Date: Fri, 8 Mar 2024 23:21:03 +0100
To: Marcin Wisnicki <mwisnicki@gmail.com>, cygwin@cygwin.com
Subject: Re: ls/stat on OneDrive causes download of files
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 Jeffrey Altman <jaltman@secure-endpoints.com>,
 Thomas Wolff <towo@towo.net>
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From: Corinna Vinschen via Cygwin <cygwin@cygwin.com>
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Cc: Corinna Vinschen <corinna-cygwin@cygwin.com>
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On Mar  8 14:56, Corinna Vinschen via Cygwin wrote:
> On Mar  8 08:15, Jeffrey Altman via Cygwin wrote:
> > On 3/8/2024 7:52 AM, Thomas Wolff via Cygwin wrote:
> > > Am 08.03.2024 um 11:37 schrieb Corinna Vinschen via Cygwin:
> > > >    FILE_OPEN_NO_RECALL (0x00400000)
> > > > [...]
> > > > This sounds like we could simply add this flag to all NtOpenFile
> > > > used for path conversion or stat-like calls, without having to care
> > > > for any file attributes specificially.
> > > > 
> > > > Does that make sense?
> > > Sounds good, without even studying the other details...
> > > I speculate some more handling would still be needed to avoid executable
> > > detection via magic tags.
> > > 
> > Agreed.   FILE_OPEN_NO_RECALL has been defined for at least a decade but was
> > not documented by Microsoft relatively recently.
> 
> Thanks for the feedback, guys.
> 
> > Another suggestion would be to try opening the file with
> > FILE_READ_ATTRIBUTES instead of GENERIC_READ if the file data is not
> > required.  See
> > 
> > https://github.com/microsoft/BuildXL/commit/4fb8e7ce07d243ccd95de0d66da551538a794493
> 
> Cygwin uses the minimum of required permissions in NtCreateFile/
> NtOpenFile calls anyway.
> 
> I'm just running a test cygwin DLL locally with a lot of added
> FILE_OPEN_NO_RECALL bits and a couple of added attribute checks for
> being offline to allow skipping some code.
> 
> I think I'll push this change in a bit so we get a test release out
> so people using OneDrive can test.

I pushed this change as well as a followup change to make sure we don't
inadvertently recall an offline file.  I also added handling for the
Pinned and Unpinned attributes to chattr(1) and lsattr(1).

The full set of changes can be tested by installing the Cygwin test
release 3.6.0-0.77.g06aa5a751682.

Please give it a try.  If you encounter a situation which still results
in recalling an offline file in a situation which doesn't qualify for
it, please report.  We will have to analyze that situation further
then.


Thanks,
Corinna

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