linux-kernel - Re: [PATCH v2] cpufreq/pasemi: fix an use-after-free in pas_cpufreq_cpu

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Message-ID: <20190708074432.56q2e3ig5ehiee5f@vireshk-i7>
Date:   Mon, 8 Jul 2019 13:14:32 +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 v2] cpufreq/pasemi: fix an use-after-free in
 pas_cpufreq_cpu_init()

On 08-07-19, 15:19, 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
> ---
> v2: clean up the code according to the advice of viresh.
> 
>  drivers/cpufreq/pasemi-cpufreq.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/cpufreq/pasemi-cpufreq.c b/drivers/cpufreq/pasemi-cpufreq.c
> index 6b1e4ab..c6d464b 100644
> --- a/drivers/cpufreq/pasemi-cpufreq.c
> +++ b/drivers/cpufreq/pasemi-cpufreq.c
> @@ -128,20 +128,18 @@ static int pas_cpufreq_cpu_init(struct cpufreq_policy *policy)
>  	int cur_astate, idx;
>  	struct resource res;
>  	struct device_node *cpu, *dn;
> -	int err = -ENODEV;
> +	int err;
>  
>  	cpu = of_get_cpu_node(policy->cpu, NULL);
> -
> -	of_node_put(cpu);
>  	if (!cpu)
> -		goto out;
> +		return -ENODEV;
>  


>  	dn = of_find_compatible_node(NULL, NULL, "1682m-sdc");
>  	if (!dn)
>  		dn = of_find_compatible_node(NULL, NULL,
>  					     "pasemi,pwrficient-sdc");
>  	if (!dn)
> -		goto out;
> +		return -ENODEV;

This change looks incorrect. You still need to drop reference to cpu ?

>  	err = of_address_to_resource(dn, 0, &res);
>  	of_node_put(dn);
>  	if (err)
> @@ -196,6 +194,7 @@ static int pas_cpufreq_cpu_init(struct cpufreq_policy *policy)
>  	policy->cur = pas_freqs[cur_astate].frequency;
>  	ppc_proc_freq = policy->cur * 1000ul;
>  
> +	of_node_put(cpu);
>  	return cpufreq_generic_init(policy, pas_freqs, get_gizmo_latency());
>  
>  out_unmap_sdcpwr:
> @@ -204,6 +203,7 @@ static int pas_cpufreq_cpu_init(struct cpufreq_policy *policy)
>  out_unmap_sdcasr:
>  	iounmap(sdcasr_mapbase);
>  out:
> +	of_node_put(cpu);
>  	return err;
>  }
>  
> -- 
> 2.9.5

-- 
viresh