linux-kernel - [PATCH] cpufreq: s3c: avoid use after free issue in xxx_cpufreq_reboot_notifier

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Date:   Sat, 28 Dec 2019 14:43:59 +0800
From:   qiwuchen55@...il.com
To:     kgene@...nel.org, krzk@...nel.org, rjw@...ysocki.net,
        viresh.kumar@...aro.org
Cc:     linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, chenqiwu <chenqiwu@...omi.com>
Subject: [PATCH] cpufreq: s3c: avoid use after free issue in xxx_cpufreq_reboot_notifier_evt()

From: chenqiwu <chenqiwu@...omi.com>

There is a potential UAF issue in xxx_cpufreq_reboot_notifier_evt() that
the cpufreq policy of cpu0 has been released before using it. So we should
make a judgement to avoid it.

Signed-off-by: chenqiwu <chenqiwu@...omi.com>
---
 drivers/cpufreq/s3c2416-cpufreq.c | 11 ++++++++++-
 drivers/cpufreq/s5pv210-cpufreq.c | 10 +++++++++-
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/drivers/cpufreq/s3c2416-cpufreq.c b/drivers/cpufreq/s3c2416-cpufreq.c
index 1069103..0f576ba 100644
--- a/drivers/cpufreq/s3c2416-cpufreq.c
+++ b/drivers/cpufreq/s3c2416-cpufreq.c
@@ -304,6 +304,7 @@ static int s3c2416_cpufreq_reboot_notifier_evt(struct notifier_block *this,
 {
 	struct s3c2416_data *s3c_freq = &s3c2416_cpufreq;
 	int ret;
+	struct cpufreq_policy policy;
 
 	mutex_lock(&cpufreq_lock);
 
@@ -318,7 +319,15 @@ static int s3c2416_cpufreq_reboot_notifier_evt(struct notifier_block *this,
 	 */
 	if (s3c_freq->is_dvs) {
 		pr_debug("cpufreq: leave dvs on reboot\n");
-		ret = cpufreq_driver_target(cpufreq_cpu_get(0), FREQ_SLEEP, 0);
+
+		memset(&policy, 0, sizeof(policy));
+		ret = cpufreq_get_policy(&policy, 0);
+		if (ret < 0) {
+			pr_debug("cpufreq: get no policy for cpu0\n");
+			return NOTIFY_BAD;
+		}
+
+		ret = cpufreq_driver_target(&policy, FREQ_SLEEP, 0);
 		if (ret < 0)
 			return NOTIFY_BAD;
 	}
diff --git a/drivers/cpufreq/s5pv210-cpufreq.c b/drivers/cpufreq/s5pv210-cpufreq.c
index 5d10030..d99b4b1 100644
--- a/drivers/cpufreq/s5pv210-cpufreq.c
+++ b/drivers/cpufreq/s5pv210-cpufreq.c
@@ -555,8 +555,16 @@ static int s5pv210_cpufreq_reboot_notifier_event(struct notifier_block *this,
 						 unsigned long event, void *ptr)
 {
 	int ret;
+	struct cpufreq_policy *policy;
 
-	ret = cpufreq_driver_target(cpufreq_cpu_get(0), SLEEP_FREQ, 0);
+	policy = cpufreq_cpu_get(0);
+	if (!policy) {
+		pr_debug("cpufreq: get no policy for cpu0\n");
+		return NOTIFY_BAD;
+	}
+
+	ret = cpufreq_driver_target(policy, SLEEP_FREQ, 0);
+	cpufreq_cpu_put(policy);
 	if (ret < 0)
 		return NOTIFY_BAD;
 
-- 
1.9.1