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Subject[ 098/149] usbnet: increase URB reference count before usb_unlink_urb
3.2-stable review patch.  If anyone has any objections, please let me know.


From: "" <>

commit 0956a8c20b23d429e79ff86d4325583fc06f9eb4 upstream.

Commit 4231d47e6fe69f061f96c98c30eaf9fb4c14b96d(net/usbnet: avoid
recursive locking in usbnet_stop()) fixes the recursive locking
problem by releasing the skb queue lock, but it makes usb_unlink_urb
racing with defer_bh, and the URB to being unlinked may be freed before
or during calling usb_unlink_urb, so use-after-free problem may be
triggerd inside usb_unlink_urb.

The patch fixes the use-after-free problem by increasing URB
reference count with skb queue lock held before calling
usb_unlink_urb, so the URB won't be freed until return from

Cc: Sebastian Andrzej Siewior <>
Cc: Alan Stern <>
Cc: Oliver Neukum <>
Reported-by: Dave Jones <>
Signed-off-by: Ming Lei <>
Acked-by: Greg Kroah-Hartman <>
Signed-off-by: David S. Miller <>
Signed-off-by: Greg Kroah-Hartman <>

drivers/net/usb/usbnet.c | 9 +++++++++
1 file changed, 9 insertions(+)

--- a/drivers/net/usb/usbnet.c
+++ b/drivers/net/usb/usbnet.c
@@ -589,6 +589,14 @@ static int unlink_urbs (struct usbnet *d
entry = (struct skb_data *) skb->cb;
urb = entry->urb;

+ /*
+ * Get reference count of the URB to avoid it to be
+ * freed during usb_unlink_urb, which may trigger
+ * use-after-free problem inside usb_unlink_urb since
+ * usb_unlink_urb is always racing with .complete
+ * handler(include defer_bh).
+ */
+ usb_get_urb(urb);
spin_unlock_irqrestore(&q->lock, flags);
// during some PM-driven resume scenarios,
// these (async) unlinks complete immediately
@@ -597,6 +605,7 @@ static int unlink_urbs (struct usbnet *d
netdev_dbg(dev->net, "unlink urb err, %d\n", retval);
+ usb_put_urb(urb);
spin_lock_irqsave(&q->lock, flags);
spin_unlock_irqrestore (&q->lock, flags);

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