[PATCH] drm/i915/hwmon: Get rid of devm

[Ashutosh Dixit]

When both hwmon and hwmon drvdata (on which hwmon depends) are device
managed resources, the expectation, on device unbind, is that hwmon will be
released before the drvdata. However, it appears devres does not do this
consistently, so that we occasionally see drvdata being released before
hwmon itself. This results in a uaf if hwmon sysfs is accessed during
device unbind.

The only way out of this seems to be do get rid of devm_ and release/free
everything explicitly during device unbind.

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/10366
Signed-off-by: Ashutosh Dixit <ashutosh.dixit at intel.com>
---
 drivers/gpu/drm/i915/i915_hwmon.c | 46 ++++++++++++++++++++++++-------
 1 file changed, 36 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_hwmon.c b/drivers/gpu/drm/i915/i915_hwmon.c
index 8c3f443c8347..5f6022b148d7 100644
--- a/drivers/gpu/drm/i915/i915_hwmon.c
+++ b/drivers/gpu/drm/i915/i915_hwmon.c
@@ -792,7 +792,7 @@ void i915_hwmon_register(struct drm_i915_private *i915)
 	if (!IS_DGFX(i915))
 		return;
 
-	hwmon = devm_kzalloc(dev, sizeof(*hwmon), GFP_KERNEL);
+	hwmon = kzalloc(sizeof(*hwmon), GFP_KERNEL);
 	if (!hwmon)
 		return;
 
@@ -818,10 +818,10 @@ void i915_hwmon_register(struct drm_i915_private *i915)
 	hwm_get_preregistration_info(i915);
 
 	/*  hwmon_dev points to device hwmon<i> */
-	hwmon_dev = devm_hwmon_device_register_with_info(dev, ddat->name,
-							 ddat,
-							 &hwm_chip_info,
-							 hwm_groups);
+	hwmon_dev = hwmon_device_register_with_info(dev, ddat->name,
+						    ddat,
+						    &hwm_chip_info,
+						    hwm_groups);
 	if (IS_ERR(hwmon_dev)) {
 		i915->hwmon = NULL;
 		return;
@@ -838,10 +838,10 @@ void i915_hwmon_register(struct drm_i915_private *i915)
 		if (!hwm_gt_is_visible(ddat_gt, hwmon_energy, hwmon_energy_input, 0))
 			continue;
 
-		hwmon_dev = devm_hwmon_device_register_with_info(dev, ddat_gt->name,
-								 ddat_gt,
-								 &hwm_gt_chip_info,
-								 NULL);
+		hwmon_dev = hwmon_device_register_with_info(dev, ddat_gt->name,
+							    ddat_gt,
+							    &hwm_gt_chip_info,
+							    NULL);
 		if (!IS_ERR(hwmon_dev))
 			ddat_gt->hwmon_dev = hwmon_dev;
 	}
@@ -849,5 +849,31 @@ void i915_hwmon_register(struct drm_i915_private *i915)
 
 void i915_hwmon_unregister(struct drm_i915_private *i915)
 {
-	fetch_and_zero(&i915->hwmon);
+	struct i915_hwmon *hwmon;
+	struct hwm_drvdata *ddat;
+	struct intel_gt *gt;
+	int i;
+
+	hwmon = fetch_and_zero(&i915->hwmon);
+	if (!hwmon)
+		return;
+
+	ddat = &hwmon->ddat;
+
+	for_each_gt(gt, i915, i) {
+		struct hwm_drvdata *ddat_gt;
+
+		ddat_gt = hwmon->ddat_gt + i;
+
+		if (ddat_gt->hwmon_dev) {
+			hwmon_device_unregister(ddat_gt->hwmon_dev);
+			ddat_gt->hwmon_dev = NULL;
+		}
+	}
+
+	if (ddat->hwmon_dev)
+		hwmon_device_unregister(ddat->hwmon_dev);
+
+	mutex_destroy(&hwmon->hwmon_lock);
+	kfree(hwmon);
 }
-- 
2.41.0