Commit bc5bd37c authored Oct 16, 2013 by Chris Wilson Committed by Dave Airlie Oct 18, 2013

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>

parent b062672e

include/uapi/drm/drm_mode.h

+2 −0

Original line number	Original line	Diff line number	Diff line
	@@ -223,6 +223,8 @@ struct drm_mode_get_connector {
	__u32 connection;		__u32 connection;
	__u32 mm_width, mm_height; /*< HxW in millimeters /		__u32 mm_width, mm_height; /*< HxW in millimeters /
	__u32 subpixel;		__u32 subpixel;

			__u32 pad;
	};		};

	#define DRM_MODE_PROP_PENDING (1<<0)		#define DRM_MODE_PROP_PENDING (1<<0)