USB: fix race between hub_disconnect and recursively_mark_NOTATTACHED

There is a race in the hub driver between hub_disconnect() and
recursively_mark_NOTATTACHED().  This race can be triggered if the
driver is unbound from a device at the same time as the bus's root hub
is removed.  When the race occurs, it can cause an oops:

BUG: unable to handle kernel NULL pointer dereference at 0000015c
IP: [<c16d5fb0>] recursively_mark_NOTATTACHED+0x20/0x60
Call Trace:
 [<c16d5fc4>] recursively_mark_NOTATTACHED+0x34/0x60
 [<c16d5fc4>] recursively_mark_NOTATTACHED+0x34/0x60
 [<c16d5fc4>] recursively_mark_NOTATTACHED+0x34/0x60
 [<c16d5fc4>] recursively_mark_NOTATTACHED+0x34/0x60
 [<c16d6082>] usb_set_device_state+0x92/0x120
 [<c16d862b>] usb_disconnect+0x2b/0x1a0
 [<c16dd4c0>] usb_remove_hcd+0xb0/0x160
 [<c19ca846>] ? _raw_spin_unlock_irqrestore+0x26/0x50
 [<c1704efc>] ehci_mid_remove+0x1c/0x30
 [<c1704f26>] ehci_mid_stop_host+0x16/0x30
 [<c16f7698>] penwell_otg_work+0xd28/0x3520
 [<c19c945b>] ? __schedule+0x39b/0x7f0
 [<c19cdb9d>] ? sub_preempt_count+0x3d/0x50
 [<c125e97d>] process_one_work+0x11d/0x3d0
 [<c19c7f4d>] ? mutex_unlock+0xd/0x10
 [<c125e0e5>] ? manage_workers.isra.24+0x1b5/0x270
 [<c125f009>] worker_thread+0xf9/0x320
 [<c19ca846>] ? _raw_spin_unlock_irqrestore+0x26/0x50
 [<c125ef10>] ? rescuer_thread+0x2b0/0x2b0
 [<c1264ac4>] kthread+0x94/0xa0
 [<c19d0f77>] ret_from_kernel_thread+0x1b/0x28
 [<c1264a30>] ? kthread_create_on_node+0xc0/0xc0

One problem is that recursively_mark_NOTATTACHED() uses the intfdata
value and hub->hdev->maxchild while hub_disconnect() is clearing them.
Another problem is that it uses hub->ports[i] while the port device is
being released.

To fix this race, we need to hold the device_state_lock while
hub_disconnect() changes the values.  (Note that usb_disconnect()
and hub_port_connect_change() already acquire this lock at similar
critical times during a USB device's life cycle.)  We also need to
remove the port devices after maxchild has been set to 0, instead of
before.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reported-by: "Du, Changbin" <changbinx.du@intel.com>
Tested-by: "Du, Changbin" <changbinx.du@intel.com>
CC: <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/core/hub.c

@@ -1600,7 +1600,7 @@ static void hub_disconnect(struct usb_interface *intf)
 {
 	struct usb_hub *hub = usb_get_intfdata(intf);
 	struct usb_device *hdev = interface_to_usbdev(intf);
-	int i;
+	int port1;
 
 	/* Take the hub off the event list and don't let it be added again */
 	spin_lock_irq(&hub_event_lock);
@@ -1615,11 +1615,15 @@ static void hub_disconnect(struct usb_interface *intf)
 	hub->error = 0;
 	hub_quiesce(hub, HUB_DISCONNECT);
 
-	usb_set_intfdata (intf, NULL);
+	/* Avoid races with recursively_mark_NOTATTACHED() */
+	spin_lock_irq(&device_state_lock);
+	port1 = hdev->maxchild;
+	hdev->maxchild = 0;
+	usb_set_intfdata(intf, NULL);
+	spin_unlock_irq(&device_state_lock);
 
-	for (i = 0; i < hdev->maxchild; i++)
-		usb_hub_remove_port_device(hub, i + 1);
-	hub->hdev->maxchild = 0;
+	for (; port1 > 0; --port1)
+		usb_hub_remove_port_device(hub, port1);
 
 	if (hub->hdev->speed == USB_SPEED_HIGH)
 		highspeed_hubs--;