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Date: Sun, 22 Apr 2012 22:15:34 +0800
From: Ming Lei <tom.leiming@...il.com>
To: Huajun Li <huajun.li.lee@...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 Sun, Apr 22, 2012 at 9:15 PM, Huajun Li <huajun.li.lee@...il.com> wrote:
> On Sun, Apr 22, 2012 at 8:05 PM, Ming Lei <tom.leiming@...il.com> wrote:
>> On Sun, Apr 22, 2012 at 10:19 AM, Huajun Li <huajun.li.lee@...il.com> wrote:
>>> 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?
>>
>> The flag is a percpu variable, so it can't change during the
>> above code piece.
>>
>
> No, maybe you misunderstood it.
> Legacy code stack has 'flags' variable to save irq information, and at
> the end defer_bh(), spin_unlock_irqrestore(&dev->done.lock, flags)
> will use it. However, the variable may not be initialized in your
> patch.
Got it, it is easy to fix it by replace the below line:
spin_unlock_irqrestore(&dev->done.lock, flags);
with these:
if (!test_cpu_bit(URB_UNLINKING, dev->cpuflags))
spin_unlock_irqrestore(&dev->done.lock, flags);
else
spin_unlock(&dev->done.lock);
>
>>>
>>>
>>>> @@ -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.
>>
>> It should be defined as percpu variable. The URB complete handler
>> may be triggered inside unlink path, or it can be triggered in hardirq path
>> from other CPUs at the same time.
>>
>
> Then the potential issue is, in defer_bh(), __skb_unlink() may be
> called without holding the lock. This can cause current issue too,
No, URB_UNLINKING being set means the lock has been held during unlink,
see unlink_urbs related changes in the percpu flag patch.
> because __skb_unlink() may move 'skb->next' out of txq/rxq, and even
> free it.
>
>>>
>>>> };
>>>>
>>>> +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
>>
>>
>>
>> --
>> Ming Lei
--
Ming Lei
--
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