• Johannes Berg's avatar
    mac80211: fix spurious delBA handling · 827d42c9
    Johannes Berg authored
    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 d75636ef
      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 d92684e6
      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: default avatarLennert Buytenhek <buytenh@marvell.com>
    Cc: stable@kernel.org
    Signed-off-by: default avatarJohannes Berg <johannes@sipsolutions.net>
    Signed-off-by: default avatarJohn W. Linville <linville@tuxdriver.com>
agg-tx.c 19.6 KB