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

[David Gibson]

On Tue, Jun 28, 2016 at 07:24:16AM +0200, Greg Kurz wrote:
> On Tue, 28 Jun 2016 12:55:07 +1000
> David Gibson <address@hidden> 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 <address@hidden>
> > > ---
> > >  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?

> 
> > > diff --git a/hw/ppc/spapr_cpu_core.c b/hw/ppc/spapr_cpu_core.c
> > > index 3a5da09b9902..8b802a6fcf0b 100644
> > > --- a/hw/ppc/spapr_cpu_core.c
> > > +++ b/hw/ppc/spapr_cpu_core.c
> > > @@ -309,10 +309,9 @@ static void spapr_cpu_core_realize(DeviceState *dev, 
> > > Error **errp)
> > >      }
> > >  
> > >  err:
> > > -    while (i >= 0) {
> > > +    while (--i >= 0) {
> > >          obj = sc->threads + i * size;
> > >          object_unparent(obj);
> > > -        i--;
> > >      }
> > >      g_free(sc->threads);
> > >      error_propagate(errp, local_err);
> > >   
> > 
> 



-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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