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

Casey Schaufler
2023-04-27T15:31:52Z

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@schaufler-ca.com>
> Reviewed-by: Kees Cook <keescook@chromium.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.