RE: [PATCH v3 06/15] vfio/mtty: Use the new device life cycle helpers
> From: Alex Williamson
> Sent: Wednesday, September 21, 2022 3:17 AM
>
> On Fri, 9 Sep 2022 18:22:38 +0800
> Kevin Tian wrote:
>
> > From: Yi Liu
> >
> > and manage available ports inside @init/@release.
> >
> > Signed-off-by: Yi Liu
> > Signed-off-by: Kevin Tian
> > Reviewed-by: Jason Gunthorpe
> > ---
> > samples/vfio-mdev/mtty.c | 67 +++-
> > 1 file changed, 39 insertions(+), 28 deletions(-)
> >
> > diff --git a/samples/vfio-mdev/mtty.c b/samples/vfio-mdev/mtty.c
> > index f42a59ed2e3f..41301d50b247 100644
> > --- a/samples/vfio-mdev/mtty.c
> > +++ b/samples/vfio-mdev/mtty.c
> ...
> > +static int mtty_probe(struct mdev_device *mdev)
> > +{
> > + struct mdev_state *mdev_state;
> > + int ret;
> > +
> > + mdev_state = vfio_alloc_device(mdev_state, vdev, >dev,
> > + _dev_ops);
> > + if (IS_ERR(mdev_state))
> > + return PTR_ERR(mdev_state);
> >
> > ret = vfio_register_emulated_iommu_dev(_state->vdev);
> > if (ret)
> > - goto err_vconfig;
> > + goto err_put_vdev;
> > dev_set_drvdata(>dev, mdev_state);
> > return 0;
> >
> > -err_vconfig:
> > - kfree(mdev_state->vconfig);
> > -err_state:
> > - vfio_uninit_group_dev(_state->vdev);
> > - kfree(mdev_state);
> > -err_nr_ports:
> > - atomic_add(nr_ports, _avail_ports);
> > +err_put_vdev:
> > + vfio_put_device(_state->vdev);
> > return ret;
> > }
> >
> > +static void mtty_release_dev(struct vfio_device *vdev)
> > +{
> > + struct mdev_state *mdev_state =
> > + container_of(vdev, struct mdev_state, vdev);
> > +
> > + kfree(mdev_state->vconfig);
> > + vfio_free_device(vdev);
> > + atomic_add(mdev_state->nr_ports, _avail_ports);
>
> I must be missing something, isn't this a use-after-free?
Yes, it's a use-after-free indeed. Thanks for catching it!
>
> mdev_state is allocated via vfio_alloc_device(), where vdev is the
> first entry in that structure, so this is equivalent to
> kvfree(mdev_state). mbochs has the same issue. mdpy and vfio-ap
> adjust global counters after vfio_free_device(), which I think muddies
> the situation. Shouldn't we look suspiciously at any .release callback
> where vfio_free_device() isn't the last thing executed? Thanks,
>
Yes. I'll scrutinize it again. To be consistent I'll make sure the free
is the last line in all .release callbacks though not required for
some (e.g. mdpy and vfio-ap).
Re: [PATCH v3 06/15] vfio/mtty: Use the new device life cycle helpers
On Fri, 9 Sep 2022 18:22:38 +0800
Kevin Tian wrote:
> From: Yi Liu
>
> and manage available ports inside @init/@release.
>
> Signed-off-by: Yi Liu
> Signed-off-by: Kevin Tian
> Reviewed-by: Jason Gunthorpe
> ---
> samples/vfio-mdev/mtty.c | 67 +++-
> 1 file changed, 39 insertions(+), 28 deletions(-)
>
> diff --git a/samples/vfio-mdev/mtty.c b/samples/vfio-mdev/mtty.c
> index f42a59ed2e3f..41301d50b247 100644
> --- a/samples/vfio-mdev/mtty.c
> +++ b/samples/vfio-mdev/mtty.c
...
> +static int mtty_probe(struct mdev_device *mdev)
> +{
> + struct mdev_state *mdev_state;
> + int ret;
> +
> + mdev_state = vfio_alloc_device(mdev_state, vdev, >dev,
> +_dev_ops);
> + if (IS_ERR(mdev_state))
> + return PTR_ERR(mdev_state);
>
> ret = vfio_register_emulated_iommu_dev(_state->vdev);
> if (ret)
> - goto err_vconfig;
> + goto err_put_vdev;
> dev_set_drvdata(>dev, mdev_state);
> return 0;
>
> -err_vconfig:
> - kfree(mdev_state->vconfig);
> -err_state:
> - vfio_uninit_group_dev(_state->vdev);
> - kfree(mdev_state);
> -err_nr_ports:
> - atomic_add(nr_ports, _avail_ports);
> +err_put_vdev:
> + vfio_put_device(_state->vdev);
> return ret;
> }
>
> +static void mtty_release_dev(struct vfio_device *vdev)
> +{
> + struct mdev_state *mdev_state =
> + container_of(vdev, struct mdev_state, vdev);
> +
> + kfree(mdev_state->vconfig);
> + vfio_free_device(vdev);
> + atomic_add(mdev_state->nr_ports, _avail_ports);
I must be missing something, isn't this a use-after-free?
mdev_state is allocated via vfio_alloc_device(), where vdev is the
first entry in that structure, so this is equivalent to
kvfree(mdev_state). mbochs has the same issue. mdpy and vfio-ap
adjust global counters after vfio_free_device(), which I think muddies
the situation. Shouldn't we look suspiciously at any .release callback
where vfio_free_device() isn't the last thing executed? Thanks,
Alex
[PATCH v3 06/15] vfio/mtty: Use the new device life cycle helpers
From: Yi Liu
and manage available ports inside @init/@release.
Signed-off-by: Yi Liu
Signed-off-by: Kevin Tian
Reviewed-by: Jason Gunthorpe
---
samples/vfio-mdev/mtty.c | 67 +++-
1 file changed, 39 insertions(+), 28 deletions(-)
diff --git a/samples/vfio-mdev/mtty.c b/samples/vfio-mdev/mtty.c
index f42a59ed2e3f..41301d50b247 100644
--- a/samples/vfio-mdev/mtty.c
+++ b/samples/vfio-mdev/mtty.c
@@ -703,9 +703,11 @@ static ssize_t mdev_access(struct mdev_state *mdev_state,
u8 *buf, size_t count,
return ret;
}
-static int mtty_probe(struct mdev_device *mdev)
+static int mtty_init_dev(struct vfio_device *vdev)
{
- struct mdev_state *mdev_state;
+ struct mdev_state *mdev_state =
+ container_of(vdev, struct mdev_state, vdev);
+ struct mdev_device *mdev = to_mdev_device(vdev->dev);
int nr_ports = mdev_get_type_group_id(mdev) + 1;
int avail_ports = atomic_read(_avail_ports);
int ret;
@@ -716,58 +718,65 @@ static int mtty_probe(struct mdev_device *mdev)
} while (!atomic_try_cmpxchg(_avail_ports,
_ports, avail_ports - nr_ports));
- mdev_state = kzalloc(sizeof(struct mdev_state), GFP_KERNEL);
- if (mdev_state == NULL) {
- ret = -ENOMEM;
- goto err_nr_ports;
- }
-
- vfio_init_group_dev(_state->vdev, >dev, _dev_ops);
-
mdev_state->nr_ports = nr_ports;
mdev_state->irq_index = -1;
mdev_state->s[0].max_fifo_size = MAX_FIFO_SIZE;
mdev_state->s[1].max_fifo_size = MAX_FIFO_SIZE;
mutex_init(_state->rxtx_lock);
- mdev_state->vconfig = kzalloc(MTTY_CONFIG_SPACE_SIZE, GFP_KERNEL);
- if (mdev_state->vconfig == NULL) {
+ mdev_state->vconfig = kzalloc(MTTY_CONFIG_SPACE_SIZE, GFP_KERNEL);
+ if (!mdev_state->vconfig) {
ret = -ENOMEM;
- goto err_state;
+ goto err_nr_ports;
}
mutex_init(_state->ops_lock);
mdev_state->mdev = mdev;
-
mtty_create_config_space(mdev_state);
+ return 0;
+
+err_nr_ports:
+ atomic_add(nr_ports, _avail_ports);
+ return ret;
+}
+
+static int mtty_probe(struct mdev_device *mdev)
+{
+ struct mdev_state *mdev_state;
+ int ret;
+
+ mdev_state = vfio_alloc_device(mdev_state, vdev, >dev,
+ _dev_ops);
+ if (IS_ERR(mdev_state))
+ return PTR_ERR(mdev_state);
ret = vfio_register_emulated_iommu_dev(_state->vdev);
if (ret)
- goto err_vconfig;
+ goto err_put_vdev;
dev_set_drvdata(>dev, mdev_state);
return 0;
-err_vconfig:
- kfree(mdev_state->vconfig);
-err_state:
- vfio_uninit_group_dev(_state->vdev);
- kfree(mdev_state);
-err_nr_ports:
- atomic_add(nr_ports, _avail_ports);
+err_put_vdev:
+ vfio_put_device(_state->vdev);
return ret;
}
+static void mtty_release_dev(struct vfio_device *vdev)
+{
+ struct mdev_state *mdev_state =
+ container_of(vdev, struct mdev_state, vdev);
+
+ kfree(mdev_state->vconfig);
+ vfio_free_device(vdev);
+ atomic_add(mdev_state->nr_ports, _avail_ports);
+}
+
static void mtty_remove(struct mdev_device *mdev)
{
struct mdev_state *mdev_state = dev_get_drvdata(>dev);
- int nr_ports = mdev_state->nr_ports;
vfio_unregister_group_dev(_state->vdev);
-
- kfree(mdev_state->vconfig);
- vfio_uninit_group_dev(_state->vdev);
- kfree(mdev_state);
- atomic_add(nr_ports, _avail_ports);
+ vfio_put_device(_state->vdev);
}
static int mtty_reset(struct mdev_state *mdev_state)
@@ -1287,6 +1296,8 @@ static struct attribute_group *mdev_type_groups[] = {
static const struct vfio_device_ops mtty_dev_ops = {
.name = "vfio-mtty",
+ .init = mtty_init_dev,
+ .release = mtty_release_dev,
.read = mtty_read,
.write = mtty_write,
.ioctl = mtty_ioctl,
--
2.21.3
