Return-path: Received: from mail-wm0-f45.google.com ([74.125.82.45]:32822 "EHLO mail-wm0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751748AbeCNUoY (ORCPT ); Wed, 14 Mar 2018 16:44:24 -0400 Received: by mail-wm0-f45.google.com with SMTP id s206so20194016wme.0 for ; Wed, 14 Mar 2018 13:44:24 -0700 (PDT) Subject: Re: [PATCH] brcmfmac: drop Inter-Access Point Protocol packets by default To: =?UTF-8?B?UmFmYcWCIE1pxYJlY2tp?= References: <20180314110119.13631-1-zajec5@gmail.com> <5AA91C67.90001@broadcom.com> Cc: =?UTF-8?B?UmFmYcWCIE1pxYJlY2tp?= , Kalle Valo , Franky Lin , Hante Meuleman , Chi-Hsien Lin , Wright Feng , Pieter-Paul Giesberts , James Hughes , linux-wireless@vger.kernel.org, brcm80211-dev-list.pdl@broadcom.com, brcm80211-dev-list@cypress.com, netdev@vger.kernel.org, =?UTF-8?Q?Linus_L=c3=bcssing?= , Felix Fietkau , bridge@lists.linux-foundation.org From: Arend van Spriel Message-ID: <5AA989A5.5060400@broadcom.com> (sfid-20180314_214555_840483_DB32CB65) Date: Wed, 14 Mar 2018 21:44:21 +0100 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Sender: linux-wireless-owner@vger.kernel.org List-ID: On 3/14/2018 4:57 PM, Rafał Miłecki wrote: > 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 >>>> >>>> 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 >>>> Signed-off-by: Rafał Miłecki >>>> --- >>>> 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. >> >> >>>> diff --git a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/core.c >>>> b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/core.c >>>> index 19048526b4af..db6987015fb1 100644 >>>> --- a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/core.c >>>> +++ b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/core.c >>> >>> [...] >>> >>>> static netdev_tx_t brcmf_netdev_start_xmit(struct sk_buff *skb, >>>> struct net_device *ndev) >>>> { >>>> @@ -250,6 +278,12 @@ static netdev_tx_t >>>> brcmf_netdev_start_xmit(struct sk_buff *skb, >>>> goto done; >>>> } >>>> >>>> + if (!IS_ENABLED(CONFIG_BRCMFMAC_IAPP) && brcmf_skb_is_iapp(skb)) { >>>> + dev_kfree_skb(skb); >>>> + ret = -EINVAL; >>>> + goto done; >>>> + } >>> >>> This is not right. The function must return netdev_tx_t type. Here is >>> kerneldoc of .start_xmit(): >>> >>> * netdev_tx_t (*ndo_start_xmit)(struct sk_buff *skb, >>> * struct net_device *dev); >>> * Called when a packet needs to be transmitted. >>> * Returns NETDEV_TX_OK. Can return NETDEV_TX_BUSY, but you >>> should stop >>> * the queue before that can happen; it's for obsolete devices and >>> weird >>> * corner cases, but the stack really does a non-trivial amount >>> * of useless work if you return NETDEV_TX_BUSY. >>> * Required; cannot be NULL. >> >> Please take a closer look at how brcmf_netdev_start_xmit() works. Above >> code *will* return netdev_tx_t. >> >> >>> You may want to increase dropped netstat or add driver internal >>> statistic counter so there is visibility of IAPP packets being >>> dropped. >> >> OK, I'll try to find a stat to increase. > > So after checking brcmf_netdev_start_xmit() again, I realized I actually > *do* that. Doing: > ret = -EINVAL; > goto done; > results in increasing tx_dropped. Okay, okay. Admittedly I only looked at the patch. Feel free to remove the Reviewed-by. Regards, Arend