linux-kernel - Re: [PATCH 11/18] LSM: Lift LSM selection out of individual LSMs

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Date:   Sat, 15 Sep 2018 18:47:30 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Jann Horn <jannh@...gle.com>
Cc:     James Morris <jmorris@...ei.org>,
        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>,
        Casey Schaufler <casey.schaufler@...el.com>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        kernel list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 11/18] LSM: Lift LSM selection out of individual LSMs

On Sat, Sep 15, 2018 at 6:32 PM, Jann Horn <jannh@...gle.com> wrote:
> On Sun, Sep 16, 2018 at 3:14 AM Kees Cook <keescook@...omium.org> wrote:
>> In order to adjust LSM selection logic in the future, this moves the
>> selection logic up out of the individual LSMs, making their init functions
>> only run when actually enabled.
> [...]
>> +/* Is an LSM allowed to be enabled? */
>> +static bool __init lsm_enabled(struct lsm_info *lsm)
>> +{
>> +       /* Report explicit disabling. */
>> +       if (lsm->enabled && !*lsm->enabled) {
>> +               pr_info("%s disabled with boot parameter\n", lsm->name);
>> +               return false;
>> +       }
>> +
>> +       /* If LSM isn't exclusive, ignore exclusive LSM selection rules. */
>> +       if (lsm->type != LSM_TYPE_EXCLUSIVE)
>> +               return true;
>> +
>> +       /* Disabled if another exclusive LSM already selected. */
>> +       if (exclusive)
>> +               return false;
>
> What is this check for, given that you have the strcmp() just below
> here? From a quick look, it (together with everything else that
> touches the "exclusive" variable) seems superfluous to me, unless
> there are two LSMs with the same name (which really shouldn't happen,
> right?).
>
>> +       /* Disabled if this LSM isn't the chosen one. */
>> +       if (strcmp(lsm->name, chosen_lsm) != 0)
>> +               return false;
>> +
>> +       return true;
>> +}

Mainly it's for composition with later patches where the name check is
moved. It seemed easier to explain the logical progression with the
hunk here.

-Kees

-- 
Kees Cook
Pixel Security