mac80211: lock rate control

Both minstrel (reported by Sven Eckelmann) and the iwlwifi rate
control aren't properly taking concurrency into account. It's
likely that the same is true for other rate control algorithms.

In the case of minstrel this manifests itself in crashes when an
update and other data access are run concurrently, for example
when the stations change bandwidth or similar. In iwlwifi, this
can cause firmware crashes.

Since fixing all rate control algorithms will be very difficult,
just provide locking for invocations. This protects the internal
data structures the algorithms maintain.

I've manipulated hostapd to test this, by having it change its
advertised bandwidth roughly ever 150ms. At the same time, I'm
running a flood ping between the client and the AP, which causes
this race of update vs. get_rate/status to easily happen on the
client. With this change, the system survives this test.
Reported-by: Sven Eckelmann <sven@open-mesh.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/rate.c

@@ -683,7 +683,13 @@ void rate_control_get_rate(struct ieee80211_sub_if_data *sdata,
 	if (sdata->local->hw.flags & IEEE80211_HW_HAS_RATE_CONTROL)
 		return;
 
-	ref->ops->get_rate(ref->priv, ista, priv_sta, txrc);
+	if (ista) {
+		spin_lock_bh(&sta->rate_ctrl_lock);
+		ref->ops->get_rate(ref->priv, ista, priv_sta, txrc);
+		spin_unlock_bh(&sta->rate_ctrl_lock);
+	} else {
+		ref->ops->get_rate(ref->priv, NULL, NULL, txrc);
+	}
 
 	if (sdata->local->hw.flags & IEEE80211_HW_SUPPORTS_RC_TABLE)
 		return;

net/mac80211/rate.h

@@ -42,10 +42,12 @@ static inline void rate_control_tx_status(struct ieee80211_local *local,
 	if (!ref || !test_sta_flag(sta, WLAN_STA_RATE_CONTROL))
 		return;
 
+	spin_lock_bh(&sta->rate_ctrl_lock);
 	if (ref->ops->tx_status)
 		ref->ops->tx_status(ref->priv, sband, ista, priv_sta, skb);
 	else
 		ref->ops->tx_status_noskb(ref->priv, sband, ista, priv_sta, info);
+	spin_unlock_bh(&sta->rate_ctrl_lock);
 }
 
 static inline void
@@ -64,7 +66,9 @@ rate_control_tx_status_noskb(struct ieee80211_local *local,
 	if (WARN_ON_ONCE(!ref->ops->tx_status_noskb))
 		return;
 
+	spin_lock_bh(&sta->rate_ctrl_lock);
 	ref->ops->tx_status_noskb(ref->priv, sband, ista, priv_sta, info);
+	spin_unlock_bh(&sta->rate_ctrl_lock);
 }
 
 static inline void rate_control_rate_init(struct sta_info *sta)
@@ -91,8 +95,10 @@ static inline void rate_control_rate_init(struct sta_info *sta)
 
 	sband = local->hw.wiphy->bands[chanctx_conf->def.chan->band];
 
+	spin_lock_bh(&sta->rate_ctrl_lock);
 	ref->ops->rate_init(ref->priv, sband, &chanctx_conf->def, ista,
 			    priv_sta);
+	spin_unlock_bh(&sta->rate_ctrl_lock);
 	rcu_read_unlock();
 	set_sta_flag(sta, WLAN_STA_RATE_CONTROL);
 }
@@ -115,18 +121,20 @@ static inline void rate_control_rate_update(struct ieee80211_local *local,
 			return;
 		}
 
+		spin_lock_bh(&sta->rate_ctrl_lock);
 		ref->ops->rate_update(ref->priv, sband, &chanctx_conf->def,
 				      ista, priv_sta, changed);
+		spin_unlock_bh(&sta->rate_ctrl_lock);
 		rcu_read_unlock();
 	}
 	drv_sta_rc_update(local, sta->sdata, &sta->sta, changed);
 }
 
 static inline void *rate_control_alloc_sta(struct rate_control_ref *ref,
-					   struct ieee80211_sta *sta,
-					   gfp_t gfp)
+					   struct sta_info *sta, gfp_t gfp)
 {
-	return ref->ops->alloc_sta(ref->priv, sta, gfp);
+	spin_lock_init(&sta->rate_ctrl_lock);
+	return ref->ops->alloc_sta(ref->priv, &sta->sta, gfp);
 }
 
 static inline void rate_control_free_sta(struct sta_info *sta)

net/mac80211/sta_info.c

@@ -269,7 +269,7 @@ static int sta_prepare_rate_control(struct ieee80211_local *local,
 
 	sta->rate_ctrl = local->rate_ctrl;
 	sta->rate_ctrl_priv = rate_control_alloc_sta(sta->rate_ctrl,
-						     &sta->sta, gfp);
+						     sta, gfp);
 	if (!sta->rate_ctrl_priv)
 		return -ENOMEM;
 

net/mac80211/sta_info.h

@@ -353,6 +353,7 @@ struct sta_info {
 	u8 ptk_idx;
 	struct rate_control_ref *rate_ctrl;
 	void *rate_ctrl_priv;
+	spinlock_t rate_ctrl_lock;
 	spinlock_t lock;
 
 	struct work_struct drv_deliver_wk;