On Wed, Sep 21, 2016 at 06:57:12PM +0200, Greg Kurz 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>
> ---
> v2: - added out_free_pdu: label for errors or when virtqueue is empty
> ---
> hw/9pfs/virtio-9p-device.c | 20 ++++++++++++++++----
> 1 file changed, 16 insertions(+), 4 deletions(-)
>
> diff --git a/hw/9pfs/virtio-9p-device.c b/hw/9pfs/virtio-9p-device.c
> index e7ea0e45f3dd..5f3a67cfc717 100644
> --- a/hw/9pfs/virtio-9p-device.c
> +++ b/hw/9pfs/virtio-9p-device.c
> @@ -52,17 +52,24 @@ static void handle_9p_output(VirtIODevice *vdev,
> VirtQueue *vq)
>
> elem = virtqueue_pop(vq, sizeof(VirtQueueElement));
> if (!elem) {
> - pdu_free(pdu);
> - break;
> + goto out_free_pdu;
> }
>
> - 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");
> + goto out_free_pdu;
> + }I'm not sure this check is even necessary since we check iov_to_buf(elem->out_sg[]) and pdu_marshall() avoids overflowing elem->in_sg[]. Either way, your change is correct: Reviewed-by: Stefan Hajnoczi <stefa...@redhat.com>
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