linux-kernel - Re: [PATCH v9 02/11] LSM: Maintain a table of LSM attribute data

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Date:   Thu, 27 Apr 2023 08:31:39 -0700
From:   Casey Schaufler <casey@...aufler-ca.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     paul@...l-moore.com, linux-security-module@...r.kernel.org,
        jmorris@...ei.org, john.johansen@...onical.com,
        penguin-kernel@...ove.sakura.ne.jp, stephen.smalley.work@...il.com,
        linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        mic@...ikod.net, Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [PATCH v9 02/11] LSM: Maintain a table of LSM attribute data

On 4/21/2023 12:20 PM, Kees Cook wrote:
> On Fri, Apr 21, 2023 at 10:42:50AM -0700, Casey Schaufler wrote:
>> As LSMs are registered add their lsm_id pointers to a table.
>> This will be used later for attribute reporting.
>>
>> Determine the number of possible security modules based on
>> their respective CONFIG options. This allows the number to be
>> known at build time. This allows data structures and tables
>> to use the constant.
>>
>> Signed-off-by: Casey Schaufler <casey@...aufler-ca.com>
> Reviewed-by: Kees Cook <keescook@...omium.org>
>
> Nit below...
>
>> [...]
>> @@ -513,6 +531,15 @@ void __init security_add_hooks(struct security_hook_list *hooks, int count,
>>  {
>>  	int i;
>>  
>> +	if (lsm_active_cnt >= LSM_COUNT)
>> +		panic("%s Too many LSMs registered.\n", __func__);
>> +	/*
>> +	 * A security module may call security_add_hooks() more
>> +	 * than once. Landlock is one such case.
>> +	 */
>> +	if (lsm_active_cnt == 0 || lsm_idlist[lsm_active_cnt - 1] != lsmid)
>> +		lsm_idlist[lsm_active_cnt++] = lsmid;
>> +
> I find this logic hard to parse. I think this might be better, since
> lsm_idlist will be entirely initialized to LSM_UNDEF, yes?
>
> 	/*
> 	 * A security module may call security_add_hooks() more
> 	 * than once during initialization, and LSM initialization
> 	 * is serialized. Landlock is one such case.
> 	 */
> 	if (lsm_idlist[lsm_active_cnt] != lsmid)
> 		lsm_idlist[lsm_active_cnt++] = lsmid;

This code won't do the job. lsm_active_count indexes the first unset
entry, not the last set entry.