linux-kernel - Re: [PATCH v5] cpufreq/pasemi: fix an use-after-free in pas_cpufreq_cpu

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Message-ID: <20190709081205.a5sjsqo2el6zt24b@vireshk-i7>
Date:   Tue, 9 Jul 2019 13:42:05 +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>,
        Michael Ellerman <mpe@...erman.id.au>,
        linuxppc-dev@...ts.ozlabs.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH v5] cpufreq/pasemi: fix an use-after-free in
 pas_cpufreq_cpu_init()

On 09-07-19, 16:04, 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: Michael Ellerman <mpe@...erman.id.au>
> Cc: linuxppc-dev@...ts.ozlabs.org
> Cc: linux-pm@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> ---
> v5: put together the code to get, use, and release cpu device_node.
> v4: restore the blank line.
> v3: fix a leaked reference.
> v2: clean up the code according to the advice of viresh.
> 
>  drivers/cpufreq/pasemi-cpufreq.c | 21 +++++++++------------
>  1 file changed, 9 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/cpufreq/pasemi-cpufreq.c b/drivers/cpufreq/pasemi-cpufreq.c
> index 6b1e4ab..1f0beb7 100644
> --- a/drivers/cpufreq/pasemi-cpufreq.c
> +++ b/drivers/cpufreq/pasemi-cpufreq.c
> @@ -131,10 +131,17 @@ static int pas_cpufreq_cpu_init(struct cpufreq_policy *policy)
>  	int err = -ENODEV;
>  
>  	cpu = of_get_cpu_node(policy->cpu, NULL);
> -
> -	of_node_put(cpu);
>  	if (!cpu)
>  		goto out;

I would have loved a blank line here :)

> +	max_freqp = of_get_property(cpu, "clock-frequency", NULL);
> +	of_node_put(cpu);
> +	if (!max_freqp) {
> +		err = -EINVAL;
> +		goto out;
> +	}
> +
> +	/* we need the freq in kHz */
> +	max_freq = *max_freqp / 1000;
>  
>  	dn = of_find_compatible_node(NULL, NULL, "1682m-sdc");
>  	if (!dn)
> @@ -171,16 +178,6 @@ static int pas_cpufreq_cpu_init(struct cpufreq_policy *policy)
>  	}
>  
>  	pr_debug("init cpufreq on CPU %d\n", policy->cpu);
> -
> -	max_freqp = of_get_property(cpu, "clock-frequency", NULL);
> -	if (!max_freqp) {
> -		err = -EINVAL;
> -		goto out_unmap_sdcpwr;
> -	}
> -
> -	/* we need the freq in kHz */
> -	max_freq = *max_freqp / 1000;
> -
>  	pr_debug("max clock-frequency is at %u kHz\n", max_freq);
>  	pr_debug("initializing frequency table\n");

Though, enough versions have happened now.

Acked-by: Viresh Kumar <viresh.kumar@...aro.org>

-- 
viresh