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Date:   Mon, 9 Sep 2019 03:12:38 -0700 (PDT)
From:   James Morris <jmorris@namei.org>
To:     =?ISO-8859-15?Q?Micka=EBl_Sala=FCn?= <mickael.salaun@ssi.gouv.fr>
cc:     Jeff Layton <jlayton@kernel.org>,
        Florian Weimer <fweimer@redhat.com>,
        =?ISO-8859-15?Q?Micka=EBl_Sala=FCn?= <mic@digikod.net>,
        linux-kernel@vger.kernel.org, Aleksa Sarai <cyphar@cyphar.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Andy Lutomirski <luto@kernel.org>,
        Christian Heimes <christian@python.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Eric Chiang <ericchiang@google.com>, Jan Kara <jack@suse.cz>,
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        Matthew Garrett <mjg59@google.com>,
        Matthew Wilcox <willy@infradead.org>,
        Michael Kerrisk <mtk.manpages@gmail.com>,
        Mimi Zohar <zohar@linux.ibm.com>,
        =?ISO-8859-15?Q?Philippe_Tr=E9buchet?= 
        <philippe.trebuchet@ssi.gouv.fr>,
        Scott Shell <scottsh@microsoft.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Shuah Khan <shuah@kernel.org>,
        Song Liu <songliubraving@fb.com>,
        Steve Dower <steve.dower@python.org>,
        Steve Grubb <sgrubb@redhat.com>,
        Thibaut Sautereau <thibaut.sautereau@ssi.gouv.fr>,
        Vincent Strubel <vincent.strubel@ssi.gouv.fr>,
        Yves-Alexis Perez <yves-alexis.perez@ssi.gouv.fr>,
        kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org,
        linux-security-module@vger.kernel.org,
        linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v2 1/5] fs: Add support for an O_MAYEXEC flag on
 sys_open()
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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@namei.org>

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