On 2025-02-23 Lasse Collin wrote:
> On 2025-02-23 Pali Rohár wrote:
> > WinAPI \\?\ has meaning to not do any normalization, so consumer
> > should not add or remove some characters.
[...]
> In the new dirent, GetFullPathNameW converts mixed \/ usage to \, then
> * is appended and FindFirstFileW is called. The old code calls
> GetFileAttributes before constructing a full path
Even the old dirent has a problem: \??\ is broken because "\??\C:\"
works with GetFileAttributes, but _fullpath converts it to "C:\??\C:\",
and then readdir fails.
I attached a patch to the new dirent. It's shorter to read if white
space change is ignored. It skips GetFullPathNameW with the \\?\ and
\??\ prefixes. I didn't test but maybe this helps if there is a weird
directory name which doesn't survive filename normalization.
I will comment GetFileAttributesW considerations later.
--
Lasse Collin
From c849f103459c12599bcaf0d7f6674bb8541f02fe Mon Sep 17 00:00:00 2001
From: Lasse Collin <lasse.col...@tukaani.org>
Date: Mon, 24 Feb 2025 16:30:00 +0200
Subject: [PATCH] ... Skip GetFullPathNameW for \\?\ and \??\ paths
---
mingw-w64-crt/misc/dirent.c | 93 ++++++++++++++++++++++++++-----------
1 file changed, 65 insertions(+), 28 deletions(-)
diff --git a/mingw-w64-crt/misc/dirent.c b/mingw-w64-crt/misc/dirent.c
index 1f7a726ce..ffea4adc7 100644
--- a/mingw-w64-crt/misc/dirent.c
+++ b/mingw-w64-crt/misc/dirent.c
@@ -40,7 +40,8 @@
/* Maximum number of wide characters allowed in a pathname including
- * the terminating \0. This constant is based on the behavior of
+ * the terminating \0. This is the limit for paths that begin with \\?\
+ * and for all paths in long path aware applications.
* GetFullPathNameW which rejects input strings that exceed this size. */
#define DIRENT_WPATH_MAX 32767
@@ -122,6 +123,7 @@ get_code_page (void)
DIR *
_wopendir (const wchar_t *path)
{
+ BOOL normalize_path;
DWORD full_path_alloc_size;
DWORD full_path_len;
int err;
@@ -141,31 +143,52 @@ _wopendir (const wchar_t *path)
}
/*
- * Make an absolute pathname.
+ * We need an absolute pathname so that things keep working even if
+ * the current directory is changed.
*
- * When buffer is too small or not provided, the return value of
- * GetFullPathNameW includes the space needed for the terminating \0.
+ * If the pathname begins with "\\?\" or "\??\" it is used as is.
+ * Otherwise GetFullPathNameW is used, including variations with
+ * forward slashes like "//?/" or "/\?\".
*/
- full_path_alloc_size = GetFullPathNameW (path, 0, NULL, NULL);
- if (full_path_alloc_size == 0)
+ if (path[0] == '\\' &&
+ (path[1] == '\\' || path[1] == '?') &&
+ path[2] == '?' &&
+ path[3] == '\\')
{
- switch (GetLastError ())
+ normalize_path = FALSE;
+ full_path_alloc_size = wcslen (path) + 1;
+ if (full_path_alloc_size > DIRENT_WPATH_MAX)
{
- case ERROR_CALL_NOT_IMPLEMENTED:
- /* Windows 95/98/ME is not supported by this dirent code. */
- errno = ENOSYS;
- return NULL;
+ errno = ENAMETOOLONG;
+ return NULL;
+ }
+ }
+ else
+ {
+ /* When buffer is too small or not provided, the return value of
+ * GetFullPathNameW includes the space needed for the terminating \0. */
+ normalize_path = TRUE;
+ full_path_alloc_size = GetFullPathNameW (path, 0, NULL, NULL);
+ if (full_path_alloc_size == 0)
+ {
+ switch (GetLastError ())
+ {
+ case ERROR_CALL_NOT_IMPLEMENTED:
+ /* Windows 95/98/ME is not supported by this dirent code. */
+ errno = ENOSYS;
+ return NULL;
- case ERROR_FILENAME_EXCED_RANGE:
- /* The limit is 32767 wide chars including the terminating \0. */
- errno = ENAMETOOLONG;
- return NULL;
+ case ERROR_FILENAME_EXCED_RANGE:
+ /* See the comment of DIRENT_WPATH_MAX in this file. */
+ errno = ENAMETOOLONG;
+ return NULL;
- default:
- /* GetFullPathNameW accepts various invalid inputs so errors
- * should be uncommon. */
- errno = ENOENT;
- return NULL;
+ default:
+ /* GetFullPathNameW accepts various invalid inputs so errors
+ * should be uncommon. */
+ errno = ENOENT;
+ return NULL;
+ }
}
}
@@ -179,15 +202,24 @@ _wopendir (const wchar_t *path)
return NULL;
}
- /* On success, the return value from GetFullPathNameW does not include
- * the terminating \0. */
- full_path_len = GetFullPathNameW (path, full_path_alloc_size,
- dirp->dd_name, NULL);
- if (full_path_len >= full_path_alloc_size)
+ if (normalize_path)
{
- free (dirp);
- errno = ENOENT;
- return NULL;
+ /* On success, the return value from GetFullPathNameW does not include
+ * the terminating \0. */
+ full_path_len = GetFullPathNameW (path, full_path_alloc_size,
+ dirp->dd_name, NULL);
+ if (full_path_len >= full_path_alloc_size)
+ {
+ free (dirp);
+ errno = ENOENT;
+ return NULL;
+ }
+ }
+ else
+ {
+ /* Copy the \\?\ or \??\ pathname as is. */
+ memcpy (dirp->dd_name, path, full_path_alloc_size * sizeof (wchar_t));
+ full_path_len = full_path_alloc_size - 1;
}
/* Create the search expression:
@@ -308,6 +340,11 @@ _wopendir (const wchar_t *path)
* That error shouldn't be possible with FindFirstFileW.
*/
+ case ERROR_CALL_NOT_IMPLEMENTED:
+ /* We might get here if GetFullPathNameW wasn't called. */
+ errno = ENOSYS;
+ return NULL;
+
default:
/* Unknown error. */
err = EIO;
--
2.48.1
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