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

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Message-ID: <20200302081207.3kogqwxbkujqgc7z@vireshk-i7>
Date:   Mon, 2 Mar 2020 13:42:07 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org,
        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>
Subject: Re: [PATCH] KVM: X86: Fix dereference null cpufreq policy

On 02-03-20, 08:55, Paolo Bonzini wrote:
> 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);
> > +		}

I think this change makes sense and I am not sure why should we even
try to support cpufreq_cpu_put(NULL).

-- 
viresh