[CPUFREQ] Fix use after free on governor restore
Currently on governer backup/restore path we storing governor's pointer.
This is wrong because one may unload governor's module after cpu goes
offline. As result use-after-free will take place on restored cpu.
It is not easy to exploit this bug, but still we have to close this
issue ASAP. Issue was introduced by following commit
084f34939424161669467c19280dbcf637730314
##TESTCASE##
#!/bin/sh -x
modprobe acpi_cpufreq
# Any non default governor, in may case it is "ondemand"
modprobe cpufreq_ondemand
echo ondemand > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
rmmod acpi_cpufreq
rmmod cpufreq_ondemand
modprobe acpi_cpufreq # << use-after-free here.
Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: Dave Jones <davej@redhat.com>
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 3938c78..dab1410 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -41,7 +41,7 @@
static DEFINE_PER_CPU(struct cpufreq_policy *, cpufreq_cpu_data);
#ifdef CONFIG_HOTPLUG_CPU
/* This one keeps track of the previously set governor of a removed CPU */
-static DEFINE_PER_CPU(struct cpufreq_governor *, cpufreq_cpu_governor);
+static DEFINE_PER_CPU(char[CPUFREQ_NAME_LEN], cpufreq_cpu_governor);
#endif
static DEFINE_SPINLOCK(cpufreq_driver_lock);
@@ -774,10 +774,12 @@
#ifdef CONFIG_SMP
unsigned long flags;
unsigned int j;
-
#ifdef CONFIG_HOTPLUG_CPU
- if (per_cpu(cpufreq_cpu_governor, cpu)) {
- policy->governor = per_cpu(cpufreq_cpu_governor, cpu);
+ struct cpufreq_governor *gov;
+
+ gov = __find_governor(per_cpu(cpufreq_cpu_governor, cpu));
+ if (gov) {
+ policy->governor = gov;
dprintk("Restoring governor %s for cpu %d\n",
policy->governor->name, cpu);
}
@@ -1111,7 +1113,8 @@
#ifdef CONFIG_SMP
#ifdef CONFIG_HOTPLUG_CPU
- per_cpu(cpufreq_cpu_governor, cpu) = data->governor;
+ strncpy(per_cpu(cpufreq_cpu_governor, cpu), data->governor->name,
+ CPUFREQ_NAME_LEN);
#endif
/* if we have other CPUs still registered, we need to unlink them,
@@ -1135,7 +1138,8 @@
continue;
dprintk("removing link for cpu %u\n", j);
#ifdef CONFIG_HOTPLUG_CPU
- per_cpu(cpufreq_cpu_governor, j) = data->governor;
+ strncpy(per_cpu(cpufreq_cpu_governor, j),
+ data->governor->name, CPUFREQ_NAME_LEN);
#endif
cpu_sys_dev = get_cpu_sysdev(j);
sysfs_remove_link(&cpu_sys_dev->kobj, "cpufreq");
