Xen devel - May 2013 - [PATCH net-next] xen-netfront: avoid leaking resources when setup_netfront fails

We should correctly free related resources (grant ref, memory page, evtchn)
when setup_netfront fails.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
---
 drivers/net/xen-netfront.c |   31 ++++++++++++++++++++-----------
 1 file changed, 20 insertions(+), 11 deletions(-)

diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index 1db10141..2dff4eb 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -1532,39 +1532,48 @@ static int setup_netfront(struct xenbus_device *dev,
struct netfront_info *info)
 	FRONT_RING_INIT(&info->tx, txs, PAGE_SIZE);
 
 	err = xenbus_grant_ring(dev, virt_to_mfn(txs));
-	if (err < 0) {
-		free_page((unsigned long)txs);
-		goto fail;
-	}
+	if (err < 0)
+		goto grant_tx_ring_fail;
 
 	info->tx_ring_ref = err;
 	rxs = (struct xen_netif_rx_sring *)get_zeroed_page(GFP_NOIO | __GFP_HIGH);
 	if (!rxs) {
 		err = -ENOMEM;
 		xenbus_dev_fatal(dev, err, "allocating rx ring page");
-		goto fail;
+		goto alloc_rx_ring_fail;
 	}
 	SHARED_RING_INIT(rxs);
 	FRONT_RING_INIT(&info->rx, rxs, PAGE_SIZE);
 
 	err = xenbus_grant_ring(dev, virt_to_mfn(rxs));
-	if (err < 0) {
-		free_page((unsigned long)rxs);
-		goto fail;
-	}
+	if (err < 0)
+		goto grant_rx_ring_fail;
 	info->rx_ring_ref = err;
 
 	err = xenbus_alloc_evtchn(dev, &info->evtchn);
 	if (err)
-		goto fail;
+		goto alloc_evtchn_fail;
 
 	err = bind_evtchn_to_irqhandler(info->evtchn, xennet_interrupt,
 					0, netdev->name, netdev);
 	if (err < 0)
-		goto fail;
+		goto bind_fail;
 	netdev->irq = err;
 	return 0;
 
+ /* If we fail to setup netfront, it is safe to just revoke access to granted
+  * pages because backend is not accessing it at this point.
+  */
+ bind_fail:
+	xenbus_free_evtchn(dev, info->evtchn);
+ alloc_evtchn_fail:
+	gnttab_end_foreign_access_ref(info->rx_ring_ref, 0);
+ grant_rx_ring_fail:
+	free_page((unsigned long)rxs);
+ alloc_rx_ring_fail:
+	gnttab_end_foreign_access_ref(info->tx_ring_ref, 0);
+ grant_tx_ring_fail:
+	free_page((unsigned long)txs);
  fail:
 	return err;
 }
-- 
1.7.10.4

From: Wei Liu <wei.liu2@citrix.com>
Date: Fri, 17 May 2013 10:43:58 +0100
>  
> + /* If we fail to setup netfront, it is safe to just revoke access to
granted
> +  * pages because backend is not accessing it at this point.
> +  */
> + bind_fail:
> +	xenbus_free_evtchn(dev, info->evtchn);
> + alloc_evtchn_fail:
> +	gnttab_end_foreign_access_ref(info->rx_ring_ref, 0);
> + grant_rx_ring_fail:
> +	free_page((unsigned long)rxs);
> + alloc_rx_ring_fail:
> +	gnttab_end_foreign_access_ref(info->tx_ring_ref, 0);
> + grant_tx_ring_fail:
> +	free_page((unsigned long)txs);
>   fail:
>  	return err;
>  }
This is not even close to adhering to proper coding style.

The comment should be indented by one tab not one space:

	/* Like
	 * this.
	 */

And the code labels should appear at the first column, not
with a leading space.

On Sun, May 19, 2013 at 11:28:33PM -0700, David Miller
wrote:
> From: Wei Liu <wei.liu2@citrix.com>
> Date: Fri, 17 May 2013 10:43:58 +0100
> 
> >  
> > + /* If we fail to setup netfront, it is safe to just revoke access to
granted
> > +  * pages because backend is not accessing it at this point.
> > +  */
> > + bind_fail:
> > +	xenbus_free_evtchn(dev, info->evtchn);
> > + alloc_evtchn_fail:
> > +	gnttab_end_foreign_access_ref(info->rx_ring_ref, 0);
> > + grant_rx_ring_fail:
> > +	free_page((unsigned long)rxs);
> > + alloc_rx_ring_fail:
> > +	gnttab_end_foreign_access_ref(info->tx_ring_ref, 0);
> > + grant_tx_ring_fail:
> > +	free_page((unsigned long)txs);
> >   fail:
> >  	return err;
> >  }
> 
> This is not even close to adhering to proper coding style.
> 
> The comment should be indented by one tab not one space:
> 
> 	/* Like
> 	 * this.
> 	 */
> 
> And the code labels should appear at the first column, not
> with a leading space.
Thanks, coding style problems are fixed now.

For some reason some other labels in this file appear to have the same
style problem, I will fix them when I touch other part of the file in
the future.


Wei.