[PATCH 15/26] wpa_supplicant: Fix CSA related IE's order

[Andrei Otcheretianski]

On Sat, Oct 3, 2015 at 8:44 PM, Jouni Malinen <j at w1.fi> wrote:
> On Tue, Sep 08, 2015 at 12:46:22PM +0300, Ilan Peer wrote:
>> Fix the order of CSA, eCSA, secondary channel and wide bandwidth
>> channel switch wrapper elements in beacons and probe responses.
>
>>  static u8 * hostapd_gen_probe_resp(struct hostapd_data *hapd,
>
>> +     csa_pos = hostapd_eid_csa(hapd, pos);
>
>> +     csa_pos = hostapd_eid_ecsa(hapd, pos);
>
>> +     /* Secondary channel IE */
>> +     /* TODO: The spec doesn't specify a position for this IE */
>> +     pos = hostapd_eid_secondary_channel(hapd, pos);
>
> I could not find any language in REVmc/D4.2 that would indicate that the
> Secondary Channel Offset element would be included in Probe Response or
> Beacon frames. Could you please clarify why this element is added here
> (and same for ieee802_11_build_ap_params() below)?

I went over the spec again, and it is indeed looks that Secondary channel offset
shouldn't be added if CSA is done with CSA elements and not action frames.
Anyway, this element is needed for 40mhz channel switch (since we don't have
operating class). If we don't add this element it will break 40 mhz
channel switch -
so I don't understand how it is supposed to work if we comply with the spec.

> Please also note that
> there is an explicit note stating that Secondary Channel Offset element
> is never present with the Extended Channel Switch Announcement element
> in a frame.

You're right, I found this note now :). However, if CSA is used
together with ECSA
for 40 mhz it will break the CSA only clients.

I think the spec is buggy here.. But I guess we need to comply with the spec
anyway, do we?
Though, I'm not sure whether we can do anything other than disabling 40mhz CSA
to fix this.

Andrei

>
> --
> Jouni Malinen                                            PGP id EFC895FA
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