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Message-ID: <77d685ec-aba2-6a2c-5d25-1172279ceb83@linux.microsoft.com>
Date: Tue, 11 Aug 2020 10:18:08 -0700
From: Deven Bowers <deven.desai@...ux.microsoft.com>
To: Mickaël Salaün <mic@...ikod.net>,
Jann Horn <jannh@...gle.com>, Kees Cook <keescook@...omium.org>,
Mimi Zohar <zohar@...ux.ibm.com>
Cc: Al Viro <viro@...iv.linux.org.uk>,
Andrew Morton <akpm@...ux-foundation.org>,
kernel list <linux-kernel@...r.kernel.org>, Aleksa Sarai
<cyphar@...har.com>, Alexei Starovoitov <ast@...nel.org>,
Andy Lutomirski <luto@...nel.org>,
Christian Brauner <christian.brauner@...ntu.com>,
Christian Heimes <christian@...hon.org>,
Daniel Borkmann <daniel@...earbox.net>, Dmitry Vyukov <dvyukov@...gle.com>,
Eric Biggers <ebiggers@...nel.org>, Eric Chiang <ericchiang@...gle.com>,
Florian Weimer <fweimer@...hat.com>, James Morris <jmorris@...ei.org>,
Jan Kara <jack@...e.cz>, Jonathan Corbet <corbet@....net>,
Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>,
Matthew Garrett <mjg59@...gle.com>, Matthew Wilcox <willy@...radead.org>,
Michael Kerrisk <mtk.manpages@...il.com>,
Philippe Trébuchet <philippe.trebuchet@....gouv.fr>,
Scott Shell <scottsh@...rosoft.com>,
Sean Christopherson <sean.j.christopherson@...el.com>,
Shuah Khan <shuah@...nel.org>, Steve Dower <steve.dower@...hon.org>,
Steve Grubb <sgrubb@...hat.com>,
Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
Thibaut Sautereau <thibaut.sautereau@...p-os.org>,
Vincent Strubel <vincent.strubel@....gouv.fr>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
Linux API <linux-api@...r.kernel.org>, linux-integrity@...r.kernel.org,
linux-security-module <linux-security-module@...r.kernel.org>,
linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH v7 0/7] Add support for O_MAYEXEC
On 8/11/2020 1:48 AM, Mickaël Salaün wrote:
[...snip]
>>> 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:
> https://lore.kernel.org/lkml/1544699060.6703.11.camel@linux.ibm.com/
>
> 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.
[...snip]
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