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Date: Tue, 11 Aug 2020 10:18:08 -0700
From: Deven Bowers <>
To: Mickaël Salaün <>,
 Jann Horn <>, Kees Cook <>,
 Mimi Zohar <>
Cc: Al Viro <>,
 Andrew Morton <>,
 kernel list <>, Aleksa Sarai
 <>, Alexei Starovoitov <>,
 Andy Lutomirski <>,
 Christian Brauner <>,
 Christian Heimes <>,
 Daniel Borkmann <>, Dmitry Vyukov <>,
 Eric Biggers <>, Eric Chiang <>,
 Florian Weimer <>, James Morris <>,
 Jan Kara <>, Jonathan Corbet <>,
 Lakshmi Ramasubramanian <>,
 Matthew Garrett <>, Matthew Wilcox <>,
 Michael Kerrisk <>,
 Philippe Trébuchet <>,
 Scott Shell <>,
 Sean Christopherson <>,
 Shuah Khan <>, Steve Dower <>,
 Steve Grubb <>,
 Tetsuo Handa <>,
 Thibaut Sautereau <>,
 Vincent Strubel <>,
 Kernel Hardening <>,
 Linux API <>,,
 linux-security-module <>,
 linux-fsdevel <>
Subject: Re: [PATCH v7 0/7] Add support for O_MAYEXEC

On 8/11/2020 1:48 AM, Mickaël Salaün wrote:


>>> It is a
>>> good practice to check as soon as possible such properties, and it may
>>> enables to avoid (user space) time-of-check to time-of-use (TOCTOU)
>>> attacks (i.e. misuse of already open resources).
>> The assumption that security checks should happen as early as possible
>> can actually cause security problems. For example, because seccomp was
>> designed to do its checks as early as possible, including before
>> ptrace, we had an issue for a long time where the ptrace API could be
>> abused to bypass seccomp filters.
>> Please don't decide that a check must be ordered first _just_ because
>> it is a security check. While that can be good for limiting attack
>> surface, it can also create issues when the idea is applied too
>> broadly.
> I'd be interested with such security issue examples.
> I hope that delaying checks will not be an issue for mechanisms such as
> IMA or IPE:
> Any though Mimi, Deven, Chrome OS folks?

I don't see an issue with IPE. As long as the hypothetical new syscall
and associated security hook have the file struct available in the
hook, it should integrate fairly easily.


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