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Date:	Sun, 22 Apr 2012 10:19:33 +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 Sat, Apr 21, 2012 at 3:45 PM, Ming Lei <tom.leiming@...il.com> wrote:
> Hi Huajun,
>
> On Sat, Apr 21, 2012 at 3:06 PM, Ming Lei <tom.leiming@...il.com> wrote:
>>> Just skip trying this per your following email's comments.
>>
>> I will prepare a new patch later, if you'd like to try it.
>
> The below patch reverts the below commits:
>
>       0956a8c20b23d429e79ff86d4325583fc06f9eb4
>      (usbnet: increase URB reference count before usb_unlink_urb)
>
>      4231d47e6fe69f061f96c98c30eaf9fb4c14b96d
>      (net/usbnet: avoid recursive locking in usbnet_stop())
>
> and keep holding tx/rx queue lock during unlinking, but avoid
> to acquire the same queue lock inside complete handler triggered by
> usb_unlink_urb.
>
> diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
> index db99536..effb34e 100644
> --- a/drivers/net/usb/usbnet.c
> +++ b/drivers/net/usb/usbnet.c
> @@ -291,9 +291,11 @@ static void defer_bh(struct usbnet *dev, struct
> sk_buff *skb, struct sk_buff_hea
>  {
>        unsigned long           flags;
>
> -       spin_lock_irqsave(&list->lock, flags);
> +       if (!test_cpu_bit(URB_UNLINKING, dev->cpuflags))
> +               spin_lock_irqsave(&list->lock, flags);
>        __skb_unlink(skb, list);
> -       spin_unlock(&list->lock);
> +       if (!test_cpu_bit(URB_UNLINKING, dev->cpuflags))
> +               spin_unlock(&list->lock);
>        spin_lock(&dev->done.lock);
>        __skb_queue_tail(&dev->done, skb);
>        if (dev->done.qlen == 1)


Then 'flags' may not be initialized, and this will cause problem while
calling spin_unlock_irqrestore(&dev->done.lock, flags), right?


> @@ -345,7 +347,8 @@ static int rx_submit (struct usbnet *dev, struct
> urb *urb, gfp_t flags)
>        usb_fill_bulk_urb (urb, dev->udev, dev->in,
>                skb->data, size, rx_complete, skb);
>
> -       spin_lock_irqsave (&dev->rxq.lock, lockflags);
> +       if (!test_cpu_bit(URB_UNLINKING, dev->cpuflags))
> +               spin_lock_irqsave (&dev->rxq.lock, lockflags);
>
>        if (netif_running (dev->net) &&
>            netif_device_present (dev->net) &&
> @@ -377,7 +380,8 @@ static int rx_submit (struct usbnet *dev, struct
> urb *urb, gfp_t flags)
>                netif_dbg(dev, ifdown, dev->net, "rx: stopped\n");
>                retval = -ENOLINK;
>        }
> -       spin_unlock_irqrestore (&dev->rxq.lock, lockflags);
> +       if (!test_cpu_bit(URB_UNLINKING, dev->cpuflags))
> +               spin_unlock_irqrestore (&dev->rxq.lock, lockflags);
>        if (retval) {
>                dev_kfree_skb_any (skb);
>                usb_free_urb (urb);
> @@ -582,6 +586,7 @@ static int unlink_urbs (struct usbnet *dev, struct
> sk_buff_head *q)
>        int                     count = 0;
>
>        spin_lock_irqsave (&q->lock, flags);
> +       set_cpu_bit(URB_UNLINKING, dev->cpuflags);
>        skb_queue_walk_safe(q, skb, skbnext) {
>                struct skb_data         *entry;
>                struct urb              *urb;
> @@ -590,15 +595,6 @@ 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
>                retval = usb_unlink_urb (urb);
> @@ -606,9 +602,8 @@ static int unlink_urbs (struct usbnet *dev, struct
> sk_buff_head *q)
>                        netdev_dbg(dev->net, "unlink urb err, %d\n", retval);
>                else
>                        count++;
> -               usb_put_urb(urb);
> -               spin_lock_irqsave(&q->lock, flags);
>        }
> +       clear_cpu_bit(URB_UNLINKING, dev->cpuflags);
>        spin_unlock_irqrestore (&q->lock, flags);
>        return count;
>  }
> @@ -1283,6 +1278,7 @@ void usbnet_disconnect (struct usb_interface *intf)
>        usb_kill_urb(dev->interrupt);
>        usb_free_urb(dev->interrupt);
>
> +       free_percpu(dev->cpuflags);
>        free_netdev(net);
>        usb_put_dev (xdev);
>  }
> @@ -1353,6 +1349,13 @@ usbnet_probe (struct usb_interface *udev, const
> struct usb_device_id *prod)
>        SET_NETDEV_DEV(net, &udev->dev);
>
>        dev = netdev_priv(net);
> +
> +       dev->cpuflags = alloc_percpu(unsigned long);
> +       if (!dev->cpuflags) {
> +               status = -ENOMEM;
> +               goto out1;
> +       }
> +
>        dev->udev = xdev;
>        dev->intf = udev;
>        dev->driver_info = info;
> @@ -1396,7 +1399,7 @@ usbnet_probe (struct usb_interface *udev, const
> struct usb_device_id *prod)
>        if (info->bind) {
>                status = info->bind (dev, udev);
>                if (status < 0)
> -                       goto out1;
> +                       goto out2;
>
>                // heuristic:  "usb%d" for links we know are two-host,
>                // else "eth%d" when there's reasonable doubt.  userspace
> @@ -1465,6 +1468,8 @@ usbnet_probe (struct usb_interface *udev, const
> struct usb_device_id *prod)
>  out3:
>        if (info->unbind)
>                info->unbind (dev, udev);
> +out2:
> +       free_percpu(dev->cpuflags);
>  out1:
>        free_netdev(net);
>  out:
> diff --git a/include/linux/usb/usbnet.h b/include/linux/usb/usbnet.h
> index 605b0aa..2dc46f5 100644
> --- a/include/linux/usb/usbnet.h
> +++ b/include/linux/usb/usbnet.h
> @@ -69,8 +69,28 @@ struct usbnet {
>  #              define EVENT_DEV_WAKING 6
>  #              define EVENT_DEV_ASLEEP 7
>  #              define EVENT_DEV_OPEN   8
> +       unsigned long __percpu *cpuflags;
> +#              define URB_UNLINKING    0

Is it possible using a simple bool variable to track whether q->lock
is hold by unlink_urb() ?  If yes, it can avoid introducing following
new codes into current code stack.

>  };
>
> +static inline void set_cpu_bit(int nr, unsigned long __percpu *addr)
> +{
> +       unsigned long *fl = __this_cpu_ptr(addr);
> +       set_bit(nr, fl);
> +}
> +
> +static inline void clear_cpu_bit(int nr, unsigned long __percpu *addr)
> +{
> +       unsigned long *fl = __this_cpu_ptr(addr);
> +       clear_bit(nr, fl);
> +}
> +
> +static inline int test_cpu_bit(int nr, unsigned long __percpu *addr)
> +{
> +       unsigned long *fl = __this_cpu_ptr(addr);
> +       return test_bit(nr, fl);
> +}
> +
>  static inline struct usb_driver *driver_of(struct usb_interface *intf)
>  {
>        return to_usb_driver(intf->dev.driver);
>
>
> Thanks,
> --
> Ming Lei
--
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