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

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Date:   Mon, 16 Oct 2023 14:16:35 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Cédric Le Goater <clg@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] vfio/mtty: Fix eventfd leak

On Mon, 16 Oct 2023 09:52:41 +0200
Cédric Le Goater <clg@...hat.com> wrote:

> 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.

Of course.

> > 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() ?

The state of mtty interrupt handling is really quite atrocious, it's a
pretty significant overhaul to really make it comply with the SET_IRQS
ioctl.  I'll see what I can do, but it's so broken that I hope you
won't insist on splitting out each fix.  Thanks,

Alex

> >   					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 = {  
>