[PATCH 09/13] mbssid: set extended capabilities

[Aloka Dixit]

On 4/7/2022 1:44 PM, Jouni Malinen wrote:
> On Wed, Mar 02, 2022 at 02:26:30PM -0800, Aloka Dixit wrote:
>> Set extended capabilities as described in IEEE Std 802.11-2020
>> section 9.4.2.26 Extended Capabilities element.
> 
> EMA is not defined in IEEE Std 802.11-2020, so this should also include
> IEEE Std 802.11ax-2021.
> 
>> diff --git a/src/ap/beacon.c b/src/ap/beacon.c
>> +static u8 * hostapd_ext_capab_mbssid(struct hostapd_data *hapd, u8 *eid,
>> +				     u8 *eid_ext_cap, u8 ema_periodicity)
>> +{
>> +	size_t len;
>> +
>> +	if (eid == eid_ext_cap)
>> +		return eid;
>> +
>> +	len = eid_ext_cap[1];
>> +	eid_ext_cap += 2;
>> +
>> +	if (!hapd->iconf->mbssid && len >= 3)
>> +		eid_ext_cap[2] &= ~0x40;
>> +
>> +	if (!hapd->iconf->ema && len >= 11)
>> +		eid_ext_cap[10] &= ~0x08;
> ...
> 
> This looks really confusing. Why would this separate function be used to
> modify what hostapd_eid_ext_capab() wrote instead of modifying
> hostapd_eid_ext_capab() with these extensions?
> 
Will try to add the code in the existing function itself.

>> +	if (hapd->iconf->mbssid && ema_periodicity <= 1) {
>> +		while (len < 11) {
>> +			*eid++ = 0x00;
>> +			len++;
>> +		}
> 
> And what exactly is this trying to do? Clear a lot of unrelated bits?!
> 
Set the "complete list of non-tx profiles bit when applicable

The second part which clears bunch of bits is because we saw issues 
during inter-op with some specific client devices which failed in 
association if MBSSID/EMA extended capabilities bit were set to '1' when 
MBSSID was not actually in use.


>>   static u8 * hostapd_gen_probe_resp(struct hostapd_data *hapd,
>> +	ext_cap_pos = pos;
>>   	pos = hostapd_eid_ext_capab(hapd, pos);
>> +	pos = hostapd_ext_capab_mbssid(hapd, pos, ext_cap_pos, 1);
> 
>> @@ -1656,7 +1687,10 @@ int ieee802_11_build_ap_params(struct hostapd_data *hapd,
>> +	ext_cap_pos = tailpos;
>>   	tailpos = hostapd_eid_ext_capab(hapd, tailpos);
>> +	tailpos = hostapd_ext_capab_mbssid(hapd, tailpos, ext_cap_pos,
>> +					   params->mbssid_elem_count);
> 
> What about other frames than Beacon and Probe Response frames?
> hostapd_eid_ext_capab() is used for (Re)Association Response frames as
> well. This would not modify hostapd_build_ap_extra_ies() either.
> 

Got it, will fix this.

Thanks.