kernel-hardening - Re: [PATCH v2 1/5] fs: Add support for an O_MAYEXEC flag on sys

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Date: Fri, 06 Sep 2019 20:44:03 +0200
From: Florian Weimer <fweimer@...hat.com>
To: Jeff Layton <jlayton@...nel.org>
Cc: Mickaël Salaün <mickael.salaun@....gouv.fr>,
  Mickaël Salaün
 <mic@...ikod.net>,  linux-kernel@...r.kernel.org,  Aleksa Sarai
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  Scott Shell
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 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()

* Jeff Layton:

> Even better would be to declare the new flag in some openat2-only flag
> space, so there's no confusion about it being supported by legacy open
> calls.

Isn't that desirable anyway because otherwise fcntl with F_GETFL will
give really confusing results?

> If glibc wants to implement an open -> openat2 wrapper in userland
> later, it can set that flag in the wrapper implicitly to emulate the old
> behavior.

I see us rather doing the opposite, i.e. implement openat2 with
non-exotic flags using openat.  But we've bitten by this in the past, so
maybe that's not such a great idea.  It's tempting to make the same
mistake again for every new system call.

Thanks,
Florian

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