Virtualization - Mar 2022 - [PATCH 1/1] vhost: Protect the virtqueue from being cleared whilst still in use

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.

Also WARN() as a precautionary measure.  The purpose of this is to
capture possible future race conditions which may pop up over time.

Cc: <stable at vger.kernel.org>
Signed-off-by: Lee Jones <lee.jones at 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);
 	}
 	vhost_dev_free_iovecs(dev);
 	if (dev->log_ctx)
-- 
2.35.1.723.g4982287a31-goog

On Mon, Mar 14, 2022 at 08:43:02AM +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.
> 
> Also WARN() as a precautionary measure.  The purpose of this is to
> capture possible future race conditions which may pop up over time.
These two sentances do not match your actual patch :(
> Cc: <stable at vger.kernel.org>
> Signed-off-by: Lee Jones <lee.jones at linaro.org>
What commit caused this problem?  Can you add a Fixes: line as well for
this?

thanks,

greg k-h

On Mon, Mar 14, 2022 at 08:43:02AM +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.
> 
> Also WARN() as a precautionary measure.  The purpose of this is to
> capture possible future race conditions which may pop up over time.
> 
> Cc: <stable at vger.kernel.org>
> Signed-off-by: Lee Jones <lee.jones at linaro.org>
Pls refer to my previous responses to this patch.  I'd like to see an
argument for why this will make future bugs less and not more likely.

> ---
>  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);
>  	}
>  	vhost_dev_free_iovecs(dev);
>  	if (dev->log_ctx)
> -- 
> 2.35.1.723.g4982287a31-goog