On Wed, 21 Sep 2016 15:14:00 +0200
Greg Kurz <gr...@kaod.org> wrote:
> A broken guest may send a request with only non-empty out buffers
> or only non-empty in buffers, virtqueue_pop() will then return a
> VirtQueueElement with out_num == 0 or in_num == 0 respectively.
>
> All 9P requests are expected to start with the following 7-byte header:
>
> uint32_t size_le;
> uint8_t id;
> uint16_t tag_le;
>
> If iov_to_buf() fails to return these 7 bytes, then something is wrong in
> the guest.
>
> In both cases, it is wrong to crash QEMU, since the root cause lies in the
> guest. Let's switch the device to the broken state instead.
>
> Signed-off-by: Greg Kurz <gr...@kaod.org>
> ---
> hw/9pfs/virtio-9p-device.c | 14 ++++++++++++--
> 1 file changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/hw/9pfs/virtio-9p-device.c b/hw/9pfs/virtio-9p-device.c
> index 009b43f6d045..0f09bef13392 100644
> --- a/hw/9pfs/virtio-9p-device.c
> +++ b/hw/9pfs/virtio-9p-device.c
> @@ -56,13 +56,23 @@ static void handle_9p_output(VirtIODevice *vdev,
> VirtQueue *vq)
> break;
> }
>
> - BUG_ON(elem->out_num == 0 || elem->in_num == 0);
> + if (elem->out_num == 0 || elem->in_num == 0) {
> + virtio_error(vdev,
> + "The guest sent a VirtFS request without headers");
> + pdu_free(pdu);
> + return;
Make that 'break;' to be more consistent with the code right above?
> + }
> QEMU_BUILD_BUG_ON(sizeof out != 7);
>
> v->elems[pdu->idx] = elem;
> len = iov_to_buf(elem->out_sg, elem->out_num, 0,
> &out, sizeof out);
> - BUG_ON(len != sizeof out);
> + if (len != sizeof out) {
I always find 'sizeof foo' instead of 'sizeof(foo)' a bit jarring...
> + virtio_error(vdev, "The guest sent a malformed VirtFS request: "
> + "header size is %zd, should be 7", len);
> + pdu_free(pdu);
> + return;
> + }
>
> pdu->size = le32_to_cpu(out.size_le);
>
>
Looks good to me.
