linux-kernel - Re: [PATCH] cpufreq/pasemi: fix an use-after-free in pas_cpufreq_cpu

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Date:   Mon, 8 Jul 2019 11:57:08 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Wen Yang <wen.yang99@....com.cn>
Cc:     linux-kernel@...r.kernel.org, xue.zhihong@....com.cn,
        wang.yi59@....com.cn, cheng.shengyu@....com.cn,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        linuxppc-dev@...ts.ozlabs.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH] cpufreq/pasemi: fix an use-after-free in
 pas_cpufreq_cpu_init()

On 08-07-19, 14:19, Wen Yang wrote:
> The cpu variable is still being used in the of_get_property() call
> after the of_node_put() call, which may result in use-after-free.
> 
> Fixes: a9acc26b75f ("cpufreq/pasemi: fix possible object reference leak")
> Signed-off-by: Wen Yang <wen.yang99@....com.cn>
> Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
> Cc: Viresh Kumar <viresh.kumar@...aro.org>
> Cc: linuxppc-dev@...ts.ozlabs.org
> Cc: linux-pm@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> ---
>  drivers/cpufreq/pasemi-cpufreq.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)

I will suggest some changes here.

> diff --git a/drivers/cpufreq/pasemi-cpufreq.c b/drivers/cpufreq/pasemi-cpufreq.c
> index 6b1e4ab..d2dd47b 100644
> --- a/drivers/cpufreq/pasemi-cpufreq.c
> +++ b/drivers/cpufreq/pasemi-cpufreq.c
> @@ -132,7 +132,6 @@ static int pas_cpufreq_cpu_init(struct cpufreq_policy *policy)

Don't initialize "err" anymore.

>  	cpu = of_get_cpu_node(policy->cpu, NULL);
>  
> -	of_node_put(cpu);
>  	if (!cpu)
>  		goto out;

Do return -ENODEV; here.

>  
> @@ -141,15 +140,15 @@ static int pas_cpufreq_cpu_init(struct cpufreq_policy *policy)
>  		dn = of_find_compatible_node(NULL, NULL,
>  					     "pasemi,pwrficient-sdc");
>  	if (!dn)
> -		goto out;
> +		goto out_put_cpu_node;
>  	err = of_address_to_resource(dn, 0, &res);
>  	of_node_put(dn);
>  	if (err)
> -		goto out;
> +		goto out_put_cpu_node;
>  	sdcasr_mapbase = ioremap(res.start + SDCASR_OFFSET, 0x2000);
>  	if (!sdcasr_mapbase) {
>  		err = -EINVAL;
> -		goto out;
> +		goto out_put_cpu_node;
>  	}

Don't do above changes.

>  
>  	dn = of_find_compatible_node(NULL, NULL, "1682m-gizmo");
> @@ -177,6 +176,7 @@ static int pas_cpufreq_cpu_init(struct cpufreq_policy *policy)
>  		err = -EINVAL;
>  		goto out_unmap_sdcpwr;
>  	}
> +	of_node_put(cpu);
>  
>  	/* we need the freq in kHz */
>  	max_freq = *max_freqp / 1000;
> @@ -203,6 +203,8 @@ static int pas_cpufreq_cpu_init(struct cpufreq_policy *policy)
>  
>  out_unmap_sdcasr:
>  	iounmap(sdcasr_mapbase);
> +out_put_cpu_node:

Don't add this label, instead use "out" for also having the below
code.

> +	of_node_put(cpu);
>  out:
>  	return err;
>  }
> -- 
> 2.9.5

-- 
viresh