netdev - Re: use-after-free in usbnet

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Message-ID: <CACVXFVP9-Ao_UyBoxkxzq5dg8TfkZ9CECqEUFW5bD_JRzfQybw@mail.gmail.com>
Date:	Wed, 21 Mar 2012 09:04:15 +0800
From:	Ming Lei <tom.leiming@...il.com>
To:	Dave Jones <davej@...hat.com>
Cc:	netdev@...r.kernel.org, linux-usb@...r.kernel.org,
	Fedora Kernel Team <kernel-team@...oraproject.org>
Subject: Re: use-after-free in usbnet

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();
 		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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