linux-kernel - [PATCH V4 01/17] thermal: cpu_cooling: Avoid accessing potentially freed structures

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Message-Id: <b75219c6511ff0cf9a4c9c7603091286b803ae22.1493115651.git.viresh.kumar@linaro.org>
Date:   Tue, 25 Apr 2017 15:57:08 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Javi Merino <javi.merino@...nel.org>,
        Zhang Rui <rui.zhang@...el.com>,
        Eduardo Valentin <edubezval@...il.com>,
        Lukasz Luba <lukasz.luba@....com>,
        Amit Daniel Kachhap <amit.kachhap@...il.com>,
        Viresh Kumar <viresh.kumar@...aro.org>
Cc:     linaro-kernel@...ts.linaro.org, Rafael Wysocki <rjw@...ysocki.net>,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Punit Agrawal <punit.agrawal@....com>,
        "4 . 2+" <stable@...r.kernel.org>
Subject: [PATCH V4 01/17] thermal: cpu_cooling: Avoid accessing potentially freed structures

After the lock is dropped, it is possible that the cpufreq_dev gets
freed before we call get_level() and that can cause kernel to crash.

Drop the lock after we are done using the structure.

Cc: 4.2+ <stable@...r.kernel.org> # 4.2+
Fixes: 02373d7c69b4 ("thermal: cpu_cooling: fix lockdep problems in cpu_cooling")
Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
Tested-by: Lukasz Luba <lukasz.luba@....com>
---
 drivers/thermal/cpu_cooling.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/thermal/cpu_cooling.c b/drivers/thermal/cpu_cooling.c
index 69d0f430b2d1..be29489dd247 100644
--- a/drivers/thermal/cpu_cooling.c
+++ b/drivers/thermal/cpu_cooling.c
@@ -153,8 +153,10 @@ unsigned long cpufreq_cooling_get_level(unsigned int cpu, unsigned int freq)
 	mutex_lock(&cooling_list_lock);
 	list_for_each_entry(cpufreq_dev, &cpufreq_dev_list, node) {
 		if (cpumask_test_cpu(cpu, &cpufreq_dev->allowed_cpus)) {
+			unsigned long level = get_level(cpufreq_dev, freq);
+
 			mutex_unlock(&cooling_list_lock);
-			return get_level(cpufreq_dev, freq);
+			return level;
 		}
 	}
 	mutex_unlock(&cooling_list_lock);
-- 
2.12.0.432.g71c3a4f4ba37