mac80211: protect AP VLAN list with local->mtx

It was impossible to change chanctx of master AP
for AP VLANs because the copy function requires
RTNL which can't be simply taken in mac80211 code
due to possible deadlocks.

This is required for future chanctx reservation
that re-bind vifs to new chanctx. This requires
safe AP VLAN iteration without RTNL.

Now VLANs can be iterated while holding either
RTNL or local->mtx because the list is modified
while holding both of these locks.

Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Luciano Coelho <luciano.coelho@intel.com>

4 files changed, 14 insertions, 6 deletions

diff --git a/net/mac80211/cfg.c b/net/mac80211/cfg.c
index fae76f79e2f8fb..137d3793398a1a 100644
--- a/net/mac80211/cfg.c
+++ b/net/mac80211/cfg.c
@@ -983,10 +983,11 @@ static int ieee80211_start_ap(struct wiphy *wiphy, struct net_device *dev,
 	mutex_lock(&local->mtx);
 	err = ieee80211_vif_use_channel(sdata, &params->chandef,
 					IEEE80211_CHANCTX_SHARED);
+	if (!err)
+		ieee80211_vif_copy_chanctx_to_vlans(sdata, false);
 	mutex_unlock(&local->mtx);
 	if (err)
 		return err;
-	ieee80211_vif_copy_chanctx_to_vlans(sdata, false);
 
 	/*
 	 * Apply control port protocol, this allows us to
@@ -1139,8 +1140,8 @@ static int ieee80211_stop_ap(struct wiphy *wiphy, struct net_device *dev)
 	local->total_ps_buffered -= skb_queue_len(&sdata->u.ap.ps.bc_buf);
 	skb_queue_purge(&sdata->u.ap.ps.bc_buf);
 
-	ieee80211_vif_copy_chanctx_to_vlans(sdata, true);
 	mutex_lock(&local->mtx);
+	ieee80211_vif_copy_chanctx_to_vlans(sdata, true);
 	ieee80211_vif_release_channel(sdata);
 	mutex_unlock(&local->mtx);
 
diff --git a/net/mac80211/chan.c b/net/mac80211/chan.c
index 384f3c72bbbee5..1ae6ba30c105d1 100644
--- a/net/mac80211/chan.c
+++ b/net/mac80211/chan.c
@@ -706,7 +706,7 @@ void ieee80211_vif_copy_chanctx_to_vlans(struct ieee80211_sub_if_data *sdata,
 	struct ieee80211_sub_if_data *vlan;
 	struct ieee80211_chanctx_conf *conf;
 
-	ASSERT_RTNL();
+	lockdep_assert_held(&local->mtx);
 
 	if (WARN_ON(sdata->vif.type != NL80211_IFTYPE_AP))
 		return;
diff --git a/net/mac80211/ieee80211_i.h b/net/mac80211/ieee80211_i.h
index 54bc43e0c1551e..e2103b4d8df5be 100644
--- a/net/mac80211/ieee80211_i.h
+++ b/net/mac80211/ieee80211_i.h
@@ -260,7 +260,7 @@ struct ieee80211_if_ap {
 
 	/* to be used after channel switch. */
 	struct cfg80211_beacon_data *next_beacon;
-	struct list_head vlans;
+	struct list_head vlans; /* write-protected with RTNL and local->mtx */
 
 	struct ps_data ps;
 	atomic_t num_mcast_sta; /* number of stations receiving multicast */
@@ -276,7 +276,7 @@ struct ieee80211_if_wds {
 };
 
 struct ieee80211_if_vlan {
-	struct list_head list;
+	struct list_head list; /* write-protected with RTNL and local->mtx */
 
 	/* used for all tx if the VLAN is configured to 4-addr mode */
 	struct sta_info __rcu *sta;
diff --git a/net/mac80211/iface.c b/net/mac80211/iface.c
index 4c554818871d58..e753d722dcea63 100644
--- a/net/mac80211/iface.c
+++ b/net/mac80211/iface.c
@@ -496,7 +496,9 @@ int ieee80211_do_open(struct wireless_dev *wdev, bool coming_up)
 		if (!sdata->bss)
 			return -ENOLINK;
 
+		mutex_lock(&local->mtx);
 		list_add(&sdata->u.vlan.list, &sdata->bss->vlans);
+		mutex_unlock(&local->mtx);
 
 		master = container_of(sdata->bss,
 				      struct ieee80211_sub_if_data, u.ap);
@@ -726,8 +728,11 @@ int ieee80211_do_open(struct wireless_dev *wdev, bool coming_up)
 		drv_stop(local);
  err_del_bss:
 	sdata->bss = NULL;
-	if (sdata->vif.type == NL80211_IFTYPE_AP_VLAN)
+	if (sdata->vif.type == NL80211_IFTYPE_AP_VLAN) {
+		mutex_lock(&local->mtx);
 		list_del(&sdata->u.vlan.list);
+		mutex_unlock(&local->mtx);
+	}
 	/* might already be clear but that doesn't matter */
 	clear_bit(SDATA_STATE_RUNNING, &sdata->state);
 	return res;
@@ -879,7 +884,9 @@ static void ieee80211_do_stop(struct ieee80211_sub_if_data *sdata,
 
 	switch (sdata->vif.type) {
 	case NL80211_IFTYPE_AP_VLAN:
+		mutex_lock(&local->mtx);
 		list_del(&sdata->u.vlan.list);
+		mutex_unlock(&local->mtx);
 		rcu_assign_pointer(sdata->vif.chanctx_conf, NULL);
 		/* no need to tell driver */
 		break;