ath9k: discard undersized packets

Sometimes the hardware will push small packets that trigger a WARN_ON
in mac80211. Discard them early to avoid this issue.

Reported-by: Stijn Tintel <stijn@linux-ipv6.be>
Signed-off-by: Felix Fietkau <nbd@nbd.name>

package/kernel/mac80211/patches/322-ath9k-discard-undersized-packets.patch

@@ -0,0 +1,25 @@
+From: Felix Fietkau <nbd@nbd.name>
+Date: Wed, 17 Jan 2018 11:11:17 +0100
+Subject: [PATCH] ath9k: discard undersized packets
+
+Sometimes the hardware will push small packets that trigger a WARN_ON
+in mac80211. Discard them early to avoid this issue.
+
+Reported-by: Stijn Tintel <stijn@linux-ipv6.be>
+Signed-off-by: Felix Fietkau <nbd@nbd.name>
+---
+
+--- a/drivers/net/wireless/ath/ath9k/recv.c
++++ b/drivers/net/wireless/ath/ath9k/recv.c
+@@ -826,9 +826,9 @@ static int ath9k_rx_skb_preprocess(struc
+ 	sc->rx.discard_next = false;
+ 
+ 	/*
+-	 * Discard zero-length packets.
++	 * Discard zero-length packets and packets smaller than an ACK
+ 	 */
+-	if (!rx_stats->rs_datalen) {
++	if (rx_stats->rs_datalen < 10) {
+ 		RX_STAT_INC(rx_len_err);
+ 		goto corrupt;
+ 	}