[PATCH] drm: Pad drm_mode_get_connector to 64-bit boundary

[Chris Wilson]

Pavel Roskin reported that DRM_IOCTL_MODE_GETCONNECTOR was overwritting
the 4 bytes beyond the end of its structure with a 32-bit userspace
running on a 64-bit kernel. This is due to the padding gcc inserts as
the drm_mode_get_connector struct includes a u64 and its size is not a
natural multiple of u64s.

64-bit kernel:

sizeof(drm_mode_get_connector)=80, alignof=8
sizeof(drm_mode_get_encoder)=20, alignof=4
sizeof(drm_mode_modeinfo)=68, alignof=4

32-bit userspace:

sizeof(drm_mode_get_connector)=76, alignof=4
sizeof(drm_mode_get_encoder)=20, alignof=4
sizeof(drm_mode_modeinfo)=68, alignof=4

Fortuituously we can insert explicit padding to the tail of our
structures without breaking ABI.

Reported-by: Pavel Roskin <proski at gnu.org>
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Dave Airlie <airlied at redhat.com>
Cc: dri-devel at lists.freedesktop.org
Cc: stable at vger.kernel.org
---
 include/uapi/drm/drm_mode.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
index 550811712f78..28acbaf4a81e 100644
--- a/include/uapi/drm/drm_mode.h
+++ b/include/uapi/drm/drm_mode.h
@@ -223,6 +223,8 @@ struct drm_mode_get_connector {
 	__u32 connection;
 	__u32 mm_width, mm_height; /**< HxW in millimeters */
 	__u32 subpixel;
+
+	__u32 pad;
 };
 
 #define DRM_MODE_PROP_PENDING	(1<<0)
-- 
1.8.4.rc3