Re: [PATCH v3 2/5] LSM: security_lsmblob_to_secctx module selection

[Casey Schaufler]

On 3/25/2025 4:44 PM, Fan Wu wrote:
> On Wed, Mar 19, 2025 at 7:50 PM Casey Schaufler <casey@xxxxxxxxxxxxxxxx> wrote:
>> Add a parameter lsmid to security_lsmblob_to_secctx() to identify which
>> of the security modules that may be active should provide the security
>> context. If the value of lsmid is LSM_ID_UNDEF the first LSM providing
>> a hook is used. security_secid_to_secctx() is unchanged, and will
>> always report the first LSM providing a hook.
>>
>> Signed-off-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
> ..
>> diff --git a/security/security.c b/security/security.c
>> index 143561ebc3e8..55f9c7ad3f89 100644
>> --- a/security/security.c
>> +++ b/security/security.c
>> @@ -4312,6 +4312,7 @@ EXPORT_SYMBOL(security_ismaclabel);
>>   * security_secid_to_secctx() - Convert a secid to a secctx
>>   * @secid: secid
>>   * @cp: the LSM context
>> + * @lsmid: which security module to report
>>   *
>>   * Convert secid to security context.  If @cp is NULL the length of the
>>   * result will be returned, but no data will be returned.  This
>> @@ -4338,9 +4339,17 @@ EXPORT_SYMBOL(security_secid_to_secctx);
>>   *
>>   * Return: Return length of data on success, error on failure.
>>   */
>> -int security_lsmprop_to_secctx(struct lsm_prop *prop, struct lsm_context *cp)
>> +int security_lsmprop_to_secctx(struct lsm_prop *prop, struct lsm_context *cp,
>> +                              int lsmid)
>>  {
>> -       return call_int_hook(lsmprop_to_secctx, prop, cp);
>> +       struct lsm_static_call *scall;
>> +
>> +       lsm_for_each_hook(scall, lsmprop_to_secctx) {
>> +               if (lsmid != 0 && lsmid != scall->hl->lsmid->id)
> It took me some time to figure out why if LSM_ID_UNDEF is passed the
> first LSM providing a hook is used, might be better to change it to:
>
>                if (lsmid != LSM_ID_UNDEF && lsmid != scall->hl->lsmid->id)

Thank you. That change will be in v4.

>
> Otherwise, it works as described. I'm working on adding a new IPE
> property based on SELinux file labels, and this just came up as I
> needed it. Thank you.
>
> Tested-by: Fan Wu <wufan@xxxxxxxxxx>
>
>> +                       continue;
>> +               return scall->hl->hook.lsmprop_to_secctx(prop, cp);
>> +       }
>> +       return LSM_RET_DEFAULT(lsmprop_to_secctx);
>>  }
>>  EXPORT_SYMBOL(security_lsmprop_to_secctx);
>>
>> --
>> 2.47.0
>>
>>