linux-kernel - Re: [PATCH v4a 8/8] module: replace the existing LSM hook in init

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Date:   Tue, 05 Jun 2018 18:40:11 -0400
From:   Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Paul Moore <paul@...l-moore.com>,
        linux-integrity <linux-integrity@...r.kernel.org>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        David Howells <dhowells@...hat.com>,
        "Luis R . Rodriguez" <mcgrof@...nel.org>,
        Eric Biederman <ebiederm@...ssion.com>,
        Kexec Mailing List <kexec@...ts.infradead.org>,
        Andres Rodriguez <andresx7@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Jeff Vander Stoep <jeffv@...gle.com>,
        Casey Schaufler <casey@...aufler-ca.com>,
        James Morris <jmorris@...ei.org>
Subject: Re: [PATCH v4a 8/8] module: replace the existing LSM hook in
 init_module

On Tue, 2018-06-05 at 15:26 -0700, Kees Cook wrote:
> On Tue, Jun 5, 2018 at 2:35 PM, Mimi Zohar <zohar@...ux.vnet.ibm.com> wrote:
> > On Tue, 2018-06-05 at 12:45 -0700, Kees Cook wrote:
> >
> >> And if you must have a separate enum, please change this to fail
> >> closed instead of open (and mark the fall-through):
> >>
> >> int rc = -EPERM;
> >>
> >> switch (id) {
> >> case LOADING_MODULE:
> >>     rc = loadpin_read_file(NULL, READING_MODULE);
> >>     /* Fall-through */
> >> default:
> >>     break;
> >> }
> >
> > This will fail the sysfs firmware fallback loading and the kexec_load
> > syscall without any message, as you have for init_module.  Is that
> > what you want?
> 
> I'd prefer there be a full mapping of the enums so that everything
> gets passed into loadpin_read_file() :)
> 
> Can the enum be shared or is that nonsensical?

Considering this is v4 of the patch set, it's pretty obvious I did
everything possible not to define a new LSM hook.  Even if we can't
re-use the existing enum, we could define the new enum in terms
of __kernel_read_file_id.

enum kernel_load_data_id {
        __kernel_read_file_id(__data_id_enumify)
};

static const char * const kernel_load_data_str[] = {
        __kernel_read_file_id(__data_id_stringify)
};

Eric, Serge, would using either the existing __kernel_read_file_id
enum or the above definitions be acceptable?

Mimi