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

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Message-ID: <YO8VjgdgHXoAcOMY@sashalap>
Date:   Wed, 14 Jul 2021 12:49:18 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     Pavel Machek <pavel@...x.de>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Xie Yongji <xieyongji@...edance.com>,
        Gerd Hoffmann <kraxel@...hat.com>,
        dri-devel@...ts.freedesktop.org,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH AUTOSEL 4.4 08/31] drm/virtio: Fixes a potential NULL
 pointer dereference on probe failure

On Mon, Jul 12, 2021 at 11:59:37PM +0200, Pavel Machek wrote:
>Hi!
>
>> From: Xie Yongji <xieyongji@...edance.com>
>>
>> [ 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