[PATCH 6.1.y 2/2] hwrng: virtio - prevent use-after-free after a failed restore

[Sasha Levin <sashal@kernel.org>]

From: Thorsten Blum <blum@kernel.org>

[ Upstream commit 0f7bf47f5a0cc26320aa4b14f4504d03a07f4b74 ]

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>
Reviewed-by: PrasannaKumar Muralidharan <prasannatsmkumar@gmail.com>.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Message-ID: <20261016103640.4989-2-blum@kernel.org>
Signed-off-by: Sasha Levin <sashal@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 14ab1c2a7350b..0c32991e5754d 100644
--- a/drivers/char/hw_random/virtio-rng.c
+++ b/drivers/char/hw_random/virtio-rng.c
@@ -188,6 +188,7 @@ 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;
 }
@@ -196,6 +197,11 @@ 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;
@@ -205,6 +211,7 @@ 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);
 }
 
-- 
2.53.0