Re: [PATCH 1/1] vhost: Protect the virtqueue from being cleared whilst still in use

Michael S. Tsirkin
2022-03-02T13:31:08Z

On Wed, Mar 02, 2022 at 07:54:21AM +0000, Lee Jones wrote:
> vhost_vsock_handle_tx_kick() already holds the mutex during its call
> to vhost_get_vq_desc(). All we have to do is take the same lock
> during virtqueue clean-up and we mitigate the reported issues.
>
> Link: https://syzkaller.appspot.com/bug?extid=279432d30d825e63ba00
>
> Cc: <stable@vger.kernel.org>
> Reported-by: syzbot+adc3cb32385586bec859@syzkaller.appspotmail.com
> Signed-off-by: Lee Jones <lee.jones@linaro.org>
> ---
> drivers/vhost/vhost.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 59edb5a1ffe28..bbaff6a5e21b8 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -693,6 +693,7 @@ void vhost_dev_cleanup(struct vhost_dev *dev)
> int i;
>
> for (i = 0; i < dev->nvqs; ++i) {
> + mutex_lock(&dev->vqs[i]->mutex);
> if (dev->vqs[i]->error_ctx)
> eventfd_ctx_put(dev->vqs[i]->error_ctx);
> if (dev->vqs[i]->kick)
> @@ -700,6 +701,7 @@ void vhost_dev_cleanup(struct vhost_dev *dev)
> if (dev->vqs[i]->call_ctx.ctx)
> eventfd_ctx_put(dev->vqs[i]->call_ctx.ctx);
> vhost_vq_reset(dev, dev->vqs[i]);
> + mutex_unlock(&dev->vqs[i]->mutex);
> }

So this is a mitigation plan but the bug is still there though
we don't know exactly what it is. I would prefer adding something like
WARN_ON(mutex_is_locked(vqs[i]->mutex) here - does this make sense?

> vhost_dev_free_iovecs(dev);
> if (dev->log_ctx)
> --
> 2.35.1.574.g5d30c73bfb-goog