Bluetooth: l2cap: introduce l2cap_conn ref-counting

If we want to use l2cap_conn outside of l2cap_core.c, we need refcounting
for these objects. Otherwise, we cannot synchronize l2cap locks with
outside locks and end up with deadlocks.

Hence, introduce ref-counting for l2cap_conn objects. This doesn't affect
l2cap internals at all, as they use a direct synchronization.
We also keep a reference to the parent hci_conn for locking purposes as
l2cap_conn depends on this. This doesn't affect the connection itself but
only the lifetime of the (dead) object.

Signed-off-by: David Herrmann <[e-mail]>
Acked-by: Marcel Holtmann <[e-mail]>
Signed-off-by: Gustavo Padovan <[e-mail]>

include/net/bluetooth/l2cap.h

···
 
 	struct list_head	chan_l;
 	struct mutex		chan_lock;
+	struct kref		ref;
 };
 
 #define L2CAP_INFO_CL_MTU_REQ_SENT	0x01
···
 void l2cap_logical_cfm(struct l2cap_chan *chan, struct hci_chan *hchan,
 		       u8 status);
 void __l2cap_physical_cfm(struct l2cap_chan *chan, int result);
+
+void l2cap_conn_get(struct l2cap_conn *conn);
+void l2cap_conn_put(struct l2cap_conn *conn);
 
 #endif /* __L2CAP_H */

net/bluetooth/l2cap_core.c

···
 	}
 
 	hcon->l2cap_data = NULL;
-	kfree(conn);
+	conn->hchan = NULL;
+	l2cap_conn_put(conn);
 }
 
 static void security_timeout(struct work_struct *work)
···
 		return NULL;
 	}
 
+	kref_init(&conn->ref);
 	hcon->l2cap_data = conn;
 	conn->hcon = hcon;
+	hci_conn_get(conn->hcon);
 	conn->hchan = hchan;
 
 	BT_DBG("hcon %p conn %p hchan %p", hcon, conn, hchan);
···
 
 	return conn;
 }
+
+static void l2cap_conn_free(struct kref *ref)
+{
+	struct l2cap_conn *conn = container_of(ref, struct l2cap_conn, ref);
+
+	hci_conn_put(conn->hcon);
+	kfree(conn);
+}
+
+void l2cap_conn_get(struct l2cap_conn *conn)
+{
+	kref_get(&conn->ref);
+}
+EXPORT_SYMBOL(l2cap_conn_get);
+
+void l2cap_conn_put(struct l2cap_conn *conn)
+{
+	kref_put(&conn->ref, l2cap_conn_free);
+}
+EXPORT_SYMBOL(l2cap_conn_put);
 
 /* ---- Socket interface ---- */