[WIP PATCH 09/15] drm/nouveau: Fix potential use-after-frees for MSTCs

[Lyude Paul]

Now that we finally have a sane way to keep port allocations around, use
it to fix the potential unchecked ->port accesses that nouveau makes by
making sure we keep the mst port allocated for as long as it's
drm_connector is accessible.

Additionally, now that we've guaranteed that mstc->port is allocated for
as long as we keep mstc around we can remove the connector registration
checks for codepaths which release payloads, allowing us to release
payloads on active topologies properly. These registration checks were
only required before in order to avoid situations where mstc->port could
technically be pointing at freed memory.

Signed-off-by: Lyude Paul <lyude@xxxxxxxxxx>
---
 drivers/gpu/drm/nouveau/dispnv50/disp.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/nouveau/dispnv50/disp.c b/drivers/gpu/drm/nouveau/dispnv50/disp.c
index 0f7d72518604..982054bbcc8b 100644
--- a/drivers/gpu/drm/nouveau/dispnv50/disp.c
+++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c
@@ -964,7 +964,11 @@ static void
 nv50_mstc_destroy(struct drm_connector *connector)
 {
 	struct nv50_mstc *mstc = nv50_mstc(connector);
+
 	drm_connector_cleanup(&mstc->connector);
+	if (mstc->port)
+		drm_dp_mst_put_port_malloc(mstc->port);
+
 	kfree(mstc);
 }
 
@@ -1012,6 +1016,7 @@ nv50_mstc_new(struct nv50_mstm *mstm, struct drm_dp_mst_port *port,
 	drm_object_attach_property(&mstc->connector.base, dev->mode_config.path_property, 0);
 	drm_object_attach_property(&mstc->connector.base, dev->mode_config.tile_property, 0);
 	drm_connector_set_path_property(&mstc->connector, path);
+	drm_dp_mst_get_port_malloc(port);
 	return 0;
 }
 
@@ -1077,6 +1082,7 @@ nv50_mstm_destroy_connector(struct drm_dp_mst_topology_mgr *mgr,
 	drm_fb_helper_remove_one_connector(&drm->fbcon->helper, &mstc->connector);
 
 	drm_modeset_lock(&drm->dev->mode_config.connection_mutex, NULL);
+	drm_dp_mst_put_port_malloc(mstc->port);
 	mstc->port = NULL;
 	drm_modeset_unlock(&drm->dev->mode_config.connection_mutex);
 
-- 
2.19.2