Hostap-Patch causes strange behavior in scan results

[Dan Williams]

On Tue, 2017-07-25 at 18:07 +0200, Vincent wrote:
> Hi,
> I wrote a patch to give me feedback about ht and vht capabilities in
> probe requests. (LEDE)
> 
> https://github.com/berlin-open-wireless-lab/patches-pending/blob/mast
> er/patches/hostap_patches/601-probe-mgmt.patch
> 
> I'm just adding
> 
> +			struct ieee80211_ht_capabilities ht_capab;
> +			struct ieee80211_vht_capabilities vht_capab;

That's the problem.  This struct describes the over-the-air probe
response (or the beacon, can't tell which you added these to) from the
AP.  The only fixed fields are the ones at the start of the struct
(timestamp, beacon_int, capab_info).  The rest are information elements
that can be given in any order by the AP.

Which includes the HT/VHT fields that you're trying to add as fixed
fields. They can appear anywhere in the rest of the frame, but you're
assuming they are appearing right after the capability info.  Which
they don't, as you've found out :)

You'll need to parse the actual probe response variable info (pointed
to by the 'variable' member) as information elements and find the
HT/VHT IEs and then parse those.  Or something.

But what are you actually trying to do?  If the AP is sending the
HT/VHT IEs, they will already appear in the probe response frame, so
whatever is parsing that ieee80211_mgmt struct that you've pasted into
your mail either isn't finding those IEs, or doesn't have code to parse
them.

Dan

> to struct ieee80211_mgmt in the beacon struct:
> 
> u.beacon.ht_capab
> 
> Now I made a scan and the result looks like this:
> 
> ESSID:""
> ESSID:""
> ESSID:""
> ESSID:""
> ESSID:""
> ESSID:""
> ESSID:""
> ESSID:""
> ESSID:"LEDE_50"
> 
> I have no idea what happens...
> Can you give me some hints?
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