netdev - Re: use-after-free in usbnet

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Message-ID: <CA+v9cxajCyBg4-MeW50_emD96-ujTXXx+q+Pv2gcK2DQGzT_RA@mail.gmail.com>
Date:	Fri, 20 Apr 2012 23:07:40 +0800
From:	Huajun Li <huajun.li.lee@...il.com>
To:	Ming Lei <tom.leiming@...il.com>
Cc:	Oliver Neukum <oneukum@...e.de>,
	Alan Stern <stern@...land.harvard.edu>,
	Dave Jones <davej@...hat.com>, netdev@...r.kernel.org,
	linux-usb@...r.kernel.org,
	Fedora Kernel Team <kernel-team@...oraproject.org>
Subject: Re: use-after-free in usbnet

On Fri, Apr 20, 2012 at 10:56 PM, Huajun Li <huajun.li.lee@...il.com> wrote:
> On Fri, Apr 20, 2012 at 10:22 PM, Ming Lei <tom.leiming@...il.com> wrote:
>> On Fri, Apr 20, 2012 at 9:37 PM, Huajun Li <huajun.li.lee@...il.com> wrote:
>>>
>>> Above patch has already been integrated to mainline. However, maybe
>>> there still exists another potentail use-after-free issue, here is a
>>> case:
>>>      After release the lock in unlink_urbs(), defer_bh() may move
>>> current skb from rxq/txq to dev->done queue, even cause the skb be
>>> released. Then in next loop cycle, it can't refer to expected skb, and
>>> may Oops again.
>>
>> Could you explain in a bit detail? Why can't the expected skb be refered
>> to in next loop?
>
>
>      unlink_urbs()                                           complete handler
> --------------------------------------
> -------------------------------------------------
>     spin_unlock_irqrestore()
>                                                                  rx_complete()
>                                                                  derver_bh()
>
>  __skb_unlink()
>
>  __skb_queue_tail(&dev->done, skb)   =======> skb is moved to
> dev->done, and can be freed by usbnet_bh()
>      skb_queue_walk_safe()
>                      tmp = skb->next   ===> refer to freed skb
>

Sorry, email client messed up these lines, resend it:

  unlink_urbs()                    complete handler
------------------------               ------------------------------
spin_unlock_irqrestore()
                                       rx_complete()
                                       derver_bh()
                                          __skb_unlink()
                                          __skb_queue_tail(&dev->done, skb)
                                          =======> skb is moved to dev->done,
                                        and can be freed by usbnet_bh()

skb_queue_walk_safe()
        tmp = skb->next   ===> refer to freed skb
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