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[filesystem] Don't error on weird system files (#2715)
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Co-authored-by: nicole mazzuca <mazzucan@outlook.com>
Co-authored-by: Stephan T. Lavavej <stl@nuwen.net>
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@strega-nil-ms @strega-nil @StephanTLavavej
3 people authored May 17, 2022
1 parent 9ca4a29 commit 1134982
Showing 1 changed file with 41 additions and 48 deletions.
89 changes: 41 additions & 48 deletions stl/src/filesystem.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -154,6 +154,10 @@ namespace {

return __std_win_error{GetLastError()};
}

[[nodiscard]] unsigned long long _Merge_to_ull(unsigned long _High, unsigned long _Low) noexcept {
return (static_cast<unsigned long long>(_High) << 32) | static_cast<unsigned long long>(_Low);
}
} // unnamed namespace

_EXTERN_C
Expand Down Expand Up @@ -774,43 +778,9 @@ _Success_(return == __std_win_error::_Success) __std_win_error
return {_Size, __std_win_error::_Success};
}

// This structure is meant to be embedded into __std_fs_stats that properly aligned it,
// so that 64-bit values are fully aligned. Note that _File_size fields are flipped to be in low:high order
// and represented by __std_fs_filetime which is a pair of ulongs.
// If this structure is used in GetFileAttributesEx, after successful read, File_size parts must be put in
// low:high order, as GetFileAttributesEx returns them in high:low order.
struct _File_attr_data { // typedef struct _WIN32_FILE_ATTRIBUTE_DATA {
__std_fs_file_attr _Attributes; // DWORD dwFileAttributes;
__std_fs_filetime _Creation_time; // FILETIME ftCreationTime;
__std_fs_filetime _Last_access_time; // FILETIME ftLastAccessTime;
__std_fs_filetime _Last_write_time; // FILETIME ftLastWriteTime;
unsigned long _File_size_high; // DWORD nFileSizeHigh;
unsigned long _File_size_low; // DWORD nFileSizeLow;
}; // } WIN32_FILE_ATTRIBUTE_DATA, *LPWIN32_FILE_ATTRIBUTE_DATA;

struct alignas(long long) _Aligned_file_attrs {
unsigned long _Padding; // align the __std_fs_filetime inside _Data to make the memcpy below an ordinary 64-bit load
_File_attr_data _Data;

[[nodiscard]] long long _Last_write_time() const noexcept {
long long _Result;
_CSTD memcpy(&_Result, &_Data._Last_write_time, sizeof(_Result));
return _Result;
}

[[nodiscard]] unsigned long long _File_size() const noexcept {
return (static_cast<unsigned long long>(_Data._File_size_high) << 32) + _Data._File_size_low;
}
};

[[nodiscard]] _Success_(return == __std_win_error::_Success) __std_win_error
__stdcall __std_fs_get_stats(_In_z_ const wchar_t* const _Path, __std_fs_stats* const _Stats,
_In_ __std_fs_stats_flags _Flags, _In_ const __std_fs_file_attr _Symlink_attribute_hint) noexcept {
static_assert((offsetof(_Aligned_file_attrs, _Data._Last_write_time) % 8) == 0, "_Last_write_time not aligned");
static_assert(sizeof(_File_attr_data) == sizeof(WIN32_FILE_ATTRIBUTE_DATA));
static_assert(alignof(_File_attr_data) == alignof(WIN32_FILE_ATTRIBUTE_DATA));
static_assert(alignof(_File_attr_data) == 4);

const bool _Follow_symlinks = _Bitmask_includes(_Flags, __std_fs_stats_flags::_Follow_symlinks);
_Flags &= ~__std_fs_stats_flags::_Follow_symlinks;
if (_Follow_symlinks && _Bitmask_includes(_Flags, __std_fs_stats_flags::_Reparse_tag)) {
Expand All @@ -831,25 +801,48 @@ struct alignas(long long) _Aligned_file_attrs {

constexpr auto _Get_file_attributes_data =
__std_fs_stats_flags::_Attributes | __std_fs_stats_flags::_File_size | __std_fs_stats_flags::_Last_write_time;
if (_Bitmask_includes(
_Flags, _Get_file_attributes_data)) { // caller wants something GetFileAttributesExW might provide
if (_Bitmask_includes(_Flags, _Get_file_attributes_data)) {
// caller wants something GetFileAttributesExW/FindFirstFileW might provide
if (_Symlink_attribute_hint == __std_fs_file_attr::_Invalid
|| !_Bitmask_includes(_Symlink_attribute_hint, __std_fs_file_attr::_Reparse_point)
|| !_Follow_symlinks) { // we might not be a symlink or not following symlinks, so GetFileAttributesExW
// would return the right answer
_Aligned_file_attrs _Aligned_attrs;
auto& _Data = _Aligned_attrs._Data;
|| !_Follow_symlinks) { // we might not be a symlink or not following symlinks, so
// GetFileAttributesExW/FindFirstFileW would return the right answer

WIN32_FILE_ATTRIBUTE_DATA _Data;
if (!GetFileAttributesExW(_Path, GetFileExInfoStandard, &_Data)) {
return __std_win_error{GetLastError()};
// In some cases, ERROR_SHARING_VIOLATION is returned from GetFileAttributesExW;
// FindFirstFileW will work in those cases if we have read permissions on the directory.
if (const __std_win_error _Last_error{GetLastError()};
_Last_error != __std_win_error::_Sharing_violation) {
return _Last_error;
}

// Note that FindFirstFileW does allow globbing characters and has extra behavior with them
// that we don't want. However, GetFileAttributesExW would've failed with ERROR_INVALID_NAME
// if there were any globbing characters in _Path.
WIN32_FIND_DATAW _Find_data;
{
HANDLE _Find_handle = FindFirstFileW(_Path, &_Find_data);
if (_Find_handle == INVALID_HANDLE_VALUE) {
return __std_win_error{GetLastError()};
}
FindClose(_Find_handle);
}

_Data.dwFileAttributes = _Find_data.dwFileAttributes;
_Data.nFileSizeHigh = _Find_data.nFileSizeHigh;
_Data.nFileSizeLow = _Find_data.nFileSizeLow;
_Data.ftLastWriteTime = _Find_data.ftLastWriteTime;
}

if (!_Follow_symlinks
|| !_Bitmask_includes(_Data._Attributes,
__std_fs_file_attr::_Reparse_point)) { // if we aren't following symlinks or can't be a
// symlink, that data was useful, record
_Stats->_Attributes = _Data._Attributes;
_Stats->_File_size = _Aligned_attrs._File_size();
_Stats->_Last_write_time = _Aligned_attrs._Last_write_time();
const __std_fs_file_attr _Attributes{_Data.dwFileAttributes};
if (!_Follow_symlinks || !_Bitmask_includes(_Attributes, __std_fs_file_attr::_Reparse_point)) {
// if we aren't following symlinks or can't be a symlink, that data was useful, record
_Stats->_Attributes = _Attributes;
_Stats->_File_size = _Merge_to_ull(_Data.nFileSizeHigh, _Data.nFileSizeLow);
_Stats->_Last_write_time = static_cast<long long>(
_Merge_to_ull(_Data.ftLastWriteTime.dwHighDateTime, _Data.ftLastWriteTime.dwLowDateTime));

_Flags &= ~_Get_file_attributes_data;
}
}
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