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Date: Mon, 9 Sep 2019 03:12:38 -0700 (PDT)
From: James Morris <jmorris@...ei.org>
To: Mickaël Salaün <mickael.salaun@....gouv.fr>
cc: Jeff Layton <jlayton@...nel.org>, Florian Weimer <fweimer@...hat.com>,
        Mickaël Salaün <mic@...ikod.net>,
        linux-kernel@...r.kernel.org, Aleksa Sarai <cyphar@...har.com>,
        Alexei Starovoitov <ast@...nel.org>, Al Viro <viro@...iv.linux.org.uk>,
        Andy Lutomirski <luto@...nel.org>,
        Christian Heimes <christian@...hon.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Eric Chiang <ericchiang@...gle.com>, Jan Kara <jack@...e.cz>,
        Jann Horn <jannh@...gle.com>, Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>, Matthew Garrett <mjg59@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Philippe Trébuchet <philippe.trebuchet@....gouv.fr>,
        Scott Shell <scottsh@...rosoft.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Shuah Khan <shuah@...nel.org>, Song Liu <songliubraving@...com>,
        Steve Dower <steve.dower@...hon.org>, Steve Grubb <sgrubb@...hat.com>,
        Thibaut Sautereau <thibaut.sautereau@....gouv.fr>,
        Vincent Strubel <vincent.strubel@....gouv.fr>,
        Yves-Alexis Perez <yves-alexis.perez@....gouv.fr>,
        kernel-hardening@...ts.openwall.com, linux-api@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v2 1/5] fs: Add support for an O_MAYEXEC flag on
 sys_open()

On Mon, 9 Sep 2019, Mickaël Salaün wrote:

> 
> On 06/09/2019 21:03, James Morris wrote:
> > On Fri, 6 Sep 2019, Jeff Layton wrote:
> >
> >> The fact that open and openat didn't vet unknown flags is really a bug.
> >>
> >> Too late to fix it now, of course, and as Aleksa points out, we've
> >> worked around that in the past. Now though, we have a new openat2
> >> syscall on the horizon. There's little need to continue these sorts of
> >> hacks.
> >>
> >> New open flags really have no place in the old syscalls, IMO.
> >
> > Agree here. It's unfortunate but a reality and Linus will reject any such
> > changes which break existing userspace.
> 
> Do you mean that adding new flags to open(2) is not possible?
> 
> Does it means that unspecified behaviors are definitely part of the
> Linux specification and can't be fixed?

This is my understanding.

> 
> As I said, O_MAYEXEC should be ignored if it is not supported by the
> kernel, which perfectly fit with the current open(2) flags behavior, and
> should also behave the same with openat2(2).

The problem here is programs which are already using the value of 
O_MAYEXEC, which will break.  Hence, openat2(2).


-- 
James Morris
<jmorris@...ei.org>

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