drm: avoid exposing kernel stack in compat_drm_getstats

The C standard does not specify the size of the integer used
to store an enum. Hence in structure drm_stats32_t alignment
bytes may exist.

To avoid exposing bytes from the kernel stack it is
necessary to initialize variable s32 completely.
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1471802179-2886-1-git-send-email-xypron.glpk@gmx.de

drivers/gpu/drm/drm_ioc32.c

@@ -346,6 +346,7 @@ static int compat_drm_getstats(struct file *file, unsigned int cmd,
 	struct drm_stats __user *stats;
 	int i, err;
 
+	memset(&s32, 0, sizeof(drm_stats32_t));
 	stats = compat_alloc_user_space(sizeof(*stats));
 	if (!stats)
 		return -EFAULT;