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From:   Kees Cook <keescook@chromium.org>
Date:   Thu, 20 Sep 2018 20:02:01 -0700
Message-ID: <CAGXu5j+QhU2HOicYKqfNo17n9k6DKgt1upa3O2p1b5Gvn6icbQ@mail.gmail.com>
Subject: Re: [PATCH security-next v2 26/26] LSM: Add all exclusive LSMs to
 ordered initialization
To:     John Johansen <john.johansen@canonical.com>
Cc:     Casey Schaufler <casey@schaufler-ca.com>,
        James Morris <jmorris@namei.org>,
        Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        Paul Moore <paul@paul-moore.com>,
        Stephen Smalley <sds@tycho.nsa.gov>,
        "Schaufler, Casey" <casey.schaufler@intel.com>,
        LSM <linux-security-module@vger.kernel.org>,
        Jonathan Corbet <corbet@lwn.net>,
        "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Thu, Sep 20, 2018 at 7:14 PM, John Johansen
<john.johansen@canonical.com> wrote:
> On 09/20/2018 07:05 PM, Kees Cook wrote:
>> On Thu, Sep 20, 2018 at 6:39 PM, John Johansen
>> <john.johansen@canonical.com> wrote:
>>> On 09/20/2018 06:10 PM, Casey Schaufler wrote:
>>>> On 9/20/2018 5:45 PM, Kees Cook wrote:
>>>>> On Thu, Sep 20, 2018 at 5:25 PM, Casey Schaufler <casey@schaufler-ca.com> wrote:
>>>>>> On 9/20/2018 9:23 AM, Kees Cook wrote:
>>>>>>>  config LSM_ORDER
>>>>>>>       string "Default initialization order of builtin LSMs"
>>>>>>> -     default "yama,loadpin,integrity"
>>>>>>> +     default "yama,loadpin,integrity,selinux,smack,tomoyo,apparmor"
>>>>>> If I want to compile all the major modules into my kernel and use
>>>>>> AppArmor by default would I use
>>>>>>
>>>>>>         default "yama,loadpin,integrity,apparmor,selinux,smack,tomoyo"
>>>>>>
>>>>>> or
>>>>>>
>>>>>>         default "yama,loadpin,integrity,apparmor"
>>>>> I was expecting the former, but the latter will have the same result.
>>>
>>> t find having the two be equivalent violates expectations. At least
>>> when considering the end goal of full/extreme stacking, its trivially
>>> the same with current major lsms being exclusive
>>
>> This mixes "enablement" with "ordering", though, and I think the past
>> threads have shown this to be largely problematic.
>>
>> However, with CONFIG_LSM_ENABLED, we get the effect you're looking for, IIUC.
>
> no, I was just stating in a world where we have full stacking those two
> are not equivalent, as I would assume the order of any lsm not listed
> may end up being different.

Right, the ordering would be defined first by runtime (lsm.order=)
followed any missing LSMs then ordered by their order in
CONFIG_LSM_ORDER=, followed by any still missing LSMs then ordered by
their order at link-time (which *may* be Makefile order, but could
change with LTO, etc).

>>>>>> When we have "blob-sharing" how could I compile in tomoyo,
>>>>>> but exclude it without a boot line option?
>>>>> Ooh, yes, this series has no way to do that. Perhaps
>>>>> CONFIG_LSM_DISABLE in the same form as CONFIG_LSM_ORDER? I would
>>>>> totally remove LoadPin's CONFIG for this in favor it.
>>>>
>>>> I would generally prefer an optional CONFIG_LSM_ENABLE to
>>>> CONFIG_LSM_DISABLE, but I understand the logic behind your
>>>> approach. I would be looking for something like
>>>>
>>> +1 on the CONFIG_LSM_ENABLE ove DISABLE
>>>
>>>> CONFIG LSM_ENABLE
>>>>       string "Default set of enabled LSMs"
>>>>       default ""
>>>>
>>>> as opposed to
>>>>
>>>> CONFIG LSM_DISABLE
>>>>       string "Default set of disabled LSMs"
>>>>       default ""
>>>>
>>>> where an empty string is interpreted as "use 'em all"
>>>> in either case.
>>
>> Yes, I like CONFIG_LSM_ENABLE if "empty" means "enable all". Should
>> CONFIG_LSM_ENABLE replace all the other CONFIG-based LSM
>> enabling/disabling?
>
> I don't particularly like "empty" being "enable all". With that
> how would I disable all builtin lsms so that I just boot with
> capability.
>
> An option of all or even * is more explicit and leaves the empty
> set to mean disable everything

Okay, that works. I prefer "all" FWIW.

-Kees

-- 
Kees Cook
Pixel Security