[PATCH v4 3/4] phy: qcom: qmp-usb-legacy: Fix possible NULL-deref on early runtime suspend

[Loic Poulain <loic.poulain@oss.qualcomm.com>]

Runtime PM has to be enabled before creating the PHY, since phy_create()
only enables runtime PM on the PHY device if it is already enabled on
this parent device. However, the runtime suspend/resume callbacks
dereference the qmp->phy pointer, which is only assigned by
devm_phy_create(), later in probe:
        `if (!qmp->phy->init_count) {`

There is thus a small window where the callback may run after
pm_runtime_enable() but before qmp->phy is set, dereferencing a NULL
pointer. This can also happen if user re-enables runtime-pm via the
sysfs attribute before qmp phy is initialized.

Take a runtime PM usage reference with pm_runtime_get_noresume() before
enabling runtime PM and release it once qmp->phy has been created, so
that no runtime suspend can run while the phy pointer is still
uninitialized.

Fixes: e464a3180a43 ("phy: qcom-qmp-usb: split off the legacy USB+dp_com support")
Reviewed-by: Abel Vesa <abel.vesa@oss.qualcomm.com>
Signed-off-by: Loic Poulain <loic.poulain@oss.qualcomm.com>
---
 drivers/phy/qualcomm/phy-qcom-qmp-usb-legacy.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/drivers/phy/qualcomm/phy-qcom-qmp-usb-legacy.c b/drivers/phy/qualcomm/phy-qcom-qmp-usb-legacy.c
index 8bf951b0490cfd811635df8940de1b789e21b46c..8b91eec0b5eee0c76b64e2c2b7a15f0169ce4b09 100644
--- a/drivers/phy/qualcomm/phy-qcom-qmp-usb-legacy.c
+++ b/drivers/phy/qualcomm/phy-qcom-qmp-usb-legacy.c
@@ -1277,10 +1277,16 @@ static int qmp_usb_legacy_probe(struct platform_device *pdev)
 	if (ret)
 		goto err_node_put;
 
+	/*
+	 * Enable runtime PM before creating the PHY, phy_create() only enables
+	 * it on the PHY device if already enabled on the parent. Hold a usage
+	 * reference so callbacks cannot run before qmp->phy is assigned.
+	 */
+	pm_runtime_get_noresume(dev);
 	pm_runtime_set_active(dev);
 	ret = devm_pm_runtime_enable(dev);
 	if (ret)
-		goto err_node_put;
+		goto err_pm_put;
 	/*
 	 * Prevent runtime pm from being ON by default. Users can enable
 	 * it using power/control in sysfs.
@@ -1289,23 +1295,27 @@ static int qmp_usb_legacy_probe(struct platform_device *pdev)
 
 	ret = phy_pipe_clk_register(qmp, np);
 	if (ret)
-		goto err_node_put;
+		goto err_pm_put;
 
 	qmp->phy = devm_phy_create(dev, np, &qmp_usb_legacy_phy_ops);
 	if (IS_ERR(qmp->phy)) {
 		ret = PTR_ERR(qmp->phy);
 		dev_err(dev, "failed to create PHY: %d\n", ret);
-		goto err_node_put;
+		goto err_pm_put;
 	}
 
 	phy_set_drvdata(qmp->phy, qmp);
 
+	pm_runtime_put(dev);
+
 	of_node_put(np);
 
 	phy_provider = devm_of_phy_provider_register(dev, of_phy_simple_xlate);
 
 	return PTR_ERR_OR_ZERO(phy_provider);
 
+err_pm_put:
+	pm_runtime_put_noidle(dev);
 err_node_put:
 	of_node_put(np);
 	return ret;

-- 
2.34.1