mac80211: fix spurious delBA handling

Lennert Buytenhek noticed that delBA handling in mac80211
was broken and has remotely triggerable problems, some of
which are due to some code shuffling I did that ended up
changing the order in which things were done -- this was

  commit d75636ef9c1af224f1097941879d5a8db7cd04e5
  Author: Johannes Berg <johannes@sipsolutions.net>
  Date:   Tue Feb 10 21:25:53 2009 +0100

    mac80211: RX aggregation: clean up stop session

and other parts were already present in the original

  commit d92684e66091c0f0101819619b315b4bb8b5bcc5
  Author: Ron Rindjunsky <ron.rindjunsky@intel.com>
  Date:   Mon Jan 28 14:07:22 2008 +0200

      mac80211: A-MPDU Tx add delBA from recipient support

The first problem is that I moved a BUG_ON before various
checks -- thereby making it possible to hit. As the comment
indicates, the BUG_ON can be removed since the ampdu_action
callback must already exist when the state is != IDLE.

The second problem isn't easily exploitable but there's a
race condition due to unconditionally setting the state to
OPERATIONAL when a delBA frame is received, even when no
aggregation session was ever initiated. All the drivers
accept stopping the session even then, but that opens a
race window where crashes could happen before the driver
accepts it. Right now, a WARN_ON may happen with non-HT
drivers, while the race opens only for HT drivers.

For this case, there are two things necessary to fix it:
 1) don't process spurious delBA frames, and be more careful
    about the session state; don't drop the lock

 2) HT drivers need to be prepared to handle a session stop
    even before the session was really started -- this is
    true for all drivers (that support aggregation) but
    iwlwifi which can be fixed easily. The other HT drivers
    (ath9k and ar9170) are behaving properly already.

Reported-by: Lennert Buytenhek <buytenh@marvell.com>
Cc: stable@kernel.org
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 3 insertions, 5 deletions

diff --git a/net/mac80211/ht.c b/net/mac80211/ht.c
index 48ef1a282b9..cdc58e61d92 100644
--- a/net/mac80211/ht.c
+++ b/net/mac80211/ht.c
@@ -141,7 +141,6 @@ void ieee80211_process_delba(struct ieee80211_sub_if_data *sdata,
 			     struct sta_info *sta,
 			     struct ieee80211_mgmt *mgmt, size_t len)
 {
-	struct ieee80211_local *local = sdata->local;
 	u16 tid, params;
 	u16 initiator;
 
@@ -161,10 +160,9 @@ void ieee80211_process_delba(struct ieee80211_sub_if_data *sdata,
 						 WLAN_BACK_INITIATOR, 0);
 	else { /* WLAN_BACK_RECIPIENT */
 		spin_lock_bh(&sta->lock);
-		sta->ampdu_mlme.tid_state_tx[tid] =
-				HT_AGG_STATE_OPERATIONAL;
+		if (sta->ampdu_mlme.tid_state_tx[tid] & HT_ADDBA_REQUESTED_MSK)
+			___ieee80211_stop_tx_ba_session(sta, tid,
+							WLAN_BACK_RECIPIENT);
 		spin_unlock_bh(&sta->lock);
-		ieee80211_stop_tx_ba_session(&local->hw, sta->sta.addr, tid,
-					     WLAN_BACK_RECIPIENT);
 	}
 }