[RFC-v2,6/6] virtio-scsi: Fix incorrect VirtIOSCSI->cmd_vqs[0] definition

From: Nicholas Bellinger <nab@linux-iscsi.org>

This patch fixes bug in the definition of VirtIOSCSI->cmd_vqs[0],
where the return of virtio_add_queue() in virtio_scsi_init() ends up
overwriting past the end of ->cmd_vqs[0].

Since virtio_scsi currently assumes a single vqs for data, this patch
simply changes ->cmd_vqs[1] to handle the single VirtQueue.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
---
 hw/virtio-scsi.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

On Mon, 2012-08-13 at 12:02 +0300, Michael S. Tsirkin wrote:
> On Mon, Aug 13, 2012 at 08:35:17AM +0000, Nicholas A. Bellinger wrote:
> > From: Nicholas Bellinger <nab@linux-iscsi.org>
> > 
> > This patch fixes bug in the definition of VirtIOSCSI->cmd_vqs[0],
> > where the return of virtio_add_queue() in virtio_scsi_init() ends up
> > overwriting past the end of ->cmd_vqs[0].
> > 
> > Since virtio_scsi currently assumes a single vqs for data, this patch
> > simply changes ->cmd_vqs[1] to handle the single VirtQueue.
> > 
> > Cc: Paolo Bonzini <pbonzini@redhat.com>
> > Cc: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
> > Cc: Michael S. Tsirkin <mst@redhat.com>
> > Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
> 
> This is a bugfix we need even without vhost, right?
> 

I believe so, as it appears to be stomping past the end of memory for
every virtio-scsi initialization regardless of vhost usage.. 

Paolo, can you pickup this fix now for stable so it can be dropped from
RFC-v3..?

--nab

> > ---
> >  hw/virtio-scsi.c |    2 +-
> >  1 files changed, 1 insertions(+), 1 deletions(-)
> > 
> > diff --git a/hw/virtio-scsi.c b/hw/virtio-scsi.c
> > index 5e2ff6b..2c70f89 100644
> > --- a/hw/virtio-scsi.c
> > +++ b/hw/virtio-scsi.c
> > @@ -150,7 +150,7 @@ typedef struct {
> >      bool events_dropped;
> >      VirtQueue *ctrl_vq;
> >      VirtQueue *event_vq;
> > -    VirtQueue *cmd_vqs[0];
> > +    VirtQueue *cmd_vqs[1];
> >  
> >      bool vhost_started;
> >      VHostSCSI *vhost_scsi;
> > -- 
> > 1.7.2.5
> --
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Il 14/08/2012 22:20, Nicholas A. Bellinger ha scritto:
>>> > > Since virtio_scsi currently assumes a single vqs for data, this patch
>>> > > simply changes ->cmd_vqs[1] to handle the single VirtQueue.

Wrong, multiqueue works just fine. :)  It's just the kernel driver that
doesn't support it yet.

>>> > > Cc: Paolo Bonzini <pbonzini@redhat.com>
>>> > > Cc: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
>>> > > Cc: Michael S. Tsirkin <mst@redhat.com>
>>> > > Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
>> > 
>> > This is a bugfix we need even without vhost, right?
>> > 
> I believe so, as it appears to be stomping past the end of memory for
> every virtio-scsi initialization regardless of vhost usage.. 

You just did a wrong merge.  When commit d2ad7dd (virtio-scsi: add
multiqueue capability, 2012-04-06) changed cmd_vq from pointer to array
of pointers, you should have moved the following fields to the middle of
the struct, just like that commit did.

Paolo

On Sat, 2012-08-18 at 20:52 +0200, Paolo Bonzini wrote:
> Il 14/08/2012 22:20, Nicholas A. Bellinger ha scritto:
> >>> > > Since virtio_scsi currently assumes a single vqs for data, this patch
> >>> > > simply changes ->cmd_vqs[1] to handle the single VirtQueue.
> 
> Wrong, multiqueue works just fine. :)  It's just the kernel driver that
> doesn't support it yet.
> 

<nod>

> >>> > > Cc: Paolo Bonzini <pbonzini@redhat.com>
> >>> > > Cc: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
> >>> > > Cc: Michael S. Tsirkin <mst@redhat.com>
> >>> > > Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
> >> > 
> >> > This is a bugfix we need even without vhost, right?
> >> > 
> > I believe so, as it appears to be stomping past the end of memory for
> > every virtio-scsi initialization regardless of vhost usage.. 
> 
> You just did a wrong merge.  When commit d2ad7dd (virtio-scsi: add
> multiqueue capability, 2012-04-06) changed cmd_vq from pointer to array
> of pointers, you should have moved the following fields to the middle of
> the struct, just like that commit did.

Ahh, I see how virtio_scsi_init() -> virtio_common_init() are setting up
the memory now..  Apologies, my mistake.

So moving the vhost-scsi related structure members ahead of the
VirtQueue releated definitions for RFC-v3, and dropping this patch.

Thanks Paolo!

--nab