Re: wpa_supplicant 2.8 fails in brcmf_cfg80211_set_pmk

From: Marcel Holtmann <marcel@holtmann.org>
To: Arend Van Spriel <arend.vanspriel@broadcom.com>
Cc: Chi-Hsien Lin <Chi-Hsien.Lin@cypress.com>,
	Stefan Wahren <wahrenst@gmx.net>,
	Stanley Hsu <Stanley.Hsu@cypress.com>,
	Franky Lin <franky.lin@broadcom.com>,
	Hante Meuleman <hante.meuleman@broadcom.com>,
	Wright Feng <Wright.Feng@cypress.com>,
	"linux-wireless@vger.kernel.org" <linux-wireless@vger.kernel.org>,
	"brcm80211-dev-list.pdl@broadcom.com" 
	<brcm80211-dev-list.pdl@broadcom.com>,
	brcm80211-dev-list <brcm80211-dev-list@cypress.com>,
	Jouni Malinen <j@w1.fi>
Subject: Re: wpa_supplicant 2.8 fails in brcmf_cfg80211_set_pmk
Date: Thu, 20 Jun 2019 20:39:10 +0200	[thread overview]
Message-ID: <D3FC6B1E-ABC8-408E-8CAD-75F1D5BA8469@holtmann.org> (raw)
In-Reply-To: <a65a9b67-8307-12d0-9ef7-94bd2eb5badf@broadcom.com>

Hi Arend,

>>>>>>>> i was able to reproduce an (maybe older issue) with 4-way handshake
>>>>>>>> offloading for 802.1X in the brcmfmac driver. My setup consists of
>>>>>>>> Raspberry Pi 3 B (current linux-next, arm64/defconfig) on STA side and a
>>>>>>>> Raspberry Pi 3 A+ (Linux 4.19) on AP side.
>>>>>>> 
>>>>>>> Looks like Raspberry Pi isn't the only affected platform [3], [4].
>>>>>>> 
>>>>>>> [3] - https://bugzilla.redhat.com/show_bug.cgi?id=1665608
>>>>>>> [4] - https://bugzilla.kernel.org/show_bug.cgi?id=202521
>>>>>> 
>>>>>> Stefan,
>>>>>> 
>>>>>> Could you please try the attached patch for your wpa_supplicant? We'll
>>>>>> upstream if it works for you.
>>>>> 
>>>>> I hope that someone is also providing a kernel patch to fix the issue. Hacking around a kernel issue in userspace is not enough. Fix the root cause in the kernel.
>>>> Marcel,
>>>> This is a kernel warning for invalid application PMK set actions, so the
>>>> fix is to only set PMK to wifi driver when 4-way is offloaded. I think
>>>> Arend added the WARN_ON() intentionally to catch application misuse of
>>>> PMK setting.
>>>> You may also remove the warnings with the attached patch, but let's see
>>>> what Arend says first.
>>>> Arend,
>>>> Any comment?
>>> 
>>> Hi Chi-Hsien, Marcel
>>> 
>>> From the kernel side I do not see an issue. In order to use 802.1X offload the NL80211_ATTR_WANT_1X_4WAY_HS flag must be set in NL80211_CMD_CONNECT. Otherwise, NL80211_CMD_SET_PMK is not accepted. The only improvement would be to document this more clearly in the "WPA/WPA2 EAPOL handshake offload" DOC section in nl80211.h.
>> so nl80211 is an API. And an application can use that API wrongly (be that intentionally or unintentionally), the kernel can not just go WARN_ON and print a backtrace. That is your bug. So please handle wrong user input properly.
> 
> You are right. However, the kernel does also return an error if the WARN_ON is hit. We can improve by using the EXT_ACK functionality to provide more info than just -EINVAL, eg. "PMK not accepted; no 802.1X offload requested on connect”.

just remove the WARN_ON and replace it with a dev_warn. Userspace should not be able to trigger WARN_ON by using nl80211.

>> Frankly, I don’t get why nl80211 itself is not validating the input and this is left to the driver. I think we need a nl80211 fuzzer that really exercises this API with random values and parameters to provide invalid input.
> 
> That would mean nl80211 should keep state info between commands. From what I remember that has been avoided from day one because of the experiences with that in the WEXT days. I welcome any testing be it fuzzer or something else.

And now driver bugs are bleeding into the API. I expect from a kernel API that it hides driver details. From an userspace program perspective I expect exactly the same input validation and behavior no matter what hardware is used underneath. If we can not do that, then this API has a broken design.

Regards

Marcel