mac80211: modify beacon using sdata/wdev-lock, not rtnl lock

The csa finalize worker needs to change the beacon information (for
different modes). These are normally protected under rtnl lock, but the
csa finalize worker is called by drivers and should not acquire the RTNL
lock. Therefore change access protection for beacons to sdata/wdev lock.

Reported-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
[fix sdata_dereference]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/cfg.c

@@ -857,7 +857,7 @@ static int ieee80211_set_probe_resp(struct ieee80211_sub_if_data *sdata,
 	if (!resp || !resp_len)
 		return 1;
 
-	old = rtnl_dereference(sdata->u.ap.probe_resp);
+	old = sdata_dereference(sdata->u.ap.probe_resp, sdata);
 
 	new = kzalloc(sizeof(struct probe_resp) + resp_len, GFP_KERNEL);
 	if (!new)
@@ -881,7 +881,8 @@ int ieee80211_assign_beacon(struct ieee80211_sub_if_data *sdata,
 	int size, err;
 	u32 changed = BSS_CHANGED_BEACON;
 
-	old = rtnl_dereference(sdata->u.ap.beacon);
+	old = sdata_dereference(sdata->u.ap.beacon, sdata);
+
 
 	/* Need to have a beacon head if we don't have one yet */
 	if (!params->head && !old)
@@ -958,7 +959,7 @@ static int ieee80211_start_ap(struct wiphy *wiphy, struct net_device *dev,
 		      BSS_CHANGED_P2P_PS;
 	int err;
 
-	old = rtnl_dereference(sdata->u.ap.beacon);
+	old = sdata_dereference(sdata->u.ap.beacon, sdata);
 	if (old)
 		return -EALREADY;
 
@@ -1020,7 +1021,8 @@ static int ieee80211_start_ap(struct wiphy *wiphy, struct net_device *dev,
 
 	err = drv_start_ap(sdata->local, sdata);
 	if (err) {
-		old = rtnl_dereference(sdata->u.ap.beacon);
+		old = sdata_dereference(sdata->u.ap.beacon, sdata);
+
 		if (old)
 			kfree_rcu(old, rcu_head);
 		RCU_INIT_POINTER(sdata->u.ap.beacon, NULL);
@@ -1051,7 +1053,7 @@ static int ieee80211_change_beacon(struct wiphy *wiphy, struct net_device *dev,
 	if (sdata->vif.csa_active)
 		return -EBUSY;
 
-	old = rtnl_dereference(sdata->u.ap.beacon);
+	old = sdata_dereference(sdata->u.ap.beacon, sdata);
 	if (!old)
 		return -ENOENT;
 
@@ -1071,10 +1073,10 @@ static int ieee80211_stop_ap(struct wiphy *wiphy, struct net_device *dev)
 	struct probe_resp *old_probe_resp;
 	struct cfg80211_chan_def chandef;
 
-	old_beacon = rtnl_dereference(sdata->u.ap.beacon);
+	old_beacon = sdata_dereference(sdata->u.ap.beacon, sdata);
 	if (!old_beacon)
 		return -ENOENT;
-	old_probe_resp = rtnl_dereference(sdata->u.ap.probe_resp);
+	old_probe_resp = sdata_dereference(sdata->u.ap.probe_resp, sdata);
 
 	/* abort any running channel switch */
 	sdata->vif.csa_active = false;
@@ -1975,7 +1977,7 @@ static int ieee80211_change_bss(struct wiphy *wiphy,
 	enum ieee80211_band band;
 	u32 changed = 0;
 
-	if (!rtnl_dereference(sdata->u.ap.beacon))
+	if (!sdata_dereference(sdata->u.ap.beacon, sdata))
 		return -ENOENT;
 
 	band = ieee80211_get_sdata_band(sdata);
@@ -3045,6 +3047,8 @@ static int ieee80211_channel_switch(struct wiphy *wiphy, struct net_device *dev,
 	struct ieee80211_if_mesh __maybe_unused *ifmsh;
 	int err, num_chanctx;
 
+	lockdep_assert_held(&sdata->wdev.mtx);
+
 	if (!list_empty(&local->roc_list) || local->scanning)
 		return -EBUSY;
 

net/mac80211/ieee80211_i.h

@@ -813,6 +813,9 @@ static inline void sdata_unlock(struct ieee80211_sub_if_data *sdata)
 	__release(&sdata->wdev.mtx);
 }
 
+#define sdata_dereference(p, sdata) \
+	rcu_dereference_protected(p, lockdep_is_held(&sdata->wdev.mtx))
+
 static inline void
 sdata_assert_lock(struct ieee80211_sub_if_data *sdata)
 {