mac80211: don't overwrite QoS TID of injected frames

Currently ieee80211_set_qos_hdr sets the QoS TID of all frames based
on the value assigned to skb->priority. This means it will also
overwrite the QoS TID of injected frames. The commit 753ffad3d6
("mac80211: fix TID field in monitor mode transmit") prevented
injected frames from being modified because of this by setting
skb->priority to the TID of the injected frame, which assured the
QoS TID will not be changed to a different value. Unfortunately,
this workaround complicates the handling of injected frames because
we can't set skb->priority without affecting the TID value in the
QoS field of injected frames.

To avoid this, and to simplify the next patch, detect if a frame is
injected in ieee80211_set_qos_hdr and if so do not change its QoS
field.

Signed-off-by: Mathy Vanhoef <Mathy.Vanhoef@kuleuven.be>
Link: https://lore.kernel.org/r/20201104061823.197407-4-Mathy.Vanhoef@kuleuven.be
[fix typos in commit message]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/tx.c

@@ -2271,10 +2271,7 @@ netdev_tx_t ieee80211_monitor_start_xmit(struct sk_buff *skb,
 						    payload[7]);
 	}
 
-	/*
-	 * Initialize skb->priority for QoS frames. This is put in the TID field
-	 * of the frame before passing it to the driver.
-	 */
+	/* Initialize skb->priority for QoS frames */
 	if (ieee80211_is_data_qos(hdr->frame_control)) {
 		u8 *p = ieee80211_get_qos_ctl(hdr);
 		skb->priority = *p & IEEE80211_QOS_CTL_TAG1D_MASK;

net/mac80211/wme.c

@@ -252,6 +252,14 @@ void ieee80211_set_qos_hdr(struct ieee80211_sub_if_data *sdata,
 
 	p = ieee80211_get_qos_ctl(hdr);
 
+	/* don't overwrite the QoS field of injected frames */
+	if (info->flags & IEEE80211_TX_CTL_INJECTED) {
+		/* do take into account Ack policy of injected frames */
+		if (*p & IEEE80211_QOS_CTL_ACK_POLICY_NOACK)
+			info->flags |= IEEE80211_TX_CTL_NO_ACK;
+		return;
+	}
+
 	/* set up the first byte */
 
 	/*