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Subject: Re: [RFC PATCH v1 0/5] Add support for O_MAYEXEC
From:   Mimi Zohar <zohar@linux.ibm.com>
To:     Matthew Wilcox <willy@infradead.org>,
        =?ISO-8859-1?Q?Micka=EBl_Sala=FCn?= <mic@digikod.net>
Cc:     linux-kernel@vger.kernel.org, Al Viro <viro@zeniv.linux.org.uk>,
        James Morris <jmorris@namei.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Kees Cook <keescook@chromium.org>,
        Matthew Garrett <mjg59@google.com>,
        Michael Kerrisk <mtk.manpages@gmail.com>,
        =?ISO-8859-1?Q?Micka=EBl_Sala=FCn?= <mickael.salaun@ssi.gouv.fr>,
        Philippe =?ISO-8859-1?Q?Tr=E9buchet?= 
        <philippe.trebuchet@ssi.gouv.fr>, Shuah Khan <shuah@kernel.org>,
        Thibaut Sautereau <thibaut.sautereau@ssi.gouv.fr>,
        Vincent Strubel <vincent.strubel@ssi.gouv.fr>,
        Yves-Alexis Perez <yves-alexis.perez@ssi.gouv.fr>,
        kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org,
        linux-security-module@vger.kernel.org,
        linux-fsdevel@vger.kernel.org
Date:   Thu, 13 Dec 2018 06:04:20 -0500
In-Reply-To: <20181213030228.GM6830@bombadil.infradead.org>
References: <20181212081712.32347-1-mic@digikod.net>
         <20181213030228.GM6830@bombadil.infradead.org>
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On Wed, 2018-12-12 at 19:02 -0800, Matthew Wilcox wrote:
> 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.

The indication needs to be set during file open, before the open
returns to the caller.  This is the point where ima_file_check()
verifies the file's signature.  On failure, access to the file is
denied.

Mimi