Hi Dean, * Dean Jenkins <djenkins@xxxxxxxxxx> [2012-08-11 19:47:09 +0100]: > rfcomm_session_timeout() protects the scenario of the remote > Bluetooth device failing to send a DISC on the rfcomm control > channel after the last data DLC channel has been closed. > > There is a race condition between the timer expiring causing > rfcomm_session_timeout() to run and the rfcomm session being > deleted. If the rfcomm session is deleted then > rfcomm_session_timeout() would use a freed rfcomm session > pointer resulting in a potential kernel crash or memory corruption. > Note the timer is cleared before the rfcomm session is deleted > by del_timer() so the circumstances for a failure to occur are > as follows: > > rfcomm_session_timeout() needs to be executing before the > del_timer() is called to clear the timer but > rfcomm_session_timeout() needs to be delayed from using the > rfcomm session pointer until after the session has been deleted. > Therefore, there is a very small window of opportunity for failure. > > The solution is to use del_timer_sync() instead of del_timer() > as this ensures that rfcomm_session_timeout() is not running > when del_timer_sync() returns. This means that it is not > possible for rfcomm_session_timeout() to run after the rfcomm > session has been deleted. > > Signed-off-by: Dean Jenkins <djenkins@xxxxxxxxxx> > --- > net/bluetooth/rfcomm/core.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/net/bluetooth/rfcomm/core.c b/net/bluetooth/rfcomm/core.c > index 24d4d3c..c7921fd 100644 > --- a/net/bluetooth/rfcomm/core.c > +++ b/net/bluetooth/rfcomm/core.c > @@ -264,8 +264,8 @@ static void rfcomm_session_clear_timer(struct rfcomm_session *s) > { > BT_DBG("session %p state %ld", s, s->state); > > - if (timer_pending(&s->timer)) > - del_timer(&s->timer); > + /* ensure rfcomm_session_timeout() is not running past this point */ > + del_timer_sync(&s->timer); I'm not happy of the idea of let the stack broken between patches 2 and 3 (this one). As you said if we use del_timer_sync() we don't need rfcnt here, can you add this as a first patch, maybe? and after this continue to remove the rest of the refcount code? Gustavo -- To unsubscribe from this list: send the line "unsubscribe linux-bluetooth" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html