[PATCH] drm/vmwgfx: Fix invalid reads in fence signaled events

[Zack Rusin]

Correctly set the length of the drm_event to the size of the structure
that's actually used.

The length of the drm_event was set to the parent structure instead of
to the drm_vmw_event_fence which is supposed to be read. drm_read
uses the length parameter to copy the event to the user space thus
resuling in oob reads.

Signed-off-by: Zack Rusin <zack.rusin@xxxxxxxxxxxx>
Fixes: 8b7de6aa8468 ("vmwgfx: Rework fence event action")
Reported-by: zdi-disclosures@xxxxxxxxxxxxxx # ZDI-CAN-23566
Cc: David Airlie <airlied@xxxxxxxxx>
CC: Daniel Vetter <daniel@xxxxxxxx>
Cc: Zack Rusin <zack.rusin@xxxxxxxxxxxx>
Cc: Broadcom internal kernel review list <bcm-kernel-feedback-list@xxxxxxxxxxxx>
Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: <stable@xxxxxxxxxxxxxxx> # v3.4+
---
 drivers/gpu/drm/vmwgfx/vmwgfx_fence.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_fence.c b/drivers/gpu/drm/vmwgfx/vmwgfx_fence.c
index 2a0cda324703..5efc6a766f64 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_fence.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_fence.c
@@ -991,7 +991,7 @@ static int vmw_event_fence_action_create(struct drm_file *file_priv,
 	}
 
 	event->event.base.type = DRM_VMW_EVENT_FENCE_SIGNALED;
-	event->event.base.length = sizeof(*event);
+	event->event.base.length = sizeof(event->event);
 	event->event.user_data = user_data;
 
 	ret = drm_event_reserve_init(dev, file_priv, &event->base, &event->event.base);
-- 
2.40.1