Re: use-after-free in usbnet

On Tue, Mar 20, 2012 at 5:40 PM, Ming Lei [off-list ref] wrote:

Hi,

On Mon, Mar 19, 2012 at 11:12 PM, Dave Jones [off-list ref] wrote:

quoted

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();
 		if (retval != -EINPROGRESS && retval != 0)
 			netdev_dbg(dev->net, "unlink urb err, %d\n", retval);
 		else

@@ -1028,7 +1030,6 @@ static void tx_complete (struct urb *urb)
 	}

 	usb_autopm_put_interface_async(dev->intf);
-	urb->dev = NULL;
 	entry->state = tx_done;
 	defer_bh(dev, skb, &dev->txq);
 }

Thanks,
-- 
Ming Lei
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