drm/vmwgfx: Do not drop the reference to the handle too soon

From: Zack Rusin <[email protected]>

v2: Update the commit message to include note describing why the second usag of vmw_gem_object_create_with_handle in vmwgfx_surface.c wasn't changed

It is possible for userspace to predict the next buffer handle and to destroy the buffer while it's still used by the kernel. Delay dropping the internal reference on the buffers until kernel is done with them.

Also fixes the second usage of vmw_gem_object_create_with_handle in vmwgfx_surface.c which wasn't grabbing an explicit reference to the gem object which could have been destroyed by the userspace on the owning surface at any point.

Signed-off-by Zack Rusin <[email protected]>

Fixes 8afa13a0583f ("drm/vmwgfx: Implement DRIVER_GEM")

Cc <[email protected]> # v5.17+

---
  drivers/gpu/drm/vmwgfx/vmwgfx_bo.c      | 3 ++-
  drivers/gpu/drm/vmwgfx/vmwgfx_gem.c     | 4 ++--
  drivers/gpu/drm/vmwgfx/vmwgfx_surface.c | 1 -
  3 files changed, 4 insertions(+), 4 deletions(-)

drivers/gpu/drm/vmwgfx/vmwgfx_bo.c +2 -1

index 43ffa5c7acbd..65bd88c8fef9 100644
@@ -708,7 +708,8 @@ int vmw_dumb_create(struct drm_file *file_priv,
  	ret = vmw_gem_object_create_with_handle(dev_priv, file_priv,
  						args->size, &args->handle,
  						&vbo);
-
+	/* drop reference from allocate - handle holds it now */
+	drm_gem_object_put(&vbo->tbo.base);
  	return ret;
  }
 

drivers/gpu/drm/vmwgfx/vmwgfx_gem.c +2 -2

index 51bd1f8c5cc4..d6baf73a6458 100644
@@ -133,8 +133,6 @@ int vmw_gem_object_create_with_handle(struct vmw_private *dev_priv,
  	(*p_vbo)->tbo.base.funcs = &vmw_gem_object_funcs;
 
  	ret = drm_gem_handle_create(filp, &(*p_vbo)->tbo.base, handle);
-	/* drop reference from allocate - handle holds it now */
-	drm_gem_object_put(&(*p_vbo)->tbo.base);
  out_no_bo:
  	return ret;
  }

@@ -161,6 +159,8 @@ int vmw_gem_object_create_ioctl(struct drm_device *dev, void *data,
  	rep->map_handle = drm_vma_node_offset_addr(&vbo->tbo.base.vma_node);
  	rep->cur_gmr_id = handle;
  	rep->cur_gmr_offset = 0;
+	/* drop reference from allocate - handle holds it now */
+	drm_gem_object_put(&vbo->tbo.base);
  out_no_bo:
  	return ret;
  }

drivers/gpu/drm/vmwgfx/vmwgfx_surface.c +0 -1

index 9d4ae9623a00..d18fec953fa7 100644
@@ -867,7 +867,6 @@ int vmw_surface_define_ioctl(struct drm_device *dev, void *data,
  			goto out_unlock;
  		}
  		vmw_bo_reference(res->guest_memory_bo);
-		drm_gem_object_get(&res->guest_memory_bo->tbo.base);
  	}
 
  	tmp = vmw_resource_reference(&srf->res);