On Wed, 21 Sep 2016 16:16:59 +0200
Cornelia Huck <cornelia.h...@de.ibm.com> wrote:
> 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?
>
The code right above isn't an error path, unlike here. Maybe I should
even add an out_err: label to make it explicit.
> > + }
> > 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;
And same here.
> > + }
> >
> > pdu->size = le32_to_cpu(out.size_le);
> >
> >
>
> Looks good to me.
>
