linux-kernel - [PATCH] powercap: DTPM: Fix reference leak in cpuhp_dtpm_cpu

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Date:   Fri, 10 Dec 2021 15:28:58 +0800
From:   Jianglei Nie <niejianglei2021@....com>
To:     daniel.lezcano@...nel.org, rafael@...nel.org
Cc:     linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jianglei Nie <niejianglei2021@....com>
Subject: [PATCH] powercap: DTPM: Fix reference leak in cpuhp_dtpm_cpu_offline()

In line 153 (#1), cpufreq_cpu_get() increments the kobject reference
counter of the policy it returned on success. According to the
document, the policy returned by cpufreq_cpu_get() has to be
released with the help of cpufreq_cpu_put() to balance its kobject
reference counter properly. Forgetting the cpufreq_cpu_put()
operation will result in reference leak.This bug influences all
stable versions from v5.15 to v5.15.7.

We can fix it by calling cpufreq_cpu_put() before the function
returns (#2, #3 and #4).

147 static int cpuhp_dtpm_cpu_offline(unsigned int cpu)
148 {
153     policy = cpufreq_cpu_get(cpu);
        // #1: reference increment

155     if (!policy)
156         return 0;

158     pd = em_cpu_get(cpu);
159     if (!pd)
160         return -EINVAL; // #2: missing reference decrement

166     if (cpumask_weight(policy->cpus) != 1)
167         return 0; // #3: missing reference decrement

174     return 0; // #4: missing reference decrement
175 }

Signed-off-by: Jianglei Nie <niejianglei2021@....com>
---
 drivers/powercap/dtpm_cpu.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/powercap/dtpm_cpu.c b/drivers/powercap/dtpm_cpu.c
index 51c366938acd..6c94515b21ef 100644
--- a/drivers/powercap/dtpm_cpu.c
+++ b/drivers/powercap/dtpm_cpu.c
@@ -156,21 +156,25 @@ static int cpuhp_dtpm_cpu_offline(unsigned int cpu)
 		return 0;
 
 	pd = em_cpu_get(cpu);
-	if (!pd)
+	if (!pd) {
+		cpufreq_cpu_put(policy);
 		return -EINVAL;
+	}
 
 	dtpm = per_cpu(dtpm_per_cpu, cpu);
 
 	power_sub(dtpm, pd);
 
-	if (cpumask_weight(policy->cpus) != 1)
+	if (cpumask_weight(policy->cpus) != 1) {
+		cpufreq_cpu_put(policy);
 		return 0;
+	}
 
 	for_each_cpu(cpu, policy->related_cpus)
 		per_cpu(dtpm_per_cpu, cpu) = NULL;
 
 	dtpm_unregister(dtpm);
-
+	cpufreq_cpu_put(policy);
 	return 0;
 }
 
-- 
2.25.1