DMARC-Filter: OpenDMARC Filter v1.4.2 delorie.com 55N8PuZ33577376
Authentication-Results: delorie.com; dmarc=pass (p=none dis=none) header.from=cygwin.com
Authentication-Results: delorie.com; spf=pass smtp.mailfrom=cygwin.com
DKIM-Filter: OpenDKIM Filter v2.11.0 delorie.com 55N8PuZ33577376
Authentication-Results: delorie.com;
	dkim=pass (1024-bit key, unprotected) header.d=cygwin.com header.i=@cygwin.com header.a=rsa-sha256 header.s=default header.b=vGl/BbAA
X-Recipient: archive-cygwin AT delorie DOT com
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 08A9A38844CA
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cygwin.com;
	s=default; t=1750667154;
	bh=2/sskQYDajAGy6azFbqFSUZaanWQyPUbZGcHjgGBM1U=;
	h=Date:To:Subject:References:In-Reply-To:List-Id:List-Unsubscribe:
	 List-Archive:List-Post:List-Help:List-Subscribe:From:Reply-To:Cc:
	 From;
	b=vGl/BbAAlp1PgEwD7vkO+WytBm7bqisqgOqYQM7+mTOyyx+matdHHhJ00Lr4daJ3P
	 aYYkGWsSJ3vEm8vkl9cWj/5yqs/IXcwT/SuVYAAVRG1OtoaseNFkI/3iz+PVQxsXKN
	 yl0rgqFLvU+kdL14ox/qVv9dkYooRfCq06tzfDW8=
X-Original-To: cygwin AT cygwin DOT com
Delivered-To: cygwin AT cygwin DOT com
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org C672A388223B
Date: Mon, 23 Jun 2025 10:24:48 +0200
To: cygwin-patches AT cygwin DOT com, cygwin AT cygwin DOT com
Subject: Re: symlink_native() bug with case-sensitive file-systems Re:
 [PATCH] symlink_native: allow linking to `..`
Message-ID: <aFkPUI22HlYnYhZh@calimero.vinschen.de>
Mail-Followup-To: cygwin-patches AT cygwin DOT com, cygwin AT cygwin DOT com
References: <6058889e2ae8c9c827a8d6678f09b3b1741e2fcf DOT 1750413578 DOT git DOT johannes DOT schindelin AT gmx DOT de>
 <CAHnbEGLjsy4MZD+oqjGbd=JrX+q8an3mhT38xndEgjmTpWyOnw AT mail DOT gmail DOT com>
MIME-Version: 1.0
Content-Disposition: inline
In-Reply-To: <CAHnbEGLjsy4MZD+oqjGbd=JrX+q8an3mhT38xndEgjmTpWyOnw@mail.gmail.com>
X-BeenThere: cygwin AT cygwin DOT com
X-Mailman-Version: 2.1.30
Precedence: list
List-Id: General Cygwin discussions and problem reports <cygwin.cygwin.com>
List-Unsubscribe: <https://cygwin.com/mailman/options/cygwin>,
 <mailto:cygwin-request AT cygwin DOT com?subject=unsubscribe>
List-Archive: <https://cygwin.com/pipermail/cygwin/>
List-Post: <mailto:cygwin AT cygwin DOT com>
List-Help: <mailto:cygwin-request AT cygwin DOT com?subject=help>
List-Subscribe: <https://cygwin.com/mailman/listinfo/cygwin>,
 <mailto:cygwin-request AT cygwin DOT com?subject=subscribe>
From: Corinna Vinschen via Cygwin <cygwin AT cygwin DOT com>
Reply-To: cygwin-patches AT cygwin DOT com
Cc: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
Content-Type: text/plain; charset="utf-8"
Errors-To: cygwin-bounces~archive-cygwin=delorie DOT com AT cygwin DOT com
Sender: "Cygwin" <cygwin-bounces~archive-cygwin=delorie DOT com AT cygwin DOT com>
Content-Transfer-Encoding: 8bit
X-MIME-Autoconverted: from base64 to 8bit by delorie.com id 55N8PuZ33577376

On Jun 20 13:33, Sebastian Feld wrote:
> On Fri, Jun 20, 2025 at 12:03 PM Johannes Schindelin
> <johannes DOT schindelin AT gmx DOT de> wrote:
> >  winsup/cygwin/path.cc | 21 ++++++++++++++++-----
> >  1 file changed, 16 insertions(+), 5 deletions(-)
> >
> > diff --git a/winsup/cygwin/path.cc b/winsup/cygwin/path.cc
> > index 42919a7cf5..ed08398930 100644
> > --- a/winsup/cygwin/path.cc
> > +++ b/winsup/cygwin/path.cc
> > @@ -1855,9 +1855,18 @@ symlink_native (const char *oldpath, path_conv &win32_newpath)
> >        while (towupper (*++c_old) == towupper (*++c_new))
> 
> 1 unrelated issue:
> I think this towupper() code is WRONG if the filesystem (e.g. WSL) is
> case-sensitive!

The preceding comment tries to explain why we always compare case
insensitive.  There's a high probability that the symlink will be used
by native (non-Cygwin) processes which are insensitive.

> How can code in cygwin.dll test whether the current path is on a
> case-sensitive volume, or not?

There's a twist here.  NTFS or ReFS or other filesystems (but not FAT)
are usually case sensitive.  It's the OS which makes them case insensitve
by using a specific flag at open time, combined with a kernel registry
key.  So apart from FAT, the creator of a file decides if it's created
sensitive or insensitive, and the one searching for and opening a file
is deciding if the search/open is sensitive or insensitive.

Also, we're creating the symlink via CreateSymbolicLinkW, which is
probably acting case insensitive anyway...

What if the perr-dir case-sensitive
> feature is ON, should that be probed and handled too?

...unless the symlink is created in a case sensitive dir, I assume.

Right now we don't handle case sensitive dirs in the path_conv code.  We
only check for the kernel registry key and the FILE_CASE_SENSITIVE_SEARCH
filesystem flag.

To add the sensitive dirs to the picture, path_conv() would have to
check every directory on NTFS for
NtQueryInformationFile(FileCaseSensitiveInformation). It would then
set the path_conv::caseinsensitive flag accordingly.


Corinna

-- 
Problem reports:      https://cygwin.com/problems.html
FAQ:                  https://cygwin.com/faq/
Documentation:        https://cygwin.com/docs.html
Unsubscribe info:     https://cygwin.com/ml/#unsubscribe-simple