On Fri, Apr 20, 2012 at 9:37 PM, Huajun Li <huajun.li.lee@xxxxxxxxx> 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?
>
> To easily reproduce it, in unlink_urbs(), you can delay a short time
> after usb_put_urb(urb), then disconnect your device while transferring
> data, and repeat it times you will find errors on your screen.
Could you post out the error log?
>
> Following is a draft patch to guarantee the queue consistent, and
> refer to expected skb in each loop cycle:
>
> diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
> index b7b3f5b..6da0141 100644
> --- a/drivers/net/usb/usbnet.c
> +++ b/drivers/net/usb/usbnet.c
> @@ -578,16 +578,28 @@ EXPORT_SYMBOL_GPL(usbnet_purge_paused_rxq);
> static int unlink_urbs (struct usbnet *dev, struct sk_buff_head *q)
> {
> unsigned long flags;
> - struct sk_buff *skb, *skbnext;
> + struct sk_buff *skb;
> int count = 0;
>
> spin_lock_irqsave (&q->lock, flags);
> - skb_queue_walk_safe(q, skb, skbnext) {
> + while (!skb_queue_empty(q)) {
> struct skb_data *entry;
> struct urb *urb;
> int retval;
>
> - entry = (struct skb_data *) skb->cb;
> + skb_queue_walk(q, skb) {
> + entry = (struct skb_data *)skb->cb;
> + if (entry->state == rx_done ||
> + entry->state == tx_done ||
> + entry->state == rx_cleanup)
Maybe it is not necessary, if the state has been changed to rx_done
or tx_done or rx_cleanup, it means the URB referenced to by the skb
has been completed, and the coming usb_unlink_urb can handle the
case correctly.
> + continue;
> + else
> + break;
> + }
> +
> + if (skb == (struct sk_buff *)(q))
> + break;
> +
> urb = entry->urb;
>
>
> Thanks,
> --Huajun Li
Thanks,
--
Ming Lei
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