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

["Linus Lüssing" <linus.luessing@c0d3.blue>]

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;
+	}
+
 	ath10k_dbg(ar, ATH10K_DBG_DATA,
 		   "rx skb %pK len %u peer %pM %s %s sn %u %s%s%s%s%s%s %srate_idx %u vht_nss %u freq %u band %u flag 0x%x fcs-err %i mic-err %i amsdu-more %i\n",
 		   skb,
-- 
2.24.0.rc2


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