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From:   Kees Cook <keescook@chromium.org>
Date:   Mon, 1 Oct 2018 15:29:08 -0700
Message-ID: <CAGXu5jKm3yp8VFjTrRd1dibMVQeCmsHawNMyvtiCcEjxT7S57Q@mail.gmail.com>
Subject: Re: [PATCH security-next v3 14/29] LSM: Plumb visibility into
 optional "enabled" state
To:     John Johansen <john.johansen@canonical.com>
Cc:     James Morris <jmorris@namei.org>,
        Casey Schaufler <casey@schaufler-ca.com>,
        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 Mon, Oct 1, 2018 at 3:20 PM, John Johansen
<john.johansen@canonical.com> wrote:
> On 10/01/2018 02:56 PM, Kees Cook wrote:
>> On Mon, Oct 1, 2018 at 2:47 PM, James Morris <jmorris@namei.org> wrote:
>>> On Mon, 24 Sep 2018, Kees Cook wrote:
>>>
>>>> In preparation for lifting the "is this LSM enabled?" logic out of the
>>>> individual LSMs, pass in any special enabled state tracking (as needed
>>>> for SELinux, AppArmor, and LoadPin). This should be an "int" to include
>>>> handling any future cases where "enabled" is exposed via sysctl which
>>>> has no "bool" type.
>>>>
>>>> Signed-off-by: Kees Cook <keescook@chromium.org>
>>>> ---
>>>>  include/linux/lsm_hooks.h | 1 +
>>>>  security/apparmor/lsm.c   | 5 +++--
>>>>  security/selinux/hooks.c  | 1 +
>>>>  3 files changed, 5 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
>>>> index 5056f7374b3d..2a41e8e6f6e5 100644
>>>> --- a/include/linux/lsm_hooks.h
>>>> +++ b/include/linux/lsm_hooks.h
>>>> @@ -2044,6 +2044,7 @@ extern void security_add_hooks(struct security_hook_list *hooks, int count,
>>>>  struct lsm_info {
>>>>       const char *name;       /* Populated automatically. */
>>>>       unsigned long flags;    /* Optional: flags describing LSM */
>>>> +     int *enabled;           /* Optional: NULL means enabled. */
>>>
>>> This seems potentially confusing.
>>>
>>> Perhaps initialize 'enabled' to a default int pointer, like:
>>>
>>>         static int lsm_default_enabled = 1;
>>>
>>> Then,
>>>
>>>         DEFINE_LSM(foobar)
>>>         flags = LSM_FLAG_LEGACY_MAJOR,
>>>         .enabled = &lsm_default_enabled,
>>>         .init = foobar_init,
>>>         END_LSM;
>>
>> The reason I didn't do this is because there are only two LSMs that
>> expose this "enabled" variable, so I didn't like making the other LSMs
>> have to declare this. Internally, though, this is exactly what the
>> infrastructure does: if it finds a NULL, it aims it at
>> &lsm_default_enabled (in a later patch).
>>
>> However, it seems more discussion is needed on the "enable" bit of
>> this, so I'll reply to John in a moment...
>>
> fwiw the apparmor.enabled config is really only a meant to be used to
> disable apparmor. I'd drop it entirely except its part of the userspace
> api now and needs to show up in
>
>   /sys/module/apparmor/parameters/enabled

Showing the enabled-ness there can be wired up. What should happen if
someone sets apparmor.enabled=0/1 in new-series-world? (See other
thread...)

-Kees

-- 
Kees Cook
Pixel Security