If arch/x86/kernel/cpuid.c is a module, a CPU might offline or online
between the for_each_online_cpu() loop and the call to
register_hotcpu_notifier in cpuid_init or the call to
unregister_hotcpu_notifier in cpuid_exit. The potential races can
lead to leaks/duplicates, attempts to destroy non-existant devices, or
random pointer dereferences.
For example, in cpuid_exit if:
for_each_online_cpu(cpu)
cpuid_device_destroy(cpu);
class_destroy(cpuid_class);
__unregister_chrdev(CPUID_MAJOR, 0, NR_CPUS, "cpu/cpuid");
<----- CPU onlines
unregister_hotcpu_notifier(&cpuid_class_cpu_notifier);
the hotcpu notifier will attempt to create a device for the
cpuid_class, which the module already destroyed.
This fix surrounds for_each_online_cpu and register_hotcpu_notifier or
unregister_hotcpu_notifier with get_online_cpus+put_online_cpus.
Tested on a VM.
Signed-off-by: Silas Boyd-Wickizer <[email protected]>
---
arch/x86/kernel/cpuid.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/arch/x86/kernel/cpuid.c b/arch/x86/kernel/cpuid.c
index 39472dd..60c7891 100644
--- a/arch/x86/kernel/cpuid.c
+++ b/arch/x86/kernel/cpuid.c
@@ -199,12 +199,14 @@ static int __init cpuid_init(void)
goto out_chrdev;
}
cpuid_class->devnode = cpuid_devnode;
+ get_online_cpus();
for_each_online_cpu(i) {
err = cpuid_device_create(i);
if (err != 0)
goto out_class;
}
register_hotcpu_notifier(&cpuid_class_cpu_notifier);
+ put_online_cpus();
err = 0;
goto out;
@@ -214,6 +216,7 @@ out_class:
for_each_online_cpu(i) {
cpuid_device_destroy(i);
}
+ put_online_cpus();
class_destroy(cpuid_class);
out_chrdev:
__unregister_chrdev(CPUID_MAJOR, 0, NR_CPUS, "cpu/cpuid");
@@ -225,11 +228,13 @@ static void __exit cpuid_exit(void)
{
int cpu = 0;
+ get_online_cpus();
for_each_online_cpu(cpu)
cpuid_device_destroy(cpu);
class_destroy(cpuid_class);
__unregister_chrdev(CPUID_MAJOR, 0, NR_CPUS, "cpu/cpuid");
unregister_hotcpu_notifier(&cpuid_class_cpu_notifier);
+ put_online_cpus();
}
module_init(cpuid_init);
--
1.7.10.4
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