
   212  		SYNCHRONIZE|FILE_READ_ATTRIBUTES|DELETE,
   213  		objAttrs,
   214  		&IO_STATUS_BLOCK{},
   215  		FILE_SHARE_DELETE|FILE_SHARE_READ|FILE_SHARE_WRITE,
   216  		FILE_OPEN_REPARSE_POINT|FILE_OPEN_FOR_BACKUP_INTENT|FILE_SYNCHRONOUS_IO_NONALERT|options,
   217  	)
   218  	if err != nil {
   219  		return ntCreateFileError(err, 0)
   220  	}
   221  	defer syscall.CloseHandle(h)
   222  
   223  	if TestDeleteatFallback {
   224  		return deleteatFallback(h)
   225  	}
   226  
   227  	const FileDispositionInformationEx = 64
   228  
   229  	// First, attempt to delete the file using POSIX semantics
   230  	// (which permit a file to be deleted while it is still open).
   231  	// This matches the behavior of DeleteFileW.
   232  	//
   233  	// The following call uses features available on different Windows versions:
   234  	// - FILE_DISPOSITION_INFORMATION_EX: Windows 10, version 1607 (aka RS1)
   235  	// - FILE_DISPOSITION_POSIX_SEMANTICS: Windows 10, version 1607 (aka RS1)
   236  	// - FILE_DISPOSITION_IGNORE_READONLY_ATTRIBUTE: Windows 10, version 1809 (aka RS5)
   237  	//
   238  	// Also, some file systems, like FAT32, don't support POSIX semantics.
   239  	err = NtSetInformationFile(
   240  		h,
   241  		&IO_STATUS_BLOCK{},
   242  		unsafe.Pointer(&FILE_DISPOSITION_INFORMATION_EX{
   243  			Flags: FILE_DISPOSITION_DELETE |
   244  				FILE_DISPOSITION_FORCE_IMAGE_SECTION_CHECK |
   245  				FILE_DISPOSITION_POSIX_SEMANTICS |
   246  				// This differs from DeleteFileW, but matches os.Remove's
   247  				// behavior on Unix platforms of permitting deletion of
   248  				// read-only files.
   249  				FILE_DISPOSITION_IGNORE_READONLY_ATTRIBUTE,
   250  		}),
   251  		uint32(unsafe.Sizeof(FILE_DISPOSITION_INFORMATION_EX{})),
   252  		FileDispositionInformationEx,
   253  	)
   254  	switch err {
   255  	case nil:
   256  		return nil
   257  	case STATUS_INVALID_INFO_CLASS, // the operating system doesn't support FileDispositionInformationEx
   258  		STATUS_INVALID_PARAMETER, // the operating system doesn't support one of the flags
   259  		STATUS_NOT_SUPPORTED:     // the file system doesn't support FILE_DISPOSITION_INFORMATION_EX or one of the flags
   260  		return deleteatFallback(h)
   261  	default:
   262  		return err.(NTStatus).Errno()
   263  	}
   264  }
   265  
   266  // TestDeleteatFallback should only be used for testing purposes.
   267  // When set, [Deleteat] uses the fallback path unconditionally.
   268  var TestDeleteatFallback bool
   269  
   270  // deleteatFallback is a deleteat implementation that strives
   271  // for compatibility with older Windows versions and file systems
   272  // over performance.
   273  func deleteatFallback(h syscall.Handle) error {
   274  	var data syscall.ByHandleFileInformation
   275  	if err := syscall.GetFileInformationByHandle(h, &data); err == nil && data.FileAttributes&syscall.FILE_ATTRIBUTE_READONLY != 0 {
   276  		// Remove read-only attribute. Reopen the file, as it was previously open without FILE_WRITE_ATTRIBUTES access
   277  		// in order to maximize compatibility in the happy path.
   278  		wh, err := ReOpenFile(h,
   279  			FILE_WRITE_ATTRIBUTES,
   280  			FILE_SHARE_READ|FILE_SHARE_WRITE|FILE_SHARE_DELETE,
   281  			syscall.FILE_FLAG_OPEN_REPARSE_POINT|syscall.FILE_FLAG_BACKUP_SEMANTICS,
   282  		)
   283  		if err != nil {
   284  			return err
   285  		}
   286  		err = SetFileInformationByHandle(
   287  			wh,
   288  			FileBasicInfo,
   289  			unsafe.Pointer(&FILE_BASIC_INFO{
   290  				FileAttributes: data.FileAttributes &^ FILE_ATTRIBUTE_READONLY,
   291  			}),
   292  			uint32(unsafe.Sizeof(FILE_BASIC_INFO{})),
   293  		)
   294  		syscall.CloseHandle(wh)
   295  		if err != nil {
   296  			return err
   297  		}
   298  	}
   299  
   300  	return SetFileInformationByHandle(
   301  		h,
   302  		FileDispositionInfo,
   303  		unsafe.Pointer(&FILE_DISPOSITION_INFO{
   304  			DeleteFile: true,
   305  		}),
   306  		uint32(unsafe.Sizeof(FILE_DISPOSITION_INFO{})),
   307  	)
   308  }
   309  
   310  func Renameat(olddirfd syscall.Handle, oldpath string, newdirfd syscall.Handle, newpath string) error {
   311  	objAttrs := &OBJECT_ATTRIBUTES{}
   312  	if err := objAttrs.init(olddirfd, oldpath); err != nil {
   313  		return err
   314  	}
   315  	var h syscall.Handle
   316  	err := NtOpenFile(
   317  		&h,
   318  		SYNCHRONIZE|DELETE,
   319  		objAttrs,
   320  		&IO_STATUS_BLOCK{},
   321  		FILE_SHARE_DELETE|FILE_SHARE_READ|FILE_SHARE_WRITE,
   322  		FILE_OPEN_REPARSE_POINT|FILE_OPEN_FOR_BACKUP_INTENT|FILE_SYNCHRONOUS_IO_NONALERT,
   323  	)
   324  	if err != nil {
   325  		return ntCreateFileError(err, 0)
   326  	}
   327  	defer syscall.CloseHandle(h)
   328  
   329  	renameInfoEx := FILE_RENAME_INFORMATION_EX{
   330  		Flags: FILE_RENAME_REPLACE_IF_EXISTS |
   331  			FILE_RENAME_POSIX_SEMANTICS,
   332  		RootDirectory: newdirfd,
   333  	}
   334  	p16, err := syscall.UTF16FromString(newpath)
   335  	if err != nil {
   336  		return err
   337  	}
   338  	if len(p16) > len(renameInfoEx.FileName) {
   339  		return syscall.EINVAL
   340  	}
   341  	copy(renameInfoEx.FileName[:], p16)
   342  	renameInfoEx.FileNameLength = uint32((len(p16) - 1) * 2)
   343  
   344  	const (
   345  		FileRenameInformation   = 10
   346  		FileRenameInformationEx = 65
   347  	)
   348  	err = NtSetInformationFile(
   349  		h,
   350  		&IO_STATUS_BLOCK{},
   351  		unsafe.Pointer(&renameInfoEx),
   352  		uint32(unsafe.Sizeof(FILE_RENAME_INFORMATION_EX{})),
   353  		FileRenameInformationEx,
   354  	)
   355  	if err == nil {
   356  		return nil
   357  	}
   358  
   359  	// If the prior rename failed, the filesystem might not support
   360  	// POSIX semantics (for example, FAT), or might not have implemented
   361  	// FILE_RENAME_INFORMATION_EX.
   362  	//
   363  	// Try again.
   364  	renameInfo := FILE_RENAME_INFORMATION{
   365  		ReplaceIfExists: true,
   366  		RootDirectory:   newdirfd,
   367  	}
   368  	copy(renameInfo.FileName[:], p16)
   369  	renameInfo.FileNameLength = renameInfoEx.FileNameLength
   370  
   371  	err = NtSetInformationFile(
   372  		h,
   373  		&IO_STATUS_BLOCK{},
   374  		unsafe.Pointer(&renameInfo),
   375  		uint32(unsafe.Sizeof(FILE_RENAME_INFORMATION{})),
   376  		FileRenameInformation,
   377  	)
   378  	if st, ok := err.(NTStatus); ok {
   379  		return st.Errno()
   380  	}
   381  	return err
   382  }
   383  
   384  func Linkat(olddirfd syscall.Handle, oldpath string, newdirfd syscall.Handle, newpath string) error {
   385  	objAttrs := &OBJECT_ATTRIBUTES{}
   386  	if err := objAttrs.init(olddirfd, oldpath); err != nil {
   387  		return err
   388  	}
   389  	var h syscall.Handle
   390  	err := NtOpenFile(
   391  		&h,
   392  		SYNCHRONIZE|FILE_WRITE_ATTRIBUTES,
   393  		objAttrs,
   394  		&IO_STATUS_BLOCK{},
   395  		FILE_SHARE_DELETE|FILE_SHARE_READ|FILE_SHARE_WRITE,
   396  		FILE_OPEN_REPARSE_POINT|FILE_OPEN_FOR_BACKUP_INTENT|FILE_SYNCHRONOUS_IO_NONALERT,
   397  	)
   398  	if err != nil {
   399  		return ntCreateFileError(err, 0)
   400  	}
   401  	defer syscall.CloseHandle(h)
   402  
   403  	linkInfo := FILE_LINK_INFORMATION{
   404  		RootDirectory: newdirfd,
   405  	}
   406  	p16, err := syscall.UTF16FromString(newpath)
   407  	if err != nil {
   408  		return err
   409  	}
   410  	if len(p16) > len(linkInfo.FileName) {
   411  		return syscall.EINVAL
   412  	}
   413  	copy(linkInfo.FileName[:], p16)
   414  	linkInfo.FileNameLength = uint32((len(p16) - 1) * 2)
   415  
   416  	const (
   417  		FileLinkInformation = 11
   418  	)
   419  	err = NtSetInformationFile(
   420  		h,
   421  		&IO_STATUS_BLOCK{},
   422  		unsafe.Pointer(&linkInfo),
   423  		uint32(unsafe.Sizeof(FILE_LINK_INFORMATION{})),
   424  		FileLinkInformation,
   425  	)
   426  	if st, ok := err.(NTStatus); ok {
   427  		return st.Errno()
   428  	}
   429  	return err
   430  }
   431  
   432  // SymlinkatFlags configure Symlinkat.
   433  //
   434  // Symbolic links have two properties: They may be directory or file links,
   435  // and they may be absolute or relative.
   436  //
   437  // The Windows API defines flags describing these properties
   438  // (SYMBOLIC_LINK_FLAG_DIRECTORY and SYMLINK_FLAG_RELATIVE),
   439  // but the flags are passed to different system calls and
   440  // do not have distinct values, so we define our own enumeration
   441  // that permits expressing both.
   442  type SymlinkatFlags uint
   443  
   444  const (
   445  	SYMLINKAT_DIRECTORY = SymlinkatFlags(1 << iota)
   446  	SYMLINKAT_RELATIVE
   447  )
   448  
   449  func Symlinkat(oldname string, newdirfd syscall.Handle, newname string, flags SymlinkatFlags) error {
   450  	// Temporarily acquire symlink-creating privileges if possible.
   451  	// This is the behavior of CreateSymbolicLinkW.
   452  	//
   453  	// (When passed the SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE flag,
   454  	// CreateSymbolicLinkW ignores errors in acquiring privileges, as we do here.)
   455  	return withPrivilege("SeCreateSymbolicLinkPrivilege", func() error {
   456  		return symlinkat(oldname, newdirfd, newname, flags)
   457  	})
   458  }
   459  
   460  func symlinkat(oldname string, newdirfd syscall.Handle, newname string, flags SymlinkatFlags) error {
   461  	oldnameu16, err := syscall.UTF16FromString(oldname)
   462  	if err != nil {
   463  		return err
   464  	}
   465  	oldnameu16 = oldnameu16[:len(oldnameu16)-1] // trim off terminal NUL
   466  
   467  	var options uint32
   468  	if flags&SYMLINKAT_DIRECTORY != 0 {
   469  		options |= FILE_DIRECTORY_FILE
   470  	} else {
   471  		options |= FILE_NON_DIRECTORY_FILE
   472  	}
   473  
   474  	objAttrs := &OBJECT_ATTRIBUTES{}
   475  	if err := objAttrs.init(newdirfd, newname); err != nil {
   476  		return err
   477  	}
   478  	var h syscall.Handle
   479  	err = NtCreateFile(
   480  		&h,
   481  		SYNCHRONIZE|FILE_WRITE_ATTRIBUTES|DELETE,
   482  		objAttrs,
   483  		&IO_STATUS_BLOCK{},
   484  		nil,
   485  		syscall.FILE_ATTRIBUTE_NORMAL,
   486  		0,
   487  		FILE_CREATE,
   488  		FILE_OPEN_REPARSE_POINT|FILE_OPEN_FOR_BACKUP_INTENT|FILE_SYNCHRONOUS_IO_NONALERT|options,
   489  		nil,
   490  		0,
   491  	)
   492  	if err != nil {
   493  		return ntCreateFileError(err, 0)
   494  	}
   495  	defer syscall.CloseHandle(h)
   496  
   497  	// https://learn.microsoft.com/en-us/windows-hardware/drivers/ddi/ntifs/ns-ntifs-_reparse_data_buffer
   498  	type reparseDataBufferT struct {
   499  		_ structs.HostLayout
   500  
   501  		ReparseTag        uint32
   502  		ReparseDataLength uint16
   503  		Reserved          uint16
   504  
   505  		SubstituteNameOffset uint16
   506  		SubstituteNameLength uint16
   507  		PrintNameOffset      uint16
   508  		PrintNameLength      uint16
   509  		Flags                uint32
   510  	}
   511  
   512  	const (
   513  		headerSize = uint16(unsafe.Offsetof(reparseDataBufferT{}.SubstituteNameOffset))
   514  		bufferSize = uint16(unsafe.Sizeof(reparseDataBufferT{}))
   515  	)
   516  
   517  	// Data buffer containing a SymbolicLinkReparseBuffer followed by the link target.
   518  	rdbbuf := make([]byte, bufferSize+uint16(2*len(oldnameu16)))
   519  
   520  	rdb := (*reparseDataBufferT)(unsafe.Pointer(&rdbbuf[0]))
   521  	rdb.ReparseTag = syscall.IO_REPARSE_TAG_SYMLINK
   522  	rdb.ReparseDataLength = uint16(len(rdbbuf)) - uint16(headerSize)
   523  	rdb.SubstituteNameOffset = 0
   524  	rdb.SubstituteNameLength = uint16(2 * len(oldnameu16))
   525  	rdb.PrintNameOffset = 0
   526  	rdb.PrintNameLength = rdb.SubstituteNameLength
   527  	if flags&SYMLINKAT_RELATIVE != 0 {
   528  		rdb.Flags = SYMLINK_FLAG_RELATIVE
   529  	}
   530  
   531  	namebuf := rdbbuf[bufferSize:]
   532  	copy(namebuf, unsafe.String((*byte)(unsafe.Pointer(&oldnameu16[0])), 2*len(oldnameu16)))
   533  
   534  	err = syscall.DeviceIoControl(
   535  		h,
   536  		FSCTL_SET_REPARSE_POINT,
   537  		&rdbbuf[0],
   538  		uint32(len(rdbbuf)),
   539  		nil,
   540  		0,
   541  		nil,
   542  		nil)
   543  	if err != nil {
   544  		// Creating the symlink has failed, so try to remove the file.
   545  		const FileDispositionInformation = 13
   546  		NtSetInformationFile(
   547  			h,
   548  			&IO_STATUS_BLOCK{},
   549  			unsafe.Pointer(&FILE_DISPOSITION_INFORMATION{
   550  				DeleteFile: true,
   551  			}),
   552  			uint32(unsafe.Sizeof(FILE_DISPOSITION_INFORMATION{})),
   553  			FileDispositionInformation,
   554  		)
   555  		return err
   556  	}
   557  
   558  	return nil
   559  }
   560  
   561  // withPrivilege temporariliy acquires the named privilege and runs f.
   562  // If the privilege cannot be acquired it runs f anyway,
   563  // which should fail with an appropriate error.
   564  func withPrivilege(privilege string, f func() error) error {
   565  	runtime.LockOSThread()
   566  	defer runtime.UnlockOSThread()
   567  
   568  	err := ImpersonateSelf(SecurityImpersonation)
   569  	if err != nil {
   570  		return f()
   571  	}
   572  	defer RevertToSelf()
   573  
   574  	curThread, err := GetCurrentThread()
   575  	if err != nil {
   576  		return f()
   577  	}
   578  	var token syscall.Token
   579  	err = OpenThreadToken(curThread, syscall.TOKEN_QUERY|TOKEN_ADJUST_PRIVILEGES, false, &token)
   580  	if err != nil {
   581  		return f()
   582  	}
   583  	defer syscall.CloseHandle(syscall.Handle(token))
   584  
   585  	privStr, err := syscall.UTF16PtrFromString(privilege)
   586  	if err != nil {
   587  		return f()
   588  	}
   589  	var tokenPriv TOKEN_PRIVILEGES
   590  	err = LookupPrivilegeValue(nil, privStr, &tokenPriv.Privileges[0].Luid)
   591  	if err != nil {
   592  		return f()
   593  	}
   594  
   595  	tokenPriv.PrivilegeCount = 1
   596  	tokenPriv.Privileges[0].Attributes = SE_PRIVILEGE_ENABLED
   597  	err = AdjustTokenPrivileges(token, false, &tokenPriv, 0, nil, nil)
   598  	if err != nil {
   599  		return f()
   600  	}
   601  
   602  	return f()
   603  }
   604
View as plain text