linux-kernel - Re: [kernel-hardening] Re: [PATCH RFC v2 1/3] LSM: Allow per LSM module per "struct task

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Date:   Wed, 12 Apr 2017 18:22:01 +0200
From:   Djalal Harouni <tixxdz@...il.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Casey Schaufler <casey@...aufler-ca.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        LSM List <linux-security-module@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Dongsu Park <dpark@...teo.net>,
        James Morris <james.l.morris@...cle.com>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Paul Moore <paul@...l-moore.com>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [kernel-hardening] Re: [PATCH RFC v2 1/3] LSM: Allow per LSM
 module per "struct task_struct" blob.

On Tue, Apr 11, 2017 at 6:43 AM, Kees Cook <keescook@...omium.org> wrote:
> On Mon, Apr 10, 2017 at 1:00 PM, Djalal Harouni <tixxdz@...il.com> wrote:
>> On Mon, Apr 10, 2017 at 9:26 PM, Casey Schaufler <casey@...aufler-ca.com> wrote:
>>> I think that would be the prudent approach. There is still
>>> the possibility that blob sharing (or full stacking, if you
>>> prefer) won't be accepted any time soon.
>>
>> Ok Casey! I will wait for more feedback, and if other maintainers do
>> not object, I will convert it back to rhashtables in next iterations
>> making sure that it should be simple to convert later to a blob
>> sharing mechanism.
>
> Would it be possible just to add a single field to task_struct if this
> LSM is built in? I feel like rhashtables is a huge overhead when a
> single field is all that's needed.

Well, yes rhashtables can have an overhead especially when reclaiming
memory back, I could not identify a way how to separate tables unless
we use cgroups as an ID. Anyway this of course could be added in
task_struct and updated to work like the capability security hooks
rather than a proper LSM with its own name. But as noted in the other
response, we may need task->security field for Yama anyway. I'm open
to suggestion ? I may try to converge the task->security blob with
what Casey is proposing and see! otherwise fallback to task_struct as
a last resort!

Thanks!

-- 
tixxdz