drm: Pad drm_mode_get_connector to 64-bit boundary

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@gnu.org>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Dave Airlie <airlied@redhat.com>
Cc: dri-devel@lists.freedesktop.org
Cc: stable@vger.kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>

diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
index 550811712f78c71aad43b4a531b07e1df536b64f..28acbaf4a81ec091a54740c54adfd57ec2f9ad59 100644 (file)
--- 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)