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Date: Tue, 14 Sep 2010 21:02:08 +0200
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: 1.7.5: Occasional failure of CreatePipe or signal handing due to 	thread-unsafe code in cwdstuff::set
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On Sep 14 20:59, Corinna Vinschen wrote:
> On Sep 14 17:39, John Carey wrote:
> > On Sep 14 01:12, Corinna Vinschen wrote:
> > > Hmm, I'm still wondering.  In theory we don't have to replace the
> > > directory name.  We just have to InterlockedExchange the handle, since
> > > we only need to replace the original handle which does not allow
> > > sharing-for-delete with our own handle which does.
> > > 
> > > All other border cases (virtual dir, directory with restricted rights)
> > > can be rightfully handled by setting the Win32 CWD to \\?\PIPE\ again.
> > > 
> > > That's at least worth a try, isn't it?
> > 
> > Oh, I had thought that you wanted it for long paths
> > and directories with restricted rights, too.
> 
> That would be nice, but to me it looks like the Win32 API is just too
> restricted for that, so that it won't make much sense.  The native API
> can't make any assumption that it would work in such a scenario.
> 
> Most Win32 calls will still not work in a restricted rights CWD, because
> they neglect to set the FILE_OPEN_FOR_BACKUP_INTENT flag.  And most Apps
> don't set the FILE_FLAG_BACKUP_SEMANTICS flag incalls to CreateFile.
> 
> As for long paths, there's some chance that the internal calls creating
> an absolute path from a relative path fail or crash if the CWD is longer
> than MAX_PATH.  What MSDN has to say about the maximum path length of
> relative paths(*) is not very promising, at least.  Also, even if
> Vista++ allows to create VistaCwd entries with a longer path, this would
> probably break starting native child processes due to the MAX_PATH
> restriction for the CWD in calls to CreateProcess.
> 
> > There's one other issue: the new directory will limit deletion
> > very briefly, until replaced.  I don't know if that will bother
> > people as much as the current situation.
> 
> True.  Implementing a full replacement for SetCurrentDirectory as in
> your PoC is still an option.  However, I can't do that anymore since
> I'm tainted by reading your code.  If you would contemplate to sign
> a copyright assignment(**), we could create a more thorough solution
> with code scanning and all that in the long run.
> 
> In the meantime, I could apply my patch and we can try how well it
> works, hacked as it is.
> 
> 
> Corinna
> 
> 
> (*) http://msdn.microsoft.com/en-us/library/aa365247%28VS.85%29.aspx

Sorry, I forgot the URL:

(**) http://cygwin.com/contrib.html, the "Before you get started" section.


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Project Co-Leader          cygwin AT cygwin DOT com
Red Hat

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