linux-kernel - Re: [PATCH v7 0/7] Add support for O

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Message-ID: <c0224c08-f669-168e-3bb4-35eceec96a8b@digikod.net>
Date:   Tue, 11 Aug 2020 10:50:53 +0200
From:   Mickaël Salaün <mic@...ikod.net>
To:     David Laight <David.Laight@...lab.com>,
        Al Viro <viro@...iv.linux.org.uk>
Cc:     Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "linux-kernel@...r.kernel.org" <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>,
        Deven Bowers <deven.desai@...ux.microsoft.com>,
        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>,
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        Philippe Trébuchet 
        <philippe.trebuchet@....gouv.fr>,
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        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Thibaut Sautereau <thibaut.sautereau@...p-os.org>,
        Vincent Strubel <vincent.strubel@....gouv.fr>,
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        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
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        <linux-security-module@...r.kernel.org>,
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Subject: Re: [PATCH v7 0/7] Add support for O_MAYEXEC


On 11/08/2020 10:09, David Laight wrote:
>> On 11/08/2020 00:28, Al Viro wrote:
>>> On Mon, Aug 10, 2020 at 10:09:09PM +0000, David Laight wrote:
>>>>> On Mon, Aug 10, 2020 at 10:11:53PM +0200, Mickaël Salaün wrote:
>>>>>> It seems that there is no more complains nor questions. Do you want me
>>>>>> to send another series to fix the order of the S-o-b in patch 7?
>>>>>
>>>>> There is a major question regarding the API design and the choice of
>>>>> hooking that stuff on open().  And I have not heard anything resembling
>>>>> a coherent answer.
>>>>
>>>> To me O_MAYEXEC is just the wrong name.
>>>> The bit would be (something like) O_INTERPRET to indicate
>>>> what you want to do with the contents.
>>
>> The properties is "execute permission". This can then be checked by
>> interpreters or other applications, then the generic O_MAYEXEC name.
> 
> The english sense of MAYEXEC is just wrong for what you are trying
> to check.

We think it reflects exactly what it's purpose is.

> 
>>> ... which does not answer the question - name of constant is the least of
>>> the worries here.  Why the hell is "apply some unspecified checks to
>>> file" combined with opening it, rather than being an independent primitive
>>> you apply to an already opened file?  Just in case - "'cuz that's how we'd
>>> done it" does not make a good answer...
> 
> Maybe an access_ok() that acts on an open fd would be more
> appropriate.
> Which might end up being an fcntrl() action.
> That would give you a full 32bit mask of options.

I previously talk about fcntl(2):
https://lore.kernel.org/lkml/eaf5bc42-e086-740b-a90c-93e67c535eee@digikod.net/