[3.2,75/87] drm: Pad drm_mode_get_connector to 64-bit boundary

Commit Message

Ben Hutchings Nov. 25, 2013, 1:44 p.m. UTC

3.2.53-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Chris Wilson <[e-mail]>

commit bc5bd37ce48c66e9192ad2e7231e9678880f6f8e upstream.

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 <[e-mail]>
Signed-off-by: Chris Wilson <[e-mail]>
Cc: Dave Airlie <[e-mail]>
Cc: [e-mail]
Signed-off-by: Dave Airlie <[e-mail]>
[bwh: Backported to 3.2: adjust filename]
Signed-off-by: Ben Hutchings <[e-mail]>
---
 include/uapi/drm/drm_mode.h | 2 ++
 1 file changed, 2 insertions(+)

Patch

--- a/include/drm/drm_mode.h
+++ b/include/drm/drm_mode.h
@@ -184,6 +184,8 @@  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)