bpo-37834: Normalise handling of reparse points on Windows (GH-15231)

bpo-37834: Normalise handling of reparse points on Windows
* ntpath.realpath() and nt.stat() will traverse all supported reparse points (previously was mixed)
* nt.lstat() will let the OS traverse reparse points that are not name surrogates (previously would not traverse any reparse point)
* nt.[l]stat() will only set S_IFLNK for symlinks (previous behaviour)
* nt.readlink() will read destinations for symlinks and junction points only

bpo-1311: os.path.exists('nul') now returns True on Windows
* nt.stat('nul').st_mode is now S_IFCHR (previously was an error)
This commit is contained in:
Steve Dower 2019-08-21 15:27:33 -07:00 committed by GitHub
parent bcc446f525
commit df2d4a6f3d
No known key found for this signature in database
GPG key ID: 4AEE18F83AFDEB23
16 changed files with 477 additions and 240 deletions

View file

@ -1625,6 +1625,7 @@ win32_wchdir(LPCWSTR path)
*/
#define HAVE_STAT_NSEC 1
#define HAVE_STRUCT_STAT_ST_FILE_ATTRIBUTES 1
#define HAVE_STRUCT_STAT_ST_REPARSE_TAG 1
static void
find_data_to_file_info(WIN32_FIND_DATAW *pFileData,
@ -1658,136 +1659,178 @@ attributes_from_dir(LPCWSTR pszFile, BY_HANDLE_FILE_INFORMATION *info, ULONG *re
return TRUE;
}
static BOOL
get_target_path(HANDLE hdl, wchar_t **target_path)
{
int buf_size, result_length;
wchar_t *buf;
/* We have a good handle to the target, use it to determine
the target path name (then we'll call lstat on it). */
buf_size = GetFinalPathNameByHandleW(hdl, 0, 0,
VOLUME_NAME_DOS);
if(!buf_size)
return FALSE;
buf = (wchar_t *)PyMem_RawMalloc((buf_size + 1) * sizeof(wchar_t));
if (!buf) {
SetLastError(ERROR_OUTOFMEMORY);
return FALSE;
}
result_length = GetFinalPathNameByHandleW(hdl,
buf, buf_size, VOLUME_NAME_DOS);
if(!result_length) {
PyMem_RawFree(buf);
return FALSE;
}
buf[result_length] = 0;
*target_path = buf;
return TRUE;
}
static int
win32_xstat_impl(const wchar_t *path, struct _Py_stat_struct *result,
BOOL traverse)
{
int code;
HANDLE hFile, hFile2;
BY_HANDLE_FILE_INFORMATION info;
ULONG reparse_tag = 0;
wchar_t *target_path;
const wchar_t *dot;
HANDLE hFile;
BY_HANDLE_FILE_INFORMATION fileInfo;
FILE_ATTRIBUTE_TAG_INFO tagInfo = { 0 };
DWORD fileType, error;
BOOL isUnhandledTag = FALSE;
int retval = 0;
hFile = CreateFileW(
path,
FILE_READ_ATTRIBUTES, /* desired access */
0, /* share mode */
NULL, /* security attributes */
OPEN_EXISTING,
/* FILE_FLAG_BACKUP_SEMANTICS is required to open a directory */
/* FILE_FLAG_OPEN_REPARSE_POINT does not follow the symlink.
Because of this, calls like GetFinalPathNameByHandle will return
the symlink path again and not the actual final path. */
FILE_ATTRIBUTE_NORMAL|FILE_FLAG_BACKUP_SEMANTICS|
FILE_FLAG_OPEN_REPARSE_POINT,
NULL);
DWORD access = FILE_READ_ATTRIBUTES;
DWORD flags = FILE_FLAG_BACKUP_SEMANTICS; /* Allow opening directories. */
if (!traverse) {
flags |= FILE_FLAG_OPEN_REPARSE_POINT;
}
hFile = CreateFileW(path, access, 0, NULL, OPEN_EXISTING, flags, NULL);
if (hFile == INVALID_HANDLE_VALUE) {
/* Either the target doesn't exist, or we don't have access to
get a handle to it. If the former, we need to return an error.
If the latter, we can use attributes_from_dir. */
DWORD lastError = GetLastError();
if (lastError != ERROR_ACCESS_DENIED &&
lastError != ERROR_SHARING_VIOLATION)
return -1;
/* Could not get attributes on open file. Fall back to
reading the directory. */
if (!attributes_from_dir(path, &info, &reparse_tag))
/* Very strange. This should not fail now */
return -1;
if (info.dwFileAttributes & FILE_ATTRIBUTE_REPARSE_POINT) {
if (traverse) {
/* Should traverse, but could not open reparse point handle */
SetLastError(lastError);
/* Either the path doesn't exist, or the caller lacks access. */
error = GetLastError();
switch (error) {
case ERROR_ACCESS_DENIED: /* Cannot sync or read attributes. */
case ERROR_SHARING_VIOLATION: /* It's a paging file. */
/* Try reading the parent directory. */
if (!attributes_from_dir(path, &fileInfo, &tagInfo.ReparseTag)) {
/* Cannot read the parent directory. */
SetLastError(error);
return -1;
}
}
} else {
if (!GetFileInformationByHandle(hFile, &info)) {
CloseHandle(hFile);
return -1;
}
if (info.dwFileAttributes & FILE_ATTRIBUTE_REPARSE_POINT) {
if (!win32_get_reparse_tag(hFile, &reparse_tag)) {
CloseHandle(hFile);
return -1;
}
/* Close the outer open file handle now that we're about to
reopen it with different flags. */
if (!CloseHandle(hFile))
return -1;
if (traverse) {
/* In order to call GetFinalPathNameByHandle we need to open
the file without the reparse handling flag set. */
hFile2 = CreateFileW(
path, FILE_READ_ATTRIBUTES, FILE_SHARE_READ,
NULL, OPEN_EXISTING,
FILE_ATTRIBUTE_NORMAL|FILE_FLAG_BACKUP_SEMANTICS,
NULL);
if (hFile2 == INVALID_HANDLE_VALUE)
return -1;
if (!get_target_path(hFile2, &target_path)) {
CloseHandle(hFile2);
if (fileInfo.dwFileAttributes & FILE_ATTRIBUTE_REPARSE_POINT) {
if (traverse ||
!IsReparseTagNameSurrogate(tagInfo.ReparseTag)) {
/* The stat call has to traverse but cannot, so fail. */
SetLastError(error);
return -1;
}
if (!CloseHandle(hFile2)) {
return -1;
}
code = win32_xstat_impl(target_path, result, FALSE);
PyMem_RawFree(target_path);
return code;
}
} else
CloseHandle(hFile);
}
_Py_attribute_data_to_stat(&info, reparse_tag, result);
break;
/* Set S_IEXEC if it is an .exe, .bat, ... */
dot = wcsrchr(path, '.');
if (dot) {
if (_wcsicmp(dot, L".bat") == 0 || _wcsicmp(dot, L".cmd") == 0 ||
_wcsicmp(dot, L".exe") == 0 || _wcsicmp(dot, L".com") == 0)
result->st_mode |= 0111;
case ERROR_INVALID_PARAMETER:
/* \\.\con requires read or write access. */
hFile = CreateFileW(path, access | GENERIC_READ,
FILE_SHARE_READ | FILE_SHARE_WRITE, NULL,
OPEN_EXISTING, flags, NULL);
if (hFile == INVALID_HANDLE_VALUE) {
SetLastError(error);
return -1;
}
break;
case ERROR_CANT_ACCESS_FILE:
/* bpo37834: open unhandled reparse points if traverse fails. */
if (traverse) {
traverse = FALSE;
isUnhandledTag = TRUE;
hFile = CreateFileW(path, access, 0, NULL, OPEN_EXISTING,
flags | FILE_FLAG_OPEN_REPARSE_POINT, NULL);
}
if (hFile == INVALID_HANDLE_VALUE) {
SetLastError(error);
return -1;
}
break;
default:
return -1;
}
}
return 0;
if (hFile != INVALID_HANDLE_VALUE) {
/* Handle types other than files on disk. */
fileType = GetFileType(hFile);
if (fileType != FILE_TYPE_DISK) {
if (fileType == FILE_TYPE_UNKNOWN && GetLastError() != 0) {
retval = -1;
goto cleanup;
}
DWORD fileAttributes = GetFileAttributesW(path);
memset(result, 0, sizeof(*result));
if (fileAttributes != INVALID_FILE_ATTRIBUTES &&
fileAttributes & FILE_ATTRIBUTE_DIRECTORY) {
/* \\.\pipe\ or \\.\mailslot\ */
result->st_mode = _S_IFDIR;
} else if (fileType == FILE_TYPE_CHAR) {
/* \\.\nul */
result->st_mode = _S_IFCHR;
} else if (fileType == FILE_TYPE_PIPE) {
/* \\.\pipe\spam */
result->st_mode = _S_IFIFO;
}
/* FILE_TYPE_UNKNOWN, e.g. \\.\mailslot\waitfor.exe\spam */
goto cleanup;
}
/* Query the reparse tag, and traverse a non-link. */
if (!traverse) {
if (!GetFileInformationByHandleEx(hFile, FileAttributeTagInfo,
&tagInfo, sizeof(tagInfo))) {
/* Allow devices that do not support FileAttributeTagInfo. */
switch (GetLastError()) {
case ERROR_INVALID_PARAMETER:
case ERROR_INVALID_FUNCTION:
case ERROR_NOT_SUPPORTED:
tagInfo.FileAttributes = FILE_ATTRIBUTE_NORMAL;
tagInfo.ReparseTag = 0;
break;
default:
retval = -1;
goto cleanup;
}
} else if (tagInfo.FileAttributes &
FILE_ATTRIBUTE_REPARSE_POINT) {
if (IsReparseTagNameSurrogate(tagInfo.ReparseTag)) {
if (isUnhandledTag) {
/* Traversing previously failed for either this link
or its target. */
SetLastError(ERROR_CANT_ACCESS_FILE);
retval = -1;
goto cleanup;
}
/* Traverse a non-link, but not if traversing already failed
for an unhandled tag. */
} else if (!isUnhandledTag) {
CloseHandle(hFile);
return win32_xstat_impl(path, result, TRUE);
}
}
}
if (!GetFileInformationByHandle(hFile, &fileInfo)) {
switch (GetLastError()) {
case ERROR_INVALID_PARAMETER:
case ERROR_INVALID_FUNCTION:
case ERROR_NOT_SUPPORTED:
retval = -1;
goto cleanup;
}
/* Volumes and physical disks are block devices, e.g.
\\.\C: and \\.\PhysicalDrive0. */
memset(result, 0, sizeof(*result));
result->st_mode = 0x6000; /* S_IFBLK */
goto cleanup;
}
}
_Py_attribute_data_to_stat(&fileInfo, tagInfo.ReparseTag, result);
if (!(fileInfo.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY)) {
/* Fix the file execute permissions. This hack sets S_IEXEC if
the filename has an extension that is commonly used by files
that CreateProcessW can execute. A real implementation calls
GetSecurityInfo, OpenThreadToken/OpenProcessToken, and
AccessCheck to check for generic read, write, and execute
access. */
const wchar_t *fileExtension = wcsrchr(path, '.');
if (fileExtension) {
if (_wcsicmp(fileExtension, L".exe") == 0 ||
_wcsicmp(fileExtension, L".bat") == 0 ||
_wcsicmp(fileExtension, L".cmd") == 0 ||
_wcsicmp(fileExtension, L".com") == 0) {
result->st_mode |= 0111;
}
}
}
cleanup:
if (hFile != INVALID_HANDLE_VALUE) {
CloseHandle(hFile);
}
return retval;
}
static int
@ -1806,9 +1849,8 @@ win32_xstat(const wchar_t *path, struct _Py_stat_struct *result, BOOL traverse)
default does not traverse symlinks and instead returns attributes for
the symlink.
Therefore, win32_lstat will get the attributes traditionally, and
win32_stat will first explicitly resolve the symlink target and then will
call win32_lstat on that result. */
Instead, we will open the file (which *does* traverse symlinks by default)
and GetFileInformationByHandle(). */
static int
win32_lstat(const wchar_t* path, struct _Py_stat_struct *result)
@ -1876,6 +1918,9 @@ static PyStructSequence_Field stat_result_fields[] = {
#endif
#ifdef HAVE_STRUCT_STAT_ST_FSTYPE
{"st_fstype", "Type of filesystem"},
#endif
#ifdef HAVE_STRUCT_STAT_ST_REPARSE_TAG
{"st_reparse_tag", "Windows reparse tag"},
#endif
{0}
};
@ -1928,6 +1973,12 @@ static PyStructSequence_Field stat_result_fields[] = {
#define ST_FSTYPE_IDX ST_FILE_ATTRIBUTES_IDX
#endif
#ifdef HAVE_STRUCT_STAT_ST_REPARSE_TAG
#define ST_REPARSE_TAG_IDX (ST_FSTYPE_IDX+1)
#else
#define ST_REPARSE_TAG_IDX ST_FSTYPE_IDX
#endif
static PyStructSequence_Desc stat_result_desc = {
"stat_result", /* name */
stat_result__doc__, /* doc */
@ -2155,6 +2206,10 @@ _pystat_fromstructstat(STRUCT_STAT *st)
PyStructSequence_SET_ITEM(v, ST_FSTYPE_IDX,
PyUnicode_FromString(st->st_fstype));
#endif
#ifdef HAVE_STRUCT_STAT_ST_REPARSE_TAG
PyStructSequence_SET_ITEM(v, ST_REPARSE_TAG_IDX,
PyLong_FromUnsignedLong(st->st_reparse_tag));
#endif
if (PyErr_Occurred()) {
Py_DECREF(v);
@ -3877,8 +3932,9 @@ os__getfinalpathname_impl(PyObject *module, path_t *path)
}
result = PyUnicode_FromWideChar(target_path, result_length);
if (path->narrow)
if (result && path->narrow) {
Py_SETREF(result, PyUnicode_EncodeFSDefault(result));
}
cleanup:
if (target_path != buf) {
@ -3888,44 +3944,6 @@ cleanup:
return result;
}
/*[clinic input]
os._isdir
path as arg: object
/
Return true if the pathname refers to an existing directory.
[clinic start generated code]*/
static PyObject *
os__isdir(PyObject *module, PyObject *arg)
/*[clinic end generated code: output=404f334d85d4bf25 input=36cb6785874d479e]*/
{
DWORD attributes;
path_t path = PATH_T_INITIALIZE("_isdir", "path", 0, 0);
if (!path_converter(arg, &path)) {
if (PyErr_ExceptionMatches(PyExc_ValueError)) {
PyErr_Clear();
Py_RETURN_FALSE;
}
return NULL;
}
Py_BEGIN_ALLOW_THREADS
attributes = GetFileAttributesW(path.wide);
Py_END_ALLOW_THREADS
path_cleanup(&path);
if (attributes == INVALID_FILE_ATTRIBUTES)
Py_RETURN_FALSE;
if (attributes & FILE_ATTRIBUTE_DIRECTORY)
Py_RETURN_TRUE;
else
Py_RETURN_FALSE;
}
/*[clinic input]
os._getvolumepathname
@ -7796,11 +7814,10 @@ os_readlink_impl(PyObject *module, path_t *path, int dir_fd)
return PyBytes_FromStringAndSize(buffer, length);
#elif defined(MS_WINDOWS)
DWORD n_bytes_returned;
DWORD io_result;
DWORD io_result = 0;
HANDLE reparse_point_handle;
char target_buffer[_Py_MAXIMUM_REPARSE_DATA_BUFFER_SIZE];
_Py_REPARSE_DATA_BUFFER *rdb = (_Py_REPARSE_DATA_BUFFER *)target_buffer;
const wchar_t *print_name;
PyObject *result;
/* First get a handle to the reparse point */
@ -7813,42 +7830,51 @@ os_readlink_impl(PyObject *module, path_t *path, int dir_fd)
OPEN_EXISTING,
FILE_FLAG_OPEN_REPARSE_POINT|FILE_FLAG_BACKUP_SEMANTICS,
0);
Py_END_ALLOW_THREADS
if (reparse_point_handle == INVALID_HANDLE_VALUE) {
return path_error(path);
if (reparse_point_handle != INVALID_HANDLE_VALUE) {
/* New call DeviceIoControl to read the reparse point */
io_result = DeviceIoControl(
reparse_point_handle,
FSCTL_GET_REPARSE_POINT,
0, 0, /* in buffer */
target_buffer, sizeof(target_buffer),
&n_bytes_returned,
0 /* we're not using OVERLAPPED_IO */
);
CloseHandle(reparse_point_handle);
}
Py_BEGIN_ALLOW_THREADS
/* New call DeviceIoControl to read the reparse point */
io_result = DeviceIoControl(
reparse_point_handle,
FSCTL_GET_REPARSE_POINT,
0, 0, /* in buffer */
target_buffer, sizeof(target_buffer),
&n_bytes_returned,
0 /* we're not using OVERLAPPED_IO */
);
CloseHandle(reparse_point_handle);
Py_END_ALLOW_THREADS
if (io_result == 0) {
return path_error(path);
}
if (rdb->ReparseTag != IO_REPARSE_TAG_SYMLINK)
wchar_t *name = NULL;
Py_ssize_t nameLen = 0;
if (rdb->ReparseTag == IO_REPARSE_TAG_SYMLINK)
{
PyErr_SetString(PyExc_ValueError,
"not a symbolic link");
return NULL;
name = (wchar_t *)((char*)rdb->SymbolicLinkReparseBuffer.PathBuffer +
rdb->SymbolicLinkReparseBuffer.SubstituteNameOffset);
nameLen = rdb->SymbolicLinkReparseBuffer.SubstituteNameLength / sizeof(wchar_t);
}
print_name = (wchar_t *)((char*)rdb->SymbolicLinkReparseBuffer.PathBuffer +
rdb->SymbolicLinkReparseBuffer.PrintNameOffset);
result = PyUnicode_FromWideChar(print_name,
rdb->SymbolicLinkReparseBuffer.PrintNameLength / sizeof(wchar_t));
if (path->narrow) {
Py_SETREF(result, PyUnicode_EncodeFSDefault(result));
else if (rdb->ReparseTag == IO_REPARSE_TAG_MOUNT_POINT)
{
name = (wchar_t *)((char*)rdb->MountPointReparseBuffer.PathBuffer +
rdb->MountPointReparseBuffer.SubstituteNameOffset);
nameLen = rdb->MountPointReparseBuffer.SubstituteNameLength / sizeof(wchar_t);
}
else
{
PyErr_SetString(PyExc_ValueError, "not a symbolic link");
}
if (name) {
if (nameLen > 4 && wcsncmp(name, L"\\??\\", 4) == 0) {
/* Our buffer is mutable, so this is okay */
name[1] = L'\\';
}
result = PyUnicode_FromWideChar(name, nameLen);
if (path->narrow) {
Py_SETREF(result, PyUnicode_EncodeFSDefault(result));
}
}
return result;
#endif
@ -13647,7 +13673,6 @@ static PyMethodDef posix_methods[] = {
OS_PATHCONF_METHODDEF
OS_ABORT_METHODDEF
OS__GETFULLPATHNAME_METHODDEF
OS__ISDIR_METHODDEF
OS__GETDISKUSAGE_METHODDEF
OS__GETFINALPATHNAME_METHODDEF
OS__GETVOLUMEPATHNAME_METHODDEF