2017-12-04 21:54:32

by Gustavo A. R. Silva

Subject: [PATCH] drm/vmwgfx_kms: Fix potential NULL pointer dereference

crtc_state is being null checked in a previous code block, which implies
that such pointer might be null.

crtc_state is dereferenced in drm_atomic_helper_check_plane_state, hence
there is a potential null pointer dereference.

Fix this by warning-on and returning -EINVAL in case crtc_state is null.

Addresses-Coverity-ID: 1462412 ("Dereference after null check")
Fixes: a01cb8ba3f62 ("drm: Move drm_plane_helper_check_state() into drm_atomic_helper.c")
Signed-off-by: Gustavo A. R. Silva <[email protected]>
---
drivers/gpu/drm/vmwgfx/vmwgfx_kms.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c b/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
index a2a93d7..72c3b290 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
@@ -454,6 +454,9 @@ int vmw_du_primary_plane_atomic_check(struct drm_plane *plane,
clip.y2 = crtc_state->adjusted_mode.vdisplay;
}

+ if (WARN_ON(!crtc_state))
+ return -EINVAL;
+
ret = drm_atomic_helper_check_plane_state(state, crtc_state, &clip,
DRM_PLANE_HELPER_NO_SCALING,
DRM_PLANE_HELPER_NO_SCALING,
--
2.7.4

2017-12-05 13:30:25

by Ville Syrjälä

Subject: Re: [PATCH] drm/vmwgfx_kms: Fix potential NULL pointer dereference

On Mon, Dec 04, 2017 at 03:54:18PM -0600, Gustavo A. R. Silva wrote:
> crtc_state is being null checked in a previous code block, which implies
> that such pointer might be null.
>
> crtc_state is dereferenced in drm_atomic_helper_check_plane_state, hence
> there is a potential null pointer dereference.

This is a false positive. drm_atomic_helper_check_plane_state() will not
dereference crtc_state when plane_state->crtc is NULL.

>
> Fix this by warning-on and returning -EINVAL in case crtc_state is null.
>
> Addresses-Coverity-ID: 1462412 ("Dereference after null check")
> Fixes: a01cb8ba3f62 ("drm: Move drm_plane_helper_check_state() into drm_atomic_helper.c")
> Signed-off-by: Gustavo A. R. Silva <[email protected]>
> ---
> drivers/gpu/drm/vmwgfx/vmwgfx_kms.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c b/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
> index a2a93d7..72c3b290 100644
> --- a/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
> +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
> @@ -454,6 +454,9 @@ int vmw_du_primary_plane_atomic_check(struct drm_plane *plane,
> clip.y2 = crtc_state->adjusted_mode.vdisplay;
> }
>
> + if (WARN_ON(!crtc_state))
> + return -EINVAL;

This would in fact break the driver because it would flag an error
whenever the plane is disabled.

> +
> ret = drm_atomic_helper_check_plane_state(state, crtc_state, &clip,
> DRM_PLANE_HELPER_NO_SCALING,
> DRM_PLANE_HELPER_NO_SCALING,
> --
> 2.7.4
>
> _______________________________________________
> dri-devel mailing list
> [email protected]
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

--
Ville Syrj?l?
Intel OTC

2017-12-05 15:47:26

by Gustavo A. R. Silva

Subject: Re: [PATCH] drm/vmwgfx_kms: Fix potential NULL pointer dereference

Hi Ville,

Quoting Ville Syrjälä <[email protected]>:

> On Mon, Dec 04, 2017 at 03:54:18PM -0600, Gustavo A. R. Silva wrote:
>> crtc_state is being null checked in a previous code block, which implies
>> that such pointer might be null.
>>
>> crtc_state is dereferenced in drm_atomic_helper_check_plane_state, hence
>> there is a potential null pointer dereference.
>
> This is a false positive. drm_atomic_helper_check_plane_state() will not
> dereference crtc_state when plane_state->crtc is NULL.
>

You are right.

Thank you for clarifying.
--
Gustavo A. R. Silva