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Subject[ 031/180] usbnet: increase URB reference count before usb_unlink_urb
2.6.32-longterm review patch.  If anyone has any objections, please let me know.

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

From: tom.leiming@gmail.com <tom.leiming@gmail.com>

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
usb_unlink_urb.

Cc: stable@kernel.org
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Oliver Neukum <oliver@neukum.org>
Reported-by: Dave Jones <davej@redhat.com>
Signed-off-by: Ming Lei <tom.leiming@gmail.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Willy Tarreau <w@1wt.eu>
---
drivers/net/usb/usbnet.c | 9 +++++++++
1 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
index da33dce..a92a415 100644
--- a/drivers/net/usb/usbnet.c
+++ b/drivers/net/usb/usbnet.c
@@ -584,6 +584,14 @@ static int unlink_urbs (struct usbnet *dev, struct sk_buff_head *q)
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
@@ -592,6 +600,7 @@ static int unlink_urbs (struct usbnet *dev, struct sk_buff_head *q)
devdbg (dev, "unlink urb err, %d", retval);
else
count++;
+ usb_put_urb(urb);
spin_lock_irqsave(&q->lock, flags);
}
spin_unlock_irqrestore (&q->lock, flags);
--
1.7.2.1.45.g54fbc




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