linux-kernel - [PATCH 3.8 57/91] drm: Pad drm_mode_get

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Message-Id: <1383876946-2396-58-git-send-email-kamal@canonical.com>
Date:	Thu,  7 Nov 2013 18:15:12 -0800
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Chris Wilson <chris@...is-wilson.co.uk>,
	Dave Airlie <airlied@...hat.com>,
	dri-devel@...ts.freedesktop.org,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 3.8 57/91] drm: Pad drm_mode_get_connector to 64-bit boundary

3.8.13.13 -stable review patch.  If anyone has any objections, please let me know.

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

From: Chris Wilson <chris@...is-wilson.co.uk>

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 <proski@....org>
Signed-off-by: Chris Wilson <chris@...is-wilson.co.uk>
Cc: Dave Airlie <airlied@...hat.com>
Cc: dri-devel@...ts.freedesktop.org
Signed-off-by: Dave Airlie <airlied@...hat.com>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 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 3d6301b..f604a1a 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)
-- 
1.8.1.2

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