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

Michael S. Tsirkin
2022-03-07T22:37:29Z

On Mon, Mar 07, 2022 at 07:17:57PM +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 here is take the same lock
> during virtqueue clean-up and we mitigate the reported issues.

Pls just basically copy the code comment here. this is just confuses.

> Also WARN() as a precautionary measure. The purpose of this is to
> capture possible future race conditions which may pop up over time.
>
> Link: https://syzkaller.appspot.com/bug?extid=279432d30d825e63ba00

And this is a bug we already fixed, right?

> Cc: <stable@vger.kernel.org>
> Reported-by: syzbot+adc3cb32385586bec859@syzkaller.appspotmail.com

not really applicable anymore ...

> Signed-off-by: Lee Jones <lee.jones@linaro.org>
> ---
> drivers/vhost/vhost.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 59edb5a1ffe28..ef7e371e3e649 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -693,6 +693,15 @@ void vhost_dev_cleanup(struct vhost_dev *dev)
> int i;
>
> for (i = 0; i < dev->nvqs; ++i) {
> + /* No workers should run here by design. However, races have
> + * previously occurred where drivers have been unable to flush
> + * all work properly prior to clean-up. Without a successful
> + * flush the guest will malfunction, but avoiding host memory
> + * corruption in those cases does seem preferable.
> + */
> + WARN_ON(mutex_is_locked(&dev->vqs[i]->mutex));
> +
> + 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 +709,7 @@ 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);
> }
> vhost_dev_free_iovecs(dev);
> if (dev->log_ctx)
> --
> 2.35.1.616.g0bdcbb4464-goog