linux-kernel - Re: [RESEND PATCH] cpufreq: unnecesary double free in pcc_cpufreq_do

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Date:	Fri, 01 Oct 2010 07:47:23 +0300
From:	Pekka Enberg <penberg@...nel.org>
To:	Dave Jones <davej@...hat.com>, dave@....org,
	cpufreq@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	x86 maintainers <x86@...nel.org>
Subject: Re: [RESEND PATCH] cpufreq: unnecesary double free in pcc_cpufreq_do_osc

  Hi Dave,

On 30.9.2010 23.06, Dave Jones wrote:
> On Thu, Sep 30, 2010 at 10:59:51PM +0300, Pekka Enberg wrote:
>   >  >  +++ b/arch/x86/kernel/cpu/cpufreq/pcc-cpufreq.c
>   >  >  @@ -379,6 +379,8 @@ static int __init pcc_cpufreq_do_osc(acpi_handle *handle)
>   >  >          if (!(supported&  0x1))
>   >  >                  return -ENODEV;
>   >  >
>   >  >  +       return ret;
>   >  >  +
>   >  >    out_free:
>   >  >          kfree(output.pointer);
>   >  >          return ret;
>   >
>   >  Where is the double free here? I can't see it. I do see memory leaks
>   >  happening in error handling paths of pcc_cpufreq_do_osc() which makes
>   >  me think we need something like the attached patch.
>
> I think Dave's patch is correct.  There's a kfree(output.pointer) at line 359.
> If we fall all the way through without hitting any of the return -ENODEVs,
> we end up doing a 2nd kfree in the out_free:

There's a second call to acpi_evaluate_object() which takes "output" as 
its argument and allocates more memory.
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