linux-kernel - [PATCH RFC/RFT 5/9] drm/vc4: hdmi: drop separate CEC unregistration

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20241225-drm-hdmi-connector-cec-v1-5-b80380c67221@linaro.org>
Date: Wed, 25 Dec 2024 01:10:13 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
 Dave Stevenson <dave.stevenson@...pberrypi.com>, 
 Maíra Canal <mcanal@...lia.com>, 
 Raspberry Pi Kernel Maintenance <kernel-list@...pberrypi.com>, 
 Andrzej Hajda <andrzej.hajda@...el.com>, 
 Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>, 
 Laurent Pinchart <Laurent.pinchart@...asonboard.com>, 
 Jonas Karlman <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: [PATCH RFC/RFT 5/9] drm/vc4: hdmi: drop separate CEC
 unregistration

CEC adapter functions are protected by drm_dev_enter() / _exit(), so it
is safe to keep CEC registered until DRM device is being torn down. Drop
custom CEC unsregistration code and rely on the DRM core to unregister
CEC adapter.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
---
 drivers/gpu/drm/vc4/vc4_hdmi.c | 53 ++++++------------------------------------
 1 file changed, 7 insertions(+), 46 deletions(-)

diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
index 3086c2ad3bb2e8fafdc1f37ba985aa5785d49f9a..7b39000369e50f5368384575aa81919df5a7133c 100644
--- a/drivers/gpu/drm/vc4/vc4_hdmi.c
+++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
@@ -2752,13 +2752,6 @@ static const struct cec_adap_ops vc4_hdmi_cec_adap_ops = {
 	.adap_transmit = vc4_hdmi_cec_adap_transmit,
 };
 
-static void vc4_hdmi_cec_release(void *ptr)
-{
-	struct drm_connector *connector = ptr;
-
-	drm_connector_cec_unregister(connector);
-}
-
 static int vc4_hdmi_cec_init(struct drm_connector *connector)
 {
 	struct vc4_hdmi *vc4_hdmi = connector_to_vc4_hdmi(connector);
@@ -2796,51 +2789,19 @@ static int vc4_hdmi_cec_register(struct vc4_hdmi *vc4_hdmi)
 {
 	struct platform_device *pdev = vc4_hdmi->pdev;
 	struct device *dev = &pdev->dev;
-	int ret;
 
 	if (!of_property_present(dev->of_node, "interrupts")) {
 		dev_warn(dev, "'interrupts' DT property is missing, no CEC\n");
 		return 0;
 	}
 
-	ret = drm_connector_hdmi_cec_adapter_register(&vc4_hdmi->connector,
-						      &vc4_hdmi_cec_adap_ops,
-						      vc4_hdmi->variant->card_name,
-						      1,
-						      vc4_hdmi_cec_init,
-						      NULL,
-						      &pdev->dev);
-	if (ret < 0)
-		return ret;
-
-	/*
-	 * NOTE: Strictly speaking, we should probably use a DRM-managed
-	 * registration there to avoid removing the CEC adapter by the
-	 * time the DRM driver doesn't have any user anymore.
-	 *
-	 * However, the CEC framework already cleans up the CEC adapter
-	 * only when the last user has closed its file descriptor, so we
-	 * don't need to handle it in DRM.
-	 *
-	 * By the time the device-managed hook is executed, we will give
-	 * up our reference to the CEC adapter and therefore don't
-	 * really care when it's actually freed.
-	 *
-	 * There's still a problematic sequence: if we unregister our
-	 * CEC adapter, but the userspace keeps a handle on the CEC
-	 * adapter but not the DRM device for some reason. In such a
-	 * case, our vc4_hdmi structure will be freed, but the
-	 * cec_adapter structure will have a dangling pointer to what
-	 * used to be our HDMI controller. If we get a CEC call at that
-	 * moment, we could end up with a use-after-free. Fortunately,
-	 * the CEC framework already handles this too, by calling
-	 * cec_is_registered() in cec_ioctl() and cec_poll().
-	 */
-	ret = devm_add_action_or_reset(dev, vc4_hdmi_cec_release, vc4_hdmi);
-	if (ret)
-		return ret;
-
-	return 0;
+	return drm_connector_hdmi_cec_adapter_register(&vc4_hdmi->connector,
+						       &vc4_hdmi_cec_adap_ops,
+						       vc4_hdmi->variant->card_name,
+						       1,
+						       vc4_hdmi_cec_init,
+						       NULL,
+						       &pdev->dev);
 }
 #else
 static int vc4_hdmi_cec_register(struct vc4_hdmi *vc4_hdmi)

-- 
2.39.5