linux-kernel - Re: [PATCH security-next v3 14/29] LSM: Plumb visibility into optional "enabled" state

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Date:   Mon, 1 Oct 2018 14:56:43 -0700
From:   Kees Cook <keescook@...omium.org>
To:     James Morris <jmorris@...ei.org>
Cc:     Casey Schaufler <casey@...aufler-ca.com>,
        John Johansen <john.johansen@...onical.com>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Paul Moore <paul@...l-moore.com>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        "Schaufler, Casey" <casey.schaufler@...el.com>,
        LSM <linux-security-module@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH security-next v3 14/29] LSM: Plumb visibility into
 optional "enabled" state

On Mon, Oct 1, 2018 at 2:47 PM, James Morris <jmorris@...ei.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@...omium.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...

-Kees

-- 
Kees Cook
Pixel Security