linux-kernel - Re: [PATCH 1/2] vfio/mtty: Fix eventfd leak

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Date:   Mon, 16 Oct 2023 09:52:41 +0200
From:   Cédric Le Goater <clg@...hat.com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] vfio/mtty: Fix eventfd leak

On 10/13/23 21:56, Alex Williamson wrote:
> Found via kmemleak, eventfd context is leaked if not explicitly torn
> down by userspace.  Clear pointers to track released contexts.  Also
> remove unused irq_fd field in mtty structure, set but never used.

This could be 2 different patches, one cleanup and one fix.
  
> Fixes: 9d1a546c53b4 ("docs: Sample driver to demonstrate how to use Mediated device framework.")
> Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
> ---
>   samples/vfio-mdev/mtty.c | 28 +++++++++++++++++++++++-----
>   1 file changed, 23 insertions(+), 5 deletions(-)
> 
> diff --git a/samples/vfio-mdev/mtty.c b/samples/vfio-mdev/mtty.c
> index 5af00387c519..0a2760818e46 100644
> --- a/samples/vfio-mdev/mtty.c
> +++ b/samples/vfio-mdev/mtty.c
> @@ -127,7 +127,6 @@ struct serial_port {
>   /* State of each mdev device */
>   struct mdev_state {
>   	struct vfio_device vdev;
> -	int irq_fd;
>   	struct eventfd_ctx *intx_evtfd;
>   	struct eventfd_ctx *msi_evtfd;
>   	int irq_index;
> @@ -938,8 +937,10 @@ static int mtty_set_irqs(struct mdev_state *mdev_state, uint32_t flags,
>   		{
>   			if (flags & VFIO_IRQ_SET_DATA_NONE) {
>   				pr_info("%s: disable INTx\n", __func__);
> -				if (mdev_state->intx_evtfd)
> +				if (mdev_state->intx_evtfd) {
>   					eventfd_ctx_put(mdev_state->intx_evtfd);
> +					mdev_state->intx_evtfd = NULL;
> +				}
>   				break;
>   			}
>   
> @@ -955,7 +956,6 @@ static int mtty_set_irqs(struct mdev_state *mdev_state, uint32_t flags,
>   						break;
>   					}

Shouln't mdev_state->intx_evtfd value be tested before calling
eventfd_ctx() ?

Thanks,

C.


>   					mdev_state->intx_evtfd = evt;
> -					mdev_state->irq_fd = fd;
>   					mdev_state->irq_index = index;
>   					break;
>   				}
> @@ -971,8 +971,10 @@ static int mtty_set_irqs(struct mdev_state *mdev_state, uint32_t flags,
>   			break;
>   		case VFIO_IRQ_SET_ACTION_TRIGGER:
>   			if (flags & VFIO_IRQ_SET_DATA_NONE) {
> -				if (mdev_state->msi_evtfd)
> +				if (mdev_state->msi_evtfd) {
>   					eventfd_ctx_put(mdev_state->msi_evtfd);
> +					mdev_state->msi_evtfd = NULL;
> +				}
>   				pr_info("%s: disable MSI\n", __func__);
>   				mdev_state->irq_index = VFIO_PCI_INTX_IRQ_INDEX;
>   				break;
> @@ -993,7 +995,6 @@ static int mtty_set_irqs(struct mdev_state *mdev_state, uint32_t flags,
>   					break;
>   				}
>   				mdev_state->msi_evtfd = evt;
> -				mdev_state->irq_fd = fd;
>   				mdev_state->irq_index = index;
>   			}
>   			break;
> @@ -1262,6 +1263,22 @@ static unsigned int mtty_get_available(struct mdev_type *mtype)
>   	return atomic_read(&mdev_avail_ports) / type->nr_ports;
>   }
>   
> +static void mtty_close(struct vfio_device *vdev)
> +{
> +	struct mdev_state *mdev_state =
> +		container_of(vdev, struct mdev_state, vdev);
> +
> +	if (mdev_state->intx_evtfd) {
> +		eventfd_ctx_put(mdev_state->intx_evtfd);
> +		mdev_state->intx_evtfd = NULL;
> +	}
> +	if (mdev_state->msi_evtfd) {
> +		eventfd_ctx_put(mdev_state->msi_evtfd);
> +		mdev_state->msi_evtfd = NULL;
> +	}
> +	mdev_state->irq_index = -1;
> +}
> +
>   static const struct vfio_device_ops mtty_dev_ops = {
>   	.name = "vfio-mtty",
>   	.init = mtty_init_dev,
> @@ -1273,6 +1290,7 @@ static const struct vfio_device_ops mtty_dev_ops = {
>   	.unbind_iommufd	= vfio_iommufd_emulated_unbind,
>   	.attach_ioas	= vfio_iommufd_emulated_attach_ioas,
>   	.detach_ioas	= vfio_iommufd_emulated_detach_ioas,
> +	.close_device	= mtty_close,
>   };
>   
>   static struct mdev_driver mtty_driver = {