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, 9 insertions, 1 deletions

diff --git a/drivers/net/wireless/iwlwifi/iwl-tx.c b/drivers/net/wireless/iwlwifi/iwl-tx.c
index fb9bcfa6d94..b7e196e3c8d 100644
--- a/drivers/net/wireless/iwlwifi/iwl-tx.c
+++ b/drivers/net/wireless/iwlwifi/iwl-tx.c
@@ -1277,8 +1277,16 @@ int iwl_tx_agg_stop(struct iwl_priv *priv , const u8 *ra, u16 tid)
 		return -ENXIO;
 	}
 
+	if (priv->stations[sta_id].tid[tid].agg.state ==
+				IWL_EMPTYING_HW_QUEUE_ADDBA) {
+		IWL_DEBUG_HT(priv, "AGG stop before setup done\n");
+		ieee80211_stop_tx_ba_cb_irqsafe(priv->hw, ra, tid);
+		priv->stations[sta_id].tid[tid].agg.state = IWL_AGG_OFF;
+		return 0;
+	}
+
 	if (priv->stations[sta_id].tid[tid].agg.state != IWL_AGG_ON)
-		IWL_WARN(priv, "Stopping AGG while state not IWL_AGG_ON\n");
+		IWL_WARN(priv, "Stopping AGG while state not ON or starting\n");
 
 	tid_data = &priv->stations[sta_id].tid[tid];
 	ssn = (tid_data->seq_number & IEEE80211_SCTL_SEQ) >> 4;