mac80211: fix spurious delBA handling

commit 827d42c9ac91ddd728e4f4a31fefb906ef2ceff7 upstream.

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>
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 6 insertions, 0 deletions

diff --git a/include/net/mac80211.h b/include/net/mac80211.h
index c0610447697..5edf7925406 100644
--- a/include/net/mac80211.h
+++ b/include/net/mac80211.h
@@ -1244,6 +1244,12 @@ enum ieee80211_filter_flags {
  *
  * These flags are used with the ampdu_action() callback in
  * &struct ieee80211_ops to indicate which action is needed.
+ *
+ * Note that drivers MUST be able to deal with a TX aggregation
+ * session being stopped even before they OK'ed starting it by
+ * calling ieee80211_start_tx_ba_cb(_irqsafe), because the peer
+ * might receive the addBA frame and send a delBA right away!
+ *
  * @IEEE80211_AMPDU_RX_START: start Rx aggregation
  * @IEEE80211_AMPDU_RX_STOP: stop Rx aggregation
  * @IEEE80211_AMPDU_TX_START: start Tx aggregation