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

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Message-Id: <20191105164932.11799-1-linus.luessing@c0d3.blue>
Date:   Tue,  5 Nov 2019 17:49:32 +0100
From:   Linus Lüssing <linus.luessing@...3.blue>
To:     ath10k@...ts.infradead.org
Cc:     Kalle Valo <kvalo@...eaurora.org>,
        "David S . Miller" <davem@...emloft.net>,
        Ben Greear <greearb@...delatech.com>,
        Simon Wunderlich <sw@...onwunderlich.de>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Linus Lüssing <ll@...onwunderlich.de>
Subject: [PATCH net-next] ath10k: fix RX of frames with broken FCS in monitor mode

From: Linus Lüssing <ll@...onwunderlich.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.

Cc: Simon Wunderlich <sw@...onwunderlich.de>
Signed-off-by: Linus Lüssing <ll@...onwunderlich.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.

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 | 10 ++++++++++
 3 files changed, 13 insertions(+)

diff --git a/drivers/net/wireless/ath/ath10k/core.h b/drivers/net/wireless/ath/ath10k/core.h
index 4d7db07db6ba..787065a9eb3f 100644
--- a/drivers/net/wireless/ath/ath10k/core.h
+++ b/drivers/net/wireless/ath/ath10k/core.h
@@ -1171,6 +1171,7 @@ 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 53f1095de8ff..149728588e80 100644
--- a/drivers/net/wireless/ath/ath10k/htt_rx.c
+++ b/drivers/net/wireless/ath/ath10k/htt_rx.c
@@ -1285,6 +1285,16 @@ 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) {
+		spin_lock_bh(&ar->data_lock);
+		ar->stats.rx_crc_err_drop++;
+		spin_unlock_bh(&ar->data_lock);
+
+		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