linux-kernel - Re: [RFC PATCH v1 0/5] Add support for O

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Message-ID: <87bm5qovbb.fsf@oldenburg2.str.redhat.com>
Date:   Thu, 13 Dec 2018 06:22:00 +0100
From:   Florian Weimer <fweimer@...hat.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Mickaël Salaün <mic@...ikod.net>,
        linux-kernel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>,
        James Morris <jmorris@...ei.org>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Matthew Garrett <mjg59@...gle.com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Mickaël Salaün <mickael.salaun@....gouv.fr>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Philippe Trébuchet 
        <philippe.trebuchet@....gouv.fr>, Shuah Khan <shuah@...nel.org>,
        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: [RFC PATCH v1 0/5] Add support for O_MAYEXEC

* Matthew Wilcox:

> On Wed, Dec 12, 2018 at 09:17:07AM +0100, Mickaël Salaün wrote:
>> The goal of this patch series is to control script interpretation.  A
>> new O_MAYEXEC flag used by sys_open() is added to enable userland script
>> interpreter to delegate to the kernel (and thus the system security
>> policy) the permission to interpret scripts or other files containing
>> what can be seen as commands.
>
> I don't have a problem with the concept, but we're running low on O_ bits.
> Does this have to be done before the process gets a file descriptor,
> or could we have a new syscall?  Since we're going to be changing the
> interpreters anyway, it doesn't seem like too much of an imposition to
> ask them to use:
>
> 	int verify_for_exec(int fd)
>
> instead of adding an O_MAYEXEC.

Will this work for auditing?

Maybe add an interface which explicitly upgrades O_PATH descriptors, and
give that a separate flag argument?  I suppose that would be more
friendly to auditing.

Thanks,
Florian