Re: [PATCH] drm: Test for PCI root bus to avoid NULL pointer dereference

[Alex Deucher]

On Wed, Aug 27, 2014 at 2:57 PM, Alex Williamson
<alex.williamson@xxxxxxxxxx> wrote:
> If we have a GPU on the PCI root bus that calls
> drm_pcie_get_speed_cap_mask() we end up with a NULL pointer
> dereference since pdev->bus->self is NULL.  We already protect
> against callers passing non-PCI devices, so let's also catch this
> case and return -EINVAL.
>
> Root complex graphics are not terribly likely outside of IGD, but
> when we assign a standard plugin GPU to a virtual machine, our
> assumption that we have a parent device quickly becomes invalid.
>
> Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>

Reviewed-by: Alex Deucher <alexander.deucher@xxxxxxx>

> ---
>
>  drivers/gpu/drm/drm_pci.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/drm_pci.c b/drivers/gpu/drm/drm_pci.c
> index 020cfd9..411e806 100644
> --- a/drivers/gpu/drm/drm_pci.c
> +++ b/drivers/gpu/drm/drm_pci.c
> @@ -390,7 +390,7 @@ int drm_pcie_get_speed_cap_mask(struct drm_device *dev, u32 *mask)
>         u32 lnkcap, lnkcap2;
>
>         *mask = 0;
> -       if (!dev->pdev)
> +       if (!dev->pdev || pci_is_root_bus(dev->pdev->bus))
>                 return -EINVAL;
>
>         root = dev->pdev->bus->self;
>
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