netdev - Re: [PATCH] brcmfmac: drop Inter-Access Point Protocol packets by default

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Message-ID: <9499f70ecb942df0df95512565a8f428@milecki.pl>
Date:   Wed, 14 Mar 2018 16:40:22 +0100
From:   Rafał Miłecki <rafal@...ecki.pl>
To:     Arend van Spriel <arend.vanspriel@...adcom.com>
Cc:     Rafał Miłecki <zajec5@...il.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        Franky Lin <franky.lin@...adcom.com>,
        Hante Meuleman <hante.meuleman@...adcom.com>,
        Chi-Hsien Lin <chi-hsien.lin@...ress.com>,
        Wright Feng <wright.feng@...ress.com>,
        Pieter-Paul Giesberts <pieter-paul.giesberts@...adcom.com>,
        James Hughes <james.hughes@...pberrypi.org>,
        linux-wireless@...r.kernel.org,
        brcm80211-dev-list.pdl@...adcom.com,
        brcm80211-dev-list@...ress.com, netdev@...r.kernel.org,
        Linus Lüssing <linus.luessing@...3.blue>,
        Felix Fietkau <nbd@....name>, bridge@...ts.linux-foundation.org
Subject: Re: [PATCH] brcmfmac: drop Inter-Access Point Protocol packets by
 default

On 2018-03-14 16:39, Rafał Miłecki wrote:
> On 2018-03-14 13:58, Arend van Spriel wrote:
>> On 3/14/2018 12:01 PM, Rafał Miłecki wrote:
>>> From: Rafał Miłecki <rafal@...ecki.pl>
>>> 
>>> Testing brcmfmac with more recent firmwares resulted in AP interfaces
>>> not working in some specific setups. Debugging resulted in 
>>> discovering
>>> support for IAPP in Broadcom's firmwares. This is an obsoleted 
>>> standard
>>> and its implementation is something that:
>>> 1) Most people don't need / want to use
>>> 2) Can allow local DoS attacks
>>> 3) Breaks AP interfaces in some specific bridge setups
>>> 
>>> To solve issues it can cause this commit modifies brcmfmac to drop 
>>> IAPP
>>> packets. If affects:
>>> 1) Rx path: driver won't be sending these unwanted packets up.
>>> 2) Tx path: driver will reject packets that would trigger STA
>>>     disassociation perfromed by a firmware (possible local DoS 
>>> attack).
>>> 
>>> It appears there are some Broadcom's clients/users who care about 
>>> this
>>> feature despite the drawbacks. They can switch it on by a newly added
>>> Kconfig option.
>> 
>> Thanks for taking this approach. Looks fine except for .... (see 
>> below)
>> 
>> Reviewed-by: Arend van Spriel <arend.vanspriel@...adcom.com>
>>> Signed-off-by: Rafał Miłecki <rafal@...ecki.pl>
>>> ---
>>>   drivers/net/wireless/broadcom/brcm80211/Kconfig    | 20 +++++++++++
>>>   .../wireless/broadcom/brcm80211/brcmfmac/core.c    | 39 
>>> ++++++++++++++++++++++
>>>   2 files changed, 59 insertions(+)
>>> 
>>> diff --git a/drivers/net/wireless/broadcom/brcm80211/Kconfig 
>>> b/drivers/net/wireless/broadcom/brcm80211/Kconfig
>>> index 9d99eb42d917..876787ef991a 100644
>>> --- a/drivers/net/wireless/broadcom/brcm80211/Kconfig
>>> +++ b/drivers/net/wireless/broadcom/brcm80211/Kconfig
>>> @@ -68,6 +68,26 @@ config BRCMFMAC_PCIE
>>>   	  IEEE802.11ac embedded FullMAC WLAN driver. Say Y if you want to
>>>   	  use the driver for an PCIE wireless card.
>>> 
>>> +config BRCMFMAC_IAPP
>>> +	bool "Partial support for obsoleted Inter-Access Point Protocol"
>>> +	depends on BRCMFMAC
>>> +	---help---
>>> +	  Most of Broadcom's firmwares can send 802.11f ADD frame every
>>> +	  time new STA connects to the AP interface. Some recent ones
>>> +	  can also disassociate STA when they receive such a frame.
>> 
>> I do not see any evidence that this would occur only for recent
>> firmware. That stuff is old and not touched recently.
> 
> My evidence is comparing firmwares for 4366b1: 10.10.69.3309 (r610991)
> vs. 10.10 (TOB) (r663589).
> 
> The first one is from linux-firmware.git and it doesn't implement IAPP
> in the TX path. The later one is what I got from you privately and it
> implements it.
> 
> Also a firmware for 4366c0: 10.10.122.20 (r683106) which is relatively
> new implements IAPP in the TX path.

Please also take a look at my original patch
[PATCH] brcmfmac: detect & reject faked packet generated by a firmware
https://patchwork.kernel.org/patch/10191451/