"Michael S. Tsirkin" <m...@redhat.com> writes:
> 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 :)
Then we need to fix these bugs and allocate a CVE. virtio-rng has
shipped. This code is also dumb.
There's no requirement that config_len is >= 4 so this would fail
equally awfully with config_len=1|2|3.
Regards,
Anthony Liguori
>
>
> 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
