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

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Message-ID: <CAG48ez1TPsz30WebxQPkZbjfPTyT2ui7L+4ZQ94FStCkWcJ0VA@mail.gmail.com>
Date:   Sun, 16 Sep 2018 03:32:01 +0200
From:   Jann Horn <jannh@...gle.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     James Morris <jmorris@...ei.org>,
        Casey Schaufler <casey@...aufler-ca.com>,
        John Johansen <john.johansen@...onical.com>,
        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 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;
> +}