linux-kernel - [PATCH 3.2 040/102] usb: hub: take hub->hdev reference when processing from eventlist

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Message-ID: <lsq.1414880883.739949004@decadent.org.uk>
Date:	Sat, 01 Nov 2014 22:28:03 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org,
	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
	"Alan Stern" <stern@...land.harvard.edu>,
	"Joe Lawrence" <joe.lawrence@...atus.com>,
	"David Bulkow" <david.bulkow@...atus.com>
Subject: [PATCH 3.2 040/102] usb: hub: take hub->hdev reference when
 processing from eventlist

3.2.64-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Joe Lawrence <joe.lawrence@...atus.com>

commit c605f3cdff53a743f6d875b76956b239deca1272 upstream.

During surprise device hotplug removal tests, it was observed that
hub_events may try to call usb_lock_device on a device that has already
been freed. Protect the usb_device by taking out a reference (under the
hub_event_lock) when hub_events pulls it off the list, returning the
reference after hub_events is finished using it.

Signed-off-by: Joe Lawrence <joe.lawrence@...atus.com>
Suggested-by: David Bulkow <david.bulkow@...atus.com> for using kref
Suggested-by: Alan Stern <stern@...land.harvard.edu> for placement
Acked-by: Alan Stern <stern@...land.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/usb/core/hub.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -3651,9 +3651,10 @@ static void hub_events(void)
 
 		hub = list_entry(tmp, struct usb_hub, event_list);
 		kref_get(&hub->kref);
+		hdev = hub->hdev;
+		usb_get_dev(hdev);
 		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",
@@ -3888,6 +3889,7 @@ static void hub_events(void)
 		usb_autopm_put_interface(intf);
  loop_disconnected:
 		usb_unlock_device(hdev);
+		usb_put_dev(hdev);
 		kref_put(&hub->kref, hub_release);
 
         } /* end while (1) */

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