Re: [RFC PATCH] ath10k: fix RX of frames with broken FCS in monitor mode

From: Ben Greear <greearb@candelatech.com>
To: "Linus Lüssing" <linus.luessing@c0d3.blue>, ath10k@lists.infradead.org
Cc: "Linus Lüssing" <ll@simonwunderlich.de>,
	"Simon Wunderlich" <sw@simonwunderlich.de>
Subject: Re: [RFC PATCH] ath10k: fix RX of frames with broken FCS in monitor mode
Date: Fri, 1 Nov 2019 08:46:53 -0700	[thread overview]
Message-ID: <8d256f92-a74b-1670-4493-8e36f402548b@candelatech.com> (raw)
In-Reply-To: <20191101111138.9086-1-linus.luessing@c0d3.blue>

On 11/1/19 4:11 AM, Linus Lüssing wrote:
> From: Linus Lüssing <ll@simonwunderlich.de>
> 
> So far, frames were forwarded regardless of the FCS correctness leading
> to userspace applications listening on the monitor mode interface to
> receive potentially broken frames, even with the "fcsfail" flag unset.
> 
> By default, with the "fcsfail" flag of a monitor mode interface
> unset, frames with FCS errors should be dropped. With this patch, the
> fcsfail flag is taken into account correctly.
> 
> Signed-off-by: Linus Lüssing <ll@simonwunderlich.de>
> ---
> This was tested on an Open Mesh A41 device, featuring a QCA4019. And
> with this firmware:
> 
> https://www.candelatech.com/downloads/ath10k-4019-10-4b/firmware-5-ct-full-community-12.bin-lede.011
> 
> But from looking at the code it seems that the vanilla ath10k has the
> same issue, therefore submitting it here.
> 
> I'm also not that familiar with the ath10k code yet. So not 100% sure if
> it's the right place for this check. Therefore sending as RFC.
> ---
>   drivers/net/wireless/ath/ath10k/htt_rx.c | 6 ++++++
>   1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/net/wireless/ath/ath10k/htt_rx.c b/drivers/net/wireless/ath/ath10k/htt_rx.c
> index 53f1095de8ff..ce0a16ebb8bb 100644
> --- a/drivers/net/wireless/ath/ath10k/htt_rx.c
> +++ b/drivers/net/wireless/ath/ath10k/htt_rx.c
> @@ -1285,6 +1285,12 @@ static void ath10k_process_rx(struct ath10k *ar, struct sk_buff *skb)
>   
>   	status = IEEE80211_SKB_RXCB(skb);
>   
> +	if (ar->monitor && !(ar->filter_flags & FIF_FCSFAIL) &&
> +	    status->flag & RX_FLAG_FAILED_FCS_CRC) {
> +		dev_kfree_skb_any(skb);
> +		return;
> +	}

Maybe worth adding a counter like 'rx_drop_crc' to the ath10k_debug struct and increment it here
and also show in debugfs and/or ethtool stats?

And, maybe no check for ar->monitor, in case somehow the frame is still received
with bad CRC even without monitor mode?

Thanks,
Ben

-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com

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