drm/vmwgfx: avoid null_ptr_deref in vmw_framebuffer_surface_create_handle

The 'vmw_user_object_buffer' function may return NULL with incorrect
inputs. To avoid possible null pointer dereference, add a check whether
the 'bo' is NULL in the vmw_framebuffer_surface_create_handle.

Fixes: d6667f0 ("drm/vmwgfx: Fix handling of dumb buffers")
Signed-off-by: Chen Ridong <[email protected]>
Signed-off-by: Zack Rusin <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

Author: Chen Ridong

drivers/gpu/drm/vmwgfx/vmwgfx_kms.c

@@ -1265,6 +1265,8 @@ static int vmw_framebuffer_surface_create_handle(struct drm_framebuffer *fb,
 	struct vmw_framebuffer_surface *vfbs = vmw_framebuffer_to_vfbs(fb);
 	struct vmw_bo *bo = vmw_user_object_buffer(&vfbs->uo);
 
+	if (WARN_ON(!bo))
+		return -EINVAL;
 	return drm_gem_handle_create(file_priv, &bo->tbo.base, handle);
 }