Re: [Xen-devel] [PATCH] x86/xen: avoid freeing static 'name' when kasprintf() fails

[Laszlo Ersek <lersek@xxxxxxxxxx>]

On 01/05/15 14:19, David Vrabel wrote:
> On 05/01/15 13:06, Vitaly Kuznetsov wrote:
>> In case kasprintf() fails in xen_setup_timer() we assign name to the static
>> string "<timer kasprintf failed>". We, however, don't check that fact before
>> issuing kfree() in xen_teardown_timer(), kernel is supposed to crash with
>> 'kernel BUG at mm/slub.c:3341!'
>>
>> Solve the issue by making name a fixed length string inside struct
>> xen_clock_event_device. 16 bytes should be enough.
>>
>> The issue was discovered by Laszlo Ersek.
> 
> Add Reported-by: Laszlo ... tag perhaps?
> 
>> --- a/arch/x86/xen/time.c
>> +++ b/arch/x86/xen/time.c
>> @@ -391,7 +391,7 @@ static const struct clock_event_device *xen_clockevent =
>>  
>>  struct xen_clock_event_device {
>>      struct clock_event_device evt;
>> -    char *name;
>> +    char name[16];
>>  };
>>  static DEFINE_PER_CPU(struct xen_clock_event_device, xen_clock_events) = { 
>> .evt.irq = -1 };
>>  
>> @@ -420,14 +420,11 @@ void xen_teardown_timer(int cpu)
>>      if (evt->irq >= 0) {
>>              unbind_from_irqhandler(evt->irq, NULL);
>>              evt->irq = -1;
>> -            kfree(per_cpu(xen_clock_events, cpu).name);
>> -            per_cpu(xen_clock_events, cpu).name = NULL;
>>      }
>>  }
>>  
>>  void xen_setup_timer(int cpu)
>>  {
>> -    char *name;
>>      struct clock_event_device *evt;
> 
> struct xen_clock_event_device *xevt = ...;
> 
>>      int irq;
>>  
>> @@ -438,21 +435,19 @@ void xen_setup_timer(int cpu)
>>  
>>      printk(KERN_INFO "installing Xen timer for CPU %d\n", cpu);
>>  
>> -    name = kasprintf(GFP_KERNEL, "timer%d", cpu);
>> -    if (!name)
>> -            name = "<timer kasprintf failed>";
>> +    snprintf(per_cpu(xen_clock_events, cpu).name, 16, "timer%d", cpu);
> 
> Use sizeof(xevt->name) here.

Yes, I wanted to recommend sizeof too.

Also the "standard" Reported-by tag would be nice.

Thanks!
Laszlo


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