[PATCH] drm/bridge: Fix a NULL pointer dereference in drm_atomic_bridge_chain_check()

[Boris Brezillon]

drm_atomic_bridge_chain_check() callers can pass a NULL bridge. Let's
bail out before derefencing the bridge pointer when that happens.

Reported-by: Chris Wilson <chris at chris-wilson.co.uk>
Fixes: b86d895524ab ("drm/bridge: Add an ->atomic_check() hook")
Signed-off-by: Boris Brezillon <boris.brezillon at collabora.com>
---
 drivers/gpu/drm/drm_bridge.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
index da28967bc586..f6f020854e83 100644
--- a/drivers/gpu/drm/drm_bridge.c
+++ b/drivers/gpu/drm/drm_bridge.c
@@ -941,15 +941,19 @@ int drm_atomic_bridge_chain_check(struct drm_bridge *bridge,
 				  struct drm_connector_state *conn_state)
 {
 	struct drm_connector *conn = conn_state->connector;
-	struct drm_encoder *encoder = bridge->encoder;
+	struct drm_encoder *encoder;
 	struct drm_bridge *iter;
 	int ret;
 
+	if (!bridge)
+		return 0;
+
 	ret = drm_atomic_bridge_chain_select_bus_fmts(bridge, crtc_state,
 						      conn_state);
 	if (ret)
 		return ret;
 
+	encoder = bridge->encoder;
 	list_for_each_entry_reverse(iter, &encoder->bridge_chain, chain_node) {
 		int ret;
 
-- 
2.23.0