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

[annie li <annie.li@xxxxxxxxxx>]

On 2014/1/17 14:25, 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.
> 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().
Not NULL above, it should be 0UL.

Thanks
Annie


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel