Subject: Re: Kernel oops / WiFi connection failure with wpa_supplicant 2.7
To:     Denis Kenzior <denkenz@gmail.com>, Jouni Malinen <j@w1.fi>,
        Eric Blau <eblau@eblau.com>
Cc:     hostap@lists.infradead.org,
        linux-wireless <linux-wireless@vger.kernel.org>,
        Johannes Berg <johannes@sipsolutions.net>
References: <CADU241PtPeiTQWHwb=uF6Ohuua_asOwCarCAKVC8jdVVNAsByA@mail.gmail.com>
 <20190103154921.GA25015@w1.fi>
 <41e7ccaf-c73d-b404-69fe-ad17433add37@broadcom.com>
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 <0490b8fa-bf8c-c76c-1367-70d0f4e3845f@broadcom.com>
 <206b5ae1-7fcf-9078-8399-2a8f9ff6c211@gmail.com>
From:   Arend Van Spriel <arend.vanspriel@broadcom.com>
Message-ID: <d5599cf9-5fb4-a68d-dfd9-0d10a6758ae2@broadcom.com>
Date:   Tue, 15 Jan 2019 00:04:24 +0100
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On 1/14/2019 10:18 PM, Denis Kenzior wrote:
> Hi Arend,
> 
> On 01/14/2019 02:12 PM, Arend Van Spriel wrote:
>> On 1/8/2019 6:44 PM, Denis Kenzior wrote:
>>> Hi Arend,
>>>
>>>> However, there is more to it. When these offloads were introduced, 
>>>> we discussed about having a PORT_AUTHORIZED event or not. It was 
>>>> decided passing an attribute in CONNECT and ROAMED event would 
>>>> suffice and that is what was implemented in brcmfmac. However, it 
>>>> seems time passed and the need for an explicit PORT_AUTHORIZED was 
>>>> there (probably Denis knows), which wpa_supplicant now supports thus 
>>>> ignoring the attribute in the CONNECT and ROAMED events. The 
>>>> brcmfmac driver was not changed accordingly. For this there are 
>>>> patches pending in linux-wireless which are necessary to have a 
>>>> working connection.
>>>>
>>>
>>> Coming in a bit late to this discussion, but it does raise a few 
>>> points I wouldn't mind some clarification on:
>>>
>>> - With commit 503c1fb98ba3, the kernel effectively changed the 
>>> userspace API.  So I take it that breaking userspace APIs are OK 
>>> sometimes? If so, I have lots of suggestions to make ;)
>>
>> I bet you do :-p I think the rule of thumb is that there are no 
>> drivers providing the functionality behind the user-space API and/or 
>> no user-space applications are using that API.
> 
> Maybe this is a question for Johannes as well, but define 'user-space 
> applications'?  If that includes wpa_s, wasn't the rule of thumb broken 
> with that commit?

In my previous reply I wanted to add that it would be hard to proof that 
no user-space applications are using the API. Not sure exactly when 
things were added in wpa_s, but I suspect it was 
post-commit-503c1fb98ba3 so it did not have support for the user-space 
API before the commit.

>>
>>> - Is RTNL LINK_MODE / OPER_STATE status being (supposed to be?) 
>>> affected by the driver during a roam?  E.g. if we're in a 802.1X 
>>> network with userspace authentication, and driver roamed requiring a 
>>> new 802.1X auth, then in theory the RTNL mode needs to be brought 
>>> back out of UP state...
>>
>> So do you expect the driver/cfg80211 to take care of that or the 
>> supplicant? I assumed wpa_supplicant would be doing that.
>>
> 
> With regular roaming where we trigger a Deassociate/Deathenticate 
> (either explicitly or implicitly) first, the interface goes into dormant 
> mode by virtue of the carrier going down.
> 
> With this it isn't really clear whether the same is happening and who 
> (kernel/userspace) should be doing what.  I would actually assume the 
> kernel is/should be turning carrier off for the duration of the roam 
> operation?

On what layer do we know 802.1X re-auth is required?

>>> - The new API leaves a lot to be desired in terms of race conditions. 
>>> For example, how long should userspace wait for EAPoL-EAP packets to 
>>> arrive (before triggering its own EAPoL-Start for example) if a 
>>> CMD_ROAMED event comes?
>>
>> I think that question applies to CMD_CONNECT as well, right? Not sure 
>> if the specs provide any guidance for that. I can dive into that, but 
>> maybe someone like Jouni or Johannes know. If so, let me know ;-)
> 
> With CMD_CONNECT it is a bit more clear because you're most likely not 
> specifying a PMKID for the first time, so you expect the authentication 
> to happen in all cases.  If the AP doesn't respond after some small 
> timeout, the supplicant can send its own EAPoL-Start.
> 
> With CMD_ROAMED it is less clear.
> 
>>
>>> - What happens if userspace does send an EAPoL-Start in the middle of 
>>> an offloaded 4-way handshake?
>>
>> Probably those would be dropped.
>>
> 
> I would love to have something more definitive than 'Probably', and it 
> might be worth mentioning this hint in the documentation somewhere.

I was hesitant to use that word, but decided to do so simply because I 
can not speak for every driver and even for the brcmfmac driver that I 
maintain I will need to look into the firmware to be sure. I agree that 
a remark of that possibility is worth adding.

Regards,
Arend