mingw: fix getcwd when the parent directory cannot be queried

`GetLongPathName()` function may fail when it is unable to query
the parent directory of a path component to determine the long name
for that component. It happens, because of it uses `FindFirstFile()`
function for each next short part of path. The `FindFirstFile()`
requires `List Directory` and `Synchronize` desired access for a calling
process.

In case of lacking such permission for some part of path,
the `GetLongPathName()` returns 0 as result and `GetLastError()`
returns ERROR_ACCESS_DENIED.

`GetFinalPathNameByHandle()` function can help in such cases, because
it requires `Read Attributes` and `Synchronize` desired access to the
target path only.

The `GetFinalPathNameByHandle()` function was introduced on
`Windows Server 2008/Windows Vista`. So we need to load it dynamically.

`CreateFile()` parameters:
    `lpFileName` = path to the current directory
    `dwDesiredAccess` = 0 (it means `Read Attributes` and `Synchronize`)
    `dwShareMode` = FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE
                    (it prevents `Sharing Violation`)
    `lpSecurityAttributes` = NULL (default security attributes)
    `dwCreationDisposition` = OPEN_EXISTING
                              (required to obtain a directory handle)
    `dwFlagsAndAttributes` = FILE_FLAG_BACKUP_SEMANTICS
                             (required to obtain a directory handle)
    `hTemplateFile` = NULL (when opening an existing file or directory,
                            `CreateFile` ignores this parameter)

The string that is returned by `GetFinalPathNameByHandle()` function
uses the \\?\ syntax. To skip the prefix and convert backslashes
to slashes, the `normalize_ntpath()` mingw function will be used.

Note: `GetFinalPathNameByHandle()` function returns a final path.
It is the path that is returned when a path is fully resolved.
For example, for a symbolic link named "C:\tmp\mydir" that points to
"D:\yourdir", the final path would be "D:\yourdir".

Signed-off-by: Anton Serbulov <[email protected]>

Author: skvoboo

compat/mingw.c

@@ -838,11 +838,28 @@ struct tm *localtime_r(const time_t *timep, struct tm *result)
 char *mingw_getcwd(char *pointer, int len)
 {
 	wchar_t cwd[MAX_PATH], wpointer[MAX_PATH];
+	DECLARE_PROC_ADDR(kernel32.dll, DWORD, GetFinalPathNameByHandleW,
+			  HANDLE, LPWSTR, DWORD, DWORD);
 	DWORD ret = GetCurrentDirectoryW(ARRAY_SIZE(cwd), cwd);
 
 	if (ret < 0 || ret >= ARRAY_SIZE(cwd))
 		return NULL;
 	ret = GetLongPathNameW(cwd, wpointer, ARRAY_SIZE(wpointer));
+	if (!ret && GetLastError() == ERROR_ACCESS_DENIED &&
+		INIT_PROC_ADDR(GetFinalPathNameByHandleW)) {
+		HANDLE hnd = CreateFileW(cwd, 0,
+			FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE, NULL,
+			OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, NULL);
+		if (hnd == INVALID_HANDLE_VALUE)
+			return NULL;
+		ret = GetFinalPathNameByHandleW(hnd, wpointer, ARRAY_SIZE(wpointer), 0);
+		CloseHandle(hnd);
+		if (!ret || ret >= ARRAY_SIZE(wpointer))
+			return NULL;
+		if (xwcstoutf(pointer, normalize_ntpath(wpointer), len) < 0)
+			return NULL;
+		return pointer;
+	}
 	if (!ret || ret >= ARRAY_SIZE(wpointer))
 		return NULL;
 	if (xwcstoutf(pointer, wpointer, len) < 0)