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Date: Mon, 9 Sep 2019 12:54:16 +0200
From: Mickaël Salaün <>
To: James Morris <>
CC: Jeff Layton <>, Florian Weimer <>,
	Mickaël Salaün <>,
	<>, Aleksa Sarai <>, Alexei
 Starovoitov <>, Al Viro <>, Andy
 Lutomirski <>, Christian Heimes <>, Daniel
 Borkmann <>, Eric Chiang <>, Jan
 Kara <>, Jann Horn <>, Jonathan Corbet
	<>, Kees Cook <>, Matthew Garrett
	<>, Matthew Wilcox <>, Michael Kerrisk
	<>, Mimi Zohar <>,
	Philippe Trébuchet <>, Scott
 Shell <>, Sean Christopherson
	<>, Shuah Khan <>, Song Liu
	<>, Steve Dower <>, Steve Grubb
	<>, Thibaut Sautereau <>,
	Vincent Strubel <>, Yves-Alexis Perez
	<>, <>,
	<>, <>,
Subject: Re: [PATCH v2 1/5] fs: Add support for an O_MAYEXEC flag on

On 09/09/2019 12:12, James Morris wrote:
> 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).

Well, it still depends on the sysctl, which doesn't enforce anything by
default, hence doesn't break existing behavior, and this unused flags
could be fixed/removed or reported by sysadmins or distro developers.

Mickaël Salaün

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