Re: [PATCH] vhost: svq: fix uninitialized variable

[Laurent Vivier]

On 2/17/23 12:24, Eugenio Perez Martin wrote:
> On Fri, Feb 17, 2023 at 11:42 AM Laurent Vivier <lvivier@redhat.com> wrote:
> > The problem has been reported by gcc with CFLAGS=-O3:
> >
> > .../hw/virtio/vhost-shadow-virtqueue.c: In function ‘vhost_svq_poll’:
> > .../hw/virtio/vhost-shadow-virtqueue.c:538:12:
> > error: ‘len’ may be used uninitialized [-Werror=maybe-uninitialized]
> >    538 |     return len;
> >        |            ^~~
> >
> > vhost_svq_get_buf() returns NULL if SVQ is empty but doesn't set len to 0,
> > and vhost_svq_poll() returns len without checking the return of
> > vhost_svq_get_buf(). So if the SVQ is empty vhost_svq_poll() can return
> > an random value.
>
> s/an random/a random/.
>
> I think this solves the same as
> https://www.mail-archive.com/qemu-devel@nongnu.org/msg939383.html ?

Yes, exactly.

Thanks,
Laurent

> Thanks!
>
> > Signed-off-by: Laurent Vivier <lvivier@redhat.com>
> > ---
> >   hw/virtio/vhost-shadow-virtqueue.c | 1 +
> >   1 file changed, 1 insertion(+)
> >
> > diff --git a/hw/virtio/vhost-shadow-virtqueue.c 
> > b/hw/virtio/vhost-shadow-virtqueue.c
> > index 430729635815..31cf642db267 100644
> > --- a/hw/virtio/vhost-shadow-virtqueue.c
> > +++ b/hw/virtio/vhost-shadow-virtqueue.c
> > @@ -420,6 +420,7 @@ static VirtQueueElement 
> > *vhost_svq_get_buf(VhostShadowVirtqueue *svq,
> >       vring_used_elem_t used_elem;
> >       uint16_t last_used, last_used_chain, num;
> >
> > +    *len = 0;
> >       if (!vhost_svq_more_used(svq)) {
> >           return NULL;
> >       }
> > --
> > 2.39.1