The patch below does not apply to the 6.7-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <stable@xxxxxxxxxxxxxxx>. To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.7.y git checkout FETCH_HEAD git cherry-pick -x b979f2d50a099f3402418d7ff5f26c3952fb08bb # <resolve conflicts, build, test, etc.> git commit -s git send-email --to '<stable@xxxxxxxxxxxxxxx>' --in-reply-to '2024030452-unlatch-jailer-3f13@gregkh' --subject-prefix 'PATCH 6.7.y' HEAD^.. Possible dependencies: b979f2d50a09 ("soc: qcom: pmic_glink_altmode: fix drm bridge use-after-free") 2bcca96abfbf ("soc: qcom: pmic-glink: switch to DRM_AUX_HPD_BRIDGE") thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From b979f2d50a099f3402418d7ff5f26c3952fb08bb Mon Sep 17 00:00:00 2001 From: Johan Hovold <johan+linaro@xxxxxxxxxx> Date: Sat, 17 Feb 2024 16:02:25 +0100 Subject: [PATCH] soc: qcom: pmic_glink_altmode: fix drm bridge use-after-free A recent DRM series purporting to simplify support for "transparent bridges" and handling of probe deferrals ironically exposed a use-after-free issue on pmic_glink_altmode probe deferral. This has manifested itself as the display subsystem occasionally failing to initialise and NULL-pointer dereferences during boot of machines like the Lenovo ThinkPad X13s. Specifically, the dp-hpd bridge is currently registered before all resources have been acquired which means that it can also be deregistered on probe deferrals. In the meantime there is a race window where the new aux bridge driver (or PHY driver previously) may have looked up the dp-hpd bridge and stored a (non-reference-counted) pointer to the bridge which is about to be deallocated. When the display controller is later initialised, this triggers a use-after-free when attaching the bridges: dp -> aux -> dp-hpd (freed) which may, for example, result in the freed bridge failing to attach: [drm:drm_bridge_attach [drm]] *ERROR* failed to attach bridge /soc@0/phy@88eb000 to encoder TMDS-31: -16 or a NULL-pointer dereference: Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000 ... Call trace: drm_bridge_attach+0x70/0x1a8 [drm] drm_aux_bridge_attach+0x24/0x38 [aux_bridge] drm_bridge_attach+0x80/0x1a8 [drm] dp_bridge_init+0xa8/0x15c [msm] msm_dp_modeset_init+0x28/0xc4 [msm] The DRM bridge implementation is clearly fragile and implicitly built on the assumption that bridges may never go away. In this case, the fix is to move the bridge registration in the pmic_glink_altmode driver to after all resources have been looked up. Incidentally, with the new dp-hpd bridge implementation, which registers child devices, this is also a requirement due to a long-standing issue in driver core that can otherwise lead to a probe deferral loop (see commit fbc35b45f9f6 ("Add documentation on meaning of -EPROBE_DEFER")). [DB: slightly fixed commit message by adding the word 'commit'] Fixes: 080b4e24852b ("soc: qcom: pmic_glink: Introduce altmode support") Fixes: 2bcca96abfbf ("soc: qcom: pmic-glink: switch to DRM_AUX_HPD_BRIDGE") Cc: <stable@xxxxxxxxxxxxxxx> # 6.3 Cc: Bjorn Andersson <andersson@xxxxxxxxxx> Cc: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx> Signed-off-by: Johan Hovold <johan+linaro@xxxxxxxxxx> Reviewed-by: Bjorn Andersson <andersson@xxxxxxxxxx> Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx> Link: https://patchwork.freedesktop.org/patch/msgid/20240217150228.5788-4-johan+linaro@xxxxxxxxxx diff --git a/drivers/soc/qcom/pmic_glink_altmode.c b/drivers/soc/qcom/pmic_glink_altmode.c index 5fcd0fdd2faa..b3808fc24c69 100644 --- a/drivers/soc/qcom/pmic_glink_altmode.c +++ b/drivers/soc/qcom/pmic_glink_altmode.c @@ -76,7 +76,7 @@ struct pmic_glink_altmode_port { struct work_struct work; - struct device *bridge; + struct auxiliary_device *bridge; enum typec_orientation orientation; u16 svid; @@ -230,7 +230,7 @@ static void pmic_glink_altmode_worker(struct work_struct *work) else pmic_glink_altmode_enable_usb(altmode, alt_port); - drm_aux_hpd_bridge_notify(alt_port->bridge, + drm_aux_hpd_bridge_notify(&alt_port->bridge->dev, alt_port->hpd_state ? connector_status_connected : connector_status_disconnected); @@ -454,7 +454,7 @@ static int pmic_glink_altmode_probe(struct auxiliary_device *adev, alt_port->index = port; INIT_WORK(&alt_port->work, pmic_glink_altmode_worker); - alt_port->bridge = drm_dp_hpd_bridge_register(dev, to_of_node(fwnode)); + alt_port->bridge = devm_drm_dp_hpd_bridge_alloc(dev, to_of_node(fwnode)); if (IS_ERR(alt_port->bridge)) { fwnode_handle_put(fwnode); return PTR_ERR(alt_port->bridge); @@ -510,6 +510,16 @@ static int pmic_glink_altmode_probe(struct auxiliary_device *adev, } } + for (port = 0; port < ARRAY_SIZE(altmode->ports); port++) { + alt_port = &altmode->ports[port]; + if (!alt_port->bridge) + continue; + + ret = devm_drm_dp_hpd_bridge_add(dev, alt_port->bridge); + if (ret) + return ret; + } + altmode->client = devm_pmic_glink_register_client(dev, altmode->owner_id, pmic_glink_altmode_callback,
