Re: [Qemu-devel] [PATCH] spapr: fix write-past-end-of-array error in cpu core device init code

[Bharata B Rao <bharata@linux.vnet.ibm.com>]

On Tue, Jun 28, 2016 at 04:24:22PM +1000, David Gibson wrote:
> On Tue, Jun 28, 2016 at 07:24:16AM +0200, Greg Kurz wrote:
> > On Tue, 28 Jun 2016 12:55:07 +1000
> > David Gibson <david@gibson.dropbear.id.au> wrote:
> > 
> > > On Mon, Jun 27, 2016 at 06:28:15PM +0200, Greg Kurz wrote:
> > > > This fixes a potential QEMU crash introduced by commit 3b542549661.
> > > > 
> > > > Signed-off-by: Greg Kurz <groug@kaod.org>
> > > > ---
> > > >  hw/ppc/spapr_cpu_core.c |    3 +--
> > > >  1 file changed, 1 insertion(+), 2 deletions(-)  
> > > 
> > > Ugh.  The existing code is wrong in the case where the failure happens
> > > after the loop.
> > > 
> > > But this version is wrong in the case it happens during the loop - it
> > > will fail to clean up the last object created.
> > > 
> > 
> > Hmm... unless I'm missing something, if object_property_add_child() fails to
> > add object i, we don't want to unparent it, and we should start rollback
> > at index i-1.
> 
> Good point, my mistake.  I'll apply this fix.
> 
> > 
> > Another weirdness is that I see no rollback for the object_child_foreach()
> > loop: in case of failure, we will unparent realized objects... is it
> > okay ?
> 
> Um.. I have no idea.  Bharata? Alex?

This is similar to how device_add code recovers when there is failure
during realize. So I think object_unparent() should be fine. Only other
thing I need to verify is whether an additional object_unref() is needed
after unparenting.

Regards,
Bharata.