X-Recipient: archive-cygwin AT delorie DOT com
DomainKey-Signature: a=rsa-sha1; c=nofws; d=sourceware.org; h=list-id
	:list-unsubscribe:list-subscribe:list-archive:list-post
	:list-help:sender:date:from:to:subject:message-id:reply-to
	:references:mime-version:content-type:in-reply-to; q=dns; s=
	default; b=QL2rUeIANHL0pgZGsu9HHrcjLvB3NGab81CNbqaYHZrE68Mf21668
	c7ozrnkSHcfW1keB6MZnlr26QCNxa7woOdMVJt/fZMMYnOor9PIjrl4Zg6GgGzdf
	oDavI+kwGviD750ml/Z+Ncj9iBXl78qBus3uh8om93aW4OIfhRQVVE=
DKIM-Signature: v=1; a=rsa-sha1; c=relaxed; d=sourceware.org; h=list-id
	:list-unsubscribe:list-subscribe:list-archive:list-post
	:list-help:sender:date:from:to:subject:message-id:reply-to
	:references:mime-version:content-type:in-reply-to; s=default;
	 bh=wVXsukojl+xR7yE/CTRG80tstBk=; b=gRpfCX4rTxfEyF8wfSJOZqM9FxO4
	kF9wtg5lExBlVm4XFSFTOVQlYqoRBoEXrdf8uqi2Ms9LGv1aBwzWR3VuhczIPk0R
	Kc6G+D2InwRKzkoViyGgp8JyyTeYQ61lcFo6aKRF95z02GJWfICZY7vcWogAJ4K+
	z5BLWfbXgdjqdKQ=
Mailing-List: contact cygwin-help AT cygwin DOT com; run by ezmlm
List-Id: <cygwin.cygwin.com>
List-Subscribe: <mailto:cygwin-subscribe AT cygwin DOT com>
List-Archive: <http://sourceware.org/ml/cygwin/>
List-Post: <mailto:cygwin AT cygwin DOT com>
List-Help: <mailto:cygwin-help AT cygwin DOT com>, <http://sourceware.org/ml/#faqs>
Sender: cygwin-owner AT cygwin DOT com
Mail-Followup-To: cygwin AT cygwin DOT com
Delivered-To: mailing list cygwin AT cygwin DOT com
Authentication-Results: sourceware.org; auth=none
X-Spam-SWARE-Status: No, score=-100.9 required=5.0 tests=BAYES_00,GOOD_FROM_CORINNA_CYGWIN,KAM_LAZY_DOMAIN_SECURITY,RCVD_IN_DNSWL_NONE autolearn=ham version=3.3.2 spammy=UD:aspx
X-HELO: mout.kundenserver.de
Date: Mon, 28 Jan 2019 17:51:02 +0100
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: /dev/fd/N not synonymous with file descriptor N; it is on Linux
Message-ID: <20190128165102.GP3912@calimero.vinschen.de>
Reply-To: cygwin AT cygwin DOT com
Mail-Followup-To: cygwin AT cygwin DOT com
References: <d6431739e2801a80d73e7cb68b4fcc19 AT smtp-cloud8 DOT xs4all DOT net> <1c60402837d6510667357257b5e96e88 AT xs4all DOT nl> <20190122090633 DOT GK2802 AT calimero DOT vinschen DOT de> <151898514e462bd76cda8a227d4baa16 AT xs4all DOT nl> <20190122094157 DOT GN2802 AT calimero DOT vinschen DOT de> <45382f09a86b6cf3bcabd82adb593622 AT smtp-cloud8 DOT xs4all DOT net> <20190122103928 DOT GO2802 AT calimero DOT vinschen DOT de> <6132284bb44434a89381a695fdd86c7d AT smtp-cloud7 DOT xs4all DOT net> <20190127215721 DOT GH3912 AT calimero DOT vinschen DOT de> <c09c2a73bcc7b20fcbcfafe7732053d6 AT smtp-cloud7 DOT xs4all DOT net>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha256;	protocol="application/pgp-signature"; boundary="VSVNCtZB1QZ8vhj+"
Content-Disposition: inline
In-Reply-To: <c09c2a73bcc7b20fcbcfafe7732053d6@smtp-cloud7.xs4all.net>
User-Agent: Mutt/1.10.1 (2018-07-13)

--VSVNCtZB1QZ8vhj+
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

On Jan 28 15:15, Houder wrote:
> On Sun, 27 Jan 2019 22:57:21, Corinna Vinschen  wrote:
> >=20
> > On Jan 27 19:39, Houder wrote:
> > > NO BLODA.
> > >
> > > Ok, for the record (as this is W7, i.e. pre-pre-W10 :-)
> > >
> > > Using my original STC again: (source code included below)
> > >
> > >  - create file (in /tmp) write-only, write "Hello, world!" to file, c=
lose
> > >    fd
> > >  - open file once more read-only
> > >  - unlink file
> > >  - open file, using /dev/fd/N, read-write <=3D=3D=3D=3D succeeds (and=
 the handle
> > >    shown by fcntl is read-write)
> > >  - write "*****" to file (using the fd obtained in the previous line),
> > >    lseek to begin of file
> > >   - write fails w/ "Permission denied" <=3D=3D=3D=3D so ... the file =
cannot be
> > >     written to?
> >=20
> > Yes, that scenario fails on W7 but works on W10 1709 and later.  Keep in
> > mind that the OS doesn't allow to reopen a file which has been deleted.
> > Cygwin tries a best effort by duplicating the handle.  A duplicated file
> > handle can't have more permissions than the original handle, so if the
> > original handle was opened for reading only, the duplicated handle can't
> > have write perms.
> [snip]
>=20
> Yes Corinna, I already got that from one of your previous replies. You ga=
ve
> the same explanation here:
>=20
>     https://cygwin.com/ml/cygwin/2019-01/msg00171.html
>     (Date: Tue, 22 Jan 2019 10:41:57 +0100)
>=20
>     "A duplicated file handle can't have more permissions than the origin=
al
>      handle" (i.e what occurs on pre "Windows 10 1709" systems)
>=20
> The "funny" thing is, in that same post, you showed that the STC succeeded
> on your virtual W7 system ... (contradiction!).
>=20
> The STC in that post executes the same scenario as above ...
>=20
>  - the difference is that the first 3 steps are carried out by bash, when
>    invoked as follows:
>=20
>    @@ ./stca /dev/fd/N N<<EOF
>=20
> Both STC's (stc.c and stca.c) fail on my W7 (Note: stc.c is the testcase
> that I included in my previous post -- and the one I started this thread
> with).
>=20
> Mind this: I am NOT upset that the STC's (plural) fail on (my) W7. Not at
> all!

There was a minor difference when I tested it:  My shell is not bash
but tcsh, and tcsh opens the here document with different perms.

I added debug output to fhandler_base::open and on bash the ACCESS_MASK
set on the incoming handle is 0x12019F with tcsh and 0x120089 with bash.
Compare with https://msdn.microsoft.com/en-us/library/cc246802.aspx, and
you'll see that tcsh opened the file woth O_RDWR, while bash opened the
file with O_RDONLY.

I didn't notice this before, sorry!


Corinna

--=20
Corinna Vinschen
Cygwin Maintainer

--VSVNCtZB1QZ8vhj+
Content-Type: application/pgp-signature; name="signature.asc"

-----BEGIN PGP SIGNATURE-----
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=vvd6
-----END PGP SIGNATURE-----

--VSVNCtZB1QZ8vhj+--