[PATCH v2] drivers: thermal: int340x_thermal: Fix sysfs race condition

From: Aaron Hill <aa1ronham@gmail.com>
To: linux-pm@vger.kernel.org
Cc: Zhang Rui <rui.zhang@intel.com>,
	Eduardo Valentin <edubezval@gmail.com>,
	Daniel Lezcano <daniel.lezcano@linaro.org>,
	linux-kernel@vger.kernel.org
Subject: [PATCH v2] drivers: thermal: int340x_thermal: Fix sysfs race condition
Date: Mon, 24 Dec 2018 14:23:36 -0500	[thread overview]
Message-ID: <20181224192336.GA6057@ArchLaptop> (raw)

Changes since V1:
* Use dev_info instead of printk
* Use dev_warn instead of BUG_ON

Previously, sysfs_create_group was called before all initialization had
fully run - specifically, before pci_set_drvdata was called. Since the
sysctl group is visible to userspace as soon as sysfs_create_group
returns, a small window of time existed during which a process could read
from an uninitialized/partially-initialized device.

This commit moves the creation of the sysctl group to after all
initialized is completed. This ensures that it's impossible for
userspace to read from a sysctl file before initialization has fully
completed.

To catch any future regressions, I've added a check to ensure
that proc_thermal_emum_mode is never PROC_THERMAL_NONE when a process
tries to read from a sysctl file. Previously, the aforementioned race
condition could result in the 'else' branch
running while PROC_THERMAL_NONE was set,
leading to a null pointer deference.

Signed-off-by: Aaron Hill <aa1ronham@gmail.com>
---
 .../processor_thermal_device.c                | 28 ++++++++++---------
 1 file changed, 15 insertions(+), 13 deletions(-)

diff --git a/drivers/thermal/int340x_thermal/processor_thermal_device.c b/drivers/thermal/int340x_thermal/processor_thermal_device.c
index 284cf2c5a8fd..0a43dbf0131b 100644
--- a/drivers/thermal/int340x_thermal/processor_thermal_device.c
+++ b/drivers/thermal/int340x_thermal/processor_thermal_device.c
@@ -81,10 +81,15 @@ static ssize_t power_limit_##index##_##suffix##_show(struct device *dev, \
 					struct device_attribute *attr, \
 					char *buf) \
 { \
+	if (proc_thermal_emum_mode == PROC_THERMAL_NONE) { \
+		dev_warn(dev, "Attempted to get power limit before device was initialized!\n"); \
+		return 0; \
+	} \
+	\
 	struct pci_dev *pci_dev; \
 	struct platform_device *pdev; \
 	struct proc_thermal_device *proc_dev; \
-\
+	\
 	if (proc_thermal_emum_mode == PROC_THERMAL_PLATFORM_DEV) { \
 		pdev = to_platform_device(dev); \
 		proc_dev = platform_get_drvdata(pdev); \
@@ -298,11 +303,6 @@ static int proc_thermal_add(struct device *dev,
 	*priv = proc_priv;
 
 	ret = proc_thermal_read_ppcc(proc_priv);
-	if (!ret) {
-		ret = sysfs_create_group(&dev->kobj,
-					 &power_limit_attribute_group);
-
-	}
 	if (ret)
 		return ret;
 
@@ -316,8 +316,7 @@ static int proc_thermal_add(struct device *dev,
 
 	proc_priv->int340x_zone = int340x_thermal_zone_add(adev, ops);
 	if (IS_ERR(proc_priv->int340x_zone)) {
-		ret = PTR_ERR(proc_priv->int340x_zone);
-		goto remove_group;
+		return PTR_ERR(proc_priv->int340x_zone);
 	} else
 		ret = 0;
 
@@ -331,9 +330,6 @@ static int proc_thermal_add(struct device *dev,
 
 remove_zone:
 	int340x_thermal_zone_remove(proc_priv->int340x_zone);
-remove_group:
-	sysfs_remove_group(&proc_priv->dev->kobj,
-			   &power_limit_attribute_group);
 
 	return ret;
 }
@@ -364,7 +360,10 @@ static int int3401_add(struct platform_device *pdev)
 	platform_set_drvdata(pdev, proc_priv);
 	proc_thermal_emum_mode = PROC_THERMAL_PLATFORM_DEV;
 
-	return 0;
+	dev_info(&pdev->dev, "Creating sysfs group for PROC_THERMAL_PLATFORM_DEV\n");
+
+	return sysfs_create_group(&pdev->dev.kobj,
+					 &power_limit_attribute_group);
 }
 
 static int int3401_remove(struct platform_device *pdev)
@@ -441,7 +440,10 @@ static int  proc_thermal_pci_probe(struct pci_dev *pdev,
 			dev_err(&pdev->dev, "No auxiliary DTSs enabled\n");
 	}
 
-	return 0;
+	dev_info(&pdev->dev, "Creating sysfs group for PROC_THERMAL_PCI\n");
+
+	return sysfs_create_group(&pdev->dev.kobj,
+					 &power_limit_attribute_group);
 }
 
 static void  proc_thermal_pci_remove(struct pci_dev *pdev)
-- 
2.20.1

