On Thu, Apr 25, 2013 at 03:20:20PM -0500, Anthony Liguori wrote:
> Jason Wang <jasow...@redhat.com> writes:
>
> > In fact we don't support zero length config length for virtio device.
>
> virtio-rng?
It has config_len == 0? In that case guest using virtio-rng can crash
qemu or read qemu memory:
uint32_t virtio_config_readb(VirtIODevice *vdev, uint32_t addr)
{
uint8_t val;
vdev->get_config(vdev, vdev->config);
if (addr > (vdev->config_len - sizeof(val)))
^^^^^^^^^ quiz: spot a bug above if config_len is 0 :)
return (uint32_t)-1;
val = ldub_p(vdev->config + addr);
return val;
}
how about corrupting qemu memory? That too:
void virtio_config_writeb(VirtIODevice *vdev, uint32_t addr, uint32_t data)
{
uint8_t val = data;
if (addr > (vdev->config_len - sizeof(val)))
return;
stb_p(vdev->config + addr, val);
if (vdev->set_config)
vdev->set_config(vdev, vdev->config);
}
> > And it can lead outbound memory access. So abort on zero config length
> > to catch the bug earlier.
>
> Not sure what you mean, but virtio-rng has a zero length config space.
>
> Regards,
>
> Anthony Liguori
>
> >
> > Signed-off-by: Jason Wang <jasow...@redhat.com>
> > ---
> > hw/virtio/virtio.c | 7 ++-----
> > 1 files changed, 2 insertions(+), 5 deletions(-)
> >
> > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> > index 1c2282c..a6fa667 100644
> > --- a/hw/virtio/virtio.c
> > +++ b/hw/virtio/virtio.c
> > @@ -923,6 +923,7 @@ void virtio_init(VirtIODevice *vdev, const char *name,
> > uint16_t device_id, size_t config_size)
> > {
> > int i;
> > + assert(config_size);
> > vdev->device_id = device_id;
> > vdev->status = 0;
> > vdev->isr = 0;
> > @@ -938,11 +939,7 @@ void virtio_init(VirtIODevice *vdev, const char *name,
> >
> > vdev->name = name;
> > vdev->config_len = config_size;
> > - if (vdev->config_len) {
> > - vdev->config = g_malloc0(config_size);
> > - } else {
> > - vdev->config = NULL;
> > - }
> > + vdev->config = g_malloc0(config_size);
> > vdev->vmstate = qemu_add_vm_change_state_handler(virtio_vmstate_change,
> > vdev);
> > }
> > --
> > 1.7.1
