linux-kernel - Re: [PATCH] KVM: X86: Fix dereference null cpufreq policy

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Date:   Mon, 2 Mar 2020 08:55:12 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>
Subject: Re: [PATCH] KVM: X86: Fix dereference null cpufreq policy

On 02/03/20 08:15, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@...cent.com>
> 
> cpufreq policy which is get by cpufreq_cpu_get() can be NULL if it is failure,
> this patch takes care of it.
> 
> Fixes: aaec7c03de (KVM: x86: avoid useless copy of cpufreq policy)
> Reported-by: Naresh Kamboju <naresh.kamboju@...aro.org>
> Cc: Naresh Kamboju <naresh.kamboju@...aro.org>
> Signed-off-by: Wanpeng Li <wanpengli@...cent.com>

My bad, I checked kobject_put but didn't check that kobj is first in
struct cpufreq_policy.

I think we should do this in cpufreq_cpu_put or, even better, move the
kobject struct first in struct cpufreq_policy.  Rafael, Viresh, any
objection?

Paolo

>  		policy = cpufreq_cpu_get(cpu);
> -		if (policy && policy->cpuinfo.max_freq)
> -			max_tsc_khz = policy->cpuinfo.max_freq;
> +		if (policy) {
> +			if (policy->cpuinfo.max_freq)
> +				max_tsc_khz = policy->cpuinfo.max_freq;
> +			cpufreq_cpu_put(policy);
> +		}