mac80211: fix tid_agg_rx NULL dereference

On drivers setting the SUPPORTS_REORDERING_BUFFER hardware flag,
we crash when the peer sends an AddBA request while we already
have a session open on the seame TID; this is because on those
drivers, the tid_agg_rx is left NULL even though the session is
valid, and the agg_session_valid bit is set.

To fix this, store the dialog tokens outside the tid_agg_rx to
be able to compare them to the received AddBA request.

Fixes: f89e07d4 ("mac80211: agg-rx: refuse ADDBA Request with timeout update")
Reported-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/agg-rx.c

@@ -315,11 +315,7 @@ void __ieee80211_start_rx_ba_session(struct sta_info *sta,
 	mutex_lock(&sta->ampdu_mlme.mtx);
 
 	if (test_bit(tid, sta->ampdu_mlme.agg_session_valid)) {
-		tid_agg_rx = rcu_dereference_protected(
-				sta->ampdu_mlme.tid_rx[tid],
-				lockdep_is_held(&sta->ampdu_mlme.mtx));
-
-		if (tid_agg_rx->dialog_token == dialog_token) {
+		if (sta->ampdu_mlme.tid_rx_token[tid] == dialog_token) {
 			ht_dbg_ratelimited(sta->sdata,
 					   "updated AddBA Req from %pM on tid %u\n",
 					   sta->sta.addr, tid);
@@ -396,7 +392,6 @@ void __ieee80211_start_rx_ba_session(struct sta_info *sta,
 	}
 
 	/* update data */
-	tid_agg_rx->dialog_token = dialog_token;
 	tid_agg_rx->ssn = start_seq_num;
 	tid_agg_rx->head_seq_num = start_seq_num;
 	tid_agg_rx->buf_size = buf_size;
@@ -418,6 +413,7 @@ void __ieee80211_start_rx_ba_session(struct sta_info *sta,
 	if (status == WLAN_STATUS_SUCCESS) {
 		__set_bit(tid, sta->ampdu_mlme.agg_session_valid);
 		__clear_bit(tid, sta->ampdu_mlme.unexpected_agg);
+		sta->ampdu_mlme.tid_rx_token[tid] = dialog_token;
 	}
 	mutex_unlock(&sta->ampdu_mlme.mtx);
 

net/mac80211/debugfs_sta.c

@@ -205,7 +205,7 @@ static ssize_t sta_agg_status_read(struct file *file, char __user *userbuf,
 		p += scnprintf(p, sizeof(buf) + buf - p, "%02d", i);
 		p += scnprintf(p, sizeof(buf) + buf - p, "\t\t%x", !!tid_rx);
 		p += scnprintf(p, sizeof(buf) + buf - p, "\t%#.2x",
-				tid_rx ? tid_rx->dialog_token : 0);
+				tid_rx ? sta->ampdu_mlme.tid_rx_token[i] : 0);
 		p += scnprintf(p, sizeof(buf) + buf - p, "\t%#.3x",
 				tid_rx ? tid_rx->ssn : 0);
 

net/mac80211/sta_info.h

@@ -184,7 +184,6 @@ struct tid_ampdu_tx {
  * @ssn: Starting Sequence Number expected to be aggregated.
  * @buf_size: buffer size for incoming A-MPDUs
  * @timeout: reset timer value (in TUs).
- * @dialog_token: dialog token for aggregation session
  * @rcu_head: RCU head used for freeing this struct
  * @reorder_lock: serializes access to reorder buffer, see below.
  * @auto_seq: used for offloaded BA sessions to automatically pick head_seq_and
@@ -213,7 +212,6 @@ struct tid_ampdu_rx {
 	u16 ssn;
 	u16 buf_size;
 	u16 timeout;
-	u8 dialog_token;
 	bool auto_seq;
 	bool removed;
 };
@@ -225,6 +223,7 @@ struct tid_ampdu_rx {
  *	to tid_tx[idx], which are protected by the sta spinlock)
  *	tid_start_tx is also protected by sta->lock.
  * @tid_rx: aggregation info for Rx per TID -- RCU protected
+ * @tid_rx_token: dialog tokens for valid aggregation sessions
  * @tid_rx_timer_expired: bitmap indicating on which TIDs the
  *	RX timer expired until the work for it runs
  * @tid_rx_stop_requested:  bitmap indicating which BA sessions per TID the
@@ -243,6 +242,7 @@ struct sta_ampdu_mlme {
 	struct mutex mtx;
 	/* rx */
 	struct tid_ampdu_rx __rcu *tid_rx[IEEE80211_NUM_TIDS];
+	u8 tid_rx_token[IEEE80211_NUM_TIDS];
 	unsigned long tid_rx_timer_expired[BITS_TO_LONGS(IEEE80211_NUM_TIDS)];
 	unsigned long tid_rx_stop_requested[BITS_TO_LONGS(IEEE80211_NUM_TIDS)];
 	unsigned long agg_session_valid[BITS_TO_LONGS(IEEE80211_NUM_TIDS)];