[SRU][F][PATCH 1/1] drm: bridge/panel: Cleanup connector on bridge detach

[Bethany Jamison]

From: Paul Cercueil <paul at crapouillou.net>

If we don't call drm_connector_cleanup() manually in
panel_bridge_detach(), the connector will be cleaned up with the other
DRM objects in the call to drm_mode_config_cleanup(). However, since our
drm_connector is devm-allocated, by the time drm_mode_config_cleanup()
will be called, our connector will be long gone. Therefore, the
connector must be cleaned up when the bridge is detached to avoid
use-after-free conditions.

v2: Cleanup connector only if it was created

v3: Add FIXME

v4: (Use connector->dev) directly in if() block

Fixes: 13dfc0540a57 ("drm/bridge: Refactor out the panel wrapper from the lvds-encoder bridge.")
Cc: <stable at vger.kernel.org> # 4.12+
Cc: Andrzej Hajda <a.hajda at samsung.com>
Cc: Neil Armstrong <narmstrong at baylibre.com>
Cc: Laurent Pinchart <Laurent.pinchart at ideasonboard.com>
Cc: Jonas Karlman <jonas at kwiboo.se>
Cc: Jernej Skrabec <jernej.skrabec at siol.net>
Signed-off-by: Paul Cercueil <paul at crapouillou.net>
Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210327115742.18986-2-paul@crapouillou.net
(backported from commit 4d906839d321c2efbf3fed4bc31ffd9ff55b75c0)
[bjamison: context conflict because panel_bridge_detach was supposed
to be empty but the contents of that function were removed by a
commit that can't be applied, so I accepted the fix commit as is]
CVE-2021-47063
Signed-off-by: Bethany Jamison <bethany.jamison at canonical.com>
---
 drivers/gpu/drm/bridge/panel.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/bridge/panel.c b/drivers/gpu/drm/bridge/panel.c
index b12ae3a4c5f11..8f9ddd30b2724 100644
--- a/drivers/gpu/drm/bridge/panel.c
+++ b/drivers/gpu/drm/bridge/panel.c
@@ -87,8 +87,17 @@ static int panel_bridge_attach(struct drm_bridge *bridge)
 static void panel_bridge_detach(struct drm_bridge *bridge)
 {
 	struct panel_bridge *panel_bridge = drm_bridge_to_panel_bridge(bridge);
+	struct drm_connector *connector = &panel_bridge->connector;
 
-	drm_panel_detach(panel_bridge->panel);
+	/*
+	 * Cleanup the connector if we know it was initialized.
+	 *
+	 * FIXME: This wouldn't be needed if the panel_bridge structure was
+	 * allocated with drmm_kzalloc(). This might be tricky since the
+	 * drm_device pointer can only be retrieved when the bridge is attached.
+	 */
+	if (connector->dev)
+		drm_connector_cleanup(connector);
 }
 
 static void panel_bridge_pre_enable(struct drm_bridge *bridge)
-- 
2.34.1