[PATCH] hwrng: virtio - prevent use-after-free after a failed restore

[PATCH] hwrng: virtio - prevent use-after-free after a failed restore

[Thorsten Blum]

remove_common() frees the driver data during freeze, but does not clear
vdev->priv, which points to freed memory. If probe_common() then fails
during restore, a later remove or freeze can dereference the dangling
pointer.

Clear vdev->priv on the probe_common() error cleanup path and before
freeing the driver data in remove_common(). Also reset the device and
return early from remove_common() if vdev->priv is already NULL for a
safe teardown after a failed restore.

Fixes: 08e53fbdb85c ("virtio-rng: support multiple virtio-rng devices")
Cc: stable@vger.kernel.org
Signed-off-by: Thorsten Blum <blum@kernel.org>
---
 drivers/char/hw_random/virtio-rng.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/char/hw_random/virtio-rng.c b/drivers/char/hw_random/virtio-rng.c
index 5e83ffa105e4..a9ff520975a7 100644
--- a/drivers/char/hw_random/virtio-rng.c
+++ b/drivers/char/hw_random/virtio-rng.c
@@ -190,6 +190,7 @@ static int probe_common(struct virtio_device *vdev)
 err_find:
 	ida_free(&rng_index_ida, index);
 err_ida:
+	vdev->priv = NULL;
 	kfree(vi);
 	return err;
 }
@@ -198,6 +199,11 @@ static void remove_common(struct virtio_device *vdev)
 {
 	struct virtrng_info *vi = vdev->priv;
 
+	if (!vi) {
+		virtio_reset_device(vdev);
+		return;
+	}
+
 	vi->hwrng_removed = true;
 	vi->data_avail = 0;
 	vi->data_idx = 0;
@@ -207,6 +213,7 @@ static void remove_common(struct virtio_device *vdev)
 	virtio_reset_device(vdev);
 	vdev->config->del_vqs(vdev);
 	ida_free(&rng_index_ida, vi->index);
+	vdev->priv = NULL;
 	kfree(vi);
 }
 

Re: [PATCH] hwrng: virtio - prevent use-after-free after a failed restore

[PrasannaKumar Muralidharan]

Hi Thorsten,

On Fri, 16 Oct 2026 at 16:16, Thorsten Blum <blum@kernel.org> wrote:
>
> remove_common() frees the driver data during freeze, but does not clear
> vdev->priv, which points to freed memory. If probe_common() then fails
> during restore, a later remove or freeze can dereference the dangling
> pointer.
>
> Clear vdev->priv on the probe_common() error cleanup path and before
> freeing the driver data in remove_common(). Also reset the device and
> return early from remove_common() if vdev->priv is already NULL for a
> safe teardown after a failed restore.
>
> Fixes: 08e53fbdb85c ("virtio-rng: support multiple virtio-rng devices")
> Cc: stable@vger.kernel.org
> Signed-off-by: Thorsten Blum <blum@kernel.org>
> ---
>  drivers/char/hw_random/virtio-rng.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/drivers/char/hw_random/virtio-rng.c b/drivers/char/hw_random/virtio-rng.c
> index 5e83ffa105e4..a9ff520975a7 100644
> --- a/drivers/char/hw_random/virtio-rng.c
> +++ b/drivers/char/hw_random/virtio-rng.c
> @@ -190,6 +190,7 @@ static int probe_common(struct virtio_device *vdev)
>  err_find:
>         ida_free(&rng_index_ida, index);
>  err_ida:
> +       vdev->priv = NULL;
>         kfree(vi);
>         return err;
>  }
> @@ -198,6 +199,11 @@ static void remove_common(struct virtio_device *vdev)
>  {
>         struct virtrng_info *vi = vdev->priv;
>
> +       if (!vi) {
> +               virtio_reset_device(vdev);
> +               return;
> +       }
> +

The virtio_reset_device() is always called before setting vdev->priv
to NULL. So the virtio device is already quiesced, no need to do early
return. Isn't it?

>         vi->hwrng_removed = true;
>         vi->data_avail = 0;
>         vi->data_idx = 0;
> @@ -207,6 +213,7 @@ static void remove_common(struct virtio_device *vdev)
>         virtio_reset_device(vdev);
>         vdev->config->del_vqs(vdev);
>         ida_free(&rng_index_ida, vi->index);
> +       vdev->priv = NULL;
>         kfree(vi);
>  }
>
>

The rest of the hunks are fine.

Thanks,
PrasannaKumar

Re: [PATCH] hwrng: virtio - prevent use-after-free after a failed restore

[Thorsten Blum]

Hi PrasannaKumar,

On Sun, Oct 18, 2026 at 10:30:08PM +0530, PrasannaKumar Muralidharan wrote:
> Hi Thorsten,
> 
> On Fri, 16 Oct 2026 at 16:16, Thorsten Blum <blum@kernel.org> wrote:
> >
> > remove_common() frees the driver data during freeze, but does not clear
> > vdev->priv, which points to freed memory. If probe_common() then fails
> > during restore, a later remove or freeze can dereference the dangling
> > pointer.
> >
> > Clear vdev->priv on the probe_common() error cleanup path and before
> > freeing the driver data in remove_common(). Also reset the device and
> > return early from remove_common() if vdev->priv is already NULL for a
> > safe teardown after a failed restore.
> >
> > Fixes: 08e53fbdb85c ("virtio-rng: support multiple virtio-rng devices")
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Thorsten Blum <blum@kernel.org>
> > ---
> >  drivers/char/hw_random/virtio-rng.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> >
> > diff --git a/drivers/char/hw_random/virtio-rng.c b/drivers/char/hw_random/virtio-rng.c
> > index 5e83ffa105e4..a9ff520975a7 100644
> > --- a/drivers/char/hw_random/virtio-rng.c
> > +++ b/drivers/char/hw_random/virtio-rng.c
> > @@ -190,6 +190,7 @@ static int probe_common(struct virtio_device *vdev)
> >  err_find:
> >         ida_free(&rng_index_ida, index);
> >  err_ida:
> > +       vdev->priv = NULL;
> >         kfree(vi);
> >         return err;
> >  }
> > @@ -198,6 +199,11 @@ static void remove_common(struct virtio_device *vdev)
> >  {
> >         struct virtrng_info *vi = vdev->priv;
> >
> > +       if (!vi) {
> > +               virtio_reset_device(vdev);
> > +               return;
> > +       }
> > +
> 
> The virtio_reset_device() is always called before setting vdev->priv
> to NULL. So the virtio device is already quiesced, no need to do early
> return. Isn't it?

The check is still needed.

For example, during hibernation or suspend, .freeze (virtrng_freeze() ->
remove_common()) frees vi and sets vdev->priv to NULL.

On resume, .restore (virtrng_restore()) calls probe_common(), which
could fail and leave vdev->priv NULL. A later .freeze or .remove calls
remove_common() again, which would dereference NULL without the check.

Best regards,
Thorsten