From 85d683d041121f31e1130606cf25ccbe84197208 Mon Sep 17 00:00:00 2001
From: Boris Brezillon <boris.brezillon@collabora.com>
Date: Tue, 7 Jan 2020 12:30:31 +0100
Subject: drm/bridge: Fix a NULL pointer dereference in
Git-commit: b18398c16e176513502f962b642f89225039ef1f
Patch-mainline: v5.6-rc1
References: jsc#SLE-12680, jsc#SLE-12880, jsc#SLE-12882, jsc#SLE-12883, jsc#SLE-13496, jsc#SLE-15322
 drm_atomic_bridge_chain_check()

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

Reported-by: Chris Wilson <chris@chris-wilson.co.uk>
Fixes: b86d895524ab ("drm/bridge: Add an ->atomic_check() hook")
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20200107113031.435604-1-boris.brezillon@collabora.com
Signed-off-by: Patrik Jakobsson <pjakobsson@suse.de>
---
 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 37400607e9b7..32d43bfeeca1 100644
--- a/drivers/gpu/drm/drm_bridge.c
+++ b/drivers/gpu/drm/drm_bridge.c
@@ -938,15 +938,19 @@ 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;
 
-- 
2.28.0