Having problems connection to hostapd network with HT

[Markus Ongyerth]

Hi,

We have a problem with hostapd and 80211N.
We wanted to set up an accesspoint using hostapd.
When we set the require_ht setting int he hostapd.conf
our client gets rejected. If we do not set it, we can
connect, but only get legacy data rates.

So I did a bit of digging (mainly debug output and
wireshark).
My test client here is my laptop with an
"Intel Corporation Wireless 7260 (rev bb)" wifi card.
I am using an up to date install of archlinux. I have
done this test with default kernel (4.8) and lts (4.4).
It should not be relevant though, we had the same
problems on different devices.

I found out that the probe frames are sent with the
HT-capability info, but the actual assoc (and auth)
request frames lack these fields.
Looking at the code the code, hostapd checks whether
the station supports HT when it adds it. This is done
only when the first association request is sent.
Which doesn't contain the HT information, which
explains why we get rejected with require_ht.

I have attached hexdumps (from wireshark) for the
mentioned packages and our hostapd.conf

The relevant parts in the code I found are:

src/ap/ieee802_11.c:1858+
src/ap/ieee802_11_ht.c:335+

ongy

PS. We had the same problem on hostapd 2.4 and 2.6 (debian stretch/arch)
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interface=wlp0s29u1u8
driver=nl80211
hw_mode=g
channel=6
ieee80211d=1		# limit the frequencies used to those allowed
country_code=DE
ieee80211n=1		# 802.11n support

ht_capab=[HT40+][SHORT-GI-40][DSSS_CK-40]


ssid=ongy5
auth_algs=1		# 1=wpa, 2=wep, 3=both
wpa=1			# WPA2 only
wpa_key_mgmt=WPA-PSK
rsn_pairwise=CCMP
wpa_passphrase=<censored>

ap_max_inactivity=3000
skip_inactivity_poll=0

logger_syslog_level=3

require_ht=1
wmm_enabled=1		# QoS support
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