[PATCH net-next v2] ath10k: fix RX of frames with broken FCS in monitor mode

[Linus LÃssing]

From: Linus LÃssing <ll@xxxxxxxxxxxxxxxxxx>

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.

Cc: Simon Wunderlich <sw@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus LÃssing <ll@xxxxxxxxxxxxxxxxxx>
---
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.

Changelog v2:

* removed the spinlock as only a 32 bit statistics counter is
  incremented

Changelog RFC->v1:

* removed "ar->monitor" check
* added a debug counter

---

 drivers/net/wireless/ath/ath10k/core.h   | 1 +
 drivers/net/wireless/ath/ath10k/debug.c  | 2 ++
 drivers/net/wireless/ath/ath10k/htt_rx.c | 7 +++++++
 3 files changed, 10 insertions(+)

diff --git a/drivers/net/wireless/ath/ath10k/core.h b/drivers/net/wireless/ath/ath10k/core.h
index af68eb5d0776..d445482fa945 100644
--- a/drivers/net/wireless/ath/ath10k/core.h
+++ b/drivers/net/wireless/ath/ath10k/core.h
@@ -1180,6 +1180,7 @@ struct ath10k {
 
 	struct {
 		/* protected by data_lock */
+		u32 rx_crc_err_drop;
 		u32 fw_crash_counter;
 		u32 fw_warm_reset_counter;
 		u32 fw_cold_reset_counter;
diff --git a/drivers/net/wireless/ath/ath10k/debug.c b/drivers/net/wireless/ath/ath10k/debug.c
index bd2b5628f850..5e4cd2966e6f 100644
--- a/drivers/net/wireless/ath/ath10k/debug.c
+++ b/drivers/net/wireless/ath/ath10k/debug.c
@@ -1094,6 +1094,7 @@ static const char ath10k_gstrings_stats[][ETH_GSTRING_LEN] = {
 	"d_rts_good",
 	"d_tx_power", /* in .5 dbM I think */
 	"d_rx_crc_err", /* fcs_bad */
+	"d_rx_crc_err_drop", /* frame with FCS error, dropped late in kernel */
 	"d_no_beacon",
 	"d_tx_mpdus_queued",
 	"d_tx_msdu_queued",
@@ -1193,6 +1194,7 @@ void ath10k_debug_get_et_stats(struct ieee80211_hw *hw,
 	data[i++] = pdev_stats->rts_good;
 	data[i++] = pdev_stats->chan_tx_power;
 	data[i++] = pdev_stats->fcs_bad;
+	data[i++] = ar->stats.rx_crc_err_drop;
 	data[i++] = pdev_stats->no_beacons;
 	data[i++] = pdev_stats->mpdu_enqued;
 	data[i++] = pdev_stats->msdu_enqued;
diff --git a/drivers/net/wireless/ath/ath10k/htt_rx.c b/drivers/net/wireless/ath/ath10k/htt_rx.c
index 9f0e7b4943ec..8139c9cea1d8 100644
--- a/drivers/net/wireless/ath/ath10k/htt_rx.c
+++ b/drivers/net/wireless/ath/ath10k/htt_rx.c
@@ -1285,6 +1285,13 @@ static void ath10k_process_rx(struct ath10k *ar, struct sk_buff *skb)
 
 	status = IEEE80211_SKB_RXCB(skb);
 
+	if (!(ar->filter_flags & FIF_FCSFAIL) &&
+	    status->flag & RX_FLAG_FAILED_FCS_CRC) {
+		ar->stats.rx_crc_err_drop++;
+		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