mac80211: add KCOV remote annotations to incoming frame processing

Add KCOV remote annotations to ieee80211_iface_work() and
ieee80211_rx_list(). This will enable coverage-guided fuzzing of
mac80211 code that processes incoming 802.11 frames.
Signed-off-by: Aleksandr Nogikh <nogikh@google.com>
Reviewed-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/mac80211/iface.c

@@ -1356,6 +1356,7 @@ static void ieee80211_iface_work(struct work_struct *work)
 	while ((skb = skb_dequeue(&sdata->skb_queue))) {
 		struct ieee80211_mgmt *mgmt = (void *)skb->data;
 
+		kcov_remote_start_common(skb_get_kcov_handle(skb));
 		if (ieee80211_is_action(mgmt->frame_control) &&
 		    mgmt->u.action.category == WLAN_CATEGORY_BACK) {
 			int len = skb->len;
@@ -1465,6 +1466,7 @@ static void ieee80211_iface_work(struct work_struct *work)
 		}
 
 		kfree_skb(skb);
+		kcov_remote_stop();
 	}
 
 	/* then other type-dependent work */

net/mac80211/rx.c

@@ -4742,6 +4742,8 @@ void ieee80211_rx_list(struct ieee80211_hw *hw, struct ieee80211_sta *pubsta,
 
 	status->rx_flags = 0;
 
+	kcov_remote_start_common(skb_get_kcov_handle(skb));
+
 	/*
 	 * Frames with failed FCS/PLCP checksum are not returned,
 	 * all other frames are returned without radiotap header
@@ -4749,15 +4751,15 @@ void ieee80211_rx_list(struct ieee80211_hw *hw, struct ieee80211_sta *pubsta,
 	 * Also, frames with less than 16 bytes are dropped.
 	 */
 	skb = ieee80211_rx_monitor(local, skb, rate);
-	if (!skb)
-		return;
-
+	if (skb) {
 		ieee80211_tpt_led_trig_rx(local,
 					  ((struct ieee80211_hdr *)skb->data)->frame_control,
 					  skb->len);
 
 		__ieee80211_rx_handle_packet(hw, pubsta, skb, list);
+	}
 
+	kcov_remote_stop();
 	return;
  drop:
 	kfree_skb(skb);