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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20140117120810.GA11681@zion.uk.xensource.com>
Date:	Fri, 17 Jan 2014 12:08:10 +0000
From:	Wei Liu <wei.liu2@...rix.com>
To:	annie li <annie.li@...cle.com>
CC:	David Vrabel <david.vrabel@...rix.com>, <wei.liu2@...rix.com>,
	<ian.campbell@...rix.com>, <netdev@...r.kernel.org>,
	<xen-devel@...ts.xen.org>, <andrew.bennieston@...rix.com>,
	<davem@...emloft.net>
Subject: Re: [Xen-devel] [PATCH net-next v2] xen-netfront: clean up code in
 xennet_release_rx_bufs

On Fri, Jan 17, 2014 at 02:25:40PM +0800, annie li wrote:
> 
> On 2014/1/16 19:10, David Vrabel wrote:
> >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).
> 
> Taking a reference to the page before calling
> gnttab_end_foreign_access() delays the free work until kfree_skb().
> Simply adding put_page before kfree_skb() does not make things
> different from gnttab_end_foreign_access_ref(), and the pages will
> be freed by kfree_skb(), problem will be hit in
> gnttab_handle_deferred() when freeing pages which already be freed.
> 

I think David's idea is:

	get_page
	gnttab_end_foreign_access
	kfree_skb

The get_page is to offset put_page in gnttab_end_foreign_access. You
don't need to put page before kfree_skb.

Wei.

> So put_page is required in gnttab_end_foreign_access(), this will
> ensure either free is taken by kfree_skb or gnttab_handle_deferred.
> This involves changes in blkfront/pcifront/tpmfront(just like your
> patch), this way ensure page is released when ref is end.
> 
> Another solution I am thinking is calling
> gnttab_end_foreign_access() with page parameter as NULL, then
> gnttab_end_foreign_access will only do ending grant reference work
> and releasing page work is done by kfree_skb().
> 
> Thanks
> Annie
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html