ath9k: Fix regression in channelwidth switch at the same channel

The commit "ath9k: Fix invalid noisefloor reading due to channel update"
preserves the current channel noisefloor readings before updating
channel type at the same channel index. It is also updating the curchan
pointer. As survey updation is also referring curchan pointer to fetch
the appropriate index, which might leads to invalid memory access. This
patch partially reverts the change and stores the noise floor history
buffer before updating channel type w/o updating curchan.

Cc: stable@kernel.org
Cc: Gary Morain <gmorain@google.com>
Cc: Paul Stewart <pstew@google.com>
Reported-by: Mohammed Shafi Shajakhan <mohammed@qca.qualcomm.com>
Signed-off-by: Rajkumar Manoharan <rmanohar@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath9k/calib.c

@@ -400,6 +400,7 @@ bool ath9k_hw_getnf(struct ath_hw *ah, struct ath9k_channel *chan)
 	ah->noise = ath9k_hw_getchan_noise(ah, chan);
 	return true;
 }
+EXPORT_SYMBOL(ath9k_hw_getnf);
 
 void ath9k_init_nfcal_hist_buffer(struct ath_hw *ah,
 				  struct ath9k_channel *chan)

drivers/net/wireless/ath/ath9k/main.c

@@ -1629,7 +1629,6 @@ static int ath9k_config(struct ieee80211_hw *hw, u32 changed)
 
 	if (changed & IEEE80211_CONF_CHANGE_CHANNEL) {
 		struct ieee80211_channel *curchan = hw->conf.channel;
-		struct ath9k_channel old_chan;
 		int pos = curchan->hw_value;
 		int old_pos = -1;
 		unsigned long flags;
@@ -1654,11 +1653,8 @@ static int ath9k_config(struct ieee80211_hw *hw, u32 changed)
 		 * Preserve the current channel values, before updating
 		 * the same channel
 		 */
-		if (old_pos == pos) {
-			memcpy(&old_chan, &sc->sc_ah->channels[pos],
-				sizeof(struct ath9k_channel));
-			ah->curchan = &old_chan;
-		}
+		if (ah->curchan && (old_pos == pos))
+			ath9k_hw_getnf(ah, ah->curchan);
 
 		ath9k_cmn_update_ichannel(&sc->sc_ah->channels[pos],
 					  curchan, conf->channel_type);