linux-kernel - Re: [PATCH v38 04/39] LSM: Maintain a table of LSM attribute data

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Date:   Thu, 13 Oct 2022 19:04:05 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     Casey Schaufler <casey@...aufler-ca.com>,
        casey.schaufler@...el.com, paul@...l-moore.com,
        linux-security-module@...r.kernel.org
Cc:     linux-audit@...hat.com, jmorris@...ei.org, selinux@...r.kernel.org,
        keescook@...omium.org, john.johansen@...onical.com,
        stephen.smalley.work@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v38 04/39] LSM: Maintain a table of LSM attribute data

On 2022/09/28 4:53, Casey Schaufler wrote:
> @@ -483,6 +491,16 @@ void __init security_add_hooks(struct security_hook_list *hooks, int count,
>  {
>  	int i;
>  
> +	/*
> +	 * A security module may call security_add_hooks() more
> +	 * than once. Landlock is one such case.
> +	 */
> +	if (lsm_id == 0 || lsm_idlist[lsm_id - 1] != lsmid)
> +		lsm_idlist[lsm_id++] = lsmid;
> +
> +	if (lsm_id > LSMID_ENTRIES)
> +		panic("%s Too many LSMs registered.\n", __func__);

I'm not happy with LSMID_ENTRIES. This is a way towards forever forbidding LKM-based LSMs.

I'm fine with using UAPI-visible constants for switching /proc/ files.
But TOMOYO does not need such constant because TOMOYO does not use /proc/ files.

Also, lsm_self_attr() will be limited for LSM modules which use /proc/ files, and
therefore I think prctl() will be already there.

> +
>  	for (i = 0; i < count; i++) {
>  		hooks[i].lsmid = lsmid;
>  		hlist_add_tail_rcu(&hooks[i].list, hooks[i].head);