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

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

[Greg Kurz]

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(-)

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);

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

[David Gibson]

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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.

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

[Greg Kurz]

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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.

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 ?

> > 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);
> >   
> 


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

[David Gibson]

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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?

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

[Bharata B Rao]

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.