linux-kernel - Re: [PATCH v6] cpufreq/pasemi: fix an use-after-free in pas_cpufreq_cpu

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Date:   Fri, 12 Jul 2019 09:14:09 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Wen Yang <wen.yang99@....com.cn>
Cc:     rjw@...ysocki.net, linuxppc-dev@...ts.ozlabs.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        xue.zhihong@....com.cn, wang.yi59@....com.cn,
        cheng.shengyu@....com.cn, Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH v6] cpufreq/pasemi: fix an use-after-free in
 pas_cpufreq_cpu_init()

On 12-07-19, 10:44, 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: a9acc26b75f6 ("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
> ---
> v6: keep the blank line and fix warning: label 'out_unmap_sdcpwr' defined but not used.
> 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 | 26 ++++++++++++++------------
>  1 file changed, 14 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/cpufreq/pasemi-cpufreq.c b/drivers/cpufreq/pasemi-cpufreq.c
> index 6b1e4ab..7d557f9 100644
> --- a/drivers/cpufreq/pasemi-cpufreq.c
> +++ b/drivers/cpufreq/pasemi-cpufreq.c
> @@ -131,10 +131,18 @@ static int pas_cpufreq_cpu_init(struct cpufreq_policy *policy)
>  	int err = -ENODEV;
>  
>  	cpu = of_get_cpu_node(policy->cpu, NULL);
> +	if (!cpu)
> +		goto out;
>  
> +	max_freqp = of_get_property(cpu, "clock-frequency", NULL);
>  	of_node_put(cpu);
> -	if (!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 +179,6 @@ 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");
>  
> @@ -196,7 +194,11 @@ static int pas_cpufreq_cpu_init(struct cpufreq_policy *policy)
>  	policy->cur = pas_freqs[cur_astate].frequency;
>  	ppc_proc_freq = policy->cur * 1000ul;
>  
> -	return cpufreq_generic_init(policy, pas_freqs, get_gizmo_latency());
> +	err = cpufreq_generic_init(policy, pas_freqs, get_gizmo_latency());

So you are trying to fix an earlier issue here with this. Should have
been a separate patch. Over that I have just sent a patch now to make
this routine return void.

https://lore.kernel.org/lkml/ee8cf5fb4b4a01fdf9199037ff6d835b935cfd13.1562902877.git.viresh.kumar@linaro.org/

So all you need to do is to remove the label out_unmap_sdcpwr instead.

> +	if (err)
> +		goto out_unmap_sdcpwr;
> +
> +	return 0;
>  
>  out_unmap_sdcpwr:
>  	iounmap(sdcpwr_mapbase);
> -- 
> 2.9.5

-- 
viresh