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Date: Fri, 6 Sep 2019 18:06:25 +0200
From: Mickaël Salaün <>
To: Florian Weimer <>, Mickaël Salaün
CC: <>, Aleksa Sarai <>, Alexei
 Starovoitov <>, Al Viro <>, Andy
 Lutomirski <>, Christian Heimes <>, Daniel
 Borkmann <>, Eric Chiang <>, James
 Morris <>, 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 06/09/2019 17:56, Florian Weimer wrote:
> 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?

The kernel ignore unknown open(2) flags, so yes, it is safe even for
older kernel to use O_MAYEXEC.

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

It is only a security feature if the kernel support it, otherwise it is
a no-op.

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

There is no need to probe for kernel support.

> Thanks,
> Florian

Mickaël Salaün

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