USB: make hub driver's release more robust

This revised patch (as893c) improves the method used by the hub driver
to release its private data structure.  The current code is non-robust,
relying on a memory region not getting reused by another driver after
it has been freed.  The patch adds a reference count to the structure,
resolving the question of when to release it.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 31 insertions, 28 deletions

diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index 9464eb504ae6..77a6627b18d2 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -34,6 +34,7 @@
 struct usb_hub {
         struct device           *intfdev;       /* the "interface" device */
         struct usb_device       *hdev;
+        struct kref             kref;
         struct urb              *urb;           /* for interrupt polling pipe */
 
         /* buffer for urb ... with extra space in case of babble */
@@ -66,6 +67,7 @@ struct usb_hub {
         unsigned                limited_power:1;
         unsigned                quiescing:1;
         unsigned                activating:1;
+        unsigned                disconnected:1;
 
         unsigned                has_indicators:1;
         u8                      indicator[USB_MAXCHILDREN];
@@ -321,7 +323,7 @@ static void kick_khubd(struct usb_hub *hub)
         to_usb_interface(hub->intfdev)->pm_usage_cnt = 1;
 
         spin_lock_irqsave(&hub_event_lock, flags);
-        if (list_empty(&hub->event_list)) {
+        if (!hub->disconnected & list_empty(&hub->event_list)) {
                 list_add_tail(&hub->event_list, &hub_event_list);
                 wake_up(&khubd_wait);
         }
@@ -330,6 +332,7 @@ static void kick_khubd(struct usb_hub *hub)
 
 void usb_kick_khubd(struct usb_device *hdev)
 {
+        /* FIXME: What if hdev isn't bound to the hub driver? */
         kick_khubd(hdev_to_hub(hdev));
 }
 
@@ -845,43 +848,42 @@ fail:
         return ret;
 }
 
+static void hub_release(struct kref *kref)
+{
+        struct usb_hub *hub = container_of(kref, struct usb_hub, kref);
+
+        usb_put_intf(to_usb_interface(hub->intfdev));
+        kfree(hub);
+}
+
 static unsigned highspeed_hubs;
 
 static void hub_disconnect(struct usb_interface *intf)
 {
         struct usb_hub *hub = usb_get_intfdata (intf);
-        struct usb_device *hdev;
+
+        /* Take the hub off the event list and don't let it be added again */
+        spin_lock_irq(&hub_event_lock);
+        list_del_init(&hub->event_list);
+        hub->disconnected = 1;
+        spin_unlock_irq(&hub_event_lock);
 
         /* Disconnect all children and quiesce the hub */
         hub->error = 0;
         hub_pre_reset(intf);
 
         usb_set_intfdata (intf, NULL);
-        hdev = hub->hdev;
 
-        if (hdev->speed == USB_SPEED_HIGH)
+        if (hub->hdev->speed == USB_SPEED_HIGH)
                 highspeed_hubs--;
 
         usb_free_urb(hub->urb);
-        hub->urb = NULL;
-
-        spin_lock_irq(&hub_event_lock);
-        list_del_init(&hub->event_list);
-        spin_unlock_irq(&hub_event_lock);
-
         kfree(hub->descriptor);
-        hub->descriptor = NULL;
-
         kfree(hub->status);
-        hub->status = NULL;
-
-        if (hub->buffer) {
-                usb_buffer_free(hdev, sizeof(*hub->buffer), hub->buffer,
-                                hub->buffer_dma);
-                hub->buffer = NULL;
-        }
+        usb_buffer_free(hub->hdev, sizeof(*hub->buffer), hub->buffer,
+                        hub->buffer_dma);
 
-        kfree(hub);
+        kref_put(&hub->kref, hub_release);
 }
 
 static int hub_probe(struct usb_interface *intf, const struct usb_device_id *id)
@@ -929,10 +931,12 @@ descriptor_error:
                 return -ENOMEM;
         }
 
+        kref_init(&hub->kref);
         INIT_LIST_HEAD(&hub->event_list);
         hub->intfdev = &intf->dev;
         hub->hdev = hdev;
         INIT_DELAYED_WORK(&hub->leds, led_work);
+        usb_get_intf(intf);
 
         usb_set_intfdata (intf, hub);
         intf->needs_remote_wakeup = 1;
@@ -2534,10 +2538,12 @@ static void hub_events(void)
                 list_del_init(tmp);
 
                 hub = list_entry(tmp, struct usb_hub, event_list);
-                hdev = hub->hdev;
-                intf = to_usb_interface(hub->intfdev);
-                hub_dev = &intf->dev;
+                kref_get(&hub->kref);
+                spin_unlock_irq(&hub_event_lock);
 
+                hdev = hub->hdev;
+                hub_dev = hub->intfdev;
+                intf = to_usb_interface(hub_dev);
                 dev_dbg(hub_dev, "state %d ports %d chg %04x evt %04x\n",
                                 hdev->state, hub->descriptor
                                         ? hub->descriptor->bNbrPorts
@@ -2546,13 +2552,10 @@ static void hub_events(void)
                                 (u16) hub->change_bits[0],
                                 (u16) hub->event_bits[0]);
 
-                usb_get_intf(intf);
-                spin_unlock_irq(&hub_event_lock);
-
                 /* Lock the device, then check to see if we were
                  * disconnected while waiting for the lock to succeed. */
                 usb_lock_device(hdev);
-                if (hub != usb_get_intfdata(intf))
+                if (unlikely(hub->disconnected))
                         goto loop;
 
                 /* If the hub has died, clean up after it */
@@ -2715,7 +2718,7 @@ loop_autopm:
                         usb_autopm_enable(intf);
 loop:
                 usb_unlock_device(hdev);
-                usb_put_intf(intf);
+                kref_put(&hub->kref, hub_release);
 
         } /* end while (1) */
 }