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Date: Fri, 06 Sep 2019 17:56:32 +0200
From: Florian Weimer <fweimer@...hat.com>
To: Mickaël Salaün <mic@...ikod.net>
Cc: 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>,  James Morris <jmorris@...ei.org>,  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>,  Mickaël Salaün
 <mickael.salaun@....gouv.fr>,  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()

Let's assume I want to add support for this to the glibc dynamic loader,
while still being able to run on older kernels.

Is it safe to try the open call first, with O_MAYEXEC, and if that fails
with EINVAL, try again without O_MAYEXEC?

Or do I risk disabling this security feature if I do that?

Do we need a different way for recognizing kernel support.  (Note that
we cannot probe paths in /proc for various reasons.)

Thanks,
Florian

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