Re: [PATCH] vhost: Check for valid vdev in vhost_backend_handle_iotlb_msg

[Stefano Garzarella]

On Fri, Jan 29, 2021 at 10:07:28AM +0100, Eugenio Pérez wrote:
> Not checking this can lead to invalid dev->vdev member access in
> vhost_device_iotlb_miss if backend issue an iotlb message in a bad
> timing, either maliciously or by a bug.
>
> Reproduced rebooting a guest with testpmd in txonly forward mode.
> #0  0x0000559ffff94394 in vhost_device_iotlb_miss (
>     dev=dev@entry=0x55a0012f6680, iova=10245279744, write=1)
>     at ../hw/virtio/vhost.c:1013
> #1  0x0000559ffff9ac31 in vhost_backend_handle_iotlb_msg (
>     imsg=0x7ffddcfd32c0, dev=0x55a0012f6680)
>     at ../hw/virtio/vhost-backend.c:411
> #2  vhost_backend_handle_iotlb_msg (dev=dev@entry=0x55a0012f6680,
>     imsg=imsg@entry=0x7ffddcfd32c0)
>     at ../hw/virtio/vhost-backend.c:404
> #3  0x0000559fffeded7b in slave_read (opaque=0x55a0012f6680)
>     at ../hw/virtio/vhost-user.c:1464
> #4  0x000055a0000c541b in aio_dispatch_handler (
>     ctx=ctx@entry=0x55a0010a2120, node=0x55a0012d9e00)
>     at ../util/aio-posix.c:329
>
> Fixes: 6dcdd06e3b ("spec/vhost-user spec: Add IOMMU support")

I'm not sure but IIUC vhost_backend_handle_iotlb_msg() was introduced by 
commit 020e571b8b, so maybe is better this 'Fixes' line:

Fixes: 020e571b8b ("vhost: rework IOTLB messaging")

> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> ---
> hw/virtio/vhost-backend.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/hw/virtio/vhost-backend.c b/hw/virtio/vhost-backend.c
> index 222bbcc62d..31b33bde37 100644
> --- a/hw/virtio/vhost-backend.c
> +++ b/hw/virtio/vhost-backend.c
> @@ -406,6 +406,11 @@ int vhost_backend_handle_iotlb_msg(struct vhost_dev *dev,
> {
>     int ret = 0;
>
> +    if (unlikely(!dev->vdev)) {
> +        error_report("Unexpected IOTLB message when virtio device is stopped");
> +        return -EINVAL;
> +    }
> +
>     switch (imsg->type) {
>     case VHOST_IOTLB_MISS:
>         ret = vhost_device_iotlb_miss(dev, imsg->iova,
> --
> 2.27.0

The patch LGTM:

Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>