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 not supported by syscall.Open.
    15  //
    16  // These are invented values.
    17  //
    18  // When adding a new flag here, add an unexported version to
    19  // the set of invented O_ values in syscall/types_windows.go
    20  // to avoid overlap.
    21  const (
    22  	O_DIRECTORY    = 0x100000   // target must be a directory
    23  	O_NOFOLLOW_ANY = 0x20000000 // disallow symlinks anywhere in the path
    24  	O_OPEN_REPARSE = 0x40000000 // FILE_OPEN_REPARSE_POINT, used by Lstat
    25  	O_WRITE_ATTRS  = 0x80000000 // FILE_WRITE_ATTRIBUTES, used by Chmod
    26  )
    27  
    28  func Openat(dirfd syscall.Handle, name string, flag uint64, perm uint32) (_ syscall.Handle, e1 error) {
    29  	if len(name) == 0 {
    30  		return syscall.InvalidHandle, syscall.ERROR_FILE_NOT_FOUND
    31  	}
    32  
    33  	var access, options uint32
    34  	switch flag & (syscall.O_RDONLY | syscall.O_WRONLY | syscall.O_RDWR) {
    35  	case syscall.O_RDONLY:
    36  		// FILE_GENERIC_READ includes FILE_LIST_DIRECTORY.
    37  		access = FILE_GENERIC_READ
    38  	case syscall.O_WRONLY:
    39  		access = FILE_GENERIC_WRITE
    40  		options |= FILE_NON_DIRECTORY_FILE
    41  	case syscall.O_RDWR:
    42  		access = FILE_GENERIC_READ | FILE_GENERIC_WRITE
    43  		options |= FILE_NON_DIRECTORY_FILE
    44  	default:
    45  		// Stat opens files without requesting read or write permissions,
    46  		// but we still need to request SYNCHRONIZE.
    47  		access = SYNCHRONIZE
    48  	}
    49  	if flag&syscall.O_CREAT != 0 {
    50  		access |= FILE_GENERIC_WRITE
    51  	}
    52  	if flag&syscall.O_APPEND != 0 {
    53  		access |= FILE_APPEND_DATA
    54  		// Remove FILE_WRITE_DATA access unless O_TRUNC is set,
    55  		// in which case we need it to truncate the file.
    56  		if flag&syscall.O_TRUNC == 0 {
    57  			access &^= FILE_WRITE_DATA
    58  		}
    59  	}
    60  	if flag&O_DIRECTORY != 0 {
    61  		options |= FILE_DIRECTORY_FILE
    62  		access |= FILE_LIST_DIRECTORY
    63  	}
    64  	if flag&syscall.O_SYNC != 0 {
    65  		options |= FILE_WRITE_THROUGH
    66  	}
    67  	if flag&O_WRITE_ATTRS != 0 {
    68  		access |= FILE_WRITE_ATTRIBUTES
    69  	}
    70  	// Allow File.Stat.
    71  	access |= STANDARD_RIGHTS_READ | FILE_READ_ATTRIBUTES | FILE_READ_EA
    72  
    73  	objAttrs := &OBJECT_ATTRIBUTES{}
    74  	if flag&O_NOFOLLOW_ANY != 0 {
    75  		objAttrs.Attributes |= OBJ_DONT_REPARSE
    76  	}
    77  	if flag&syscall.O_CLOEXEC == 0 {
    78  		objAttrs.Attributes |= OBJ_INHERIT
    79  	}
    80  	if err := objAttrs.init(dirfd, name); err != nil {
    81  		return syscall.InvalidHandle, err
    82  	}
    83  
    84  	if flag&O_OPEN_REPARSE != 0 {
    85  		options |= FILE_OPEN_REPARSE_POINT
    86  	}
    87  
    88  	// We don't use FILE_OVERWRITE/FILE_OVERWRITE_IF, because when opening
    89  	// a file with FILE_ATTRIBUTE_READONLY these will replace an existing
    90  	// file with a new, read-only one.
    91  	//
    92  	// Instead, we ftruncate the file after opening when O_TRUNC is set.
    93  	var disposition uint32
    94  	switch {
    95  	case flag&(syscall.O_CREAT|syscall.O_EXCL) == (syscall.O_CREAT | syscall.O_EXCL):
    96  		disposition = FILE_CREATE
    97  	case flag&syscall.O_CREAT == syscall.O_CREAT:
    98  		disposition = FILE_OPEN_IF
    99  	default:
   100  		disposition = FILE_OPEN
   101  	}
   102  
   103  	fileAttrs := uint32(FILE_ATTRIBUTE_NORMAL)
   104  	if perm&syscall.S_IWRITE == 0 {
   105  		fileAttrs = FILE_ATTRIBUTE_READONLY
   106  	}
   107  
   108  	var h syscall.Handle
   109  	err := NtCreateFile(
   110  		&h,
   111  		SYNCHRONIZE|access,
   112  		objAttrs,
   113  		&IO_STATUS_BLOCK{},
   114  		nil,
   115  		fileAttrs,
   116  		FILE_SHARE_READ|FILE_SHARE_WRITE|FILE_SHARE_DELETE,
   117  		disposition,
   118  		FILE_SYNCHRONOUS_IO_NONALERT|FILE_OPEN_FOR_BACKUP_INTENT|options,
   119  		nil,
   120  		0,
   121  	)
   122  	if err != nil {
   123  		return h, ntCreateFileError(err, flag)
   124  	}
   125  
   126  	if flag&syscall.O_TRUNC != 0 {
   127  		err = syscall.Ftruncate(h, 0)
   128  		if err != nil {
   129  			syscall.CloseHandle(h)
   130  			return syscall.InvalidHandle, err
   131  		}
   132  	}
   133  
   134  	return h, nil
   135  }
   136  
   137  // ntCreateFileError maps error returns from NTCreateFile to user-visible errors.
   138  func ntCreateFileError(err error, flag uint64) error {
   139  	s, ok := err.(NTStatus)
   140  	if !ok {
   141  		// Shouldn't really be possible, NtCreateFile always returns NTStatus.
   142  		return err
   143  	}
   144  	switch s {
   145  	case STATUS_REPARSE_POINT_ENCOUNTERED:
   146  		return syscall.ELOOP
   147  	case STATUS_NOT_A_DIRECTORY:
   148  		// ENOTDIR is the errno returned by open when O_DIRECTORY is specified
   149  		// and the target is not a directory.
   150  		//
   151  		// NtCreateFile can return STATUS_NOT_A_DIRECTORY under other circumstances,
   152  		// such as when opening "file/" where "file" is not a directory.
   153  		// (This might be Windows version dependent.)
   154  		//
   155  		// Only map STATUS_NOT_A_DIRECTORY to ENOTDIR when O_DIRECTORY is specified.
   156  		if flag&O_DIRECTORY != 0 {
   157  			return syscall.ENOTDIR
   158  		}
   159  	case STATUS_FILE_IS_A_DIRECTORY:
   160  		return syscall.EISDIR
   161  	}
   162  	return s.Errno()
   163  }
   164  
   165  func Mkdirat(dirfd syscall.Handle, name string, mode uint32) error {
   166  	objAttrs := &OBJECT_ATTRIBUTES{}
   167  	if err := objAttrs.init(dirfd, name); err != nil {
   168  		return err
   169  	}
   170  	var h syscall.Handle
   171  	err := NtCreateFile(
   172  		&h,
   173  		FILE_GENERIC_READ,
   174  		objAttrs,
   175  		&IO_STATUS_BLOCK{},
   176  		nil,
   177  		syscall.FILE_ATTRIBUTE_NORMAL,
   178  		syscall.FILE_SHARE_READ|syscall.FILE_SHARE_WRITE|syscall.FILE_SHARE_DELETE,
   179  		FILE_CREATE,
   180  		FILE_DIRECTORY_FILE,
   181  		nil,
   182  		0,
   183  	)
   184  	if err != nil {
   185  		return ntCreateFileError(err, 0)
   186  	}
   187  	syscall.CloseHandle(h)
   188  	return nil
   189  }
   190  
   191  func Deleteat(dirfd syscall.Handle, name string, options uint32) error {
   192  	objAttrs := &OBJECT_ATTRIBUTES{}
   193  	if err := objAttrs.init(dirfd, name); err != nil {
   194  		return err
   195  	}
   196  	var h syscall.Handle
   197  	err := NtOpenFile(
   198  		&h,
   199  		SYNCHRONIZE|DELETE,
   200  		objAttrs,
   201  		&IO_STATUS_BLOCK{},
   202  		FILE_SHARE_DELETE|FILE_SHARE_READ|FILE_SHARE_WRITE,
   203  		FILE_OPEN_REPARSE_POINT|FILE_OPEN_FOR_BACKUP_INTENT|FILE_SYNCHRONOUS_IO_NONALERT|options,
   204  	)
   205  	if err != nil {
   206  		return ntCreateFileError(err, 0)
   207  	}
   208  	defer syscall.CloseHandle(h)
   209  
   210  	const (
   211  		FileDispositionInformation   = 13
   212  		FileDispositionInformationEx = 64
   213  	)
   214  
   215  	// First, attempt to delete the file using POSIX semantics
   216  	// (which permit a file to be deleted while it is still open).
   217  	// This matches the behavior of DeleteFileW.
   218  	err = NtSetInformationFile(
   219  		h,
   220  		&IO_STATUS_BLOCK{},
   221  		unsafe.Pointer(&FILE_DISPOSITION_INFORMATION_EX{
   222  			Flags: FILE_DISPOSITION_DELETE |
   223  				FILE_DISPOSITION_FORCE_IMAGE_SECTION_CHECK |
   224  				FILE_DISPOSITION_POSIX_SEMANTICS |
   225  				// This differs from DeleteFileW, but matches os.Remove's
   226  				// behavior on Unix platforms of permitting deletion of
   227  				// read-only files.
   228  				FILE_DISPOSITION_IGNORE_READONLY_ATTRIBUTE,
   229  		}),
   230  		uint32(unsafe.Sizeof(FILE_DISPOSITION_INFORMATION_EX{})),
   231  		FileDispositionInformationEx,
   232  	)
   233  	switch err {
   234  	case nil:
   235  		return nil
   236  	case STATUS_CANNOT_DELETE, STATUS_DIRECTORY_NOT_EMPTY:
   237  		return err.(NTStatus).Errno()
   238  	}
   239  
   240  	// If the prior deletion failed, the filesystem either doesn't support
   241  	// POSIX semantics (for example, FAT), or hasn't implemented
   242  	// FILE_DISPOSITION_INFORMATION_EX.
   243  	//
   244  	// Try again.
   245  	err = NtSetInformationFile(
   246  		h,
   247  		&IO_STATUS_BLOCK{},
   248  		unsafe.Pointer(&FILE_DISPOSITION_INFORMATION{
   249  			DeleteFile: true,
   250  		}),
   251  		uint32(unsafe.Sizeof(FILE_DISPOSITION_INFORMATION{})),
   252  		FileDispositionInformation,
   253  	)
   254  	if st, ok := err.(NTStatus); ok {
   255  		return st.Errno()
   256  	}
   257  	return err
   258  }
   259  
   260  func Renameat(olddirfd syscall.Handle, oldpath string, newdirfd syscall.Handle, newpath string) error {
   261  	objAttrs := &OBJECT_ATTRIBUTES{}
   262  	if err := objAttrs.init(olddirfd, oldpath); err != nil {
   263  		return err
   264  	}
   265  	var h syscall.Handle
   266  	err := NtOpenFile(
   267  		&h,
   268  		SYNCHRONIZE|DELETE,
   269  		objAttrs,
   270  		&IO_STATUS_BLOCK{},
   271  		FILE_SHARE_DELETE|FILE_SHARE_READ|FILE_SHARE_WRITE,
   272  		FILE_OPEN_REPARSE_POINT|FILE_OPEN_FOR_BACKUP_INTENT|FILE_SYNCHRONOUS_IO_NONALERT,
   273  	)
   274  	if err != nil {
   275  		return ntCreateFileError(err, 0)
   276  	}
   277  	defer syscall.CloseHandle(h)
   278  
   279  	renameInfoEx := FILE_RENAME_INFORMATION_EX{
   280  		Flags: FILE_RENAME_REPLACE_IF_EXISTS |
   281  			FILE_RENAME_POSIX_SEMANTICS,
   282  		RootDirectory: newdirfd,
   283  	}
   284  	p16, err := syscall.UTF16FromString(newpath)
   285  	if err != nil {
   286  		return err
   287  	}
   288  	if len(p16) > len(renameInfoEx.FileName) {
   289  		return syscall.EINVAL
   290  	}
   291  	copy(renameInfoEx.FileName[:], p16)
   292  	renameInfoEx.FileNameLength = uint32((len(p16) - 1) * 2)
   293  
   294  	const (
   295  		FileRenameInformation   = 10
   296  		FileRenameInformationEx = 65
   297  	)
   298  	err = NtSetInformationFile(
   299  		h,
   300  		&IO_STATUS_BLOCK{},
   301  		unsafe.Pointer(&renameInfoEx),
   302  		uint32(unsafe.Sizeof(FILE_RENAME_INFORMATION_EX{})),
   303  		FileRenameInformationEx,
   304  	)
   305  	if err == nil {
   306  		return nil
   307  	}
   308  
   309  	// If the prior rename failed, the filesystem might not support
   310  	// POSIX semantics (for example, FAT), or might not have implemented
   311  	// FILE_RENAME_INFORMATION_EX.
   312  	//
   313  	// Try again.
   314  	renameInfo := FILE_RENAME_INFORMATION{
   315  		ReplaceIfExists: true,
   316  		RootDirectory:   newdirfd,
   317  	}
   318  	copy(renameInfo.FileName[:], p16)
   319  	renameInfo.FileNameLength = renameInfoEx.FileNameLength
   320  
   321  	err = NtSetInformationFile(
   322  		h,
   323  		&IO_STATUS_BLOCK{},
   324  		unsafe.Pointer(&renameInfo),
   325  		uint32(unsafe.Sizeof(FILE_RENAME_INFORMATION{})),
   326  		FileRenameInformation,
   327  	)
   328  	if st, ok := err.(NTStatus); ok {
   329  		return st.Errno()
   330  	}
   331  	return err
   332  }
   333  
   334  func Linkat(olddirfd syscall.Handle, oldpath string, newdirfd syscall.Handle, newpath string) error {
   335  	objAttrs := &OBJECT_ATTRIBUTES{}
   336  	if err := objAttrs.init(olddirfd, oldpath); err != nil {
   337  		return err
   338  	}
   339  	var h syscall.Handle
   340  	err := NtOpenFile(
   341  		&h,
   342  		SYNCHRONIZE|FILE_WRITE_ATTRIBUTES,
   343  		objAttrs,
   344  		&IO_STATUS_BLOCK{},
   345  		FILE_SHARE_DELETE|FILE_SHARE_READ|FILE_SHARE_WRITE,
   346  		FILE_OPEN_REPARSE_POINT|FILE_OPEN_FOR_BACKUP_INTENT|FILE_SYNCHRONOUS_IO_NONALERT,
   347  	)
   348  	if err != nil {
   349  		return ntCreateFileError(err, 0)
   350  	}
   351  	defer syscall.CloseHandle(h)
   352  
   353  	linkInfo := FILE_LINK_INFORMATION{
   354  		RootDirectory: newdirfd,
   355  	}
   356  	p16, err := syscall.UTF16FromString(newpath)
   357  	if err != nil {
   358  		return err
   359  	}
   360  	if len(p16) > len(linkInfo.FileName) {
   361  		return syscall.EINVAL
   362  	}
   363  	copy(linkInfo.FileName[:], p16)
   364  	linkInfo.FileNameLength = uint32((len(p16) - 1) * 2)
   365  
   366  	const (
   367  		FileLinkInformation = 11
   368  	)
   369  	err = NtSetInformationFile(
   370  		h,
   371  		&IO_STATUS_BLOCK{},
   372  		unsafe.Pointer(&linkInfo),
   373  		uint32(unsafe.Sizeof(FILE_LINK_INFORMATION{})),
   374  		FileLinkInformation,
   375  	)
   376  	if st, ok := err.(NTStatus); ok {
   377  		return st.Errno()
   378  	}
   379  	return err
   380  }
   381  
   382  // SymlinkatFlags configure Symlinkat.
   383  //
   384  // Symbolic links have two properties: They may be directory or file links,
   385  // and they may be absolute or relative.
   386  //
   387  // The Windows API defines flags describing these properties
   388  // (SYMBOLIC_LINK_FLAG_DIRECTORY and SYMLINK_FLAG_RELATIVE),
   389  // but the flags are passed to different system calls and
   390  // do not have distinct values, so we define our own enumeration
   391  // that permits expressing both.
   392  type SymlinkatFlags uint
   393  
   394  const (
   395  	SYMLINKAT_DIRECTORY = SymlinkatFlags(1 << iota)
   396  	SYMLINKAT_RELATIVE
   397  )
   398  
   399  func Symlinkat(oldname string, newdirfd syscall.Handle, newname string, flags SymlinkatFlags) error {
   400  	// Temporarily acquire symlink-creating privileges if possible.
   401  	// This is the behavior of CreateSymbolicLinkW.
   402  	//
   403  	// (When passed the SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE flag,
   404  	// CreateSymbolicLinkW ignores errors in acquiring privileges, as we do here.)
   405  	return withPrivilege("SeCreateSymbolicLinkPrivilege", func() error {
   406  		return symlinkat(oldname, newdirfd, newname, flags)
   407  	})
   408  }
   409  
   410  func symlinkat(oldname string, newdirfd syscall.Handle, newname string, flags SymlinkatFlags) error {
   411  	oldnameu16, err := syscall.UTF16FromString(oldname)
   412  	if err != nil {
   413  		return err
   414  	}
   415  	oldnameu16 = oldnameu16[:len(oldnameu16)-1] // trim off terminal NUL
   416  
   417  	var options uint32
   418  	if flags&SYMLINKAT_DIRECTORY != 0 {
   419  		options |= FILE_DIRECTORY_FILE
   420  	} else {
   421  		options |= FILE_NON_DIRECTORY_FILE
   422  	}
   423  
   424  	objAttrs := &OBJECT_ATTRIBUTES{}
   425  	if err := objAttrs.init(newdirfd, newname); err != nil {
   426  		return err
   427  	}
   428  	var h syscall.Handle
   429  	err = NtCreateFile(
   430  		&h,
   431  		SYNCHRONIZE|FILE_WRITE_ATTRIBUTES|DELETE,
   432  		objAttrs,
   433  		&IO_STATUS_BLOCK{},
   434  		nil,
   435  		syscall.FILE_ATTRIBUTE_NORMAL,
   436  		0,
   437  		FILE_CREATE,
   438  		FILE_OPEN_REPARSE_POINT|FILE_OPEN_FOR_BACKUP_INTENT|FILE_SYNCHRONOUS_IO_NONALERT|options,
   439  		nil,
   440  		0,
   441  	)
   442  	if err != nil {
   443  		return ntCreateFileError(err, 0)
   444  	}
   445  	defer syscall.CloseHandle(h)
   446  
   447  	// https://learn.microsoft.com/en-us/windows-hardware/drivers/ddi/ntifs/ns-ntifs-_reparse_data_buffer
   448  	type reparseDataBufferT struct {
   449  		_ structs.HostLayout
   450  
   451  		ReparseTag        uint32
   452  		ReparseDataLength uint16
   453  		Reserved          uint16
   454  
   455  		SubstituteNameOffset uint16
   456  		SubstituteNameLength uint16
   457  		PrintNameOffset      uint16
   458  		PrintNameLength      uint16
   459  		Flags                uint32
   460  	}
   461  
   462  	const (
   463  		headerSize = uint16(unsafe.Offsetof(reparseDataBufferT{}.SubstituteNameOffset))
   464  		bufferSize = uint16(unsafe.Sizeof(reparseDataBufferT{}))
   465  	)
   466  
   467  	// Data buffer containing a SymbolicLinkReparseBuffer followed by the link target.
   468  	rdbbuf := make([]byte, bufferSize+uint16(2*len(oldnameu16)))
   469  
   470  	rdb := (*reparseDataBufferT)(unsafe.Pointer(&rdbbuf[0]))
   471  	rdb.ReparseTag = syscall.IO_REPARSE_TAG_SYMLINK
   472  	rdb.ReparseDataLength = uint16(len(rdbbuf)) - uint16(headerSize)
   473  	rdb.SubstituteNameOffset = 0
   474  	rdb.SubstituteNameLength = uint16(2 * len(oldnameu16))
   475  	rdb.PrintNameOffset = 0
   476  	rdb.PrintNameLength = rdb.SubstituteNameLength
   477  	if flags&SYMLINKAT_RELATIVE != 0 {
   478  		rdb.Flags = SYMLINK_FLAG_RELATIVE
   479  	}
   480  
   481  	namebuf := rdbbuf[bufferSize:]
   482  	copy(namebuf, unsafe.String((*byte)(unsafe.Pointer(&oldnameu16[0])), 2*len(oldnameu16)))
   483  
   484  	err = syscall.DeviceIoControl(
   485  		h,
   486  		FSCTL_SET_REPARSE_POINT,
   487  		&rdbbuf[0],
   488  		uint32(len(rdbbuf)),
   489  		nil,
   490  		0,
   491  		nil,
   492  		nil)
   493  	if err != nil {
   494  		// Creating the symlink has failed, so try to remove the file.
   495  		const FileDispositionInformation = 13
   496  		NtSetInformationFile(
   497  			h,
   498  			&IO_STATUS_BLOCK{},
   499  			unsafe.Pointer(&FILE_DISPOSITION_INFORMATION{
   500  				DeleteFile: true,
   501  			}),
   502  			uint32(unsafe.Sizeof(FILE_DISPOSITION_INFORMATION{})),
   503  			FileDispositionInformation,
   504  		)
   505  		return err
   506  	}
   507  
   508  	return nil
   509  }
   510  
   511  // withPrivilege temporariliy acquires the named privilege and runs f.
   512  // If the privilege cannot be acquired it runs f anyway,
   513  // which should fail with an appropriate error.
   514  func withPrivilege(privilege string, f func() error) error {
   515  	runtime.LockOSThread()
   516  	defer runtime.UnlockOSThread()
   517  
   518  	err := ImpersonateSelf(SecurityImpersonation)
   519  	if err != nil {
   520  		return f()
   521  	}
   522  	defer RevertToSelf()
   523  
   524  	curThread, err := GetCurrentThread()
   525  	if err != nil {
   526  		return f()
   527  	}
   528  	var token syscall.Token
   529  	err = OpenThreadToken(curThread, syscall.TOKEN_QUERY|TOKEN_ADJUST_PRIVILEGES, false, &token)
   530  	if err != nil {
   531  		return f()
   532  	}
   533  	defer syscall.CloseHandle(syscall.Handle(token))
   534  
   535  	privStr, err := syscall.UTF16PtrFromString(privilege)
   536  	if err != nil {
   537  		return f()
   538  	}
   539  	var tokenPriv TOKEN_PRIVILEGES
   540  	err = LookupPrivilegeValue(nil, privStr, &tokenPriv.Privileges[0].Luid)
   541  	if err != nil {
   542  		return f()
   543  	}
   544  
   545  	tokenPriv.PrivilegeCount = 1
   546  	tokenPriv.Privileges[0].Attributes = SE_PRIVILEGE_ENABLED
   547  	err = AdjustTokenPrivileges(token, false, &tokenPriv, 0, nil, nil)
   548  	if err != nil {
   549  		return f()
   550  	}
   551  
   552  	return f()
   553  }
   554
View as plain text