netdev - Re: [Xen-devel][PATCH net-next v2] xen-netfront: clean up code in xennet_release_rx

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Date:	Thu, 16 Jan 2014 11:10:17 +0000
From:	David Vrabel <david.vrabel@...rix.com>
To:	Annie Li <Annie.li@...cle.com>
CC:	<xen-devel@...ts.xen.org>, <netdev@...r.kernel.org>,
	<davem@...emloft.net>, <konrad.wilk@...cle.com>,
	<ian.campbell@...rix.com>, <wei.liu2@...rix.com>,
	<andrew.bennieston@...rix.com>
Subject: Re: [Xen-devel][PATCH net-next v2] xen-netfront: clean up code in
 xennet_release_rx_bufs

On 15/01/14 23:57, Annie Li wrote:
> This patch implements two things:
> 
> * release grant reference and skb for rx path, this fixex resource leaking.
> * clean up grant transfer code kept from old netfront(2.6.18) which grants
> pages for access/map and transfer. But grant transfer is deprecated in current
> netfront, so remove corresponding release code for transfer.
> 
> gnttab_end_foreign_access_ref may fail when the grant entry is currently used
> for reading or writing. But this patch does not cover this and improvement for
> this failure may be implemented in a separate patch.

I don't think replacing a resource leak with a security bug is a good idea.

If you would prefer not to fix the gnttab_end_foreign_access() call, I
think you can fix this in netfront by taking a reference to the page
before calling gnttab_end_foreign_access().  This will ensure the page
isn't freed until the subsequent kfree_skb(), or the gref is released by
the foreign domain (whichever is later).

David
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