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   1 From: Johannes Berg <johannes.berg@intel.com>
   2 Date: Mon, 20 Nov 2017 17:01:44 +0100
   3 Subject: [PATCH] mac80211: properly free requested-but-not-started TX agg
   4  sessions
   5
   6 When deleting a station or otherwise tearing down all aggregation
   7 sessions, make sure to delete requested but not yet started ones,
   8 to avoid the following scenario:
   9
  10  * session is requested, added to tid_start_tx[]
  11  * ieee80211_ba_session_work() runs, gets past BLOCK_BA check
  12  * ieee80211_sta_tear_down_BA_sessions() runs, locks &sta->ampdu_mlme.mtx,
  13    e.g. while deleting the station - deleting all active sessions
  14  * ieee80211_ba_session_work() continues since tear down flushes it, and
  15    calls ieee80211_tx_ba_session_handle_start() for the new session, arms
  16    the timer for it
  17  * station deletion continues to __cleanup_single_sta() and frees the
  18    session struct, while the timer is armed
  19
  20 Reported-by: Fengguang Wu <fengguang.wu@intel.com>
  21 Signed-off-by: Johannes Berg <johannes.berg@intel.com>
  22 ---
  23
  24 --- a/net/mac80211/agg-tx.c
  25 +++ b/net/mac80211/agg-tx.c
  26 @@ -330,6 +330,11 @@ int ___ieee80211_stop_tx_ba_session(stru
  27
  28         spin_lock_bh(&sta->lock);
  29
  30 +       /* free struct pending for start, if present */
  31 +       tid_tx = sta->ampdu_mlme.tid_start_tx[tid];
  32 +       kfree(tid_tx);
  33 +       sta->ampdu_mlme.tid_start_tx[tid] = NULL;
  34 +
  35         tid_tx = rcu_dereference_protected_tid_tx(sta, tid);
  36         if (!tid_tx) {
  37                 spin_unlock_bh(&sta->lock);