Bluetooth: Fix rejected connection not disconnecting ACL link

When using DEFER_SETUP on a RFCOMM socket, a SABM frame triggers
authorization which when rejected send a DM response. This is fine
according to the RFCOMM spec:

the responding implementation may replace the "proper" response
on the Multiplexer Control channel with a DM frame, sent on the
referenced DLCI to indicate that the DLCI is not open, and that
the responder would not grant a request to open it later either.

But some stacks doesn't seems to cope with this leaving DLCI 0 open after
receiving DM frame.

To fix it properly a timer was introduced to rfcomm_session which is used
to set a timeout when the last active DLC of a session is unlinked, this
will give the remote stack some time to reply with a proper DISC frame on
DLCI 0 avoiding both sides sending DISC to each other on stacks that
follow the specification and taking care of those who don't by taking
down DLCI 0.

Signed-off-by: Luiz Augusto von Dentz <[e-mail]>
Signed-off-by: Marcel Holtmann <[e-mail]>

include/net/bluetooth/rfcomm.h

···
 #define RFCOMM_CONN_TIMEOUT (HZ * 30)
 #define RFCOMM_DISC_TIMEOUT (HZ * 20)
 #define RFCOMM_AUTH_TIMEOUT (HZ * 25)
+#define RFCOMM_IDLE_TIMEOUT (HZ * 2)
 
 #define RFCOMM_DEFAULT_MTU	127
 #define RFCOMM_DEFAULT_CREDITS	7
···
 struct rfcomm_session {
 	struct list_head list;
 	struct socket   *sock;
+	struct timer_list timer;
 	unsigned long    state;
 	unsigned long    flags;
 	atomic_t         refcnt;

net/bluetooth/rfcomm/core.c

···
 								auth_type);
 }
 
+static void rfcomm_session_timeout(unsigned long arg)
+{
+	struct rfcomm_session *s = (void *) arg;
+
+	BT_DBG("session %p state %ld", s, s->state);
+
+	set_bit(RFCOMM_TIMED_OUT, &s->flags);
+	rfcomm_session_put(s);
+	rfcomm_schedule(RFCOMM_SCHED_TIMEO);
+}
+
+static void rfcomm_session_set_timer(struct rfcomm_session *s, long timeout)
+{
+	BT_DBG("session %p state %ld timeout %ld", s, s->state, timeout);
+
+	if (!mod_timer(&s->timer, jiffies + timeout))
+		rfcomm_session_hold(s);
+}
+
+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))
+		rfcomm_session_put(s);
+}
+
 /* ---- RFCOMM DLCs ---- */
 static void rfcomm_dlc_timeout(unsigned long arg)
 {
···
 
 	rfcomm_session_hold(s);
 
+	rfcomm_session_clear_timer(s);
 	rfcomm_dlc_hold(d);
 	list_add(&d->list, &s->dlcs);
 	d->session = s;
···
 	list_del(&d->list);
 	d->session = NULL;
 	rfcomm_dlc_put(d);
+
+	if (list_empty(&s->dlcs))
+		rfcomm_session_set_timer(s, RFCOMM_IDLE_TIMEOUT);
 
 	rfcomm_session_put(s);
 }
···
 
 	BT_DBG("session %p sock %p", s, sock);
 
+	setup_timer(&s->timer, rfcomm_session_timeout, (unsigned long) s);
+
 	INIT_LIST_HEAD(&s->dlcs);
 	s->state = state;
 	s->sock  = sock;
···
 	if (state == BT_CONNECTED)
 		rfcomm_send_disc(s, 0);
 
+	rfcomm_session_clear_timer(s);
 	sock_release(s->sock);
 	kfree(s);
 
···
 		__rfcomm_dlc_close(d, err);
 	}
 
+	rfcomm_session_clear_timer(s);
 	rfcomm_session_put(s);
 }
 
···
 	list_for_each_safe(p, n, &session_list) {
 		struct rfcomm_session *s;
 		s = list_entry(p, struct rfcomm_session, list);
+
+		if (test_and_clear_bit(RFCOMM_TIMED_OUT, &s->flags)) {
+			s->state = BT_DISCONN;
+			rfcomm_send_disc(s, 0);
+			continue;
+		}
 
 		if (s->state == BT_LISTEN) {
 			rfcomm_accept_connection(s);