If arch/x86/kernel/msr.c is a module, a CPU might offline or online
between the for_each_online_cpu(i) loop and the call to
register_hotcpu_notifier in msr_init or the call to
unregister_hotcpu_notifier in msr_exit. The potential races can lead
to leaks/duplicates, attempts to destroy non-existant devices, or
random pointer dereferences.
For example, in msr_init if:
for_each_online_cpu(i) {
err = msr_device_create(i);
if (err != 0)
goto out_class;
}
<----- CPU offlines
register_hotcpu_notifier(&msr_class_cpu_notifier);
and the CPU never onlines before msr_exit, then the module will never
call msr_device_destroy for the associated CPU.
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/msr.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/arch/x86/kernel/msr.c b/arch/x86/kernel/msr.c
index eb11369..a7c5661 100644
--- a/arch/x86/kernel/msr.c
+++ b/arch/x86/kernel/msr.c
@@ -257,12 +257,14 @@ static int __init msr_init(void)
goto out_chrdev;
}
msr_class->devnode = msr_devnode;
+ get_online_cpus();
for_each_online_cpu(i) {
err = msr_device_create(i);
if (err != 0)
goto out_class;
}
register_hotcpu_notifier(&msr_class_cpu_notifier);
+ put_online_cpus();
err = 0;
goto out;
@@ -271,6 +273,7 @@ out_class:
i = 0;
for_each_online_cpu(i)
msr_device_destroy(i);
+ put_online_cpus();
class_destroy(msr_class);
out_chrdev:
__unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr");
@@ -281,11 +284,13 @@ out:
static void __exit msr_exit(void)
{
int cpu = 0;
+ get_online_cpus();
for_each_online_cpu(cpu)
msr_device_destroy(cpu);
class_destroy(msr_class);
__unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr");
unregister_hotcpu_notifier(&msr_class_cpu_notifier);
+ put_online_cpus();
}
module_init(msr_init);
--
1.7.10.4
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