netdev - Re: use-after-free in usbnet

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Date:	Wed, 21 Mar 2012 09:34:41 +0800
From:	Ming Lei <tom.leiming@...il.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	netdev@...r.kernel.org, linux-usb@...r.kernel.org,
	Fedora Kernel Team <kernel-team@...oraproject.org>,
	Dave Jones <davej@...hat.com>
Subject: Re: use-after-free in usbnet

On Wed, Mar 21, 2012 at 9:04 AM, Ming Lei <tom.leiming@...il.com> wrote:
> On Tue, Mar 20, 2012 at 5:40 PM, Ming Lei <tom.leiming@...il.com> wrote:
>> Hi,
>>
>> On Mon, Mar 19, 2012 at 11:12 PM, Dave Jones <davej@...hat.com> wrote:
>>> We've had two reports of this use after free in Fedora now recently..
>>
>> Could you provide output of 'dmesg' and 'lsusb -v' from the reported machine?
>
> Looks I have figured out why your problem is triggered.
>
> If the URB being unlinked is freed before usb_put_dev
> inside usb_hcd_unlink_urb, the use-after-free will be triggered.
> And the below patch[1] should fix the problem.
>
> Also there is another bug in tx_complete() of usbnet, the line below
>
>                urb->dev = NULL;
>
> should be removed to avoid possible oops or memory leak in unlink path.
>
> Please test the patch if you can reproduce the problem.
>
> [1],
> diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
> index 59681f0..4f4e028 100644
> --- a/drivers/net/usb/usbnet.c
> +++ b/drivers/net/usb/usbnet.c
> @@ -592,7 +592,9 @@ static int unlink_urbs (struct usbnet *dev, struct
> sk_buff_head *q)
>                spin_unlock_irqrestore(&q->lock, flags);
>                // during some PM-driven resume scenarios,
>                // these (async) unlinks complete immediately
> +               local_bh_disable();
>                retval = usb_unlink_urb (urb);
> +               local_bh_enable();

Looks it is a general issue about usb_hcd_unlink_urb.

Alan, how about increasing URB reference count before calling unlink1
inside usb_hcd_unlink_urb to fix this kind of problem?

Thanks,
-- 
Ming Lei
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