Re: brcmfmac: regression using AP mode

["Rafał Miłecki" <rafal@milecki.pl>]

On 2018-11-24 18:58, Stefan Wahren wrote:
> today i wanted to setup an access point on my Raspberry Pi 3 A+
> (BCM43455). Unfortunately the hostapd 2.4 shipped with Raspbian failed
> with recent Linux kernel:
> 
> (...)
> 
> I was able to bisect this issue down to this commit:
> 
> 1204aa17f3b4 ("brcmfmac: set WIPHY_FLAG_HAVE_AP_SME flag")
> 
> After reverting this commit hostapd works as expected.

It ringed a bell, I did a quick research and found it. It's because of
that ancient hostapd you're using. 2,5 years ago hostapd received a fix
for its discovery of driver capabilities:

commit f4830bed661f4adff51f50a0d37c64ceb748e780
Author: Rafał Miłecki <zajec5@gmail.com>
Date:   Mon Apr 25 17:10:47 2016 +0200

     nl80211: Try running without mgmt frame subscription (driver AP SME)

So your problem is the ancient hostapd that can't run with drivers that:
1) Report NL80211_ATTR_DEVICE_AP_SME
2) Don't support subscribing for PROBE_REQ and/or ACTION frames

Technically there is nothing wrong with such drivers and it's just a
hostapd bug (that's why it was fixed long time ago).

Now, you could try *not* reporting NL80211_ATTR_DEVICE_AP_SME but then
hostapd for drivers that:
1) Support monitor mode
2) Don't support subscribing for PROBE_REQ and/or ACTION frames
will hit yet another mode discovery path in and break as well.

That said there is no perfect solution.

brcmfmac *should* set WIPHY_FLAG_HAVE_AP_SME. It's required for a sane
capabilities discovery in hostapd. It's required to make sure other
supplicants can work with brcmfmac as well.

Possibly you can just update hostapd to anything more recent? I'm afraid
the version you're using may suffer from a lot of security issues anyway