Source file src/internal/syscall/windows/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|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  	const (
   224  		FileDispositionInformation   = 13
   225  		FileDispositionInformationEx = 64
   226  	)
   227  
   228  	// First, attempt to delete the file using POSIX semantics
   229  	// (which permit a file to be deleted while it is still open).
   230  	// This matches the behavior of DeleteFileW.
   231  	err = NtSetInformationFile(
   232  		h,
   233  		&IO_STATUS_BLOCK{},
   234  		unsafe.Pointer(&FILE_DISPOSITION_INFORMATION_EX{
   235  			Flags: FILE_DISPOSITION_DELETE |
   236  				FILE_DISPOSITION_FORCE_IMAGE_SECTION_CHECK |
   237  				FILE_DISPOSITION_POSIX_SEMANTICS |
   238  				// This differs from DeleteFileW, but matches os.Remove's
   239  				// behavior on Unix platforms of permitting deletion of
   240  				// read-only files.
   241  				FILE_DISPOSITION_IGNORE_READONLY_ATTRIBUTE,
   242  		}),
   243  		uint32(unsafe.Sizeof(FILE_DISPOSITION_INFORMATION_EX{})),
   244  		FileDispositionInformationEx,
   245  	)
   246  	switch err {
   247  	case nil:
   248  		return nil
   249  	case STATUS_CANNOT_DELETE, STATUS_DIRECTORY_NOT_EMPTY:
   250  		return err.(NTStatus).Errno()
   251  	}
   252  
   253  	// If the prior deletion failed, the filesystem either doesn't support
   254  	// POSIX semantics (for example, FAT), or hasn't implemented
   255  	// FILE_DISPOSITION_INFORMATION_EX.
   256  	//
   257  	// Try again.
   258  	err = NtSetInformationFile(
   259  		h,
   260  		&IO_STATUS_BLOCK{},
   261  		unsafe.Pointer(&FILE_DISPOSITION_INFORMATION{
   262  			DeleteFile: true,
   263  		}),
   264  		uint32(unsafe.Sizeof(FILE_DISPOSITION_INFORMATION{})),
   265  		FileDispositionInformation,
   266  	)
   267  	if st, ok := err.(NTStatus); ok {
   268  		return st.Errno()
   269  	}
   270  	return err
   271  }
   272  
   273  func Renameat(olddirfd syscall.Handle, oldpath string, newdirfd syscall.Handle, newpath string) error {
   274  	objAttrs := &OBJECT_ATTRIBUTES{}
   275  	if err := objAttrs.init(olddirfd, oldpath); err != nil {
   276  		return err
   277  	}
   278  	var h syscall.Handle
   279  	err := NtOpenFile(
   280  		&h,
   281  		SYNCHRONIZE|DELETE,
   282  		objAttrs,
   283  		&IO_STATUS_BLOCK{},
   284  		FILE_SHARE_DELETE|FILE_SHARE_READ|FILE_SHARE_WRITE,
   285  		FILE_OPEN_REPARSE_POINT|FILE_OPEN_FOR_BACKUP_INTENT|FILE_SYNCHRONOUS_IO_NONALERT,
   286  	)
   287  	if err != nil {
   288  		return ntCreateFileError(err, 0)
   289  	}
   290  	defer syscall.CloseHandle(h)
   291  
   292  	renameInfoEx := FILE_RENAME_INFORMATION_EX{
   293  		Flags: FILE_RENAME_REPLACE_IF_EXISTS |
   294  			FILE_RENAME_POSIX_SEMANTICS,
   295  		RootDirectory: newdirfd,
   296  	}
   297  	p16, err := syscall.UTF16FromString(newpath)
   298  	if err != nil {
   299  		return err
   300  	}
   301  	if len(p16) > len(renameInfoEx.FileName) {
   302  		return syscall.EINVAL
   303  	}
   304  	copy(renameInfoEx.FileName[:], p16)
   305  	renameInfoEx.FileNameLength = uint32((len(p16) - 1) * 2)
   306  
   307  	const (
   308  		FileRenameInformation   = 10
   309  		FileRenameInformationEx = 65
   310  	)
   311  	err = NtSetInformationFile(
   312  		h,
   313  		&IO_STATUS_BLOCK{},
   314  		unsafe.Pointer(&renameInfoEx),
   315  		uint32(unsafe.Sizeof(FILE_RENAME_INFORMATION_EX{})),
   316  		FileRenameInformationEx,
   317  	)
   318  	if err == nil {
   319  		return nil
   320  	}
   321  
   322  	// If the prior rename failed, the filesystem might not support
   323  	// POSIX semantics (for example, FAT), or might not have implemented
   324  	// FILE_RENAME_INFORMATION_EX.
   325  	//
   326  	// Try again.
   327  	renameInfo := FILE_RENAME_INFORMATION{
   328  		ReplaceIfExists: true,
   329  		RootDirectory:   newdirfd,
   330  	}
   331  	copy(renameInfo.FileName[:], p16)
   332  	renameInfo.FileNameLength = renameInfoEx.FileNameLength
   333  
   334  	err = NtSetInformationFile(
   335  		h,
   336  		&IO_STATUS_BLOCK{},
   337  		unsafe.Pointer(&renameInfo),
   338  		uint32(unsafe.Sizeof(FILE_RENAME_INFORMATION{})),
   339  		FileRenameInformation,
   340  	)
   341  	if st, ok := err.(NTStatus); ok {
   342  		return st.Errno()
   343  	}
   344  	return err
   345  }
   346  
   347  func Linkat(olddirfd syscall.Handle, oldpath string, newdirfd syscall.Handle, newpath string) error {
   348  	objAttrs := &OBJECT_ATTRIBUTES{}
   349  	if err := objAttrs.init(olddirfd, oldpath); err != nil {
   350  		return err
   351  	}
   352  	var h syscall.Handle
   353  	err := NtOpenFile(
   354  		&h,
   355  		SYNCHRONIZE|FILE_WRITE_ATTRIBUTES,
   356  		objAttrs,
   357  		&IO_STATUS_BLOCK{},
   358  		FILE_SHARE_DELETE|FILE_SHARE_READ|FILE_SHARE_WRITE,
   359  		FILE_OPEN_REPARSE_POINT|FILE_OPEN_FOR_BACKUP_INTENT|FILE_SYNCHRONOUS_IO_NONALERT,
   360  	)
   361  	if err != nil {
   362  		return ntCreateFileError(err, 0)
   363  	}
   364  	defer syscall.CloseHandle(h)
   365  
   366  	linkInfo := FILE_LINK_INFORMATION{
   367  		RootDirectory: newdirfd,
   368  	}
   369  	p16, err := syscall.UTF16FromString(newpath)
   370  	if err != nil {
   371  		return err
   372  	}
   373  	if len(p16) > len(linkInfo.FileName) {
   374  		return syscall.EINVAL
   375  	}
   376  	copy(linkInfo.FileName[:], p16)
   377  	linkInfo.FileNameLength = uint32((len(p16) - 1) * 2)
   378  
   379  	const (
   380  		FileLinkInformation = 11
   381  	)
   382  	err = NtSetInformationFile(
   383  		h,
   384  		&IO_STATUS_BLOCK{},
   385  		unsafe.Pointer(&linkInfo),
   386  		uint32(unsafe.Sizeof(FILE_LINK_INFORMATION{})),
   387  		FileLinkInformation,
   388  	)
   389  	if st, ok := err.(NTStatus); ok {
   390  		return st.Errno()
   391  	}
   392  	return err
   393  }
   394  
   395  // SymlinkatFlags configure Symlinkat.
   396  //
   397  // Symbolic links have two properties: They may be directory or file links,
   398  // and they may be absolute or relative.
   399  //
   400  // The Windows API defines flags describing these properties
   401  // (SYMBOLIC_LINK_FLAG_DIRECTORY and SYMLINK_FLAG_RELATIVE),
   402  // but the flags are passed to different system calls and
   403  // do not have distinct values, so we define our own enumeration
   404  // that permits expressing both.
   405  type SymlinkatFlags uint
   406  
   407  const (
   408  	SYMLINKAT_DIRECTORY = SymlinkatFlags(1 << iota)
   409  	SYMLINKAT_RELATIVE
   410  )
   411  
   412  func Symlinkat(oldname string, newdirfd syscall.Handle, newname string, flags SymlinkatFlags) error {
   413  	// Temporarily acquire symlink-creating privileges if possible.
   414  	// This is the behavior of CreateSymbolicLinkW.
   415  	//
   416  	// (When passed the SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE flag,
   417  	// CreateSymbolicLinkW ignores errors in acquiring privileges, as we do here.)
   418  	return withPrivilege("SeCreateSymbolicLinkPrivilege", func() error {
   419  		return symlinkat(oldname, newdirfd, newname, flags)
   420  	})
   421  }
   422  
   423  func symlinkat(oldname string, newdirfd syscall.Handle, newname string, flags SymlinkatFlags) error {
   424  	oldnameu16, err := syscall.UTF16FromString(oldname)
   425  	if err != nil {
   426  		return err
   427  	}
   428  	oldnameu16 = oldnameu16[:len(oldnameu16)-1] // trim off terminal NUL
   429  
   430  	var options uint32
   431  	if flags&SYMLINKAT_DIRECTORY != 0 {
   432  		options |= FILE_DIRECTORY_FILE
   433  	} else {
   434  		options |= FILE_NON_DIRECTORY_FILE
   435  	}
   436  
   437  	objAttrs := &OBJECT_ATTRIBUTES{}
   438  	if err := objAttrs.init(newdirfd, newname); err != nil {
   439  		return err
   440  	}
   441  	var h syscall.Handle
   442  	err = NtCreateFile(
   443  		&h,
   444  		SYNCHRONIZE|FILE_WRITE_ATTRIBUTES|DELETE,
   445  		objAttrs,
   446  		&IO_STATUS_BLOCK{},
   447  		nil,
   448  		syscall.FILE_ATTRIBUTE_NORMAL,
   449  		0,
   450  		FILE_CREATE,
   451  		FILE_OPEN_REPARSE_POINT|FILE_OPEN_FOR_BACKUP_INTENT|FILE_SYNCHRONOUS_IO_NONALERT|options,
   452  		nil,
   453  		0,
   454  	)
   455  	if err != nil {
   456  		return ntCreateFileError(err, 0)
   457  	}
   458  	defer syscall.CloseHandle(h)
   459  
   460  	// https://learn.microsoft.com/en-us/windows-hardware/drivers/ddi/ntifs/ns-ntifs-_reparse_data_buffer
   461  	type reparseDataBufferT struct {
   462  		_ structs.HostLayout
   463  
   464  		ReparseTag        uint32
   465  		ReparseDataLength uint16
   466  		Reserved          uint16
   467  
   468  		SubstituteNameOffset uint16
   469  		SubstituteNameLength uint16
   470  		PrintNameOffset      uint16
   471  		PrintNameLength      uint16
   472  		Flags                uint32
   473  	}
   474  
   475  	const (
   476  		headerSize = uint16(unsafe.Offsetof(reparseDataBufferT{}.SubstituteNameOffset))
   477  		bufferSize = uint16(unsafe.Sizeof(reparseDataBufferT{}))
   478  	)
   479  
   480  	// Data buffer containing a SymbolicLinkReparseBuffer followed by the link target.
   481  	rdbbuf := make([]byte, bufferSize+uint16(2*len(oldnameu16)))
   482  
   483  	rdb := (*reparseDataBufferT)(unsafe.Pointer(&rdbbuf[0]))
   484  	rdb.ReparseTag = syscall.IO_REPARSE_TAG_SYMLINK
   485  	rdb.ReparseDataLength = uint16(len(rdbbuf)) - uint16(headerSize)
   486  	rdb.SubstituteNameOffset = 0
   487  	rdb.SubstituteNameLength = uint16(2 * len(oldnameu16))
   488  	rdb.PrintNameOffset = 0
   489  	rdb.PrintNameLength = rdb.SubstituteNameLength
   490  	if flags&SYMLINKAT_RELATIVE != 0 {
   491  		rdb.Flags = SYMLINK_FLAG_RELATIVE
   492  	}
   493  
   494  	namebuf := rdbbuf[bufferSize:]
   495  	copy(namebuf, unsafe.String((*byte)(unsafe.Pointer(&oldnameu16[0])), 2*len(oldnameu16)))
   496  
   497  	err = syscall.DeviceIoControl(
   498  		h,
   499  		FSCTL_SET_REPARSE_POINT,
   500  		&rdbbuf[0],
   501  		uint32(len(rdbbuf)),
   502  		nil,
   503  		0,
   504  		nil,
   505  		nil)
   506  	if err != nil {
   507  		// Creating the symlink has failed, so try to remove the file.
   508  		const FileDispositionInformation = 13
   509  		NtSetInformationFile(
   510  			h,
   511  			&IO_STATUS_BLOCK{},
   512  			unsafe.Pointer(&FILE_DISPOSITION_INFORMATION{
   513  				DeleteFile: true,
   514  			}),
   515  			uint32(unsafe.Sizeof(FILE_DISPOSITION_INFORMATION{})),
   516  			FileDispositionInformation,
   517  		)
   518  		return err
   519  	}
   520  
   521  	return nil
   522  }
   523  
   524  // withPrivilege temporariliy acquires the named privilege and runs f.
   525  // If the privilege cannot be acquired it runs f anyway,
   526  // which should fail with an appropriate error.
   527  func withPrivilege(privilege string, f func() error) error {
   528  	runtime.LockOSThread()
   529  	defer runtime.UnlockOSThread()
   530  
   531  	err := ImpersonateSelf(SecurityImpersonation)
   532  	if err != nil {
   533  		return f()
   534  	}
   535  	defer RevertToSelf()
   536  
   537  	curThread, err := GetCurrentThread()
   538  	if err != nil {
   539  		return f()
   540  	}
   541  	var token syscall.Token
   542  	err = OpenThreadToken(curThread, syscall.TOKEN_QUERY|TOKEN_ADJUST_PRIVILEGES, false, &token)
   543  	if err != nil {
   544  		return f()
   545  	}
   546  	defer syscall.CloseHandle(syscall.Handle(token))
   547  
   548  	privStr, err := syscall.UTF16PtrFromString(privilege)
   549  	if err != nil {
   550  		return f()
   551  	}
   552  	var tokenPriv TOKEN_PRIVILEGES
   553  	err = LookupPrivilegeValue(nil, privStr, &tokenPriv.Privileges[0].Luid)
   554  	if err != nil {
   555  		return f()
   556  	}
   557  
   558  	tokenPriv.PrivilegeCount = 1
   559  	tokenPriv.Privileges[0].Attributes = SE_PRIVILEGE_ENABLED
   560  	err = AdjustTokenPrivileges(token, false, &tokenPriv, 0, nil, nil)
   561  	if err != nil {
   562  		return f()
   563  	}
   564  
   565  	return f()
   566  }
   567  

View as plain text