Re: [PATCH AUTOSEL 4.4 08/31] drm/virtio: Fixes a potential NULL pointer dereference on probe failure

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On Mon, Jul 12, 2021 at 11:59:37PM +0200, Pavel Machek wrote:
Hi!

From: Xie Yongji <xieyongji@xxxxxxxxxxxxx>

[ Upstream commit 17f46f488a5d82c5568e6e786cd760bba1c2ee09 ]

The dev->dev_private might not be allocated if virtio_gpu_pci_quirk()
or virtio_gpu_init() failed. In this case, we should avoid the cleanup
in virtio_gpu_release().

The check is in wrong place at least in 4.4:

+++ b/drivers/gpu/drm/virtio/virtgpu_kms.c
@@ -257,6 +257,9 @@ int virtio_gpu_driver_unload(struct drm_device *dev)
 	flush_work(&vgdev->config_changed_work);
 	vgdev->vdev->config->del_vqs(vgdev->vdev);

+	if (!vgdev)
+		return;
+

Pointer is dereferenced before being tested.

Heh, yes, thanks for catching that. I'll drop it for now and rework it
next week.

--
Thanks,
Sasha



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